Running Science

Find Your Forerunner By monitoring key aspects of your running and fitness progress, you get a better look at your current performance level and what you need to do to keep up the good work or continue improving. Select Garmin devices collect data while you work out in order to bring you these running metrics and physiological measurements. If your device is showing you stats, but you want to know more about what they mean, then you’ve come to the right place. What can you do with this calculated information? That’s up to you, but we’ve got some suggestions.

Physiological Measurements

Training Status

A watch screen showing training status. Training status is the first feature offered by Garmin that truly analyzes not only today’s run but also your longer-term training habits. This provides you with powerful insight into how your training is really going. If other metrics offer you a window into the process, training status knocks down the walls to let you enjoy the panoramic view.

Is your current training intense enough, or long enough, to help improve your fitness? How do you know if you’re working hard enough to make a difference in the long run or if you’re not pushing yourself hard enough? Training status helps you make decisions about future training by automatically taking into account changes in fitness level, your current acute (7-day) training load and any change in training load with respect to previous training. In essence, it tells you the effectiveness of your current training and provides guidance to help you improve your training decisions.

Provided by Firstbeat, the calculation utilizes several dimensions of a personalized model of your physiology. Changes in your VO2 max fitness level in light of your recent training loads over time indicate the effectiveness of your training.

The dynamic and interwoven nature of our physiology often makes the process of training seem more like art than science. On the surface, what we expect isn’t always what we get, and what we get isn’t always what we expect.

To explain in simple terms, when you stop training, your fitness level will decrease, but depending on your previous training load, a break from normal training routines may result in an increase in fitness level. Similarly, it’s expected that regular hard training will improve our fitness levels, but watch out — push too hard too often, and your fitness level will start to decrease due to the overtraining phenomenon.

As an example of how this works, imagine that you’ve been training consistently for a number of weeks, and your fitness with normal, small day-to-day ups and downs is nevertheless increasing. This trend is automatically identified and your current training will be classified as “productive.” Similarly, you could find yourself training very hard but with your fitness starting a pattern of decline. In this situation, your training would be identified as “overreaching,” and additional recovery will be recommended.

The recognized training states are below.

Peaking – You are in ideal race condition! Your recently reduced training load is allowing your body to recover and fully compensate for earlier training. Be sure to think ahead, since this peak state can only be maintained for a short time.

Productive – Keep up the good work! Your training load is moving your fitness in the right direction. Be sure to plan recovery periods into your training to maintain your fitness level.

Maintaining – Your current training load is enough to maintain your fitness level. To see improvement, try adding more variety to your workouts or increasing your training volume.

Recovery – Your lighter training load is allowing your body to recover, which is essential during extended periods of hard training. You can return to a higher training load when you feel ready.

Unproductive – Your training load is at a good level, but your fitness is decreasing. Your body may be struggling to recover, so pay close attention to your overall health, including stress, nutrition and rest.

Detraining – You’ve been training much less than usual for a week or more, and it’s affecting your fitness. Try increasing your training load to see improvement.

Overreaching – Your training load is very high and has become counterproductive. Your body needs a rest. Give yourself time to recover by adding lighter training to your schedule.

No Status – You typically need a week or two of training history, including recent activities with VO2 max results from running or cycling, before we can determine your training status.

VO2 Max

A watch screen showing VO2 max. Your VO2 max score is the key to seeing, understanding and, more importantly managing your personal fitness level. At a technical level, it describes the maximum rate at which you can bring oxygen into your body, transport it to your muscles and use it for efficient aerobic energy production. At a personal level, it is a remarkable and versatile tool with a variety of health and performance implications.

When it comes to understanding your VO2 max score, it’s easy to remember that low VO2 max scores represent poor fitness levels, and higher VO2 max scores indicate greater performance capacity. Like most aspects relating to physical performance, there is a genetic dimension to how efficiently your body uses oxygen and, by extension, your VO2 max range. That said, your VO2 max score is dynamic, and it reacts to how you live and train. With the right approach, practically everyone can improve their VO2 max score.

The people least likely to be able to improve their VO2 max are elite athletes, because they are already in excellent shape. This is great news for everyone else.

Studies have shown that being more active can make you happier and live longer. VO2 max is a key metric used to study and verify this from a scientific perspective. If you’re looking to improve, your device also offers the tools you need to get things headed in the right direction.

For those interested in performance, VO2 max can be used in a slightly different way. The more oxygen your body can use during exercise, the more power you can generate and, therefore, the faster you can run during a race.

Recovery Time

A watch screen showing recovery time. Recovery is a critical, but often overlooked, portion of the training process. The recovery period is marked by adaptation of your body in response to training and the replenishment of vital resources. In fact, insufficient recovery can lead to missing out on gains in fitness and performance entirely. Keeping track of your recovery levels will reveal when training hard will be beneficial and ensure your work is rewarded with the results you expect. You gain the ability to update and optimize your training programs with confidence.

After each workout, your device reveals the number of hours before you will be back near 100% and capable of performing a hard workout or running a race. Provided by Firstbeat, the calculation is produced and personalized using a unique digital model of your physiology. It utilizes a combination of the session’s training effect score, performance and fitness level assessments performed during the session and the number of hours of recovery time remaining on your clock at the start of your workout.

Recovery time ranges up to 4 days.

For best results, it’s beneficial to first go for several runs with your watch in order for the device to accurately learn your overall fitness level. Once this is established, subsequent recovery time results may be more accurate.

Training Load

A watch screen showing training load. Want to look at the bigger picture? This is where you need to go. Training load is a measure of the total volume of your training for the last 7 days. Furthermore, your compatible Garmin device compares this weekly training load to your longer-term training load — also taking into account your fitness level — and shows you if this load is in the optimal range. The volume of a workout is the EPOC it creates as estimated from heart rate data gathered during the workout. Your current training load then is just the sum of EPOC measurements for the last 7 days.

It’s true that pushing yourself is the way to get results, but overreaching and training too hard is a real possibility that is counterproductive and could even lead to injury. So look carefully at your training load, and see if you’re doing too much, too little or just the right amount.

The available training load ranges are:

High – Based on your current fitness level and recent training habits, your training load may be too high to produce positive results.

Optimal – This range is ideal for maintaining and improving your fitness level. Keep up the good work!

Low – Your training load is low for your current fitness level and training habits. If you stay in this range, you are unlikely to see further improvement.

Making the Most of Training Load Focus

Making the most of training load focus

The training load focus data screen provides you not only with a graphical depiction of how your training load is distributed among the three major intensity categories but with qualitative feedback as well.

  • Shortage: You are lacking exercise in a training intensity category.
  • Balanced: Your training is well distributed across different levels of intensity.
  • Focus: Your training variety is reasonably well structured but is particularly focused in one area.

In addition to the above three categories of load focus feedback, it is also possible to get feedback that your overall training load is too low (“Below Targets”) or too high (“Over Targets”).

Balance Is Needed for a Strong Foundation

When your training load is both optimal and balanced, it means you are active enough to support and gradually improve your fitness level, and the composition of your activities is diverse enough to provide a solid foundation for future improvement. It means your activities include enough time spent at high- and low-intensity aerobic efforts along with dynamic efforts to help enhance your explosive performance capabilities.

Focus for Winning

Every athlete knows that preparation is the key to success, and to be successful you must recognize and prepare for the unique demands of the challenge you face. With a balanced foundation in place, you can start to focus and guide the composition of your training load toward a performance profile that matches your ambition or phase of your periodization schedule.

Confirming that your training is properly targeted through training load focus gives you confidence that you are on the right track. When understood and utilized properly, this data can be transformed into your personal road map for achieving your goals and performing at a high level in a wide variety of pursuits. You can easily see when your training activities are lacking in one or more areas, and, once you have a strong foundation in place, you are able to shoot for the stars by ensuring the composition of your training activities match up with the specific real-world demands of the challenge you want to tackle.

Training Load: Training Effect Label of Primary Benefit

In newer compatible products, you can get an idea of how your run or ride affects your training load focus as soon as you save your activity. A new color-coded label added to the training effect summary screen describes the primary benefit of what you have just done and where you can mostly expect it to contribute.

Note that the background of these labels are color-coded (purple, orange and light blue) to match the anaerobic, high aerobic and low aerobic bars used for your training load focus. When a recorded activity has no meaningful impact in one of the intensity categories or it cannot be identified, the label background is simply gray, and no descriptive text is displayed.

At the bottom of this screen, you can also see the training load for the activity.

Heat and Altitude Acclimation

Heat and Altitude Acclimation

Environmental factors can have a substantial impact on your performance. At higher altitudes and in hot, humid conditions, your body is forced to work much harder than normal to produce the same performance as it would in more comfortable environments.

However, exposure to these challenging conditions triggers a natural acclimation process. Acclimation is a physiological transition that helps you perform in new, more challenging conditions.

Select Garmin devices automatically recognize when you are at higher altitudes or are being active in hotter conditions. Heat and altitude acclimation insights are provided based on activities performed above 800 meters (2,625’) and for temperatures above 22 C (72 F). This environmental information comes from a combination of GPS and weather reports from your paired compatible smartphone.

Your body simply can’t and won’t change overnight. Acclimation takes time and requires repeated exposure to the environment. Once you leave challenging conditions behind, your body starts to return to normal. Your Garmin device understands this process and combines environmental and performance data to reveal your current acclimation status. Keeping tabs on it helps you adjust your expectations and performance goals.

Automatically recognizing and accounting for the relationship between environment and performance also ensure the integrity of your training data. Struggling to keep your normal pace during a heat wave doesn’t necessarily mean your cardiorespiratory fitness (VO2 max) has dropped. Similarly, needing to catch your breath during a trip to the mountains doesn’t mean your training has been unproductive.

How long does it take to acclimate to heat and humidity?

The speed at which your body acclimates depends on several factors. One of the most significant factors is the difference between the conditions you are acclimating to and your normal environment. The bigger the change, the longer it takes to adapt. Another factor is the frequency and duration of your workouts.

Evidence shows that prolonged daily outdoor exposure to challenging climates can produce the necessary adaptations in as little as 1 to 2 weeks. Athletes with a higher VO2 max typically adapt to challenging climates at a faster rate, sometimes decreasing the acclimation period by as much as half.

Specifics of Heat Acclimation

Athletic performance involves transforming the energy stored in proteins, carbohydrates and fats. This produces heat. During intense physical activity, your body can rival a 1,000-watt space heater in terms of heat production. Getting rid of this excess heat is necessary for maintaining a normal, healthy body temperature.

Circulating blood close to the skin allows heat to escape. This natural cooling process becomes more efficient as you sweat, because the evaporation of sweat has a natural cooling effect on your skin.

Not surprisingly, it’s much easier for your body to get rid of excess heat on a cool, crisp morning compared to a hot, humid summer afternoon. Your environment matters. Acclimation triggered by hotter climates focuses on improving the efficiency of your body’s natural cooling systems.

This includes adaptations that allow you to sweat more and start sweating faster. It also includes changes that allow more blood to flow quickly just below the surface of your skin. Other key adaptations include changes to your cardiovascular system and electrolyte balance that add stability and help withstand the increased stress of hydration-dehydration cycles.

Specifics of Altitude Acclimation

At an elevation of 10,000' (3,000 meters), the amount of oxygen in the air is only about 70% compared to sea level. This means your heart, lungs and circulatory system need to work much harder at higher altitudes to deliver a similar amount of oxygen to your muscles for aerobic energy production.

Adaptations triggered by exposure to high-altitude environments focus on increased lung capacity and increasing the amount of oxygen carrying red blood cells in your blood supply. Pressure increases in the arteries running through your lungs, which forces the circulation of blood into areas of your lungs that aren’t normally used at lower altitudes. The additional red blood cells allow more oxygen than normal to be carried to your muscles with each heartbeat.

The fact that these performance-boosting adaptations are not immediately reversed upon return to lower altitudes is the basis for high-altitude training for athletes.

ClimbPro Feature

ClimbPro Feature

ClimbPro is designed to help a runner manage effort in the following two ways:

  • It shows upcoming climbs for the course, at what distance they occur and their length and gradient. This information is accessible in the course preview and is also available as a dedicated screen within the timer loop during the activity.
  • For individual climbs, a dedicated ClimbPro screen automatically appears as a runner approaches a climb. This screen shows the runner their position on the climb as well as the distance, ascent and average gradient remaining for that climb. This constantly updates as the runner makes progress to the top.

How are climbs classified?

The feature is designed to help a runner during more significant climbs by not detecting every uphill section. We expect to continue to adapt this algorithm as we get more and more feedback from runners around the world. It will currently classify a climb based on the following criteria:

  • Climb distance (in meters) multiplied by the percent of the average gradient should be greater than 3,500.
  • A climb must be a minimum of 500 meters in length.
  • Average gradient must be a minimum of 3%.

What do the colors mean?

The colors indicate the gradient of the climb in the following ways:

  • In the climb preview list, the colors indicate the overall average gradient for the climb.
  • On the individual climb page, the colors indicate the average gradient for the highlighted section.

What does a runner need for ClimbPro to work?

  • A runner needs to be following a course that includes elevation data. This course can come from Garmin Connect or third-party platforms and should ideally be in .fit format.

Daily Suggested Workouts Feature

Daily Suggested Workouts Feature

A journey of a thousand miles begins with a single step, and when it comes to achieving your big-picture fitness and performance goals, what you do today matters. The Daily Suggested Workouts feature on select Garmin GPS watches and cycling computers combines the latest sports science with fitness, activity and lifestyle data captured by your device to answer this important question: What should I do today?

The broad goal of these suggested workouts is to help you improve your fitness level (VO2 max), which translates into aerobic performance capacity. Furthermore, regularly performing suggested workouts will help you achieve an optimal training load with varied efforts ideally balanced for your development.

Each workout suggested is designed to provide an appropriate level of challenge while satisfying a specific need or improving a particular aspect of performance. Depending on the capabilities of your Garmin device, some or all of the following factors will be considered when generating your suggested workout: current training load, load focus, recovery time, sleep data and the profile of recently performed workouts.

Some days your suggested workout will focus on building your endurance base or facilitating recovery. Other days will focus on developing maximum aerobic performance capacity, including your ability to tolerate high-intensity efforts, perform and repeat dynamic intervals, or speed. The suggested workouts take advantage of Garmin’s longstanding on-device workout capabilities that give real-time guidance, telling you when to step up the intensity and when to take your foot off the gas. This can be especially helpful during lower-intensity activities where it can be easy to overshoot your mark.

Like any good workout program, consistency and variety are vital to your success. These elements are built into the workout suggestion system. Performing suggested workouts regularly will help you stay on track and keep improving. On some devices, over time you’ll notice a mixture of lighter training weeks, harder training weeks and some in between. These patterns conform to well-established training periodization methods employed by top sports scientists and exercise physiologists.

If you are following a dedicated training plan with scheduled workouts aimed at a specific event, one downloaded from Garmin Connect (either a Garmin plan or one you have created) or one downloaded from a third party, these training plan workouts will take priority over the Daily Suggested Workouts. You will still be able to locate the suggested workout in the workouts menu, but your training plan workouts will take priority in the prompts given on your watch.

Training Effect

A watch screen showing training effect. If you’re like most people, you train because you want results. Because of how our bodies work, the type of training you do determines the type of results you can expect and the types of performances you will be well prepared for in the future.

Training effect is the metric that gives you a sneak peek at how each training session is expected to impact your future fitness levels. Of course, to get the full benefits of your training, it’s important to incorporate a proper recovery schedule.

One of the most common usages of training effect is to coordinate and balance workouts that maintain and improve your current fitness level (see VO2 max).

Training effect builds over the course of your workout and is updated in real time. This means you can use it as an on-the-go resource to tailor your workout to your needs. You can push yourself harder when you are striving to improve and slow down before you wander into the overreaching range, where the results may not be what you wanted.

Aerobic Training Effect

Aerobic training:

  • Develops aerobic energy production
  • Utilization of fat for energy
  • Endurance and stamina
  • Prolonged performance capacity

Available on select Garmin watches, this measures the aerobic benefit of exercise, which should correlate with the fitness improvement you expect to get from it. When you crush a difficult run, you’ve likely given yourself a bigger dose of aerobic exercise and, therefore, a bigger training effect. What good is this information for you? Well, training effect uses your heart rate to measure the accumulated intensity of exercise on your aerobic fitness and gives you a good indication of whether you’re maintaining your current fitness level or improving it.

Aerobic training effect is the same as the original training effect feature offered on many earlier Garmin watches, except the scale has been modified slightly to account for — let’s face it — those really short or really easy activities that have no meaningful training effect. In other words, we added a “0” at the bottom of the scale.

Technically speaking, aerobic training effect is the excess post-exercise oxygen consumption (EPOC) accumulated during exercise, mapped onto a 0-to-5 scale that accounts for your fitness level and training habits. Typically, as you get fitter, you need larger “doses” of exercise to continue seeing improvement. So, while an exercise session generating an EPOC of 60 ml-O2/kg might have given you a great training benefit when you were out of shape, it might not do very much for you once you have whipped yourself into wickedly good shape. Training effect reflects this reality by giving a higher number in the first case than in the second case.

Note: The training effect scale for both aerobic and anaerobic is: 0 – None, 1 – Minor, 2 – Maintaining, 3 – Improving, 4 – Highly Improving, 5 – Overreaching.

Anaerobic Training Effect

Anaerobic training:

  • Develops anaerobic energy production
  • Sprinting abilities
  • Fatigue resistance
  • Maximal performance capacity

While there isn’t a specific metric tied to it, the aspect of performance most easily associated with anaerobic training effect is your ability to perform and repeat sprints. The flow of a soccer game is a good point of reference here, where the activity of the game is punctuated with sudden flurries of high-intensity activity.

Your body’s most efficient method of transforming fuel into energy requires oxygen, but sometimes your demand for energy exceeds the rate at which enough oxygen is immediately available. Luckily, your body has a backup process ready and waiting. While not nearly as efficient, the anaerobic energy process can jump into action and keep you going. The downside is that it becomes depleted quickly.

Whereas aerobic training effect ties nicely with increasing your aerobic fitness level — expressed in terms of VO2 max — things are a little more complicated with accounting for improvements on the anaerobic side of things.

A graph showing analysis of heart rate and speed to derive anaerobic training effect.

By analyzing both heart rate and speed (or power, in the case of cycling) the anaerobic training effect feature quantifies the anaerobic contribution to EPOC made during these periods of exertion. The higher the anaerobic training effect, the greater expected benefit to your anaerobic athletic capability. High-intensity intervals, for example, have been shown to improve several components related to your ability to perform, and anaerobic training effect quantifies this for you. However, the feature goes one step further. By analyzing the type of workout you did, it can tell you more specifically how the workout helped you. For example, if it were detected that you completed several high-speed repeats, you might get an anaerobic training effect of 3.5 saying, “This activity improved your anaerobic capacity and speed due to several high-speed/power repeats.”

Training Effect Samples

The following table should give you an idea of the typical aerobic and anaerobic training effect you can expect from a good workout.

Run Type Typical Aerobic TE Typical Anaerobic TE
Long, slow distance 2.0 - 3.0Maintaining Aerobic Fitness 0No Anaerobic Benefit
20-minute threshold 3.5+Improving Lactate Threshold 0No Anaerobic Benefit
Lactate threshold intervals 3.0+Improving Lactate Threshold 0 - 2.0Minor Anaerobic Benefit
Sprint intervals10 x 50m @
150-200% VO2 max
0 - 2.0Minor Aerobic Benefit 2.0 - 3.0Maintaining Speed
Speed intervals10 x 400m @
100-105% VO2 max
2.0 - 4.0Improving Aerobic Fitness 3.0 - 4.0Improving Economy and Anaerobic Fitness
Speed intervals10 x 400m @
110-115% VO2 max
2.0 - 4.0Improving VO2 Max 4.0+Highly Improving
Anaerobic Fitness
800m race 2.0+Maintaining Aerobic Fitness 2.5+Maintaining Anaerobic Fitness
5K race 3.5+Improving VO2 Max 1.0 - 2.0Minor Anaerobic Benefit
10K race 4.0+Highly Improving VO2 Max 0.0 - 2.0Minor Anaerobic Benefit
Note that the above training effect values and phrases are illustrative examples. Your experience may differ depending on your personal training habits. For example, if you incorporate strides or faster fartleks into your distance runs, these can add an anaerobic training effect.
As with many Garmin Firstbeat features, it may take several training sessions for the watch to learn your fitness parameters and produce the most accuraute results. While the device is still learning about you, you may see uncharacteristic training effect values.

Lactate Threshold

A graph showing lactate threshold at 90% of an athlete’s maximum heart rate.

Your lactate threshold is that specific level of effort or pace when fatigue accelerates. For a well-trained runner, this usually occurs when they’re at about 90% of their maximum heart rate corresponding to a pace somewhere between 10K and half-marathon race pace. For a less experienced runner, the lactate threshold is often below 90% of maximum heart rate.

Select Garmin devices can detect your lactate threshold either through a guided workout or automatically during a normal run. Either way, by gathering heart rate data across a range of paces, the device will estimate your lactate threshold both in terms of a running pace and a heart rate level in beats per minute. For best results, it’s very beneficial to go for several runs after first taking the watch into use in order for your device to accurately learn your overall fitness level. Then, once this is well established, subsequent lactate threshold results will be more accurate than they might be initially.

Historically, athletes hoping to utilize their lactate thresholds to personalize their training regimens needed blood testing to assess the amount of lactate accumulating during their training sessions. This process limited the number of athletes who had access to this valuable training information.

The Firstbeat method of lactate threshold detection used in Garmin devices relies on the fact that your respiration rate — how hard you are breathing — can be detected through analysis of your heart rate variability. The process of inhalation and exhalation produces tiny changes in the interval between heartbeats (HRV). When these variations are decoded and combined with other performance data, your device can recognize the simultaneous changes in your heart rate to indicate when you are performing above your lactate threshold.

How can this help you? Your lactate threshold is the single best determinant of your endurance performance capacity. As your ability to cover long distances at a faster pace increases, you’ll see increases in your lactate threshold. This metric is also a valuable resource for recognizing the personal training zones that will boost your individual performance. That’s because your training will be based on real physiological state transitions in your body instead of arbitrary percentages of your maximum heart rate.

Knowing your lactate threshold lets you train with more precision. Many coaches prescribe some running at lactate threshold as part of an overall training program. The lactate threshold feature in compatible Garmin devices helps you determine where your threshold is — without paying for an expensive lab test involving multiple blood samples.

Race Predictor

A watch screen showing race predictor. Once a VO2 max is established, your device can provide a target race time based on your current state of fitness. Projected race times can be viewed for 5K, 10K, half-marathon and marathon distances, which will get faster or slower as your fitness goes up or down. At all race distances, but especially in longer races such as marathons, there are many important and necessary factors for success that go beyond just aerobic fitness; that’s why it is important to complete proper training for an event to give yourself the best shot at reaching your predicted race times. And remember, these times are just predictions, but they give you a good idea of the kind of performances you can reasonably expect, given your physiological data. They also provide a terrific goal to try and reach.

Real-time Stamina

A watch screen showing race predictor.Real-time stamina is designed to help guide you toward your best possible performance, empowering you to push your limits with confidence. You gain context for interpreting feedback from your body, and you experience valuable insight along the way. Time and distance to exhaustion estimates predict what you can expect to achieve with your remaining stamina at your current effort.

Stamina describes your capacity for good, quality performance. Running out of stamina means reaching or rapidly approaching the point where keeping up becomes a serious struggle. How hard you are working affects how quickly your stamina drains during an activity.

Stamina (0–100%) reflects how much you have left in the tank at your current level of effort. This perspective combines general fatigue with more temporary limitations imposed by anaerobically driven efforts such as sprints, climbs and attacks.

Potential Stamina (0–100%) focuses specifically on the effects of broader, longer-lasting fatigue contributors such as muscle cell damage, central nervous system fatigue and carbohydrate (glycogen) depletion. Activities that result in near or total depletion of your potential stamina typically require several days of recovery before you are back at full capacity.

If you haven’t fully recovered from your last activity, your potential will not be at 100%.

Expect your stamina and potential to align during sustained moderate-intensity efforts. Up the intensity, exceed your lactate threshold (running) or FTP (cycling), and stamina will drain faster than your potential. Return to a moderate, sustainable effort, and stamina will gradually replenish toward your potential as the residual effects of high-intensity, anerobic exertion begin to wear off.

Calculating Stamina

Real-time stamina tracking works by combining your physiological metrics with a multi-layered analysis of your recent and longer-term activity history. This includes examining training durations, distances covered, training load accumulations and load distributions for meaningful patterns that reflect fatigue resistance and personal tolerances for aerobic and anaerobic exercise.

While general fitness levels provide some insight into your performance ability, activity-specific training adaptations substantially influence your capacity for sustained performance. In other words, running ability doesn’t directly translate into cycling ability and vice versa. As a result, real-time stamina estimates are primarily guided by running history data during running activities and cycling history data during cycling activities.

Performance Condition

A graph showing performance condition over the course of a run.

A watch screen showing performance condition. For a real-time assessment of your current ability to perform, look at your performance condition. During the first 6 to 20 minutes of your run, this metric analyzes pace, heart rate and heart rate variability. The resulting number is a real-time assessment of the deviation from your baseline VO2 max, with each point on the scale representing about 1% of your VO2 max. The higher the number, the higher you can expect to perform. Keep in mind that your results may vary a bit during your first few runs with a new device, since it’s still learning your fitness level. This will stabilize, and then checking your performance condition will become a reliable day-to-day indicator of your capability.

A graph showing performance condition declining as a run continues.

In addition to the alert during the first part of your run, you can add performance condition as a data field to your training screens, and keep an eye on it as your run unfolds. The value may move around slightly as you encounter hills or strong winds, but it will trend down once you have been going hard for a while if the run starts to take a toll on you. This is an objective way to keep an eye on how your ability to perform is or isn’t declining as you go, because it’s telling you if your body is working harder than normal to run at your current pace. So, performance condition can give you a bit of an early “wall” warning and allow you to adjust your tactics before you hit that wall too hard.

HRV Stress Test (Stress Score in Older Products)

If you’re wondering whether your body is ready for a hard run or in need of a lighter effort, it might be time to check your stress score. When you’re fresh and rested inside and out, you’re better able to absorb the training effect from a tough workout. However, the same hard workout can be counterproductive if you’re tired or on the verge of overtraining. Your stress score is calculated during a 3-minute test during which your heart rate variability (HRV) is analyzed. The resulting stress score is displayed as a number from 0 to 100, with a lower number indicating a lower stress state. This measurement helps you assess what level of activity your body is ready for. More accurate results are gathered by taking the test at the same time and under the same conditions every day (recommended prior to the workout, not after.) This also helps you get a feel for your own day-to-day and week-to-week variations.

You are required to stand to take the HRV stress test, because that makes the test more sensitive to low and medium levels of stress. When you are lying down, moderate levels of stress may not be revealed, but standing puts a slight load on your cardiovascular system. That load causes a meaningful drop in HRV when you have a moderate amount of stress compared to very low stress.

HRV (Heart Rate Variability)

A graph showing a heart rate variability stress test.

Your heart does not beat in a perfectly regular rhythm as would a metronome, and, in fact, beat-to-beat variations in your heart rate are healthy and normal. To understand more about how Garmin and Firstbeat use heart rate variability to give you better information about the state of your body, start with why heart rate variability exists.

Your heart is controlled by your autonomic nervous system (ANS), which is the involuntary part of your nervous system. Furthermore, there are 2 branches of the ANS called the sympathetic and parasympathetic branches. The sympathetic branch of your ANS is active when you’re under some kind of stress. It is the part of your ANS that puts all systems on alert. By contrast, the parasympathetic branch is the more relaxed part that just hums along when you are relaxed and not about to be charged by a mountain lion. When the sympathetic branch is more active, your heart rate typically increases, and it beats in more regular rhythm — meaning HRV decreases.

On the other hand, when the parasympathetic branch is more active, your heart rate decreases, and it beats when it gets around to it to meet the body’s needs, but not on such a strict schedule as when the sympathetic branch is in charge. In other words, HRV increases. Because of these characteristics, HRV is a great indicator of the balance between the activity of the 2 branches of the autonomic nervous system, and therefore it’s an indirect measurement of stress. Higher HRV means lower stress.

There are many different statistical methods used to characterize HRV, but the HRV stress test (formerly called stress score) feature makes life a lot easier by putting your stress on an easy-to-understand 0-to-100 scale specifically designed to be another tool for you to assess how your body is doing and how it’s handling training stress and life stress.

Although HRV decreases as you begin to exercise and continues to decline as you go harder, it still yields useful information even when you’re running fast. Available on some Garmin devices, the lactate threshold feature uses a Firstbeat feature that looks for a point of increasing HRV that corresponds closely to your lactate threshold heart rate.

EPOC

Excess post-exercise oxygen consumption is the phenomenon where for a period of time after exercise, your body will continue to use oxygen at a higher rate than it would otherwise at rest. This makes sense. When you exercise, you disturb your body’s usual state, and this disturbance requires your body to do some extra work to put things back to normal. In fact, the point of training is that after exercise, your body will build itself back up to normal and then some. It is the “and then some” — also called “supercompensation” — that makes you a little fitter and faster than you were before.

Since the oxygen used by your body is related directly to the amount of energy it uses, the EPOC measurement is perfect for quantifying how much your body’s normal state (homeostasis) is disturbed by a session of exercise. In other words, EPOC is a great measure for exercise volume or dose, since it quantifies how much work your body had to do to get back to normal — and then some.

A graph showing excess post-exercise consumption derived from heart rate data during exercise.

Directly measuring EPOC requires fancy laboratory equipment and a lot of time. However, Firstbeat created a patented method for estimating EPOC from your heart rate data during exercise. These EPOC estimates are at the core of how we determine your training effects, weekly training load and training status.

HRV Status

HRV Status

What is Heart Rate Variability?

Heart rate variability (HRV) is a physiological phenomenon that can be recorded, analyzed, and interpreted to help understand how your body is navigating the challenges of life and environment.

Specifically, HRV refers to the ever-changing length of time between consecutive heartbeats. When your heart is beating at 60 beats per minute, the beats are not evenly spaced one second apart. Look closely and you will see that some beats are slightly less than one second apart and others are a little bit more than one second apart. This irregularity is perfectly normal and healthy.

These slight changes between heartbeats can be easily documented with an accurate recording device and are typically measured in milliseconds. Without physiological knowledge and analytic methods, however, the HRV phenomenon would simply be a list of numbers.

Statistical analysis can reveal meaningful patterns in large amounts of data. RMSSD is a standard statistical measure of HRV. It represents the root mean square of successive differences between normal heartbeats for a given set of heartbeat data. This way of looking at HRV data is widely used by physiologists and exercise scientists to investigate topics like the impact of training loads and recovery processes.

HRV Status

Luckily, you do not need to be an expert in physiology or statistical analysis to benefit from HRV-based insight. A wealth of information exists on the subject, however, if you do want to explore further.

Why does HRV provide such valuable insight? The activity of your heart is regulated by your autonomic nervous system, which adjusts a wide variety of physiological systems in response to situational demands. This means that changes in how your heart beats from one moment to the next can be used as a window through which activity occurring within your autonomic nervous system can be seen.

In general, higher HRV is associated with parasympathetic dominance within your autonomic nervous system, a sign that your body is in rest-and-digest mode. On the other hand, a lower HRV is typically associated with elevated sympathetic activity within your autonomic nervous system, an indication of stress or fight-or-flight response.

How Your Compatible Garmin Watch Measures HRV

Data used to calculate your HRV is recorded by the Elevate HR sensor located on the back of your watch. This sensor uses reflected light to detect pulse wave blood flow as it is pumped by your heart and pushed through your veins. This means that technically your device is looking at pulse rate variability which effectively reflects heart rate variability in the context of this analysis and usage scenario.

Compatible Garmin devices calculate HRV continuously while you are sleeping. When you wake up, you can view your average HRV calculated using data from the entire sleep period. You can also review a chart that shows how your HRV changed while you were asleep based on analysis of 5-minute time windows.

This offers a significant advantage compared to other methods that measure HRV during only part of the night, during specific sleep stages, or involve testing at specific times of the day.

Because HRV is a statistical measure, differences in the timing and duration of the measurement affect the results. This makes it a challenge to make apples-to-apple comparisons between HRV measurements produced with alternative protocols and different devices.

Interpreting HRV and Why Your Personal Baseline Matters

You will be able to see your average HRV and overnight trends as soon as you start using your device. Simply wear your device to bed and the analysis automatically occurs. What you will missing at first is meaningful context for interpreting your results.

When it comes to making sense of any HRV metric, everything starts from you. A normal, healthy degree of variability for you is not necessarily the same as for someone else. Some people have naturally higher ranges of variation while others tend to exhibit less variability. And that is not all, what is normal for you also changes over time.

Your own personal history, then, is the single-most meaningful frame of reference for interpreting HRV data. Given this fact, documenting your personally normal range of HRV values is a necessary first step in making your HRV data actionable.

This takes time. In practice, it means that you need to routinely wear your Garmin device overnight for around three weeks before HRV status becomes fully active. While three weeks is the minimum amount of time needed to gauge your personal baseline, the analysis can utilize a few months of data to strengthen and validate your baseline range when that amount of data is available.

Key concept: Your HRV baseline is a range of values (e.g., 33-45 milliseconds) derived from your measurement history that represent a normal degree of variability for you personally. Your baseline is the lens through which future HRV measurements can be meaningfully interpreted.

Once your baseline range is identified, your overnight HRV is used to enhance insight from other Garmin features. These other features include your current Training Status and daily Training Readiness assessments on compatible devices.

Your baseline HRV range is not static and will shift over time. You may notice, for example, that your normal range of variability is lower after an extended training period compared to when you are in peak condition. Normal HRV ranges also typically decline with age.

Navigating the HRV Status Widget

As mentioned, the HRV status widget on your device offers more than just one perspective for monitoring your situation. The primary view reveals your current HRV status. Your status can be balanced, unbalanced, low or poor. At the bottom of the first screen, you can see your average HRV measured during the previous night.

HRV Status

Scroll down and you will again be able to see last night’s average HRV, but with additional context. This is where you will find your highest HRV recorded for any 5-minute period during the night. You will also discover a chart that shows how your HRV changed during the night.

The final screen shows your current 7-day average HRV and a plot of average overnight HRV values recorded over the past 7-day period.

HRV Status: Balanced, Unbalanced, Low, and Poor

When your HRV status is balanced, it means that your 7-day average HRV is within your personal baseline range. A balanced HRV status typically indicates your body maintaining homeostasis, a dynamic biological equilibrium associated with optional functioning.

An unbalanced HRV status means your current 7-day-average HRV is outside of your personal baseline range. Note that an unbalanced HRV status can be either higher or slightly lower than your baseline.

HRV Status

Given that higher HRV values are typically associated with parasympathetic dominance within your autonomic nervous system, it is easy to assume that higher is always better from the perspective of good recovery. This is not always the case. Mounting evidence shows a relationship between abnormally high HRV values relative to your personal baseline and functional overreach (overtraining), especially when that overreach is achieved through large amounts of low-intensity physical activity. In these situations, your parasympathetic system is working hyperactively towards the goal of reestablishing homeostasis.

If your 7-day average HRV drops significantly below your baseline, your HRV status is reclassified from unbalanced to low.

Your personal baseline is dynamic and changes slowly over time following trends in your normal overnight HRV values. If your personal baseline drops below age-based standards associated with good health, then your HRV status is classified as poor. When this happens, your baseline range is no longer displayed. This is to avoid scenarios where your HRV might be considered both balanced and below healthy norms.

Training Readiness

Training Readiness

Training readiness is a top-line insight designed to help you maximize training efficiency. You work hard because you want results but pushing your limits before you are ready can be counterproductive. See when you are most likely to benefit from a hard workout and when to consider dialing down to let your body catch up.

This insight is achieved with the help of a multi-layered analysis that considers combinations of activity and lifestyle data. Your training readiness is classified from poor to prime with low, moderate, and high in between. Checking the widget will reveal your current readiness score and how underlying factors contributed to your current situation. You can also view this information as part of your morning report.

How Training Readiness is Calculated

The primary drivers behind your training readiness assessment are how well you slept last night and residual recovery demands of recent activities. This information comes from your recovery time and advanced sleep tracking. Beyond that, training load trends, HRV (Heart Rate Variability) status, recent stress levels and how well you have been sleeping prior to last night also influence your results.

  • Training Readiness data on Garmin ConnectSleep Score – Your sleep score (0-100) reflects how well you slept based on how long you slept, sleep stage distribution, and evidence of recovery activity occurring in your autonomic nervous system derived from heart rate variability data. Sleep quantity and quality evaluations compare your sleep to standards established by expert organizations.
  • Recovery Time – This countdown reveals when you can expect your body to be fully recovered from your last activity. How much time is on your clock varies according to the strenuousness of your last activity and hours, if any, remaining on your Recovery Time at the start of that activity. Significant changes in your sleep quality, stress levels and daily physical activity levels can speed up or slow down your recovery countdown.
  • Acute Training Load – An optimal acute load indicates that the combined impact of your recent activities is enough to maintain and improve your current fitness levels. Unchecked over time, excessive loads can compromise your functional performance capacity and increase injury risks. When you record an activity the full impact of that activity is added to your current acute load. The effects of that activity then gradually expire over the next 10-day period.
  • HRV Status – A balanced HRV means your 7-day average HRV is within your personal baseline range. This is a good indication that your body is successfully navigating the challenges of your life. An unbalanced HRV status may point towards a lack of adequate recovery, excessive workloads, alcohol consumption or your immune system working to fight an illness.
  • Sleep History – Your sleep score reveals how well you slept last night, but one good night does not fully erase the lingering effects of a significant sleep deficit. Sleep history factors in how well you have been sleeping prior to last night.

    An exceptionally long awake period (e.g., 20 hours) before your most recent night’s sleep can also reduce training readiness.

  • Stress History – All-day stress tracking can reveal when your body’s resources are deployed to help you navigate life challenges unrelated to training activities. Stress is a normal part of life but experiencing higher stress levels for extended periods can reduce resiliency and minimize training benefits. Your stress history considers stress levels from the past three days while you are awake.

How Training Readiness Changes Around the Clock

Checking your training readiness first thing in the morning helps set reasonable expectations for the day.

The biggest adjustment to your readiness level happens right when you wake up in the morning. This is when last night’s sleep score, HRV status, and longer sleep history are updated along with big-picture insight from your acute training load and stress history.

Your training readiness then updates throughout the day according to changes in your situation. If you have hours remaining on your Recovery Time countdown, expect your readiness to increase as that time expires. Record an activity and you will notice a decrease in readiness afterwards that reflects your current recovery needs. Light efforts have minimal impact while hard workouts can significantly reduce your readiness.

Can I still train when my training readiness is low?

As any good coach or experienced athlete can tell you, there are times when looking beyond the daily horizon is the right thing to do. Training camps and high-volume training blocks are valid methods of training prescription and can be remarkably effective when properly utilized. A typical block training model often involves several consecutive days of deliberate overload offset by an extended recovery period.

If you are using a block-based training model, then a lower training readiness score during a deliberate overload period likely echoes that work. Against that background, you should still check to see which factors are driving that lower score. Higher than normal acute training loads and longer recovery time estimates can be expected during block training. Reduced readiness caused by other factors (e.g., sleep history or high stress) might be reason to re-evaluate your approach.

The insight you gain from the training readiness widget is only one of the perspectives you should use to guide your training efforts. As always, listen to your body, consider the data together with how you feel and adjust your plans and expectations accordingly.

Training readiness versus performance readiness

It is worth wondering. Are training readiness and performance readiness the same thing? Does your training readiness score the morning of a big race predict (or worse, determine) how well you will do? Does a less than prime readiness score mean it is time to scuttle your pacing strategy and lower your expectations?

There will be times when you may notice a link between training readiness and performance, but strictly speaking the training readiness analysis is not designed to predict performance. Many athletes report sleeping poorly the night before a big event and go on to achieve impressive results and set personal bests. Stress levels can also increase due to the anticipation and excitement of your big day.

Training readiness focuses on relationships between elements of strain, stress, recovery, good sleep hygiene and your ability to maintain homeostatic balance. Guidance is geared towards laying the groundwork for success, getting the most out of your workouts and improving performance abilities over time.

Race-day performance is about executing and putting those abilities to work.

Running Dynamics

Ground Contact Time

This is the amount of time in each step that you spend on the ground while running. Ground contact time is typically pretty short, so it is measured in milliseconds. In fact, ground contact time tends to be especially short for elite runners, they will often have ground contact times of less than 200 ms. Virtually all experienced runners have ground contact times under 300 ms, likely because they have learned to “pick up” their feet quickly and not to over-stride as they are landing. Over-striding describes a running style where the foot lands too far in front of the body leading to braking forces at impact and, typically, longer ground contact times.

Ground Contact Time Balance

A watch screen showing ground contact time balance. By monitoring the balance between your left and right foot ground contact time (GCT), this measures your symmetry as you run. On your Garmin watch, it’s always displayed as a percentage greater than 50% with an arrow to the left or right, to show which foot is on the ground longer. For most people, a more symmetrical running form is preferable. Color gauges on Garmin watches and Garmin Connect™ show how balanced you are compared to other runners. Many runners report that GCT balance tends to deviate farther from 50/50 when they run up or down hills, when they do speed work or when they are fatigued. Anecdotally, some runners also notice that injuries are reflected in greater imbalance.

Cadence

Simply put, this is how many steps you take per minute, counting both feet. It’s a commonly measured running metric and can tell you a lot about your form. For example, at a given pace, quicker cadence and shorter stride length result in smaller forces at many places throughout the body, such as at the ankles, knees and hips. The reduced magnitude of these forces is widely believed by experts to also reduce injury risk. It’s clear that running cadence can be increased only so far, but for more injury prone runners in particular, working on increased cadence could be beneficial. An often-cited target for running cadence is 180 steps per minute, though taller runners tend to have somewhat slower cadence. Interestingly, higher cadence is also associated with lower vertical oscillation and shorter ground contact time.

Stride Length

Another key part of measuring your running form — stride length — is how far you travel with each left and right step. It’s shown at the end of your run or as an in-activity data field you can view as you run. Later, you can view this data in more detail on Garmin Connect™ to see how your stride length varies with your pace, cadence, elevation or other metrics. Your stride length is dependent on a number of factors, including body morphology, muscular strength and flexibility.

Vertical Oscillation

This reflects the amount of “bounce” in each step while you run. Measured at the torso, it tells you, in centimeters, how much distance you are travelling up and down with each step. Many running coaches believe that lower vertical oscillation is more economical, because less energy is wasted going up and down. Garmin has researched many runners of all different levels. In general, more experienced runners tend to have lower vertical oscillation. However, faster paces often come at a cost of somewhat higher vertical oscillation. Vertical ratio (see below) takes this into account. Another advantage of lower vertical oscillation is that it typically means less stress on the lower body at impact.

Vertical Ratio

A watch screen showing vertical ratio. This reflects your running efficiency based on how well you propel yourself forward with each stride. Vertical ratio is the amount of “bounce” in your stride, divided by your stride length, then expressed as a percent. Since stride length is the horizontal movement of running, it’s the benefit of the action, whereas vertical oscillation is one of the energy costs of running. A low vertical ratio number indicates a small cost for a large benefit. That means more efficient running.

Running Power

For years, elite cyclists have used power data as the most reliable way to measure the actual exercise load of their ride. Now you, too, can train with power on your runs by downloading the Running Power app from the Connect IQ™ store onto your compatible watch. The Running Power app accounts for multiple factors to provide a more accurate and responsive exercise load calculation.

Developed by Garmin Labs, the Running Power app taps into metrics — such as pace, vertical oscillation, grade and even local wind conditions — to calculate the amount of power you’re applying at the ground as you run. When you know how much power you’re expending from minute to minute and mile to mile, you’re better able to pace yourself, which can help keep you from tiring out too quickly.

Think of your body’s energy as the battery of your smartphone. You can turn up the screen’s brightness all the way, but, as a result, the battery won’t last as long. Or you can conserve battery by dimming the screen and getting a longer battery life. Likewise, by getting to know your body and its power output while running in different conditions, you can monitor this data to conserve your energy. For marathons and other long-distance runs, this can help you fine-tune your training and performance on race day.

This running power model from Garmin determines the propulsive power applied at the road by considering the major components of the work done during running. These components, how they change and the data used to compute them are listed in the table below.

Component of Running Power What is it? Source of Data Used to Compute
Kinetic Power Power required to change your pace Speed from the watch
Potential Power Power required to run up or down a hill Elevation data from the barometer on the watch
Vertical Oscillation Power Power required for vertical oscillation on each step Running dynamics from an HRM-Run™, HRM-Tri™ or Running Dynamics Pod
Horizontal Oscillation Power Power required for horizontal oscillation on each step (you brake a bit when you hit the ground, then accelerate again as you push off) Speed from the watch Running dynamics from an HRM-Run, HRM-Tri or Running Dynamics Pod
Wind/Air Power Power to overcome air resistance — greater if running into a headwind and less if you are running with the wind at your back
  • Speed from the watch
  • Heading from the watch
  • Reported wind conditions from weather services
  • Barometric data to detect local conditions
Note: The equations to compute these components of running power also require some constant values such as your weight, acceleration due to gravity and the density of air.

Following are examples of the contributions of the components of running power from a tester with cadence in the range of 162-182, vertical oscillation 6.2 – 8.9 cm, and GCT in the range of 262 – 296 ms.

A graph showing a heart rate variability stress test.

So what does this mean for you? As you run, you will see that running power responds quickly when you speed up or slow down. You’ll also find that running power is higher when you’re running up hills than when you’re running at the same pace on flat ground. Similarly, running power will decrease when you run down a hill — though not by as much. In this way, you can use running power in addition to pace to help manage your effort over varying terrain.

With the wind power feature enabled, the Running Power app can even help you gauge your effort when running on a windy day. Wind can have a large effect on the effort required to maintain your usual pace, which shouldn’t surprise you if you’ve ever run into a stiff headwind. The Running Power app uses your heading from GPS and reported wind conditions for your area, augmented by data from the barometer on your watch, to determine how much wind you’re likely experiencing. Try running back and forth on a windy stretch of road and you will see how much higher your power is when you run into the wind. If you typically run in sheltered areas, or you just don’t want the app to account for wind, simply disable this feature within the app settings in the Garmin Connect™ Mobile app.

Many runners ask how running power correlates with heart rate. The 2 factors are certainly related as your muscles require more oxygen when they are generating more power. When viewing your charts post-run, you will see that when power goes up, heart rate follows a little while after. Avoiding this delay in response to changes (such as pace, hills or wind) is one of the advantages of using power rather than heart rate to gauge your effort when you’re running. Also, running power doesn’t depend on physiological factors — such as hydration level or how well-rested you are — the way heart rate does.

A graph showing a heart rate variability stress test.

Many runners are also surprised that their running power is so much higher than their bike power. In fact, running power is expected to be higher than bike power because metabolic efficiency is much higher for running (around 40-45%) than for cycling (around 20-25%). This means that athletes can convert the same amount of oxygen into more power when running than we can do when cycling. Or, thinking in terms of heart rate, we can produce more power for the same heart rate. This is primarily because when we run, we benefit from passive recoil of elastics elements such as tendons. Simply put, energy is stored when we land and returned as we push off. The same is not true for cycling. For more information on this, refer to our FAQs.

To help you train with running power, you can choose to download apps to show Current Running Power, Lap Running Power, Last Lap Running Power, Average Power or all 4 of those at once. Some runners also use zones or alerts to monitor their running power. The app settings enable you to set up 5 custom running power zones and/or high and low running power alerts to help you keep your running power within a target range.

If you already own the right Garmin devices, adding power to your run is free. All you need is a compatible Garmin watch¹ and 1 of these 3 accessories: HRM-Run or the Running Dynamics Pod. Download the Running Power app now to get access to real-time power data.

¹Compatible Devices