Running Dynamics and
Physiological Measurements

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

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.

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.

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.

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 TypeTypical Aerobic TETypical Anaerobic TE
Long, slow distance2.0 - 3.0Maintaining Aerobic Fitness0No Anaerobic Benefit
20-minute threshold3.5+Improving Lactate Threshold0No Anaerobic Benefit
Lactate threshold intervals3.0+Improving Lactate Threshold0 - 2.0Minor Anaerobic Benefit
Sprint intervals10 x 50m @
150-200% VO2 max
0 - 2.0Minor Aerobic Benefit2.0 - 3.0Maintaining Speed
Speed intervals10 x 400m @
100-105% VO2 max
2.0 - 4.0Improving Aerobic Fitness3.0 - 4.0Improving Economy and Anaerobic Fitness
Speed intervals10 x 400m @
110-115% VO2 max
2.0 - 4.0Improving VO2 Max4.0+Highly Improving
Anaerobic Fitness
800m race2.0+Maintaining Aerobic Fitness2.5+Maintaining Anaerobic Fitness
5K race3.5+Improving VO2 Max1.0 - 2.0Minor Anaerobic Benefit
10K race4.0+Highly Improving VO2 Max0.0 - 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.

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.

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.

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.

Heart Rate Variability (HRV)

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.


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.

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.


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.