Stryd tracks your foot through three dimensional space and records the accelerations, impacts, and forces that are being applied. From that information, we calculate power, as well as provide other commonly used run metrics like distance, pace, cadence, ground contact time, vertical oscillation, etc. All of our calculations have been validated with high resolution motion capture systems, dual force plate treadmill, and metabolic testing.
The new Stryd (with wind detection) incorporates the cost of overcoming air resistance into the total power value in real-time.
You can see the total percentage of power required to overcome air resistance (Air Power) in post-run analysis on PowerCenter and some 3rd party platforms.
Many variables go into determining how much air resistance a runner has to overcome such as the local wind conditions, the humidity of the local environment, the temperature of the local environment, the air density as determined by the altitude and local weather patterns, the air resistance you are overcoming relative to the Earth (wind speed), the air resistance you are overcoming relative to yourself (running speed), unique body morphology, and more.
If you would like more details on how Stryd determines Air Power in realtime, you should reference our white paper here: Adding Air Resistance Costs to Power Estimates in Running | White Paper
What is Form Power?
Form Power is an additional component of running power relating to vertical oscillation and cadence. It is also weight-dependent.
Why does Form Power matter?
Increased Form Power can be associated with increased metabolic cost at a given pace. By decreasing Form Power, some runners may be able to decrease metabolic power and rate of perceived exertion (RPE) at a given pace.
What is Form Power Ratio?
Form Power Ratio, or FPR, is calculated as the Form Power/total Power.
Why does Form Power Ration matter?
Lower values may indicate greater efficiency, but we do not recommend aiming for a particular FPR. Like most advanced Stryd metrics, it is best to look for the trends and patterns in how your FPR changes with paces, intensities, and fatigue states.
Ground Contact Time
What is Ground Contact Time?
Ground Contact Time (GCT), or Ground Contact, is the amount of time per stride that a runner's foot is touching the ground, in milliseconds. The starting trigger of a runner's ground contact time will vary depending on the runner's gait (heel-strike versus midfoot-strike versus forefoot-strike) but will always end at toe-off (full body removed from the ground, now in the swing phase of the gait cycle).
Why does Ground Contact Time matter?
Ground Contact Time has an inverse relationship with metabolic power, meaning a lower Ground Contact Time is typically an indicator of a higher metabolic power (within an individual rather than across different runners). It is best used as a metric to monitor trends, rather than to aim for specific values (i.e. striving to attain a GCT of 165ms). A runner may experience upward trending GCT values as they fatigue near the end of a long run. They may also see Ground Contact Time decrease over the course of a training cycle as the runner becomes stronger. Other factors that will affect a runner's GCT are shoes (cushion level and heel-to-toe offset), pace, and cadence.
What is Vertical Oscillation?
Vertical Oscillation (Vert. Osc.) is the vertical movement of a runner's center of mass between steps when running. A human's center of mass is typically at the pelvis or hip, so an easy way to think about vertical oscillation is the vertical rises and fall of a runner's pelvis over one gait cycle (expected minimum vertical position at mid-stance of ground contact, expected maximum vertical position during float period). Typical Vertical Oscillation values will range from 3-15cm.
Why does Vertical Oscillation matter?
Ideal Vertical Oscillation will vary based on the individual. It is best used as a metric to monitor trends, rather than to aim for specific values (i.e. striving to attain a Vert. Osc. of 4.0cm). Trends will also differ from one runner to the next as they get fitter or faster over a training cycle, but it can be useful in considering how a runner's body may be responding to their training.
Vertical Oscillation can also be impacted by running uphill or downhill versus running on level ground. Again, the way in which one runner's Vertical Oscillation responds to uphills and downhills may differ from another runner.
What is Cadence?
Cadence is the measure of a runner's steps per minute (SPM). Typical values for Cadence are between 150-210spm.
We have found that various platforms define and label "cadence" differently than Stryd does.
Polar uses RPM (Reps Per Minute), which will be equal to SPM divided by 2
Suunto uses SPM
Garmin uses SPM
Why does Cadence matter?
Cadence can be monitored for consistency throughout a run and may decrease with the onset of fatigue. The optimal cadence will differ by the individual due to physical characteristics (leg length, weight, etc.) and features of running form (foot strike, arm swing, etc.). It is best monitored for individual-specific trends over time to gain insight into how a runner's training may be impacting their running mechanics.
Leg Spring Stiffness
What is Leg Spring Stiffness?
Leg Spring Stiffness (LSS) is a model of elastic energy in the leg, assuming it acts like a spring. It is the maximum vertical force a person generates in a step divided by the displacement during ground contact time.
Why does it matter?
LSS can be a good monitor of changes to running mechanics over time. To compare runs effectively, conditions must be the same (surface, shoe, approximate pace, etc.). It can also be analyzed within training sessions to discern changes in running mechanics within a run, but it is again important to account for show or surface changes within a session.
Pace & Distance
Impact Loading Rate
Stryd reports all metrics each run and they are automatically recorded by Garmin, Coros, Wahoo and Apple Watches. If you use a Polar or Suunto watch, you need to upload the data from Stryd with the Stryd app to get a complete data set.
You can read more about Stryd's metrics in this article from Coach Steve Palladino.