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Stryd Race Calculations FAQ
Stryd Race Calculations FAQ

Common Race Calculations questions.

Updated over a week ago

Why are longer distance race predictions accurate for me, but shorter distance race predictions are overly optimistic? Or vice versa?

Your Critical Power maps to a duration that may range from 30-70 minutes. In order to accurately predict performance at another duration, a fatigue factor is required.

Different runners have different fatigue factors. For example, a fast-twitch fiber dominant runner would have a larger fatigue factor compared to a slow-twitch fiber dominant runner.

Our Race Power Calculator determines your fatigue factor based on your age, gender, and the characteristics of your Model Curve on the Power Duration Curve. If your Model Curve has a very steep downward slope, you will be assigned a larger fatigue factor that corresponds with the “speed demon” classification in the previous generation Race Power Calculator. Someone who has a more gentle slope on their Model Curve will have a smaller fatigue factor that corresponds with the “aerobic monster” classification.

If you have an accurate fatigue factor, the Race Power Calculator prediction will be accurate across all distances. Otherwise, you may receive overly optimistic or pessimistic results. For example, if you are an “aerobic monster” with a small fatigue factor but your Model Curve has a steep drop off because you lack a max effort in the 10-20 minute range, you will be incorrectly assigned a larger fatigue factor. This will lead to an overly optimistic prediction for a short distance race. You should log a max effort in the 10 to 20-minute range in order to correct your fatigue factor.

I am using a Suunto/Polar watch. Why are my race times inaccurate?

The race power calculator analyzes all data in your Stryd account to estimate race time based on power. Suunto nor Polar record all the available Stryd metrics. Those watches record pace, distance, power and cadence from Stryd but do not record form power and other Stryd metrics.

Therefore, the power estimate will be accurate for each distance but the predicted race times can be incorrect.

To address this problem, Suunto and Polar users should upload the Stryd data with the Stryd app on the phone. The Stryd platform will attempt to merge the watch and Stryd data into one data set.

What are the factors which will affect the Race Power Calculator result?

There are three kinds of predictions that the Race Power Calculator can make and each of these three predictions has different requirements.

Prediction Type #1: Predicting a recommended power target based on a race course

Your running data from the last 90 days need to meet the following requirements:

You must have:

  1. A valid racecourse uploaded via PowerCenter

  2. At least 1 workout conducted around your Critical Power

  3. At least 1 workout conducted around the intensity for your target race distance

  4. An accurate Model Curve on your Power Duration Curve that extends from the 10-minute duration to the 20-minute duration.

    1. Note: This means that you must have a well-balanced Power Duration Curve and max efforts around the 10 to 20-minute duration. For example, a max effort in the 7-minute duration would be effective in modeling your 10-minute duration and a 25-minute activity would be effective in modeling your 20-minute duration. Alternatively, a max effort in the 15-minute range may also effectively model your capability from the 10 to 20-minute duration.

  5. Have an accurate Critical Power

    1. Note: If you use auto-calculated Critical Power, your auto-calculated Critical Power likely will be accurate if you meet requirement #3 by having a maximum effort near the 10-minute duration and the 20-minute duration.

Prediction Type #2: Predicting a race result time based on a power target

You need to have collected sufficient data running near that power target within the last 90 days. This will allow the Race Power Calculator to effectively convert a power target to a predicted time result on a racecourse.

Prediction Type #3: Predicting a power target required to achieve a target race result time

You need to have collected sufficient data running near the pace target required to achieve that result time within the last 90 days. This will allow the Race Power Calculator to effectively convert a target race result time to a power target.

How can I improve upon my recommended power target result from the Race Power Calculator?

There is one primary way to receive more ambitious and faster recommendations from the Race Power Calculator: improve your Critical Power. You should improve your Critical Power by filling your Power Duration Curve with a diverse amount of max efforts.

There are other ways to increase the recommendations but these ways will typically only yield small improvements and they are not reliably trainable, like Critical Power is.

You should primarily focus on increasing your Critical Power if you want to race faster.

Creating a race plan for Walking and Power-Hiking

If you are training or racing in steep terrain, you inevitably will switch between running and power hiking. You will notice a significant power difference between hiking and running. You will notice that if you run up a steep slope it will take a lot of energy, and if your pace drops walking becomes more efficient and will save you energy (hence the rule of thumb in ultra events: if you cannot see the top, walk). As walking is more efficient, power drops when switching to walking.

To be able to use power in steep inclines, you need two targets: one for walking and one for jogging/running. We currently have no test to determine sustainable walking power. At this time, you need to determine your own power hiking target that you can sustain.

If you use RSS to determine training load, consider that RSS gets impacted since it relies on CP.

Why is the shortest distance 1500 meters? Why is the longest distance 50k? How can I predict performances for shorter races or ultra marathons?

Race Power Calculator uses the Critical Power model to predict your performances from 1500 meters to Marathon.

These race distances are heavily tied to your Critical Power capability.

When you race a distance shorter than 1500 meters or longer than a marathon, other factors besides your Critical Power play a major role in your race plan.

For ultramarathoning, fueling strategy, muscle fatigue, and other factors play a significant role in how you will perform.

You will need to carefully consider these external factors on your own to make a determination for a power target for this kind of race.

Specifically, we recommend this webinar from Andy Dubois for ultra race planning:

How are elevation, temperature, and humidity I trained at determined? How do I change those factors?

PowerCenter stores your elevation, temperature, and humidity for every run that you have done to determine your typical training environment. The elevation is determined by the elevation given in the activity file. Temperature and humidity are determined by finding the local temperature and humidity conditions based on your location for each run.

Each of these factors plays a role in the amount of power that you can output on race day.

If your anticipated race day conditions are different from your typical training environment, the Race Power Calculator will make an adjustment to your target to factor in how much more/less power you will output in those conditions.

Does the Race Power Calculator take my Running Stress Balance into account? Is it projecting my future performance after a taper?

No. The Race Power Calculator considers your past 90 days of data and predicts your race performance as if you have tapered and are in optimal racing condition.

Why is the result from the Race Power Calculator different from the max power for that duration indicated by my Model Curve on the Power Duration Curve?

The Model Curve and the Race Power Calculator serve two different purposes. Both of these tools use your last 90 days of training data. However, the Model Curve focuses on your theoretical capability by mapping the potential contribution to the power of your bioenergetic systems. Race Power Calculator focuses on the definite capability that you have previously displayed in your training data.

As you log more max efforts across your Power Duration Curve, you can expect that your definite capability determined by the Race Power Calculator will more closely match your theoretical capability determined by the Model Curve.

My course has steep sections. Why is it rejected when I try to upload it?

For very challenging courses that have very steep inclines, there are factors that the Race Power Calculator can currently not accommodate. When uploading a course, we look at the overall elevation gain and loss for the course. For example, a point-to-point half marathon course that is an uphill course can only have about 600 meters of gain. If there is more elevation gain (and/or loss), the course will be rejected by the Race Power Calculator.

For these types of courses, the race power calculator cannot predict the pace and power you could sustain on such climbs and descents as it requires different muscles and biomechanics. We, therefore, do currently not allow those courses.

Does the target power include Air Power if you have the new Stryd (with wind detection)?

The power target given includes the power you need to spend to overcome the air resistance as if you were running in a still air environment (i.e. there is no wind).

Here is what that means:

  1. If you are running in a windy race, your finishing time will likely be a little slower than the finishing time given by the Race Power Calculator.

  2. If you are using the previous generation of Stryd which doesn’t account for the wind, the predicted time is likely too conservative for you.

Important Note: In order for this feature to work, you need to place the Stryd pod in a consistent, central, straightforward, and stable position on your shoes.

Stryd must be placed in a consistent, central, straightforward, and stable position on every set of shoes that you wear for data collection and race power recommendations to be correct.

It is easy to place Stryd on most shoes. You can see this video for reference:

However, if you are using a shoe with a unique or novel lacing pattern such as the Nike 4% shoes or the Nike Next% shoes, you will need to take extra care to place Stryd correctly. Watch this video for help:

Does the Race Power Calculator work for the previous generation Stryd?

Yes! Race Power Calculator automatically detects if you are using the previous generation Stryd foot pod and will make an accurate race prediction for you.

Why is the prediction for an official course dead-on for me, but too pessimistic for my own course?

The elevation gain/loss of a course is an important factor when predicting your finish time. The official, preloaded courses for the Race Power Calculator have extremely accurate records of the elevation gain/loss for that course.

When you upload your own course, the quality of the data is important. If the elevation value from the FIT file you upload is noisy, this leads to an exaggerated elevation gain value. This makes the Race Power Calculator think that the course is more difficult than it is in reality and leads to an under prediction of your finishing time. The target power value will still be very accurate, as your power target for your race is the same regardless of elevation change.

If you would like to upload a higher quality elevation trace of your race course, you should find an activity sourced from a watch that contains a barometer and GPS. Typically, watches that contain a combination of a barometer and GPS produce an elevation trace that is more representative of the actual course.

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