Power Duration Curve represents the relationship between the power output a runner can sustain and the duration for which they can sustain it from short sprints to long endurance runs (up to five hours)
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Your power output is displayed on the y-axis and duration is displayed on the x-axis.
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The curve typically starts high on the y-axis (power) and drops off as the duration on the x-axis increases. At the very left, the curve shows the maximal power you can sustain for a very short period, starting from one second. As you move right, the power values decrease, showing how much power you can sustain over longer periods, like minutes to hours.

Contributing runs will have a ‘run age’. Runs that are in the last 30 days contribute fully to your fitness model (Auto-Calculated Critical Power Model Curve), after that, they begin to have a deteriorating contribution. Green and gray runs have a diminishing contribution over time (and is the reason you’ll see your Auto-Calculated CP model curve dip below your Power Curve). And gray runs are about to fall off and no longer contribute to your Auto-Calculated CP model. These classifications can help you know what power/duration you need to add to your training to maintain or improve your CP.

You can use this curve to determine your strengths and weaknesses as a runner, set training & racing intensities, and predict performance in events of various lengths.

The shape of the curve can vary significantly between athletes, depending on their training, skills, and fitness level. Some of these differences can be analyzed in the Training Distribution on PowerCenter.

Regular training and improvements can shift the curve upwards (indicating improved power output) or to the right (indicating improved endurance).

Your Power Duration Curve is shaped by your top performances across various durations over the past 90 days. Each time you surpass your previous best in power output for a specific duration, that new peak performance is plotted on the curve at the corresponding duration. This means the curve evolves to represent your highest achieved power levels for different periods, reflecting your most recent and strongest efforts.

The Power Duration Curve represents your highest sustained power for different time lengths. If your latest run didn't surpass or equal your past top performances for the same duration, it won't impact the curve. The curve is updated exclusively when you reach a new peak in power output for a particular duration, reflecting your strongest efforts.

We default to showing the last 90 days because it best represents the period of time that contributes to your Critical Power based on our model for determining CP.

Specifically, if you are not training, 90 days is long enough to capture the effects of detraining, and if you are training, it's long enough to cover the key part of your training plan (e.g., build-up phase and peak phase).

If shorter than 90 days, we may miss some of the training/detraining effects and accumulated adaptation.

Here are some resources to explain the effects of training and detraining...

For a very in-depth explanation: https://link.springer.com/article/10.2165/00007256-200030020-00002

To ensure your Power Duration Curve accurately reflects your current fitness and capabilities, it's crucial to regularly perform maximal efforts across a range of durations. This variety in training helps capture your peak performance at different lengths, keeping the curve up to date.

Key duration domains for the Power Duration Curve include:

1. Short Explosive Efforts: Engage in brief, intense activities like short sprints, hill sprints, or strides. These should last between 10 to 30 seconds and be performed at maximum effort.
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2. Short Intense Runs: Complete runs that last 3 to 5 minutes at your peak effort. This duration tests your ability to sustain high intensity over a short period.
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3. Moderate Duration Max Efforts: Runs of 10 to 20 minutes at maximum or near-maximum effort. These could be in the form of time trials or a 5k race effort, pushing your medium-duration endurance.
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4. Longer Duration Max Efforts: For those training for longer events like half or full marathons, incorporate runs lasting 40 to 60 minutes at your highest sustainable effort. This can be achieved through time trials or race efforts such as a 10k race, focusing on long-duration endurance.

If a contributing activity leaves the 90-day consideration window, you may notice that your Power Duration Curve changed substantially. This change may not be representative of your current capability. You should replace efforts that age out of your 90-day window with an equivalent or better effort to show that you are maintaining or improving your fitness.

In the Power Duration Curve, you can toggle on Modeled Ability. Modeled Ability predicts your highest sustainable power output for various durations, based on past performances. It helps gauge your sprint and endurance potentials, guiding training and race strategies.

Your Critical Power is determined by three major energy sources while running: immediate energy, oxidative energy and nonoxidative energy A change to one of these areas can tell the model that another is overestimated, and your Critical Power will correct itself, becoming more accurate. Continuing to do your best efforts at varying durations (as described above) will push your entire curve up, and result in an improved and higher Critical Power over time.

For example, a new anaerobic performance contributing to your Power Duration Curve in the 3-5 minute duration signals lower-than-previously-thought aerobic capabilities which results in a downward readjustment and more accurate Critical Power.

In theory, your Model Curve should always be equal to or higher than your best training performances. The modeled curve represents the “theoretical best effort you can hold for different periods of time” and based on your run data is the “best effort you have done in your training for different periods of time.” Since it is less likely for you to have a true best effort in your training for all periods of time, the modeled curve should be higher than your true Power Duration Curve in most parts.

The Stryd Model Curve uses a “depreciation” factor. Depreciation means that older workouts will not contribute the same as new workouts when we calculate your modeled curve.

Essentially, the value that a previous activity has to your current fitness level depreciates over time. This method of accounting for beneficial workouts is more reflective of how the body works because you will maintain fewer positive adaptations from a month-old workout compared to a day-old workout. Read this post for more details.

However, when we show your Power Duration Curve, the “depreciation” factor is not applied. So, when your modeled curve is lower than your true Power Duration Curve, that means those workouts were done further in the past, and their contribution to your modeled fitness has decreased.

Stryd’s model extracts the likely contribution of your three energy systems to predict energy production for different durations. Your Critical Power value is tied to the flatter area of your Power Duration Curve. This flat area is composed of efforts reflecting your Aerobic system, which is the primary driver for efforts at your Critical Power. The Critical Power model does not correspond to any specific time duration.