# What is the Model Curve?

Stryd’s Critical Power model, inspired by GoldenCheetah’s model, breaks down your Power Duration Curve into three components, which correspond to your three major energy sources while running: immediate energy, oxidative energy and nonoxidative energy. Your modeled power curve is your theoretical ability based on your data, the three mentioned systems, and a deprecation factor (see below). Your run data is used to fit a power curve for each of the three energy sources, and the total modeled curve is the summation of those three fit curves.

# Why is my modeled curve higher than my run data?

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.

# Why is my modeled curve lower than my best efforts for some 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 farther in the past, and their contribution to your modeled fitness has decreased.

# I had a great run, and improved my PDC but my CP went down... why?

As described above, your CP is determined from 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 CP will correct itself, becoming more accurate. Continuing to do best efforts at varying durations (as described above) will push your entire curve up, and result in an improved Critical Power.

# How do I use the modeled curve to find opportunities for Critical Power improvement?

When part of your modeled curve is lower than your Power Duration Curve, it’s typically a signal that you should make a hard effort for that duration to keep your fitness level up.

When part of your modeled curve is just a little over your Power Duration Curve, that means your training effort is close to your theoretical best effort, and you are doing a pretty good job for that duration.

When part of your modeled curve is way above your Power Duration Curve, that means your best training effort for that duration is lower than your predicted best. This could be a duration you don’t spend much time working hard and could consider doing some hard efforts in (depending on your goals).

# Where on the modeled curve is my Critical Power?

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.