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Strava’s “Fitness and Freshness” feature.

Thursday, August 7, 2014 by  
Filed under Daily Blog

August
7
2014

I’m going to be taking it easy on the bike for the next couple of days. Still riding, of course–and about the same distances as usual–but at a lower intensity.

Not only is my body telling me I need a little break, but so is my “Fitness and Freshness” chart on Strava. This morning I’d like to take a look at this very useful Strava feature. Note that this feature is for Strava Premium members, and it requires a power meter.

Strava’s “Fitness and Freshness” chart tracks three things: Fitness, Fatigue and Form. Here are the quick definitions of those terms:

Fitness: While fitness is a complicated concept, it can be simplified to just an accumulation of training. The Fitness Score is calculated using Training Load, to measure your daily training, and an impulse-response model to quantify its effect over time. This will intuitively capture the building up of fitness, as well as the loss of fitness during a break.

Fatigue: Conceptually, fatigue is easy to understand; it’s that tired feeling which limits your performance. We model it the same way as fitness, but on a shorter time scale. You’ll notice the score go up quickly after a couple hard days, but also go down quickly as you take a few days off.

Form: Being in form, or “peaking,” happens when one is very fit but not fatigued. Here we model this as the difference between your Fitness Score and your Fatigue Score.

Training Load, which is used to compute the above scores, is defined as follows:

We calculate Training Load by comparing your power during your ride to your FTP and determining how much load you put on your body during the workout. Training Load is a great way to determine how much rest you need after your workouts. The guide below will tell you how long after a workout it will take you to fully recover:

About 24 hours – 125 and lower
36-48 hours – 125-250
At least 3 days – 250-400
At least 5 days – 400+

For example, my ride on Tuesday was a 106 kilometer (66 mile) solo effort with a 230 watt Weighted Average Power; this ride was given a Training Load score of 220, which is nearing the upper end of the 48 hour recovery zone. You can see the spike from this ride on my current Fitness and Freshness chart. The dark grey line shows my Fitness as 95, and lighter grey line shows my fatigue spiked to 111, both all-time highs (click to enlarge):

My current "Fitness and Freshness" chart. Fitness is at an all-time high, however my fatigue is also quite high.

My current “Fitness and Freshness” chart. Fitness is at an all-time high, however my fatigue is also quite high.

 

I turned off the “Form” line for the sake of clarity, but you can see that the number is -16 (which is simply the Fitness score minus the Fatigue score) at top left on the chart. I can reduce my Fatigue (and increase my Form) without losing much Fitness by allowing myself a few easy days.

I believe that above all else athletes should listen to their bodies. That said, I’ve found that the Fitness and Freshness chart is amazingly accurate when it comes to predicting how I’m feeling. As a self-professed data junkie, I like having this information available, as it provides me with a nudge in the proper direction when I’m not 100% sure if I truly need a recovery ride, or if I simply need to HTFU.

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