Strava has updated its Fitness/Freshness feature, previously only available to cyclists who ride with a power meter and now open to those who train with a heart rate monitor.

The feature, one of the perks available to premium members who pay a monthly or annual subscription fee, allows riders to monitor their fitness and fatigue levels, previously measured using ‘Training Load’ and calculated from weighted average power.

However, this latest update means the Fitness/Freshness chart can also be based on ‘Suffer Score’, generated by Strava according to how much time a rider spends in each of their heart rate zones during a particular activity.

The Fitness/Freshness chart generates three numbers which represent the rider’s current fitness, fatigue and form. Strava’s method for calculating those three numbers is based on the ‘impulse-response model’ first developed by Dr. Eric W. Banister in 1975 and later applied to cycling by Dr. Andy Coggan.

Fitness can be simplified as an accumulation of training over time, according to Strava, and the score is based on a rider’s daily training, with the impulse-response model used to quantify its effect over time. Strava say this will “intuitively capture the building up of fitness, as well as the loss of fitness during a break”.

Fatigue, meanwhile, is described by Strava as the tired feeling that may dull performance. The score is calculated using the same model as fitness but over a shorter period of time, so a rider’s fatigue score may jump after a succession of hard rides, and equally it will drop after a period of rest.

Form, then, is the difference between the fitness score and the fatigue score – strike the right balance and you’ll be flying. Strava say the Fitness/Freshness chart allows you to see “when and where you’re at your freshest or most fatigued during your rides [in order to] anticipate those peaks and valleys and stay on top of your performance.” Good form all round, then?

You can read more about Strava’s Fitness/Freshness chart here.