Functional Reserve Capacity Calculator

About this calculator

The gap between a rider’s maximal aerobic power output (VO2max power) and their functional threshold power (FTP) represents a reserve of capacity usable for surges, attacks and sprints above what can be sustained at threshold — a concept closely related to W′ (anaerobic work capacity) in power-duration modeling.

Cycling coaches and power-based training platforms use this reserve to profile riders as sprinters versus diesel engines: a large reserve points to strong attacking and sprinting ability, while a small reserve suggests a rider better suited to steady, time-trial-style efforts near threshold.

This calculator takes your FTP and your maximum power (or VO2max power), and returns your reserve capacity along with what it suggests about your rider type.