An adaptive training system can determine a finite work capacity and critical power and use those determinations to generate an adaptive training programs for workout parameters. To determining a finite work capacity and critical power, the adaptive training system can receive workout data; generate data points by determining, for each workout, a maximum amount of work done for each of multiple time window sizes; fit these workout data points to a function; and determine a critical power and finite work capacity based on the fitted function. Once the adaptive training system has determined a critical power and finite work capacity, the adaptive training system can use them to generate an adaptive training program by keeping a function defined by a set of workout parameters below an ability function that is based on the critical power and finite work capacity.