Zing's AI estimates the freshness of your muscles depending on the frequency and intensity of your recent workouts. Zing calculates the muscle load of each workout you perform, which is an estimate of how tiring the workout is based on the workout type and its duration. Muscle load is calculated separately for every Muscle Group.
The muscle load of each activity decreases muscle freshness. Zing also measures the recovery period for the muscles and slowly increases their freshness.
Zing generates a workout based on the muscle freshness of each of your muscle groups. Once muscle freshness falls below a stated threshold, Zing will recommend a Recovery workout.