The formula
session = sets × set length + (sets − 1) × rest
Where it comes from
Rest between sets is not a preference: the energy pathway being restored is different in each case. Phosphocreatine, which powers a maximal strength set, takes three to five minutes to refill, and cutting that short means less weight on the next set. For hypertrophy one or two minutes is enough, because part of the stimulus comes precisely from accumulated fatigue. And for muscular endurance you deliberately do not want to recover: thirty-second rests keep the muscle under metabolic stress.
How to work it out by hand
- Pick the goal, which is what sets the rest range
- Count the total sets: sets per exercise times exercises
- Multiply the sets by how long one takes
- Add the rests, which are one fewer than the sets
What is worth knowing
The figure that surprises most is how much of a session is spent resting: in strength training with five minutes between sets it is over eighty-five per cent of the time. That is not wasted time, it is part of the training, but it explains why a pure strength session takes so long for so few sets. If time is the constraint, supersets — alternating two exercises for different groups — let you rest the same amount in half the time.