About the Effort Index
The Effort Index (EI) estimates workout difficulty:
EI = peak² / rest_per_set
peak- the largest set in the breakdown (front-loaded: any remainder lands on the leading sets).
rest_per_set- (total seconds ÷ sets) − (peak × time per rep).
Squaring peak captures the non-linear difficulty of the final reps in a maxed-out set. Dividing by rest_per_set captures the recovery tradeoff between sets — drawn from cluster-set training research.
Higher EI = harder workout. Advance picks the smallest non-negative EI jump toward your goal.