"Time under tension"- how long a muscle stays under load during a set- has its own body of research. A widely cited meta-analysis by Schoenfeld and colleagues found rep durations from roughly half a second to eight seconds produced similar strength and size gains, while a 2021 review by Wilk, Zając, and Tufano concluded that moderate tempos of about two to six seconds per rep are just as effective as faster ones, with only very slow reps, over ten seconds each losing effectiveness because they force the weight down too far. [Schoenfeld et al., 2015 · Wilk et al., Sports Medicine, 2021]

At 14 reps per set, a 40–45 second working window puts each rep at roughly three seconds, squarely inside that effective range. It's long enough to keep meaningful tension on the muscle without requiring heavy external load, which matters for anyone returning to resistance work after years away.

The short 15–20 second gap between reps keeps the muscle from fully resetting mid-set, which is what makes fourteen controlled reps feel demanding even at a moderate weight.

The longer 60-second rest between sets serves a different reason:
Research on inter-set rest intervals shows that recovery time directly affects how well movement quality holds up across repeated sets, and a one-minute window is generally enough to sustain form through three rounds without stretching a session out. [Inter-set rest interval systematic review, medRxiv, 2025]

None of this needs a maximal load. Multiple randomised controlled trials in older adults produced significant strength gains using resistance bands and bodyweight-scale loads — the format matters more than the plate count.