Systematic review — 2018 — Strength · Recovery
Effects of Rest Interval Duration in Resistance Training on Measures of Muscular Strength: A Systematic Review
What did the researchers investigate?
Chronic strength gains from resistance-training programmes that used different rest-interval durations, in a PRISMA systematic review of 23 studies with 491 participants (413 males, 78 females). All studies were of good to moderate methodological quality.
What did they find?
Robust strength gains could be achieved even with short rest intervals. For resistance-trained people, rests longer than 2 minutes were required to maximise strength gains. For untrained people, short to moderate rests (60-120 seconds) were enough.
What does this mean for training?
For strength, trained lifters may do better resting two minutes or more between demanding sets; beginners do not need to rest that long.
How does FitX AI use this evidence?
Supports the rest timer recommending longer rests after demanding lifts. The timer's exact defaults (3 minutes after heavy compound lifts, 2.5 after other compound lifts, 2 after isolation exercises) are FitX AI product choices: this review supports resting over 2 minutes for strength in trained lifters and says nothing specific about isolation exercises.
Where FitX AI's own choices go beyond this paper
Rest timer. The 180, 150 and 120 second defaults and the three exercise categories are FitX AI product choices; the timer is a recommendation and never forces a rest. The evidence is mixed. For muscle growth alone, the pooled analysis found little difference beyond about 90 seconds, while trained lifters gained more strength (and in one trial more thigh growth) with rests of about 2-3 minutes. No paper sets different rests for heavy compound, other compound and isolation exercises.
Session length. The per-set time estimates (2.75 and 2.25 minutes, plus warm-up) are planning figures, not research findings.
Limitations
Covers strength only, not muscle size. The abstract states conclusions without effect sizes, and 413 of the 491 participants were male.