Metabolic stress and mechanical tension are throught to be the main drivers of muscle growth. A recent study found that elevations in blood lactate (a proxy for metabolic stress) were similar after a full-body workout with six exercises for four sets to failure at 10RM, resting 30, 60, or 120 seconds between sets. Still, training volume was lowest when resting 30 seconds per set.
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Now, lactate isn’t the only measure of metabolic stress, so there might be more going on here that wasn’t measured (ATP, phosphocreatine and muscle pH). Blood lactate only normalize by about 7% after 2 minutes, while measures like pH normalize by 25% after 2 minutes.
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If you’re tight on time, it may be worth training with short rest intervals (or using techniques such as drop sets, rest-paused sets, or antagonist paired sets) just so you can get more total work in. Otherwise, you’re probably better off resting at least a minute (and generally 2-3+ minutes) between sets. Shorter rest intervals compromise performance without increasing metabolic stress.
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Overall, rest intervals of 60-120 seconds are probably adequate for single-joint accessory work, rest intervals of 90-180 seconds are probably adequate for general multi-joint work, and rest intervals of 3-10 minutes are probably adequate for pure strength or power training.
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THE EVIDENCE: Lopes et al. Effect of Rest Interval Length Between Sets on Total Load Lifted and Blood Lactate Response During Total-Body Resistance Exercise Session. Asian Journal of Sports Medicine - Effect of Rest Interval Length Between Sets on Total Load Lifted and Blood Lactate Response During Total-Body Resistance Exercise Session

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