Rest interval

A rest interval is the time between sets or exercises.^{1Schoenfeld and Snarr (eds.), NSCA’s Essentials of Personal Training, 3rd ed., p. 426.} As a rule, the heavier the load, the longer the rest.^{1Schoenfeld and Snarr (eds.), NSCA’s Essentials of Personal Training, 3rd ed., p. 426.}

Short rests trade the ability to lift more weight for greater metabolic stress.^{2Schoenfeld, Science and Development of Muscle Hypertrophy, 2nd ed., p. 120.} In one study, 30-second rests cut training volume by more than half over 5 sets at 10RM.^{2Schoenfeld, Science and Development of Muscle Hypertrophy, 2nd ed., p. 120.} Strength and power work relies on the ATP-CP system, which takes at least 3 minutes to mostly replenish; lifting performance held up best with 5-minute rests.^{3Hoffman, NSCA’s Guide to Program Design, p. 109.}

Where sources differ

The ISSA’s strength and conditioning text suggests 30 to 60 seconds between hypertrophy sets, citing the acute growth hormone response.^{4International Sports Sciences Association, Strength and Conditioning, p. 232.} Schoenfeld notes that 60 to 90 seconds is often prescribed for growth because of its metabolic effects, but reads the newer research as favoring at least 2 minutes, since longer rest keeps volume load higher.^{2Schoenfeld, Science and Development of Muscle Hypertrophy, 2nd ed., p. 120.},^{5Schoenfeld, Science and Development of Muscle Hypertrophy, 2nd ed., p. 121.}

In practice

• For strength and power, allow 2 to 5 minutes; for muscular endurance in circuits of dissimilar muscle groups, allow under 30 seconds.^{1Schoenfeld and Snarr (eds.), NSCA’s Essentials of Personal Training, 3rd ed., p. 426.}
• For hypertrophy, allow at least 2 minutes for multi-joint free-weight lifts.^{6Schoenfeld, Science and Development of Muscle Hypertrophy, 2nd ed., p. 123.} Single-joint and some machine exercises don’t lose volume load with shorter rest, so 60 to 90 seconds can work there.^{6Schoenfeld, Science and Development of Muscle Hypertrophy, 2nd ed., p. 123.}
• Untrained clients learning technical lifts may need 2 to 5 minutes whatever the goal.^{1Schoenfeld and Snarr (eds.), NSCA’s Essentials of Personal Training, 3rd ed., p. 426.} If technique slips, lengthen the rest.^{1Schoenfeld and Snarr (eds.), NSCA’s Essentials of Personal Training, 3rd ed., p. 426.}
• Sets to failure need longer rests to hold volume load, while stopping short of failure lets you shorten them.^{5Schoenfeld, Science and Development of Muscle Hypertrophy, 2nd ed., p. 121.}