Isolation exercise

An isolation exercise, also called a single-joint exercise, stresses one joint or major muscle group, as in a knee extension or biceps curl.^{1Hoffman, NSCA’s Guide to Program Design, p. 96.} The NSCA classes these as assistance exercises when they use one primary joint and a small amount of muscle mass.^{2Schoenfeld and Snarr (eds.), NSCA’s Essentials of Personal Training, 3rd ed., p. 414.} The pec deck and dumbbell fly count too, even though they work the large chest muscles, because only the shoulder joint moves.^{2Schoenfeld and Snarr (eds.), NSCA’s Essentials of Personal Training, 3rd ed., p. 414.}

Isolation exercises need less coordination, which suits clients with aesthetic goals, a weak muscle group, rehab after injury or a gap left by another exercise.^{3Ozemek et al., ACSM’s Guidelines for Exercise Testing and Prescription, 12th ed., p. 359.} The lower skill demand may also mean less injury risk.^{1Hoffman, NSCA’s Guide to Program Design, p. 96.}

In practice

• New clients are often taught machine and free-weight assistance exercises first, since they take less skill than core lifts.^{2Schoenfeld and Snarr (eds.), NSCA’s Essentials of Personal Training, 3rd ed., p. 414.}
• Schedule isolation exercises after the large-muscle, technically demanding lifts, since they’re less fatiguing.^{3Ozemek et al., ACSM’s Guidelines for Exercise Testing and Prescription, 12th ed., p. 359.}
• They can reach muscles that compound lifts underwork.^{4Schoenfeld, Science and Development of Muscle Hypertrophy, 2nd ed., p. 193.} The leg curl, for example, shows more hamstring activity than the squat or leg press, and the evidence suggests single-joint work adds to muscle growth.^{4Schoenfeld, Science and Development of Muscle Hypertrophy, 2nd ed., p. 193.}
• Single-joint and some machine exercises hold their volume load with rest intervals of 60 to 90 seconds.^{5Schoenfeld, Science and Development of Muscle Hypertrophy, 2nd ed., p. 123.}