Concentric muscle action

A concentric muscle action occurs when a muscle shortens because its force exceeds the resistance acting on it.^{1Haff and Triplett (eds.), Essentials of Strength Training and Conditioning, 4th ed., p. 48.} This concentric contraction is the lifting phase of a rep, such as pressing the bar off the chest in a bench press or rising from the bottom of a squat.^{2Schoenfeld and Snarr (eds.), NSCA’s Essentials of Personal Training, 3rd ed., p. 21.} Swimming and cycling use concentric actions almost exclusively, and accelerating the body or a limb in sport is generally concentric.^{1Haff and Triplett (eds.), Essentials of Strength Training and Conditioning, 4th ed., p. 48.},^{3Hoffman, NSCA’s Guide to Program Design, p. 24.}

A muscle produces less force concentrically than during an eccentric muscle action, and concentric torque falls as joint speed rises.^{4Haff and Triplett (eds.), Essentials of Strength Training and Conditioning, 4th ed., p. 49.} Clients feel this difference when lifting a weight is harder than lowering it.^{2Schoenfeld and Snarr (eds.), NSCA’s Essentials of Personal Training, 3rd ed., p. 21.} It also explains why missed squats usually fail on the way up.^{5Helms et al., The Muscle & Strength Pyramid: Training, 2nd ed., p. 191.}

In practice

The load a client can lift depends on concentric strength at the sticking region, the hardest point in the range of motion, just above parallel in a squat.^{6Hoffman, NSCA’s Guide to Program Design, p. 94.}

Coach the client to accelerate on the way up: in one bench press study, trying to accelerate the bar as hard as possible produced almost double the strength gains of deliberately lifting at half that speed.^{7Helms et al., The Muscle & Strength Pyramid: Training, 2nd ed., p. 197.}

Keep the lowering phase in a program for hypertrophy, since concentric and eccentric actions recruit fibers differently and produce different adaptations.^{8Schoenfeld, Science and Development of Muscle Hypertrophy, 2nd ed., p. 113.}