Eccentric muscle action

Eccentric muscle action, also called an eccentric contraction, occurs when a muscle lengthens because resistance exceeds the force it produces.^{1Haff and Triplett (eds.), Essentials of Strength Training and Conditioning, 4th ed., p. 48.} During the lowering phase of resistance exercise, it stops gravity from accelerating the weight downward.^{1Haff and Triplett (eds.), Essentials of Strength Training and Conditioning, 4th ed., p. 48.} It also brakes movement in sport: slowing the body or a limb is generally eccentric work.^{2Hoffman, NSCA’s Guide to Program Design, p. 24.}

Muscles are strongest eccentrically: force during lengthening can exceed maximal isometric strength by 50 to 100%.^{3Zatsiorsky, Kraemer and Fry, Science and Practice of Strength Training, 3rd ed., p. 47.} Most clients are 20 to 40% stronger lowering a load than lifting it.^{4Helms et al., The Muscle & Strength Pyramid: Training, 2nd ed., p. 197.} For a given force, eccentric actions use fewer active fibers and less energy, and cause more muscle damage.^{5Hoffman, NSCA’s Guide to Program Design, p. 94.}

In practice

• Expect soreness when clients start training or try something new: eccentric actions are the main cause of the tissue damage behind delayed onset muscle soreness (DOMS).^{6Schoenfeld and Snarr (eds.), NSCA’s Essentials of Personal Training, 3rd ed., p. 21.}
• Helms distinguishes slowing the lowering phase from eccentric overload: the latter’s benefit comes from heavier loads, while an ordinary set is capped by concentric strength.^{7Helms et al., The Muscle & Strength Pyramid: Training, 2nd ed., p. 192.}
• To overload the eccentric, lift with two limbs and lower with one, or have a spotter help only on the way up.^{8Hoffman, NSCA’s Guide to Program Design, p. 95.},^{9Schoenfeld, Science and Development of Muscle Hypertrophy, 2nd ed., p. 155.}
• Keep heavy eccentric work to four- to six-week cycles with only a few sets per workout, to limit muscle damage and the risk of overtraining and injury.^{8Hoffman, NSCA’s Guide to Program Design, p. 95.}