Eccentric load is the phase of a rep where the muscle lengthens under tension. Lowering a squat, decelerating a deadlift, pulling a chin-up back down.
Mechanism: Eccentric contractions generate more force per unit of recruitment than concentric, and produce more microscopic damage that drives hypertrophy. Tendon collagen aligns under sustained eccentric load.
Use case: Slow the lowering (3-5 second tempo) on key lifts. Specifically prescribed for tendinopathy rehab. Achilles, patellar, elbow.
Caveats: Eccentrics produce more delayed-onset soreness (DOMS). Build up gradually or rebound from rest.