An eccentric contraction is a muscle action in which the muscle-tendon unit lengthens while producing force. It occurs when the external torque at a joint is greater than the torque the muscle produces, so the joint moves opposite to the direction the muscle pulls. The muscle is active, but it is resisting and controlling the movement rather than causing it.
Eccentric actions do negative mechanical work: they absorb energy. They are central to slowing down, landing, changing direction, and lowering a load under control.
Common Examples
- The quadriceps during the downward phase of a squat
- The hamstrings slowing the lower leg late in the swing phase of sprinting
- The quadriceps and calf muscles absorbing impact when landing from a jump
- The posterior shoulder muscles decelerating the arm after a throw
Muscles can generally produce more force eccentrically than concentrically, and eccentric work is metabolically less costly. Unaccustomed eccentric exercise is also strongly associated with delayed-onset muscle soreness. Eccentric training is widely used in strength development and rehabilitation programs.
Observing It in Video
Eccentric phases can be inferred when a joint moves in the same direction as an external load while being controlled, such as knees and hips flexing during a landing. Slow-motion and frame-by-frame review can show how deep the landing goes, how long the lowering phase lasts, and whether one side absorbs the load differently from the other. Side-by-side comparison can help show changes in landing control over time.
Limits and Pitfalls
- Video cannot show how much force a muscle is producing or how fast energy is being absorbed
- A slow, controlled lowering and a fast, collapsing one may reach similar joint angles; timing matters as well as position
- Gravity-assisted movements are not automatically eccentric if no muscle is resisting them
- Muscle-level behavior can differ from joint motion because tendons also stretch and recoil
Recognizing eccentric phases helps coaches describe deceleration and landing technique more precisely, without claiming to measure internal loading from video alone.