Characteristics of isometric and dynamic strength loss following eccentric exercise‐induced muscle damage

Abstract

Angle‐specific isometric strength and angular velocity‐specific concentric strength of the knee extensors were studied in eight subjects (5 males and 3 females) following a bout of muscular damaging exercise. One hundred maximal voluntary eccentric contractions of the knee extensors were performed in the prone position through a range of motion from 40° to 140° (0°=full extension) at 1.57 rad · s⁻¹. Isometric peak torque was measured whilst seated at 10° and 80° knee flexion, corresponding to short and optimal muscle length, respectively. Isokinetic concentric peak torque was measured at 0.52 and 3.14 rad · s⁻¹. Plasma creatine kinase (CK) activity was also measured from a fingertip blood sample. These measures were taken before, immediately after and on days 1, 2, 4, and 7 following the eccentric exercise. The eccentric exercise protocol resulted in a greater relative loss of strength (P−1. CK activity was significantly elevated above baseline at days 4 (PP<0.01). The greater relative strength loss at short muscle length appeared to persist throughout the seven‐day testing period and provides indirect evidence of a shift in the angle–torque relationship towards longer muscle lengths. The results lend partial support to the popping sarcomere hypothesis of muscle damage, but could also be explained by an impairment of activation at short muscle lengths.