Exercise-induced muscle damage: absence of adaptive effect after a single session of eccentric isokinetic heavy resistance exercise.

Background: Unaccustomed eccentric exercise induces muscle damage. A single session of eccentric exercise can induce an "adaptive effect" protecting exercised muscles during several weeks. Our aim was to verify this phenomenon in isokinetic exercise. Tested hypothesis was: the progressive muscle rise in tension due to isokinetic eccentric actions would be insufficient to induce the adaptive effect.

Experimental Design: prospective study.

Setting: general community.

Participants: six healthy and moderately active (untrained) males (29.1 yr +/- 1.5 SEM).

Interventions: subjects performed two isokinetic eccentric exercises (EE1 and EE2) of the quadriceps femoris of both legs (120 degrees.s-1; 8 sets of 15 repetitions) separated by 4 weeks.

Measures: type I serum myosin heavy chains (MHC) and creatine kinase concentrations (CK), and rate of perceived soreness (DOMS) were collected before each exercise and on days 1, 2, 4, 6 and 9.

Results: Both exercises induced significant (p < 0.01) increases in MHC and CK concentrations, and DOMS score. There was no significant difference between EE1 and EE2, at any measurement time for any parameter. Mean peak values (SEM) were respectively (EE1; EE2): MHC (microU.l-1): 308 (192); 285 (191). CK (U.l-1): 1217 (760); 1297 (1039). DOMS score: 2.67 (0.52); 2.33 (0.52).

Conclusions: The first session of eccentric isokinetic exercise (EE1) had no adaptive effect against muscle damage when an identical session was performed 4 weeks later (EE2). Muscle adaptation could have resulted in increased work production (+10.2%; p < 0.05; from EE1 to EE2).