Force and EMG power spectrum during and after eccentric and concentric fatigue

Eccentric and concentric force and median frequency of the EMG power spectr um were measured during and immediately after maximal eccentric (EE) and co ncentric (CE) exercise and during the recovery period of 1 week. Eight male subjects performed EE and CE consisting of 100 maximal eccentric and conce ntric actions with elbow flexors during two separate exercise sessions. Whe n comparing maximal eccentric and concentric actions before the exercises, the average force was higher (P<0.001) in eccentric than in concentric but the average rectified EMG (aEMG) values were the same with the two types of action. The average eccentric force decreased 53.3% after EE and 30.6% aft er CE, while the average concentric force decreased 49.9% after CE and 38.4 % after EE. The recovery was slower after EE. The median frequency (MF) of biceps brachii (BB) in eccentric action decreased during both EE (P<0.01) a nd CE (P<0.05). It recovered within 2 days of the exercises but was lower a gain (P<0.01) 7 days after EE. In concentric action MF of BE decreased duri ng CE (P<0.01), while no changes were observed in EE. Blood lactate concent ration increased (P<0.001) in both exercises and serum creatine kinase (CK) activity increased in EE only, being significantly higher (P<0.001) 7 days after than before the eccentric exercise. In the absolute scale, the eccen tric force in EE decreased more than the concentric force in CE (P<0.01). F atigue response was action type specific as seen in the greater reduction i n the force of the exercise type. MF decreased immediately after both exerc ises, which may be at least partly related to elevated blood lactate concen tration. Eccentric actions led to possible muscle damage as indicated by el evated serum CK and muscle soreness, and therefore to longer recovery as co mpared to concentric actions. Decreased MF after EE may be indicative of se lective damage of the fast twitch fibers in this type of exercise. (C) 2000 Elsevier Science Ltd. All rights reserved.