Fatigue during repeated eccentric-concentric and pure concentric muscle actions of the plantar flexors

OBJECTIVE: To compare the fatigue development during pure concentric actions with eccentric-concentric actions in standardized isokinetic, open-chain conditions. DESIGN: The study was performed with measurement of muscular strength and EMG of the plantar flexors on an isokinetic dynamometer. BACKGROUND: Fatigue development on a dynamometer has mostly been studied with repeated pure concentric actions. Eccentric-concentric actions are, however, often used in normal activities. An eccentric action has an immediate effect on a following concentric action and therefore it is of interest to follow the fatigue process in repeated combined actions. METHODS: Ten healthy young women participated. The pure concentric test was performed with the same number of cycles as in the eccentric-concentric test, which was performed until exhaustion. Development of MPF and RMS of the EMG in the triceps surae, as well as work, were evaluated. RESULTS: The total amount of work was significantly higher in the eccentric-concentric test than in the pure concentric test. The work decreased similarly (32-39%) with no significant difference between the two tests. A significant decrease (12-16%) in MPF was only seen in the eccentric-concentric test. No changes in RMS were seen. CONCLUSION: The similar reductions of work seen in both tests should primarily be sought in the contractile process as such. Changes in MPF may then be viewed as a phenomenon dependent on the timing of the duty cycle. RELEVANCE: The eccentric-concentric test lead to exhaustion and showed EMG changes and should therefore be recommended when evaluating the development of fatigue in muscular performances in different groups of patients.