Effects Of Concentric And Eccentric Contractions Of The Knee Extensors On Mechanical Work, Lactate Concentration, And Surface EMG

Abstract

The purpose of this study was to determine the effects of eccentric and concentric muscle contractions on the frequency and amplitude of EMG, torque, blood lactate, and the amount of work done. Ten college-aged males performed either four sets of twenty eccentric or concentric maximal contractions to induce muscle fatigue. Pre- and post-fatigues measurements of torque, EMG, blood lactate and work done were recorded. A 2 x 2 repeated measures ANOVA was used to test for differences in condition (concentric, eccentric) and time (pre, post) for the following dependent variables: total work done, average torque, change in lactate concentrations VL EMG, RF EMG and VM EMG. Significant pre - post differences were found for torque, blood lactate and EMG median frequency. There was a significant interaction between time and condition for VL EMG amplitude. In the concentric condition VL EMG amplitude decreased due to fatigue, and increased due to fatigue in the eccentric condition. For work done the third and fourth sets were significantly lower than the first set for both the eccentric and concentric conditions.