Electromyographic behavior of the hamstrings muscles during ramp isometric contractions test

The purpose of this study was to determine the effect of ramp isometric contraction on changes in surface electromyography (sEMG) signal characteristics of the hamstrings muscles. All measurements were obtained from 20 healthy well trained females (age 19.5 ± 0.8 yrs, body mass 63.4 ± 1.5 kg, height: 1.65 ± 0.05 m). Subjects had to perform isometric ramp contractions in knee flexion with the force gradually increasing from 0 to 40% of the maximal voluntary contraction (MVC) in a 20s period. The root mean square (RMS) amplitude of sEMG signals obtained from the semitendinosus, semimembranosus and biceps femoris (caput longum) were calculated at four different force levels (10, 20, 30 and 40% MVC) from the ramp isometric contractions (5s during the 20s task %MVC). The main results were a more pronounced increase non-linear in sEMG-RMS amplitude for the three muscles. The protocol described here may provide a useful index for measuring neuromuscular fatigue.