MUSCLE ACTIVATION-LOAD RELATIONSHIPS IN DYNAMIC AND ISOMETRIC CONTRACTIONS DURING A DOUBLE-LEG PRESS

Abstract

The purpose of the study was to examine relationships between load and muscle activation during a double-leg press, in dynamic contractions versus dynamic contractions with an isometric hold. Nine healthy untrained males (22 ± 9 years old) volunteered for the study. The testing protocol comprised of participants performing 10 sets of 8 repetitions, with 4 dynamic contractions followed by 4 dynamic contractions with an isometric hold, at 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90% and 100% 8 repetition maximum (RM). Raw EMG signals were measured with wireless EMG bipolar self adhesive surface electrodes, on the vastus medialis (VM), rectus femoris (RF), vastus lateralis (VL) and biceps femoris (BF)on the right leg. Findings revealed polynomial relationships, and not simple linear relationships, best explain the association between load and peak activation. In contrast,simple linear relationships best explain the association between load and mean activation. The polynomial relationships showed an exponential increase in peak amplitude at heavier loads. This suggests that doubling the load does not necessarily double the peak muscle activation; the latter may increase relatively more at heavier loads and with an isometric hold. Overall the important finding reported is the variation in muscle activation relationship responses of the quadriceps femoris and hamstrings, to dynamic and isometric conditions at increasing intensities.