Residual Force Enhancement Is Present in Consecutive Post-Stretch Isometric Contractions of the Hamstrings during a Training Simulation

Abstract

Residual force enhancement (rFE) is observed when isometric force following an active stretch is elevated compared to an isometric contraction at corresponding muscle lengths. Acute rFE has been confirmed in vivo in upper and lower limb muscles. However, it is uncertain whether rFE persists using multiple, consecutive contractions as per a training simulation. Using the knee flexors, 10 recreationally active participants (seven males, three females; age 31.00 years ± 8.43 years) performed baseline isometric contractions at 150° knee flexion (180° representing terminal knee extension) of 50% maximal voluntary activation of semitendinosus. Participants performed post-stretch isometric (PS-ISO) contractions (three sets of 10 repetitions) starting at 90° knee extension with a joint rotation of 60° at 60°·s^-1 at 50% maximal voluntary activation of semitendinosus. Baseline isometric torque and muscle activation were compared to PS-ISO torque and muscle activation across all 30 repetitions. Significant rFE was noted in all repetitions (37.8-77.74%), with no difference in torque between repetitions or sets. There was no difference in activation of semitendinosus or biceps femoris long-head between baseline and PS-ISO contractions in all repetitions (ST; baseline ISO = 0.095-1.000 ± 0.036-0.039 Mv, PS-ISO = 0.094-0.098 ± 0.033-0.038 and BFlh; baseline ISO = 0.068-0.075 ± 0.031-0.038 Mv). This is the first investigation to observe rFE during multiple, consecutive submaximal PS-ISO contractions. PS-ISO contractions have the potential to be used as a training stimulus.

Keywords: electromyography; hamstrings; history dependence; in vivo; muscle; residual force enhancement; training simulation.

Figure 1

Baseline and experimental protocols for Group 1 and Group 2. Participants were randomly allocated into each group.

Figure 2

Mean baseline isometric and PS-ISO torque during 10 consecutive repetitions over three sets. * indicates a significant increase in mean torque from baseline isometric contractions to PS-ISO contractions across all repetitions and all sets (p ≤ 0.001).

Figure 3

Mean baseline isometric and PS-ISO muscle activation (sEMG_RMS) measured in millivolts (Mv) of semitendinosus (ST) and biceps femoris long-head (BFlh) muscles during 10 consecutive repetitions during 3 sets (i. Set 1, ii Set 2 and iii Set 3). No difference in muscle activation was observed between baseline isometric and PS-ISO contractions for all repetitions and sets of semitendinosus (p = 0.590) and biceps femoris long-head (p = 0.198). ST sEMG_RMS is depicted in the left column and BFlh sEMG_RMS is depicted in the right column for Set 1 (i Set 1), Set 2 (ii. Set 2) and Set 3 (iii. Set 3). Repetitions in each set are visualized on the x axis and sEMG_RMS on the y axis of each graph.