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.
Highlights
Introduction iationsThere is much interest in the prevention and rehabilitation of hamstring strain injuries.Hamstring strain injuries have a high incidence, during high-speed running [1].The function of the hamstring muscles during high-speed running is vigorously debated.One theory proposes that in high-speed running, the hamstring muscles act eccentrically during the late swing phase of the gait cycle [2]
Repetitions in each set are visualized on the x axis and sEMGRMS on the y axis of each graph. This is the first study to confirm Residual force enhancement (rFE), in the absence of increased muscle activation, in the hamstrings during multiple and consecutive submaximal post-stretch isometric (PS-ISO) contractions performed as a training simulation
It is evident from the findings that an increase in muscle activation cannot account for the elevated PS-ISO torque during this series of PS-ISO contractions
Summary
Introduction iationsThere is much interest in the prevention and rehabilitation of hamstring strain injuries.Hamstring strain injuries have a high incidence, during high-speed running [1].The function of the hamstring muscles during high-speed running is vigorously debated.One theory proposes that in high-speed running, the hamstring muscles act eccentrically during the late swing phase of the gait cycle [2]. Hamstring strain injuries have a high incidence, during high-speed running [1]. The function of the hamstring muscles during high-speed running is vigorously debated. One theory proposes that in high-speed running, the hamstring muscles act eccentrically during the late swing phase of the gait cycle [2]. The alternate postulation states that the hamstrings remain predominantly isometric during the late swing phase and act isometrically during foot contact [2]. Much of our current understanding of the dynamic function of the hamstrings is based on kinematic and kinetic investigations that have measured the changes in distance between osteotendinous attachments, sometimes with the calculation of corresponding joint moments [3,4,5,6,7,8,9]. Methodological limitations exist wherever inferences about the behaviour of the contractile element are based on the change
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