Effect of different knee flexion angles with a constant hip and knee torque on the muscle forces and neuromuscular activities of hamstrings and gluteus maximus muscles
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This study examined the effect of different knee flexion angles with a constant hip and knee torque on the muscle force and neuromuscular activity of the hamstrings and gluteus maximus.
Twenty healthy males lay in prone position and held their lower limb with hip flexion at 45° and knee flexion at either 10° or 80°. At these angles, the hip and knee torques are identical. Under three load conditions: passive (referred to as Unloaded), active (Loaded), and active with 3-kg weight added to the shank (Loaded + 3 kg), the muscle stiffness (i.e., an indicator of muscle force) and neuromuscular activity of the hamstrings and gluteus maximus were measured using shear wave elastography and surface electromyography.
The muscle stiffness and neuromuscular activity of the hamstrings and gluteus maximus increased significantly with the load. Muscle stiffness in the hamstrings was significantly lower at knee flexion of 80° than at 10° for Unloaded, but not for either Loaded or Loaded + 3 kg. The neuromuscular activity of the hamstrings was significantly greater at knee flexion of 80° than at 10° for both Loaded and Loaded + 3 kg. The muscle stiffness or neuromuscular activity of the gluteus maximus showed no significant differences between knee angles.
When the passive force in the hamstrings decreases with knee flexion, sufficient muscle force to maintain the hip and knee torques against an external load is generated by preferentially increasing the neuromuscular activity of the hamstrings, rather than increasing the synergetic muscle force.
KeywordsMuscle force Neuromuscular activity Shear wave elastography Electromyography Hamstrings Gluteus maximus
Maximal voluntary contraction
Shear wave elastography
The authors would like to thank all participants involved in this study. This study was not funded by any institutions, agencies, or companies.
YM, HT, SN, and NI conceived and designed the research. YM, IS, TK, and YK conducted the experiments. YM, HT, and NI analyzed the data. YM, HT, SN, and NI wrote the manuscript. All the authors have read and approved the manuscript.
Compliance with ethical standards
Conflict of interest
The authors declare no conflict of interest.
All the procedures performed in the studies involving human participants were in accordance with the ethical standards of the institutional and/or national research committee and with the 1964 Helsinki declaration and its later amendments or comparable ethical standards.
Informed consent was obtained from all individual participants involved in the study.
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