Modulation of Hamstrings Neural Drive During Isometric Contractions of the Hip Extensors and Knee Flexors.
Journal Article
Overview
abstract
The aim of the study was to compare motor-unit discharge characteristics across regions of the hamstring muscles during hip-extension and knee-flexion. Fourteen healthy adults (2 females) performed isometric contractions with the hip extensors and knee flexors at 10% and 40% of maximal voluntary contraction (MVC) torque. High-density surface electromyography was recorded from proximal and distal regions of biceps femoris and semitendinosus. Motor units were decomposed and tracked between tasks using a filter reapplication approach. The outcome measures included mean discharge rate (MDR), coefficient of variation for interspike interval (CoVISI), and standard deviation of the filtered cumulative spike train (SD of fCST). Task differences in common synaptic input were assessed at 10% MVC using within-muscle coherence derived from CSTs in the delta band. Maximal torque was ~24% higher in hip-extension than knee-flexion, accompanied by a ~31% increase in torque variability. Across all the identified motor units and those that were tracked, MDR (~5%-14%), CoVISI (~7%-11%) and SD of fCST (~10%-16%) were greater during hip-extension, whereas delta-band coherence was greater across muscles and regions during knee-flexion (p = 0.02-p < 0.001; d = 1.11-1.94). Moreover, proximal regions generally exhibited greater values for MDR (~11%) during knee-flexion, whereas modulation was greater in distal regions during hip-extension (~4%, p < 0.01). The neural-drive variability was greater proximally than distally for both tasks (~16%, p = 0.01). The neural control of motor units differs between proximal and distal regions of the hamstrings during hip-extension and knee-flexion. Hamstring testing and exercise selection need to consider the task and the muscle region being examined.
