P21 The effect of moderate-duration passive muscle stretching on persistent inward currents estimated through paired motor unit analysis.
Trajano GS[1], Taylor JL[2,3], Blazevich AJ[2]
- Queensland University of Technology, Brisbane, Australia
- Edith Cowan University, Perth, Australia
- NeuRA (Neuroscience Research Australia), Sydney, Australia
Passive muscle stretching can reduce muscle force production and neural drive to the muscle [1]. This reduction could be caused by prolonged inhibition of Ia afferents, which could consequently affect the ability to develop persistent inward currents (PICs) in motoneurons [2]. In humans, PIC amplitude can be estimated using the delta f (ΔF). The ΔF is calculated as the change in firing rates of a lower-threshold control motor unit during the recruitment and derecruitment of a higher-threshold test unit, and is proposed to be proportional to PIC amplitude [3]. Therefore, the aim of this study was to compare ΔFs before and after passive stretching.
Five healthy males performed isometric trapezoidal plantarflexor contractions to 20% of maximal force. Four contractions were performed before (Control 1) and after (Control 2) 3 min of rest (Control) and immediately after three 1-min plantarflexor stretches (Stretch). Surface electromyography (EMG) was recorded from a 32-channel electrode matrix over medial gastrocnemius (MG). EMG signals were decomposed into single motor unit discharges and ΔFs were calculated for pairs of motor units.
After exclusions, 23, 27 and 17 pairs of motor units at Control 1, Control 2 and Stretch, respectively, were analyzed. ΔFs were on average 4.5 (95% CI, 3.8 to 5) during Control 1, 4.7 (95% CI 3.9 to 5.4) during Control 2 and 4.3 (95% CI 3.1 to 5.4) after Stretch condition. There was no difference between conditions (p=0.78). In conclusion moderate-duration passive stretch did not affect estimates of PICs measured at MG.
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