Changes in neural drive to calf muscles during steady submaximal contractions after repeated static stretches

Abstract

support-information-section). Key pointsr Repeated static-stretching interventions consistently increase the range of motion about a joint and decrease total joint stiffness, but findings on the changes in muscle and connective-tissue properties are mixed.r The influence of these stretch-induced changes on muscle function at submaximal forces is unknown. To address this gap in knowledge, the changes in neural drive to the plantar flexor muscles after a static-stretch intervention were estimated.r Neural drive to the plantar flexor muscles during a low-force contraction increased after repeated static stretches.r These findings suggest that adjustments in motor unit activity are necessary at low forces to accommodate reductions in the force-generating and transmission capabilities of the muscle-tendon unit after repeated static stretches of the calf muscles.

Blockade of 5‐HT2 receptors suppresses motor unit firing and estimates of persistent inward currents during voluntary muscle contraction in humans

“…Hence, small changes in firing rate can reveal statistical significance. Recent interventional studies have demonstrated this, where firing rate can change significantly by ∼0.5 Hz through muscle stretching (Mazzo et al., 2021) and by 0.33–0.64 Hz with vibration‐induced reciprocal inhibition (Mesquita et al., 2022; Orssatto et al., 2022) when using HDsEMG techniques. However, it is important to note that each reported finding is not exclusive to human models, but also consistent with experiments using animal preparations and cellular studies.…”

Motor unit modes in the calf muscles during a submaximal isometric contraction are changed by brief stretches

“…The change in the percentage of motor units associated with the shared modes after both interventions (Table 3) likely reflect a shift in distribution of inputs delivered by premotor interneurons. The shift may be mediated by a change in afferent feedback after the two interventions (Baudry & Duchateau, 2014; Guissard & Duchateau, 2006; Loram et al., 2009; Mazzo et al., 2021). This change is supported by the depression of spinal reflex excitability due to reductions in the feedback signals transmitted by group Ia afferents after static stretching (Guissard & Duchateau, 2006).…”

“…Our study reports a computational analysis of a motor unit dataset acquired by Mazzo and colleagues in a previous study (Mazzo et al., 2021). Briefly, participants performed isometric contractions with the plantar flexor muscles on each of two visits to the laboratory.…”

“…Factorization analysis was performed on a matrix containing the smoothed discharge rates for all motor units decomposed from the LG, MG and SOL muscles during each steady contraction at 10% MVC force performed by every participant individually. The reason for focusing only on the trials at the lower target force (10% MVC), was that the stretch intervention only influenced discharge rate at this target value and not at 35% MVC force (Mazzo et al., 2021).…”

“…Given the significant role of afferent feedback in the expression of modes (Desrochers et al., 2019; Manickaraj et al., 2017; Singh et al., 2023), the purpose of our study was to investigate the influence of a stretch protocol on common modulation of discharge rate among motor units in the calf muscles during a submaximal isometric contraction. In a previous report, we found that repeated static stretches can alter the neural drive to the calf muscles during submaximal isometric contractions, likely due to adjustments in the ability of the plantar flexor muscles to generate and apply the required forces (Mazzo et al., 2021). We hypothesized that the composition of the motor unit modes would change after a stretch intervention but not after a control intervention.…”