Heavy‐resistance exercise‐induced increases in jump performance are not explained by changes in neuromuscular function

Abstract

Post-activation potentiation (PAP) is the increased involuntary muscle twitch response to stimulation following strong contraction. The enhancement to whole-body explosive muscular performance (PE) after heavy-resistance exercise is often attributed to modulations in neuromuscular function that are proposed to reflect PAP, but the evidence to support this is equivocal. We assessed the neuromuscular basis of PE using transcranial magnetic stimulation (TMS) of the primary motor cortex, and electrical stimulation of the femoral nerve. Eleven male athletes performed heavy-resistance exercise with measures of countermovement jump (CMJ) pre- and 8 min post-exercise. Pre-exercise and after the final CMJ, single- and paired-pulse TMS were delivered during submaximal isometric knee-extensor contractions to measure corticospinal excitability, short-interval intracortical inhibition (SICI), and intracortical facilitation (ICF), with motor evoked potentials recorded from rectus femoris. Twitch responses to motor nerve stimulation during and post maximum-knee-extensor contractions were studied to quantify voluntary activation (VA) and potentiated twitch (Q ). The experimental protocol successfully induced PE (+4 ± 1% change in CMJ, P = 0.01), but no changes were observed for maximum voluntary force, VA, corticospinal excitability, SICI or ICF (all P > 0.05), and Q declined (P < 0.001). An enhancement of muscular performance after heavy-resistance exercise was not accompanied by PAP, or changes in measures of neuromuscular function.

Motor cortical and corticospinal function differ during an isometric squat compared with isometric knee extension

“…In recent years, there has been an increase in the number of studies applying transcranial magnetic stimulation (TMS) in sport and exercise and movement sciences to assess intracortical and corticospinal activity in response to various interventions (Brownstein et al., ; Thomas, Toward, West, Howatson, & Goodall, ; Weier & Kidgell, ). Single‐pulse TMS permits the quantitative assessment of corticospinal excitability through the size of the compound electromyography (EMG) response, whereas paired‐pulse TMS separated by 2–5 and 10–15 ms can be used to examine intracortical inhibitory (termed short‐interval intracortical inhibition; SICI) and facilitatory circuits (termed intracortical facilitation; ICF), respectively (Kujirai et al., ).…”

“…One common training modality for improving lower limb strength is the squat. Previous studies have used the squat in both chronic training (Weier & Kidgell, ) and acute bout scenarios (Thomas et al., ), assessing neurophysiological function pre‐ and post‐intervention. Weier and Kidgell () and Weier, Pearce, and Kidgell () both showed alterations in CNS function after 4 weeks of heavy‐load squat training, whereas Thomas et al.…”

“…Weier and Kidgell () and Weier, Pearce, and Kidgell () both showed alterations in CNS function after 4 weeks of heavy‐load squat training, whereas Thomas et al. () found no changes in corticospinal or intracortical activity when assessing the neuromuscular basis of acute performance enhancement in the minutes after a heavy‐resistance squat protocol, despite inducing an increase in jump performance. However, much like the issues highlighted by Sidhu et al.…”

“…One common training modality for improving lower limb strength is the squat. Previous studies have used the squat in both chronic training and acute bout scenarios (Thomas et al, 2017b), assessing neurophysiological function pre-and post-intervention. and Weier, Pearce, and Kidgell (2012) both showed alterations in CNS function after 4 weeks of heavy-load squat training, whereas Thomas et al (2017b) found no changes in corticospinal or intracortical activity when assessing the neuromuscular basis of acute performance enhancement in the minutes after a heavy-resistance squat protocol, despite inducing an increase in jump performance.…”

“…Previous studies have used the squat in both chronic training and acute bout scenarios (Thomas et al, 2017b), assessing neurophysiological function pre-and post-intervention. and Weier, Pearce, and Kidgell (2012) both showed alterations in CNS function after 4 weeks of heavy-load squat training, whereas Thomas et al (2017b) found no changes in corticospinal or intracortical activity when assessing the neuromuscular basis of acute performance enhancement in the minutes after a heavy-resistance squat protocol, despite inducing an increase in jump performance. However, much like the issues highlighted by Sidhu et al (2013a) and Avela and Gruber (2010), the evoked CNS responses in the aforementioned studies were recorded in single-limb isometric knee extension, rather than the motor task (squat) performed during the intervention.…”