Corticospinal and intracortical excitability is modulated in the knee extensors after acute strength training
Razie J. Alibazi, Ashlyn K. Frazer, Alan J. Pearce, Jamie Tallent, Janne Avela, Dawson J. Kidgell
Abstract
The corticospinal responses to high-intensity and low-intensity strength-training of the upper limb are modulated in an intensity-dependent manner. Whether an intensity-dependent threshold occurs following acute strength training of the knee extensors (KE) remains unclear. We assessed the corticospinal responses following high-intensity (85% of maximal strength) or low-intensity (30% of maximal strength) KE strength-training with measures taken during an isometric KE task at baseline, post-5, 30 and 60-min. Twenty-eight volunteers (23 ± 3 years) were randomized to high-intensity (n = 11), low-intensity (n = 10) or to a control group (n = 7). Corticospinal responses were evoked with transcranial magnetic stimulation at intracortical and corticospinal levels. High- or low-intensity KE strength-training had no effect on maximum voluntary contraction force post-exercise (P > 0.05). High-intensity training increased corticospinal excitability (range 130–180%) from 5 to 60 min post-exercise compared to low-intensity training (17–30% increase). Large effect sizes (ES) showed that short-interval cortical inhibition (SICI) was reduced only for the high-intensity training group from 5–60 min post-exercise (24–44% decrease) compared to low-intensity (ES ranges 1–1.3). These findings show a training-intensity threshold is required to adjust CSE and SICI following strength training in the lower limb.