Effect of hypohydration on peripheral and corticospinal excitability and voluntary activation

We investigated whether altered peripheral and/or corticospinal excitatory output and voluntary activation are implicated in hypohydration-induced reductions in muscle isometric and isokinetic (90°.s(-1)) strength. Nine male athletes completed two trials (hypohydrated, euhydrated) comprising 90 min cycling at 40°C, with body weight losses replaced in euhydrated trial. Peripheral nerve and transcranial magnetic stimulations were applied during voluntary contractions pre- and 40 min post-exercise to quantify voluntary activation and peripheral (M-wave) and corticospinal (motor evoked potential) evoked responses in m. vastus medialis. Both maximum isometric (-15.3±3.1 vs -5.4±3.5%) and isokinetic eccentric (-24.8±4.6 vs -7.3±7.2%) torque decreased to a greater extent in hypohydrated than euhydrated trials (p