Effects of passive stretching on post-activation potentiation and fibre conduction velocity of biceps brachii muscle

Stretching is usually part of warm-up routines in many sports, but it affects the subsequent muscle force; therefore, it could negatively influence post-activation potentiation (PAP), one of the warm-up's main effects. The aim of this study was to evaluate the acute effects of passive stretching on PAP and fibre conduction velocity (CV). Seven subjects underwent 2 experimental sessions, control (C) and stretching (S), each consisting of 2 series (7 min resting) of 3 maximal voluntary contractions (MVC) of biceps brachii (5 s isometric contraction, 10 s recovery). During the resting phase of the S session, the biceps brachii was passively stretched (5×45 s stretches, 15 s recovery). Root mean square (RMS), mean frequency (MF) and CV were calculated from electromyography. Peak torque (pT) and half-contraction time (1/2CT) were measured and normalised by the arm muscular area (pTn). After C, pTn increased and 1/2CT decreased (p < 0.05); moreover, MF and CV increased (p < 0.05). After S, 1/2CT increased (p < 0.05) and RMS decreased (p < 0.05). Passive stretching could blunt the effects of PAP, presumably due to mechanical and neuromuscular changes. The observed changes in CV suggest a possible decrease in Ca2+ sensitivity in contractile proteins. Therefore, the use of passive stretching in warm-up routines remains questionable.