acute passive stretching alters the mechanical but not the electrical

ACUTE PASSIVE STRETCHING ALTERS THE MECHANICAL BUT NOT
THE ELECTRICAL PROPERTIES OF CALF MUSCLES IN HUMANS
Fabio Esposito, Emiliano Cè, Paola Alfieri, Giuliano Pizzini, Arsenio Veicsteinas.
Istituto di Esercizio Fisico, Salute e Attività Sportiva (IEFSAS), Università degli
Studi di Milano, Facoltà di Scienze Motorie, Via Colombo 71, 20133 Milano –
ITALY
An acute bout of passive muscle stretching has been shown to diminish maximal
force and power output. Two mechanisms have been suggested to explain these
findings: a mechanical alterations in the stretched muscle and an impaired neural
activation. Thus, the aim of this study was to evaluate the stretching-induced
changes in the electrical and mechanical properties of the muscle fibres during
maximal electrically elicited contractions of the calf muscles. Twelve subjects
(age 22±1 years, mean±s.e.m.; body mass 75±2 kg; stature 179±2 cm) underwent
6 single twitch electrical stimulation at maximal intensity before and after a bout
of passive stretching. During contractions, the force, surface EMG and
mechanomyogram (MMG) were simultaneously recorded from the medial
gastrocnemius muscle. From the analysis of the 3 signals, after stretching it
resulted that: i) the force peak, time to peak and the peak rate of force production
significantly decreased by 12.6±2.9%, 3.5±1.0% and 13.6±4.9%, respectively; ii)
the MMG amplitude (peak-to-peak) also decreased (-3.6±1.3%; p<0.05), and iii)
no differences were found in EMG parameters. In conclusion, acute passive
stretching affected the mechanical but not the electrical properties of the
maximally contracting muscles, suggesting an alteration of the musculotendinous
stiffness, but not a depression of muscle activation.