Author(s): MARIANI, A.1, DALLEAU, G.1, CADERBY, T.1, BEGON, M.2, PORTERO, P.3, Institution: UNIVERSITY OF REUNION ISLAND, Country: FRANCE, Abstract-ID: 1360

INTRODUCTION:
Stretching exercises are used in training and rehabilitation. Many studies have focused on measuring muscle mechanical stress during static stretching in controlled laboratory settings involving isokinetic dynamometers and slow-speed movements, notably without neuromuscular activation [1]. During stretching exercises performed under field conditions, in contrast, significant neuromuscular activity is typically observed [2]. Understanding muscular dynamics is crucial for accurately assessing the impact of stretching techniques in sports and rehabilitation. Shear wave elastography (SWE) is a technique that enables the study of muscle mechanical behaviour, with the elasticity modulus linearly correlated to both active and passive muscular tensions [3]. The objective of this study was to compare muscle tensions using SWE during passive calf stretching conducted using a laboratory versus a field protocol.

METHODS:
Six healthy participants (age: 22.5±1.2 years, height: 1.72±0.06 m, mass: 71.6±11.8 kg) randomly performed two calf stretching protocols each separated by 30 min rest: 1) on an isokinetic dynamometer (Dyn); 2) based on an exercise commonly used in field conditions, namely “wall calf stretching” (Wall). Each stretching lasted 80 s and was performed at 80% of maximum dorsiflexion range of motion. Subjects were asked to avoid any muscle contraction. We measured and compared the gastrocnemius medialis shear elastic modulus (SEM) and electromyography (EMG) between protocols.

RESULTS:
Mean SEM and EMG activity were significantly higher in Wall (SEM: Wall: 403±56.5 kPa, Dyn: 267±93.9 kPa, p<0.01; EMG: Wall: 2.84±2.09%, Dyn: 0.63±0.41% of EMG max, p=0.03). Furthermore, a significant decrease in the elasticity modulus between the beginning and the end of the stretching was observed in Dyn condition (p=0.02), but not in Wall condition (p=0.24).

CONCLUSION:
During field stretching protocol, the muscle mechanical response differs from laboratory stretching protocol. Muscular structure experiences more tension and does not exhibit the typical stress relaxation observed in the literature. Research conducted on animals has shown that exposing muscles to higher tension leads to an increase in markers of mechanotransduction and hypertrophy [4], [5]. These findings suggest that muscle adaptations to stretching could differ between laboratory protocols and field protocols.

REFERENCES:
[1] Freitas et al. (2015) Eur J Appl Physiol, vol. 115, no. 6, pp. 1263–1272.
[2] Portero et al. (2020) Front. Neurol., vol. 11, p. 584304.
[3] Hug et al. (2015) Exercise and Sport Sciences Reviews, vol. 43, no. 3, pp. 125–133.
[4] Kjær. (2004) Physiological Reviews, vol. 84, no. 2, pp. 649–698.
[5] Martineau et al. (2001) Journal of Applied Physiology, vol. 91, no. 2, pp. 693–702.