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J Biomech. 2019 Aug 27;93:111-117. doi: 10.1016/j.jbiomech.2019.06.018. Epub 2019 Jun 28.

Influence of low muscle activation levels on the ankle torque and muscle shear modulus during plantar flexor stretching.

Author information

1
Nantes Université, Movement - Interactions - Performance, MIP, EA 4334, F-44000 Nantes, France; School of Physiotherapy (IFM3R), Nantes, France. Electronic address: guillaume.le-sant@univ-nantes.fr.
2
Nantes Université, CHU Nantes, Movement - Interactions - Performance, MIP, EA 4334, F-44000 Nantes, France.
3
Nantes Université, Movement - Interactions - Performance, MIP, EA 4334, F-44000 Nantes, France; Institut Universitaire de France (IUF), Paris, France; The University of Queensland, Centre for Clinical Research Excellence in Spinal Pain, Injury and Health, School of Health and Rehabilitation Sciences, Brisbane, Australia.
4
Nantes Université, Movement - Interactions - Performance, MIP, EA 4334, F-44000 Nantes, France; Health and Rehabilitation Research Institute, Faculty of Health and Environmental Sciences, Auckland University of Technology, Auckland, New Zealand.

Abstract

During stretching studies, surface electromyography (sEMG) is used to ensure the passive state of the muscle, for the characterization of passive muscle mechanical properties. Different thresholds (1%, 2% or 5% of maximal) are indifferently used to set "passive state". This study aimed to investigate the effects of a slight activity on the joint and muscle mechanical properties during stretching. The joint torque and muscle shear modulus of the triceps surae muscles were measured in fifteen healthy volunteers during ankle dorsiflexions: (i) in a "fully relaxed" state, (ii) during active conditions where participants were asked to produce an sEMG amplitude of 1%, 2% or 5% of their maximal sEMG amplitude of the triceps surae. The 1% condition was the only that did not result in significant differences in joint torque or shear modulus compared to the relaxed condition. In the 2% condition, increases in joint torque were found at 80% of the maximal angle in dorsiflexion, and in the shear modulus of gastrocnemius medialis and gastrocnemius lateralis at the maximal angle in dorsiflexion. During the 5% condition, joint torque and the shear modulus of gastrocnemius medialis were higher than during relaxed condition at angles larger than 40% of maximal angle in dorsiflexion. The results provide new insights on the thresholds that should be considered for the design of stretching studies. A threshold of 1% seems much more appropriate than a 2% or 5% threshold in healthy participants. Further studies are required to define similar thresholds for patients.

KEYWORDS:

Electromyography; Plantarflexors; Shear modulus; Stretching; Torque

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