Journal of Sports Science and Medicine
Journal of Sports Science and Medicine
ISSN: 1303 - 2968   
Ios-APP Journal of Sports Science and Medicine
Androit-APP Journal of Sports Science and Medicine
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©Journal of Sports Science and Medicine (2021) 20, 17 - 25   DOI: https://doi.org/10.52082/jssm.2021.17

Research article
Acute and Prolonged Effects of Stretching on Shear Modulus of the Pectoralis Minor Muscle
Jun Umehara1,2,3, , Masatoshi Nakamura4, Junya Saeki1,2,5, Hiroki Tanaka1,6, Ko Yanase1, Kosuke Fujita7, Momoko Yamagata1,2,8, Noriaki Ichihashi1
Author Information
1 Human Health Sciences, Graduate School of Medicine, Kyoto University, Shogoin, Sakyo-ku, Kyoto, Japan
2 Research Fellow of Japan Society for the Promotion of Science, Tokyo, Japan
3 Center for Information and Neural Networks, National Institute of Information and Communications Technology, Osaka, Japan
4 Institute for Human Movement and Medical Sciences, Niigata University of Health and Welfare, Niigata, Japan
5 Faculty of Sport Sciences, Waseda University, Saitama, Japan
6 Rehabilitation Unit, Kyoto University Hospital, Kyoto, Japan
7 Department of Community Healthcare and Geriatrics, Graduate School of Medicine, Nagoya University, Aichi, Japan
8 Graduate School of Human Development and Environment, Kobe University, Hyogo, Japan

Jun Umehara
✉ PhD, PT Department of Physical Therapy, Human Health Sciences, Graduate School of Medicine, Kyoto University, 53 Kawahara-cho, Shogoin, Sakyo-ku, Kyoto, 606-8507, Japan
Email: umehara.jun.77z@st.kyoto-u.ac.jp
Publish Date
Received: 21-10-2020
Accepted: 23-11-2020
Published (online): 01-03-2021
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ABSTRACT

Increased muscle stiffness of the pectoralis minor (PMi) could deteriorate shoulder function. Stretching is useful for maintaining and improving muscle stiffness in rehabilitation and sport practice. However, the acute and prolonged effect of stretching on the PMi muscle stiffness is unclear due to limited methodology for assessing individual muscle stiffness. Using shear wave elastography, we explored the responses of shear modulus to stretching in the PMi over time. The first experiment (n = 20) aimed to clarify the acute change in the shear modulus during stretching. The shear modulus was measured at intervals of 30 s × 10 sets. The second experiment (n = 16) aimed to observe and compare the prolonged effect of different durations of stretching on the shear modulus. Short and long stretching duration groups underwent 30s × 1 set and 30s × 10 sets, respectively. The assessments of shear modulus were conducted before, immediately after, and at 5, 10, and 15 min post-stretching. In experiment I, the shear modulus decreased immediately after a bout (30 s) of stretching (p < 0.001, change: -2.3 kPa, effect size: r = 0.72) and further decreased after 3 repetitions (i.e., 90 s) of stretching (p = 0.03, change: -1.0 kPa, effect size: r = 0.53). In experiment II, the change in the shear modulus after stretching was greater in the long duration group than in the short duration group (p = 0.013, group mean difference: -2.5 kPa, partial η2 = 0.36). The shear modulus of PMi decreased immediately after stretching, and stretching for a long duration was promising to maintain the decreased shear modulus. The acute and prolonged effects on the PMi shear modulus provide information relevant to minimum and persistent stretching time in rehabilitation and sport practice.

Key words: Elastography, time-course, shoulder, stiffness, ultrasonography


           Key Points
  • Mechanical responses of the pectoralis minor muscle to stretching over time were examined.
  • Shear modulus was used as a surrogate of muscle stiffness.
  • Shear modulus of the pectoralis minor decreased after a bout (= 30s) of stretching.
  • Shear modulus further decreased after 3set (= 90s) of stretching.
  • Different prolonged effect resulted from the different stretching durations.
 
 
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