Inami Takayuki, Tsujimura Toru, Shimizu Takuya, Watanabe Takemasa, Lau Wing Yin, Nosaka Kazunori
Centre for Exercise and Sports Science Research, School of Medical and Health Sciences, Edith Cowan University, 270 Joondalup Drive, Joondalup, WA, 6027, Australia.
Faculty of Sport Sciences, Waseda University, Tokorozawa, Japan.
Eur J Appl Physiol. 2017 May;117(5):843-852. doi: 10.1007/s00421-016-3528-2. Epub 2017 Mar 13.
Ultrasound elastography is used to assess muscle hardness or stiffness; however, no previous studies have validated muscle hardness measures using ultrasound strain elastography (SE). This study investigated the relationship between plantar flexor isometric contraction intensity and gastrocnemius hardness assessed by SE. We hypothesised that the muscle would become harder linearly with an increase in the contraction intensity of the plantar flexors.
Fifteen young women (20.1 ± 0.8 years) performed isometric contractions of the ankle plantar flexors at four different intensities (25, 50, 75, 100% of maximal voluntary contraction force: MVC) at 0° plantar flexion. Using SE images, the strain ratio (SR) between the muscle and an acoustic coupler (elastic modulus 22.6 kPa) placed over the skin was calculated (muscle/coupler); pennation angle and muscle thickness were measured for the resting and contracting conditions.
SR decreased with increasing contraction intensity from rest (1.28 ± 0.20) to 25% (0.99 ± 0.21), 50% (0.61 ± 0.15), 75% (0.34 ± 0.1) and 100% MVC (0.20 ± 0.05). SR decreased linearly (P < 0.05) with increasing MVC from rest to 75% MVC, but levelled off from 75 and 100% MVC. SR was negatively correlated with pennation angle (r = -0.80, P < 0.01) and muscle thickness ( r= -0.78, P< 0.01).
SR appears to represent muscle hardness changes in response to contraction intensity changes, in the assumption that the gastrocnemius muscle contraction intensity is proportional to the plantar flexion intensity. We concluded that gastrocnemius muscle hardness changes could be validly assessed by SR, and the force-hardness relationship was not linear.
超声弹性成像用于评估肌肉硬度；然而，此前尚无研究使用超声应变弹性成像（SE）验证肌肉硬度测量方法。本研究调查了跖屈等长收缩强度与通过SE评估的腓肠肌硬度之间的关系。我们假设随着跖屈肌收缩强度的增加，肌肉会呈线性变硬。
15名年轻女性（20.1±0.8岁）在跖屈0°时以四种不同强度（最大自主收缩力的25%、50%、75%、100%：MVC）进行踝关节跖屈肌的等长收缩。使用SE图像，计算肌肉与置于皮肤上的声学耦合器（弹性模量22.6 kPa）之间的应变比（SR）（肌肉/耦合器）；测量静息和收缩状态下的羽状角和肌肉厚度。
SR随着收缩强度从静息时（1.28±0.20）增加到25%（0.99±0.21）、50%（0.61±0.15）、75%（0.34±0.1）和100%MVC（0.20±0.05）而降低。从静息到75%MVC，SR随着MVC增加呈线性降低（P<0.05），但从75%到100%MVC趋于平稳。SR与羽状角呈负相关（r=-0.80，P<0.01），与肌肉厚度呈负相关（r=-0.78，P<0.01）。
假设腓肠肌收缩强度与跖屈强度成正比，SR似乎代表了肌肉硬度随收缩强度变化的情况。我们得出结论，SR可以有效评估腓肠肌硬度变化，且力-硬度关系并非线性。
