Relationship between isometric contraction intensity and muscle hardness assessed by ultrasound strain elastography

• Published in: European journal of applied physiology 2017-05, Vol.117 (5), p.843-852
• Main Authors: Inami, Takayuki, Tsujimura, Toru, Shimizu, Takuya, Watanabe, Takemasa, Lau, Wing Yin, Nosaka, Kazunori
• Format: Article
• Language: English
• Subjects: Biomedical and Life Sciences; Biomedicine; Edema; Elasticity Imaging Techniques; Female; Human Physiology; Humans; Isometric Contraction; Legs; Muscle contraction; Muscle, Skeletal - diagnostic imaging; Muscle, Skeletal - physiology; Occupational Medicine/Industrial Medicine; Original Article; Range of Motion, Articular; Sports Medicine; Ultrasonic imaging; Young Adult
• ISSN: 1439-6319; 1439-6327
• DOI: 10.1007/s00421-016-3528-2

Introduction 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. Methods 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. Results 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