Regional Difference In Gastrocnemius Tension During Passive Stretching As Assessed With Shear Wave Elastography

Abstract

Muscle strain injuries occur when the muscle is either stretched passively or activated during stretch. Calf strain injuries are most commonly found in the medial gastrocnemius (MG), especially at the distal musculotendinous junction. One of the reasons for the susceptibility of musculotendinous junction for strain injuries may be that the distal region of MG is stretched more than the medial belly region. Muscle tension during passive stretching can be estimated from shear elastic modulus measured by shear wave elastography. PURPOSE: To investigate the regional difference in MG tension during passive stretching, shear elastic modulus at the distal and medial belly regions of the MG was assessed by shear-wave elastography. METHODS: Twenty-two healthy men and 25 healthy women participated in this study. Shear elastic moduli at the distal and medial belly regions of the MG were measured with the ankle joint positions at 30° plantarflexion (PF), a neutral anatomical position (NE), and 20° dorsiflexion (DF). The regional differences in the shear elastic modulus were tested with a two-way analysis of variance (region of the MG × ankle joint position), followed by t-tests with Bonferroni correction, with the significance set at P < 0.05. RESULTS: Shear elastic modulus was not significantly different between the distal and medial belly regions at PF (distal region: 5.7 ± 2.0 kPa; medial belly region: 5.0 ± 1.4 kPa) and NE (distal region: 9.8 ± 1.6 kPa; medial belly region: 9.9 ± 1.8 kPa), but it was significantly higher at the distal region (40.7 ± 10.1 kPa) compared with the medial belly region (35.9 ± 9.1 kPa) at DF. CONCLUSIONS: Regional difference in MG tension during passive stretching was observed in the ankle joint position where the MG is sufficiently lengthened, which could lead to muscle strain injuries at the distal musculotendinous junction of the MG. The study was supported by JSPS KAKENHI (Grant Number 15K16500).