The Influence of Daily Exercise on Muscle Echo Intensity and Stiffness in Young Women

Abstract

This study aimed to investigate the effect of daily exercise on skeletal muscle function, size, and quality in young women. Twenty-six young women participated in this study, categorized into daily exercise and non-exercise groups. The exercise group had performed exercise or training three times a week for more than six months. Knee extension and flexion, plantar flexion, and dorsiflexion peak torques were measured for muscle function. B-mode ultrasound images were taken from the thigh and calf, and muscle thickness and echo intensity were measured in the vastus lateralis and medial gastrocnemius. Shear modulus at different joint angles of the knee (0° [full extended], 40°, and 90°) and ankle (40 °plantarflexion, 0° [neutral], and 10 °dorsiflexion) was measured from the vastus lateralis and medial gastrocnemius to determine muscle stiffness. Peak torque and echo intensity did not significantly differ between the exercise and non-exercise groups. Shear modulus in the medial gastrocnemius at 10° dorsiflexion was significantly lower in the exercise group compared with the non-exercise group (34.2 ± 7.7 vs. 46.5 ± 13.1 kPa, P < 0.05). These results suggest that daily exercise and training could affect muscle stiffness, but do not lead to an increase in muscle function.

Response

“…We acknowledged such potential factors in our article (“… e.g., fiber density…”) (2). However, only small (2–4 kPa) changes in vastus lateralis shear modulus are observed during passive knee flexions through 90° (5,6) and probe alignment (similar to altering fascicle angle) has little effect on muscle shear modulus at rest (7–9). Thus, effects in vastus lateralis should be small or negligible.…”