Abstract
To examine the effect of long-term daily training on athletes’ skeletal muscle, this
study determined the relation between their muscle thickness and passive muscle stiffness,
and compared the muscle thickness and muscle stiffness between athletes and non-athletes.
Participants were elite Japanese athletes (278 men, 200 women) from various sports
and non-athletes (35 men, 35 women). Rectus femoris (RF) muscle thickness was measured
using B-mode ultrasonography and was normalized to the total body mass (muscle thickness/body
mass1/3). RF passive muscle stiffness (shear modulus) was assessed by ultrasound shear-wave
elastography. There was a negligibly significant correlation between muscle thickness
and muscle stiffness in male athletes (p=0.003; r=−0.18) but not in female athletes (p=0.764; r=0.02). Among men, muscle thickness was significantly greater in athletes
than non-athletes (p<0.001), whereas muscle stiffness was significantly less in athletes than non-athletes
(p=0.020). Among women, muscle thickness was significantly greater in athletes than
non-athletes (p<0.001), whereas muscle stiffness did not differ significantly between athletes and
non-athletes (p=0.412). These results suggest that the effect of long-term daily training performed
by athletes on muscle stiffness is more complicated than that on muscle thickness.
Key words
B-mode ultrasonography - shear-wave elastography - muscle adaptation - muscle hypertrophy
- flexibility - rectus femoris
