Different changes of muscle hardness between the rectus femoris and vastus intermedius muscle after maximal knee extension exercise

Abstract

This study aimed to determine the different changes of muscle hardness between the human rectus femoris (RF) and vastus intermedius muscle (VI) after maximal knee extension exercise. Eight healthy men (23.0±2.6 years) performed maximal isometric contraction (IM), concentric contraction (CC), and eccentric contraction (EC) exercises of the knee extensors. Muscle hardness (i.e., strain ratio, SR) and thickness in the proximal, middle, and distal parts of RF and VI were measured by using strain elastography before and after exercises. The rates of change between the values were calculated as values before exercise 100%. For VI, a significant main effect in “part” was found in IM and EC exercises in SR. Results show that SR in the distal part (IM, 89.0±27.2%; EC, 78.2±26.9%) was significantly lower than that in the middle part (IM, 105.5±34.3%; EC, 91.8±30.4%) for each exercise (p<0.05). However, no significant main effect in “part” was found in SR of RF in any exercise. A significant main effect was found in “part” in muscle thickness of RF in the IM exercise. Also, muscle thickness in the distal part (104.5±7.7%) was significantly higher than that in the proximal part (102.5±4.3%) for each exercise (p<0.05). These results suggest that changes of muscle hardness and thickness in the proximal, middle, and distal parts of the human rectus femoris and vastus intermedius muscle after maximal knee extension exercises are different.