The elasticity measuring instruments using ultrasound signal (EMIUS) can measure the thickness and hardness of muscles distinct from those of subcutaneous fat. The present study investigated whether a combination of the thickness and hardness of muscles without contraction based on EMIUS findings can estimate muscle strength during knee extension in adult males and females. Fifty-nine males and twenty-five females, whose ages ranged from 18 to 39 years, participated in this study. We measured muscle thickness and hardness (change in thickness in response to contact pressure) in the right anterior region of the thigh (rectus femoris muscle and vastus intermedius muscle) without contraction using EMIUS, and the maximal isometric strength of right knee extension (MIS). Since muscle hardness values obtained by EMIUS are influenced by muscle thickness, muscle hardness was arranged by muscle thickness, which was defined as an index of muscle hardness (IMT). Higher IMT indicates a harder muscle compared with that of other individuals showing the same muscle thickness. In the group including both male and female subjects, MIS was positively and significantly related to both MIS (r=0.605, p<0.05) and IMT (r=0.333, p<0.05). On multiple linear regression analysis for estimating the MIS of knee extension, the combination of three parameters (muscle thickness, IMT and sex) allowed accurate estimation of MIS of knee extension (r=0.833, p<0.01). Although IMT in females increased the ability to estimate muscle strength accurately, it did not contribute to a more accurate estimate in males. In conclusion, these findings suggested that the combination of muscle thickness and hardness as assessed by EMIUS is capable of effectively estimating muscle strength of knee extension without muscle contraction especially in females.

DESCENTE SPORTS SCIENCE Vol.30/THE DESCENTE AND ISHIMOTO MEMORIAL FOUNDATION FOR THE PROMOTION SPORTS SCIENCE