This study aimed to investigate the gender differences in yearly changes in the cross-sectional areas (CSAs) and dynamic torques of thigh muscles in high school volleyball players. The cross-sectional areas (CSAs) of the quadriceps femoris (QF) and hamstrings (HAM) and dynamic torques during knee extension (KE) and flexion (KF) at a pre-set velocity of 1.05 rad•s-1 were determined longitudinally with an interval of one year. Only the males showed significant increases in the CSAs of QF and HAM, without a significant change in the CSA ratio between the two muscle groups. The KF torque significantly increased in both genders, but KE torque did in the males only. Moreover, both genders showed significant increases in the ratio of KF torque to the product of HAM CSA and body height (T/CSA*ht). The relative gains in KF torque and its T/CSA*ht were significantly grater in the males than in the females. Moreover, only the males significantly increased the ratios of KF to KE in torque and T/CSA*ht. The present results indicated that, at least in high school volleyball players, absolute and muscle-size normalized torque were predominantly developed in KF for both genders while the CSAs of QF and HAM showed similar increases only in the males.
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