RÉSUMÉ
AIM: To study the development laws between isokinetic muscle strength and age increase via test flexion and extension muscle of knee joints in 216 ordinary juvenile boys aged from 9 to 20. METHODS: Kinitech isokinetic strength test was used to study the flexion and extension muscle of both sides’ knee joints at the speed of 60 (?)/s. RESULTS: The peak torque of muscles increased with the increasing ages, especially in extension muscles, which is bigger than flexion muscles (P 0.05). The ratio of flexion and extension muscles (F/E) decreased with age increasing, which a larger fluctuation during aged 9-13, especially obvious had decreased in 13-20 ages. CONCLUSION: The muscle strength and power all increases with the increasing ages, while the F/E value decrease in 9-20 boys, which demonstrates the flexion and extension muscle developed out of balance.