Age-Related Differences in the Effects of Isokinetic Training on Muscle Strength and Endurance for Thigh Muscles

Abstract

This study was designed to investigate age-related differences in isokinetic peak torque and its endurance on normal 172 boys ranging in age from 10 to 18 years served as volunteer subjects. Each subject was given a leg extension/flexion test using an isokinetic dynamometer (Cybex II), and extended/flexed at every speed of 0°, 60°, 120°, 180°, 240° and 300°/sec to measure the peak torque of thigh muscles estimated as muscle strength. He was also given an endurance test used the above Cybex II and extended maximally a leg at 180°/sec, 50 times, An endurance of thigh muscles was calculated as a ratio of (mean value for peak torque of initial 5 times-mean value of final 5 times)/mean value of initial 5 times.The peak torque, measured in the extension/flexion test, clearly increased in order of age. In the endurance test, the initial mean value for peak torque was in almost the same developing pattern as those described above in the leg extension/flexion test, but the final mean value did not respond to age over 16 years old.Therefore, 96 boys, aged 11 to 15 years old organized five age groups, and individual group was divided into two subgroups, i, e, experimental group and control group. The members in the experimental group participated in an isokinetic muscle training used Cybex II, consisted of 3 days/week, and 3 sets/day (1 set was 30-times repetition at 180°/sec) throughout 8 weeks.The training increased considerably the strength and endurance of thigh muscles for boys ages 13 years, compared to another age group. Boys aged 14 and 15 years had a larger increment of muscle strength through the training than 11 and 12 years old boys. Boys of 12 years, however, showed a comparable increase in muscle endurance through the training to those aged 14 and 15 years.As above showed, it was discernible that the effects of training on the muscle strength and endurance generally depended on physical maturing.The effect on muscle strength of thigh flexors through the training was greater than that of thigh extensor, independently of age.The improvement of muscle strength was caused by muscle hypertrophy and neurological factor, especially the latter regardless of age, irrespective of the influence due to hypertrophy extended from 10.3% at the age of eleven to 19.1% at the age of fifteen.