Since isokinetic exercise equipment can give an evaluation of muscle strength with great accuracy and objectively, it is widely used as the one of the important methods for evaluation of muscle performance.

In order to determine the changes of muscle strength while aging, we examined the main muscles in both lower extremities; hip flexor, hip abductor and adductor, knee extensor and flexor, tibial internal and external rotator, and ankle plantar-flexor and dorsiflexor by using the Cybex Ⅱ⁺ Dynamometer.

120 subjects were tested, from 3rd to 8th decade, 10 men and 10 women in each decade respectively.

The results were as follows;

1) The mean values of hip flexor peak torque (strength) were 106.30±24.92 ft-lbs in male and 52.21±11.50 ft-lbs in female, and the angle of occurrence were 20.8° and 20.6° flexion in male and female, respectively. Those of hip abductor were 80.64±18.56 ft-lbs at 4.4° abduction in male and 50.01±12.96 ft-lbs at 3.5° abduction in female. Those of hip adductor were 63.02±14.20 ft-lbs at 16.2° adduction in male and 39.17±12.11 ft-lbs at 15.7° adduction in female.

2) The mean values of knee extensor peak torque were 81.08±27.01 ft-lbs in male and 61.81±18.54 ft-lbs in female, and the angle of occurrence were 48.3° and 48.1° flexion in male and female, respectively. Those of flexor were 65.29±21.83 ft-lbs at 41.3° flexion in male, 47.77±15.07 ft-lbs at 40.7° flexion in female. Those of external rotator were 19.58±4.94 ft-lbs in male and 15.23±4.85 ft-lbs in female, and those of internal rotator were 16.23±3.7 ft-lbs and 11.44±4.23 ft-lbs in male and female, respectively.

3) The mean values of ankle plantarflexor peak torque were 62.36±14.35 ft-lbs in male and 38.75±8.5 ft-lbs in female, and the angle of occurrence were 6.5° and 2.1° dorsiflexion in male and female, respectively. Those of dorsiflexor were 20.31±3.88 ft-lbs at 13.9° plantarflexion in male and 14.48±2.87 ft-lbs at 15.6° plantarflexion in female.

4) The peak torque ratio between male and female were about 50% in hip flexor, and more than 60% in others. The peak torque to body weight ratio in female were more than 70% of those in male in all sampling muscles except hip flexor.

5) The peak torque of hip and knee joint muscles decreased as the age increases. Those of hip flexor were on statistically significant decrease from 6th decade, and others from 5th decade and especialy those of knee extensor showed a severe decrease.

6) The peak torque of ankle joint muscles did not changer with the age, and were affected by body weight.

7) The mean±2SD values of the peak torque difference between dominant and nondominant sides were about 10% in hip flexor, knee extensor and flexor and about 15% in hip abductor and adductor and adductor and about 12% in ankle joint muscles.

From these results we conclude a proper exercise program is needed before 5th decade to preserve the muscle strength of the lower extremities, and especially the exercise of knee joint muscles.