We have done the electromyographic observation on bilateral M. rectus femoris and M. biceps femoris with internal derangement of the knee (5 male, average 19.4 years). It was done during maximum contraction on shore and swimming in water. The injured side showed less electric discharge than the healthy side on shore. But it was revealed that the injured side showed strong electric discharge that was almost the same ratio as the healthy side during swimming in water.
　We investigated the effects of under-water exercise (average 6.8 months) on the hip and knee with osteoarthrosis (14 female, average 49.3 years). Under-water exercise was done especially for muscle building and soft tissue stretching of hip abduction, hip extension, knee extension and knee flexion muscles. we got some conclusions as below.
　1. The obesity, functions of respiration and circulation, muscle power around the knee and elasticity of trunk and lower limbs were improved significantly (P< 0.05) in the total osteoarthrosis group after under-water exercise by degrees.
　2. The total judgement score of Japan Orthopaedic Association for osteoarthrosis of the hip and knee were improved significantly (P< 0.01) in both groups after under-water exercise.
　3. It was revealed that isotonic resistant exercise could be done easily in water and under-water exercise was very effective treatment method on hip and knee with osteoarthrosis.

DESCENTE SPORTS SCIENCE Vol.15/THE DESCENTE AND ISHIMOTO MEMORIAL FOUNDATION FOR THE PROMOTION SPORTS SCIENCE