The laxity of shoulder is one of main factors affecting shoulder lesions in athletes.
To measure the anterior-posterior laxity of shoulder, a stress machine was arranged because the ordinary rentogenographic measurement is not suitable. The measurement of the anterior-posterior laxity was done with athletes in several kinds of sports in which shoulder joints are mainly used. The result was compared with those from clinical examinations and stress rentogenography. Conclusions :
1. The anterior-posterior displacements of the affected side in baseball, volleyball and javelin players were significantly larger than that of the control side.
2. For the anterior-posterior displacement of the shoulder joint, baseball, volleyball and javelin players showed significantly larger values than truck runners as the control whereas significantly smaller values were found in water polo players.
3. There was no correlation between the anterior-posterior laxity and the inferior laxity.

A study was conducted to investigate the influence on the shoulder joint of throwing during water polo. One hundred sixty-seven water polo players were interviewed about injuries caused by water polo, and 70 players claimed to have had shoulder pain.
In 21 players, clinical examinations were performed, and in 31 players, assessment of external rotation stability was made. Then three-dimensional analysis of hand-to-hand shoot motion was performed in 7 players.
The results were as follows;
1. The painful phases of the throwing motion were the take-back phase and the acceleration phase, the pain being present at the anterior and lateral portions of the shoulder joint,
2. Assessment of stability revealed that the external rotation displacement on the affected side was significantly larger than that on the control side in the injured players.
3. Analysis of hand-to-hand shoot motion revealed that the external rotation angle in the acceleration phase was significantly larger in non-injured subjects than in the injured.
4. The external rotation angle after ball contact was increased in the injured, but decreased in the non-injured.
5. To prevent injury, it appears important to catch and throw the ball using the upper extremity and rotation of the trunk in a high body position in the water, and to strengthen the muscles of the shoulder.

102 water polo players were interviewd about the injuries caused by water polo. 13% of the subjects had knee pain at least once a year. 73% of which were chronic cases. For 24 players, clinical examinations, including X-ray examination, A-P knee laxity measurement, isokinetic strength measurement of knee muscles, and photo analysis of the vertical egg beater kick motion were performed to elucidate the cause of knee pain.
The summary of the results were as follows;
1. The most common site of knee pain was the medial portion of the knee joint.
2. Protrusion of the medial femoral epicondyle and sharpning of the tibial intercondylar eminentia as well as spur formation of the superior pole of the patella were observed in most subjects.
3. Injured subjects had stiff knees and weak knee extensor muscles.
4. The vertical egg beater kick motion must be the main factor of the painful knee.

102 water polo players were interviewd about the injuries caused by water polo. 13% of the subjects had knee pain at least once a year. 73% of which were chronic cases. For 24 players, clinical examinations, including X-ray examination, A-P knee laxity measurement, isokinetic strength measurement of knee muscles, and photo analysis of the vertical egg beater kick motion were performed to elucidate the cause of knee pain.
The summary of the results were as follows;
1. The most common site of knee pain was the medial portion of the knee joint.
2. Protrusion of the medial femoral epicondyle and sharpning of the tibial intercondylar eminentia as well as spur formation of the superior pole of the patella were observed in most subjects.
3. Injured subjects had stiff knees and weak knee extensor muscles.
4. The vertical egg beater kick motion must be the main factor of the painful knee.

97 baseball players from high school, universities and companies were subjected to this study in order to attempt to clarify the relationship between derangement of the elbow joint and lateral instabilitly by measuring various conventional parameters and the degree of lateral instability.
From the survey by questionnaire, 29 out of 97 players complained of elbow pain, paticularily on the medial side of the joint. The painful phases of the throwing motions were the acceleration phase (23 players, 61%) and release phase (7 players, 46%) . The hyperexten sion of the elbow on the dominant side was significantly smaller than that observed on the undominant side. X-ray examination revealed osteophyte formation at the tip of olecranon and medial joint space.
On the application of 63 kg⋅cm torque force, the varus deflection angle for the dominant side was 8.3° and that for the undominant side was 8.8°. The valgus angle for the dominant side was 12.2° and that for the undominant side was 10.8°. The varus stiffness (kg⋅cm/angle) was 9.5 for the dominant side and 8.4 for the undominant side. Valgus stiffness were 6.3 for the dominant side and 9.2 for the undominant side.
Thses results indicate that the lateral side become stiffer and medial side become looser in the dominant elbow than in the undominant one.
The unphysiological valgus stress at the acceleration phase would induce the osteophyte formation as well as the elongation of the medial collateral ligament on the medial side of the elbow. At the same time the impigement of the olecranon at follow through phase, would induce the osteophyte formation around the olecranon. Thses two factors would considerably influence the range of motion and the instability of the elbow joint.