We have reported three cases of fatigue fracture of the ulna in male pitchers of fast-pitch softball. To elucidate the etiology of injury, we first selected three healthy male and three healthy female pitchers from a well-trained college team and analyzed their forearm movement by high-speed cinematography. This showed slight flexion of the elbow joints during wind-up motion, dorsal flexion of the hand joints upon releasing the ball, and extreme pronation of the forearms during the follow-through. We then took 8 mm CT scanning sections of the forearms. Using these images, we investigated shapes and areas of cross-sections of the ulna and its cortical and cancellous bones from the elbow to the hand joints. Our results reveal that the shapes of the sections are significantly different from circles at around the center of the ulna, and the cross-sectional areas are smaller in the middle one-third of the ulna than in other parts. These observations imply that fatigue fractures of the ulna in pitchers of fast-pitch softball must be torsionally induced, tending to occur at the middle one-third of the bone.

A previously reported method for electrocardiographic (ECG) telemetry in water using frequency-modulated current was improved to obtain more stable ECGs. The ECGs of seven healthy men were monitored using the improved method during and after whole-body submersion or underwater swimming. Bradycardia and arrhythmias were observed during the submersion, and transient tachycardia was detected after the start of underwater swimming, followed by bradycardia with arrhythmias. Three different types of arrhythmias were observed: sinus arrhythmia (SA), supraventricular extrasystole (SE) and ventricular extrasystole (VE). SA and SE tended to develop during the latter half of the period of submersion or underwater swimming, and especially after the restart of breathing. VEs were detected in only one subject during submersion, whereas they occurred in most subjects during and after underwater swimming. Individual variations were found in development of arrhythmias, one subject showing no arrhythmia. Bradycardia, SA and SE could depend on vagal suppression in underwater conditions, and VE may be related to the effect of muscular movement on cardiac function in addition to vagal inhibition.

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Healthy male subjects were asked to hold their breath in air at the tidal inspiratory level, and time-dependent changes in mean values of several parameters of cardiovascular function were studied. The heart rate increased abruptly after the beginning of breath-holding and then decreased slightly with time. The stroke volume (SV) remained significantly low until the end of breath-holding, so that the cardiac output was decreased in parallel. With regard to the systolic time interval, the totai eiectromechanical systole and the left-ventricular systolic time (LVET) were not significantly changed, whereas the pre-ejection period (PEP) was markedly prolonged. Therefore, ratios of PEP/LVET and SV/LVET were increased and decreased with time, respectively. As the systolic, and in particular the diastolic blood pressures were elevated, the pulse pressure was reduced. Ratios of the diastolic and systolic times in relation to the heart rate at rest, during breath-holding and during recovery after breath-holding were all proved to be described by a single regression curve. However, the ratios obtained for cycling exercise at various heart rates showed a marked shift above the curve. These results clearly indicate that cardiac performance is lowered during breathholding in air.(Jpn. J. Phys. Fitness Sports Med. 1993, 42; 475484) key words ; heart rate, cardiac output, systolic time intervals, blood pressure

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