Relationships of intracellular pH to oxygenated hemoglobin/myoglobin and to phosphate compounds in active muscle during forearm exercise / 体力科学

The purpose of this study is to find a key to clarifying the mechanism of lactic acid production during exercise. Five healthy men performed the grip and wrist flexion exercises at different occasions. Exercise intensities were increased by 5% MVC (maximum voluntary contraction force) per minute from 10% MVC. Intracellular pH, oxygenated hemoglobin/myoglobin (Oxy-Hb/Mb), inorganic phosphate (Pi), and phosphocreatin (PCr) in forearm flexor muscles were measured by <SUP>31</SUP>P-MRS and NIRS. The lowest Oxy-Hb/Mb concentrations during the grip and wrist flexion exercises were 40.7± 8.86% (average±SE) and 15.4 ± 2.26%, respectively. These results suggest that oxygen remain sufficient in the muscles at least during the grip exercise. Intracellular pH dropped as exercise intensity rose above 25% MVC for the grip and above 10% MVC for the wrist flexion exercise. These results support the idea that oxygen deficiency is not the only cause for lactic acid production during exercise. On the other hand, intracellular pH fell with either negative or positive relations to Pi/PCr ratio, Pi, and PCr in each exercise. These results support the suggestion that the main causes of lactic acid production during exercise are the changes in ADP, Pi, and PCr.

Nutritional intakes in ultraendurance exercise (triathlon) before and during competition / 体力科学

Daily activities and food consumption, for the 2 days before and the day of competition, were investigated in 18 Japanese male triathletes participating in the Ironman Japan Competition at Lake-Biwa in 1991. Energy intakes and the energy intake to expenditure ratio, one and two days before and on race day, were 4005±895 kcal and 151±40%, 5000±1356 kcal and 203±53% and 5170±1799 kcal and 55±27%, respectively. Carbohydrates constituted 62, 4±11.6%, 61.3±7.7% and 76.7±5.6%, respectively, of these meals. Mean vitamin and mineral intakes were highly variable. Total water intake at breakfast and during the events was 7488±3653 ml. Salt intake appeared to be inadequate. Some triathlestes, who consumed only meals (no supplements) or had not stored adequate nutrients prior to the competition, had transiently subnormal nutrient levels during these extremely demanding events.