Tohoku J. Exp. Med., 2004, 202(3)

Significance of Post-Exercise Increment of Urinary Bicarbonate and pH in Subjects Loaded with Submaximal Cycling Exercise

TETSUSHI MORIGUCHI, AKIO TOMODA,¹ SHIRO ICHIMURA, YUKO ODAGIRI, SHIGERU INOUE, TAKESHI NAGASAWA, HIROSHI TANAKA,² NAOKI NAKAGAWA and TERUICHI SHIMOMITSU

Department of Preventive Medicine and Public Health, ¹Department of Biochemistry, Tokyo Medical University, Tokyo 160-8402, and
²Department of Foreign Language (Physical Education), Daito Bunka University, Tokyo 175-0082

We studied the changes in urinary bicarbonate, urinary pH and some physical parameters such as minute ventilation (VE), oxygen consumption (VO2), respiratory carbon dioxide (VCO₂), heart rate, blood pressure, and blood lactate, before and after the submaximal exercise. Six male subjects aged 28-33 years were involved in the study. They performed the incremental exercise test using a bicycle ergometer until exhaustion. Levels of VE, VO2, VCO₂, heart rate, and blood pressure increased continuously with an increase in cycling intensity. These parameters markedly decreased and reached the baseline levels within 5-10 minutes after the termination of exercise. According to an increase in cycling intensity, blood lactate increased continuously during exercise, but after termination of exercise the return of lactate to the baseline level was markedly retarded. Urinary bicarbonate and pH were within the range of those at 0 time (baseline levels) from the beginning until 30 minutes after the exercise. However, they began to increase abruptly about 30 minutes after the exercise, and continued to increase extensively for 2 hours thereafter. Such marked increase in urinary bicarbonate and pH seemed to be correlated with the aerobic metabolism of lactate in the muscles, liver, and kidney, finally producing CO₂. It was also suggested that the measurement of urinary bicarbonate and pH may be useful for the estimation of physiological changes in the body after submaximal incremental cycling exercise loading.

keywords —— cycling exercise; acid-base balance; urinary HCO₃⁻

© 2004 Tohoku University Medical Press

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Address for reprints: Akio Tomoda, M.D., Ph.D., Department of Biochemistry, Tokyo Medical University, 6-1-1 Shinjuku, Shinjuku-ku, Tokyo 160-8402, Japan.

e-mail: tomoda@tokyo-med.ac.jp