Marked increase in urinary bicarbonate and pH caused by heavy muscular exercise with dynamic knee extension

In order to estimate the physiological responses to heavy muscular exercise with dynamic knee extension, the levels of urinary variables such as bicarbonate, urinary pH and blood lactate were studied before and after the exercise. Nine male volleyball players aged 19 or 20 years were involved in the present study. They performed 10%, 30% and 80% 1 repetition maximum (RM) knee extension. The levels of urinary bicarbonate and urinary pH did not change for 2.5 hours after cessation of the exercise with 10% 1 RM load, compared with the baseline levels. When 30% 1 RM loading was given, urinary bicarbonate and pH moderately increased for 2.5 hours. When 80% 1 RM loading was given, both urinary bicarbonate and pH increased immediately after cessation of the exercise, for 2.5 hours. Levels of blood lactate increased extensively within 1 minute after cessation of the exercise in the subjects with 80% 1 RM load, but no significant increase was seen in subjects with 10% 1 RM load. The changes in urinary bicarbonate and pH could be explained by the continuous production of CO2 in the muscular tissues involved in the exercise with a submaximal load where excess postexercise oxygen consumption is accelerated. It is also possible that the liver and muscle where blood lactate is aerobically metabolized could be the cause of these changes. It was also suggested that the measurement of urinary bicarbonate and pH may be useful for the estimation of events in the body after submaximal exercise loading.