A study was designed to examine the effects of exercise intensity on renal clearance parameters. Five healthy male subjects underwent exercise tests on an bicycle ergometer at 4 different work loads for 15 min. The indicators of exercise intensity employed were the percentage of maximal oxygen uptake (%VO₂max), heart rate (HR) and blood lactate level (La) . As parameters of renal clearance, para-aminohippurate clearance (CPAH), thiosulfate clearance (C_thio) and creatinine clearance (C_cr) were measured by the continuous infusion technique during the exercise.
1) The renal clearance parameters during exercise decreased linearly as the exercise intensity increased. The percentage of maximal oxygen uptake at the onset of the decreases in %C_PAH, %C_chiu and %C_cr were 36, 45 and 47%VO₂max, respectively.
2) Among the indicators of exercise intensity, the decrease in La showed the closest correlation with renal clearance during the exercise.
3) The renal plasma flow, which was measured as C_PAH, began to decrease linearly at a significantly lower exercise intensity than the glomerular filtration rate, which was measured as both C_thio and C_cr.
The above results suggest that renal clearance parameters begin to decrease at the threshold as exercise intensity increases.