Relationship between Urine Flow, Glomerular Filtration, and Urine Solute Concentrations during Prolonged Heavy Exercise

Abstract

Serum and urine electrolytes, creatinine, and urea were determined in 21 well-trained men, aged 21–56 years, in connection with a 70-km cross-country ski race, lasting 4.39–6.52 h, leading to slight dehydration. Although the race urine flow was low, averaging 0.41 (0.1-0.9) ml/min, the average urine concentrations of urea, Na, Ca, Mg, CI, and P were markedly lower than during the preceding night, while the concentrations of K and creatinine were higher, the total of measured solutes being 621 mmol/1, compared with 911 mmol/1 during the preceding night. Decreasing urine flow and endogenous creatinine clearance were accompanied by a falling urine solute concentration, particularly when the race creatinine clearance decreased to below 70 ml/min, mainly due to a fall in the urea, Na, and CI concentrations. Thus, a decrease in the glomerular filtration rate was accompanied by a progressive decline in the urine concentrating ability.

Key Words:

• Creatinine
• electrolytes
• exercise
• glomerular filtration
• osmolality
• renal concentrating ability
• renal function
• serum
• urea
• urine