Physiological and biochemical measurements during a 4-day surf-ski marathon.

We studied competitors in the 1983 Texan Challenge surf-ski paddle marathon to determine the effects of 4 days prolonged paddling on sweat rates, rectal temperatures, renal function, serum glucose, free fatty acid, porphyrin and C-reactive protein levels and serum creatine kinase activity. Sweat rates during the race varied from 0.5 to 1.0 l/h, and peak rectal temperatures did not exceed 38 degrees C, even in the most dehydrated subjects. Renal function was unchanged during the race. Plasma renin activity remained low during the race but C-reactive protein levels and serum creatine kinase activity were elevated. Seventy per cent of the subjects had immediate post-exercise blood glucose levels below 3.9 mmol/l after the 1st and 4th days, and 27% had values below 3.0 mmol/l, one competitor requiring intravenous glucose therapy on the beach. Surf-ski paddling is therefore associated with low sweat rates, low levels of dehydration, low body temperature and unchanged renal function. The low post-exercise blood glucose levels indicate that competitors must eat high-carbohydrate diets for the duration of the event and must either eat carbohydrate-containing foods or drink concentrated carbohydrate solutions while paddling.