Enzyme blood levels and water balance during a marathon race

A marathon race, 42 km, was chosen for the investigation of the influence of strenuous exercise on changes in blood enzyme levels and water balance in six trained athletes. Serum muscle and liver enzymes and red cell 2,3-diphosphoglycerate (2,3 DPG) were determined before and after the race. The serum muscle enzymes rose moderately during the race, while liver enzymes and 2,3 DPG remained constant. This finding was in contrast to the sharp elevations of muscle enzymes after exercise in untrained subjects previously reported by the authors' group. It was concluded that training prevents muscle enzyme elevation, probably since there is little or no change in membrane permeability and no tissue hypoxia occurs. Water balance: climate was comfortable (21-26°C air temperature) and cold drinks were offered at seven stations along the route. Mean hypohydration at the end of the race was 3.7% (1.7-6.7%). A paradoxical positive relationship was found between hypohydration and sweat rate, and a negative one between liquid intake and sweat rate. This may be attributed to reduced heat conductance causing elevation of core temperature which in turn caused an increased sweat rate. It was also concluded that energetic steps should be taken to prevent hypohydration even in a comfortable climate.