Muscle cell leakage of myoglobin after long-term exercise and relation to the individual performances.

Muscle protein release was studied during and after prolonged exercise by means of serum myoglobin determinations. Increased serum myoglobin levels were regularly found after performance of long-term exercise. The correlations (P less than 0.001) to muscle enzymes indicated nonselective release from muscle cells. Myoglobin measured after completed exercise was correlated to the finishing time in a ski race, i.e., the fast skiers showed lower myoglobin levels than slow skiers. Inexperienced skiers and also skiers older than 49 years of age were found to have higher myoglobin levels than the others although the mean finishing times were similar. Myoglobin measured during and after 5 h of bicycle exercise showed large differences even though the relative work load was identical. Myoglobin started to rise 1.2 h (median) after the commencement of the bicycle exercise. The time at which myoglobin started to rise correlated (P less than 0.01) with the myoglobin levels after completed exercise and was not related to the physical fitness of the individuals. The results indicated considerable individual differences with regard to muscle protein leakage during exercise. The leakage is not simply related to the individual's apparent physical fitness but probably also to constitutional factors, such as age and metabolic capacity of the muscle cells.