Myoglobin is a sensitive marker of increased muscle membrane vulnerability.

Changes in muscle proteins in serum after exercise were studied to evaluate the use of such proteins as indicators of increased muscle membrane vulnerability. Seventy-one women were asked to perform bicycle exercise for 45 min at a moderate load; four proteins (creatine kinase - CK, myoglobin - Mb, aldolase - Ald and pyruvate kinase - PK) were measured in serum up to 24 h after exercise. Twenty-one women were carriers of Duchenne's muscular dystrophy (DMD); these are known to show an elevated serum CK activity at rest, as well as increased CK response after exercise. Fifty women without a family history of neuromuscular disease were tested to obtain normal values: they showed a small peak (18%) of CK activity 8 h after exercise, and an even smaller peak of Mb (9%) 1 h after exercise. The mean post-exercise increase for both CK and Mb in the 21 DMD carriers was significantly higher than in controls; the maximum of Mb, on average 70% of baseline levels, was reached 1 h after exercise and was higher than that for CK (48%), which was reached 8 h after exercise. It is concluded that myoglobin levels after exercise are a good index of increased vulnerability of the muscle membrane.