Delayed-onset muscle damage and lipid peroxidation in man after a downhill run.

Lipid peroxidation initiated by free radical reactions is associated with tissue necrosis in a variety of conditions. We have measured serum lipid peroxide concentrations (as total thiobarbituric acid-reactive substances, TBARS) and creatine kinase (CK), lactate dehydrogenase (LDH), and aspartate aminotransferase (AST) activities and subjective muscle soreness in 16 men before and after a 45-minute downhill treadmill run. TBARS concentrations and enzyme activities were increased after exercise, with peak values observed at 6 hours (TBARS, LDH) or 24 hours (CK, AST) after exercise. Serum LDH activity returned to preexercise levels by 48 hours after exercise and TBARS by 72 hours after exercise: CK and AST activities remained elevated 72 hours after exercise. Leg muscle soreness also increased, with the greatest degree of soreness seen at 24 or 48 hours after exercise. Subjects with the greatest increase in CK, LDH, and AST also showed the highest serum TBARS concentration. This suggests a possible relationship between free radical generation and exercise-induced muscle damage.