EXERCISE METABOLISM IN HUMAN SKELETAL-MUSCLE EXPOSED TO PRIOR ECCENTRIC EXERCISE

1. The effects of unaccustomed eccentric exercise on exercise metaboli sm during a subsequent bout of graded concentric exercise were investi gated in seven healthy male subjects. Arterial and bilateral femoral v enous catheters were inserted 2 days after eccentric exercise of one t high (eccentric thigh) and blood samples were taken before and during graded two-legged concentric knee-extensor exercise. Muscle biopsies w ere obtained from the eccentric and control vastus lateralis before (r est) and after (post) the concentric exercise bout. 2. Maximal knee-ex tensor concentric exercise capacity was decreased by an average of 23 % (P < 0.05) in the eccentric compared with the control thigh. 3. The resting muscle glycogen content was lower in the eccentric thigh than in the control thigh (402 +/- 30 mmol (kg dry wt)(-1) vs. 515 +/- 26 m mol (kg dry wt)(-1), means +/- S.E.M., P < 0.05), and following the tw o-legged concentric exercise this difference substantially increased ( 190 +/- 46 mmol (kg dry wt)(-1) vs. 379 +/- 58 mmol (kg dry wt)(-1), P < 0.05) despite identical power and duration of exercise with the two thighs. 4. There was no measurable difference in glucose uptake betwe en the eccentric and control thigh before or during the graded two-leg ged concentric exercise. Lactate release was higher from the eccentric thigh at rest and, just before termination of the exercise bout, rele ase of lactate decreased from this thigh (suggesting decreased glycoge nolysis), whereas no decrease was found from the contralateral control thigh. Lower glycerol release from the eccentric thigh during the fir st, lighter part of the exercise (P < 0.05) suggested impaired triacyl glycerol breakdown. 5. At rest, sarcolemmal GLUT4 glucose transporter content and glucose transport were similar in the two thighs, and conc entric exercise increased sarcolemmal GLUT4 content and glucose transp ort capacity similarly in the two thighs. 6. It is concluded that in m uscle exposed to prior eccentric contractions, exercise at a given pow er output requires a higher relative workload than in undamaged muscle . This increases utilization of the decreased muscle glycogen stores, contributing to decreased endurance.