Exercise metabolism in human skeletal muscle exposed to prior eccentric exercise

Abstract

1. The effects of unaccustomed eccentric exercise on exercise metabolism during a subsequent bout of graded concentric exercise were investigated in seven healthy male subjects. Arterial and bilateral femoral venous catheters were inserted 2 days after eccentric exercise of one thigh (eccentric thigh) and blood samples were taken before and during graded two-legged concentric knee-extensor exercise. Muscle biopsies were obtained from the eccentric and control vastus lateralis before (rest) and after (post) the concentric exercise bout. 2. Maximal knee-extensor 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 mmol (kg dry wt)-1, means +/- s.e.m., P < 0.05), and following the two-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 between the eccentric and control thigh before or during the graded two-legged concentric exercise. Lactate release was higher from the eccentric thigh at rest and, just before termination of the exercise bout, release of lactate decreased from this thigh (suggesting decreased glycogenolysis), whereas no decrease was found from the contralateral control thigh. Lower glycerol release from the eccentric thigh during the first, lighter part of the exercise (P < 0.05) suggested impaired triacylglycerol breakdown. 5. At rest, sarcolemmal GLUT4 glucose transporter content and glucose transport were similar in the two thighs, and concentric exercise increased sarcolemmal GLUT4 content and glucose transport capacity similarly in the two thighs. 6. It is concluded that in muscle exposed to prior eccentric contractions, exercise at a given power output requires a higher relative workload than in undamaged muscle. This increases utilization of the decreased muscle glycogen stores, contributing to decreased endurance.

Figure 1. Glycogen concentration in eccentric and control muscle before and after two-legged concentric exercise

Each bar shows the mean ±s.e.m. of 7 observations, for values from the eccentric thigh that had performed eccentric exercise 2 days prior to the concentric exercise (▪) and values from the contralateral control thigh (□). Rest and Post represent the values before and after the concentric exercise bout, respectively. * Significantly (P < 0.05) different from the control thigh. † Decrease in concentration during concentric exercise is significantly (P < 0.05) different from the decrease in the control thigh.

Figure 2. Glycogen depletion pattern with concentric exercise in the different muscle fibre types in eccentric and control muscle

Histochemical estimation of glycogen distribution in the type I, II A and II B fibres in eccentric and control vastus lateralis at rest (R) and after two-legged concentric exercise (P), using a scale of dark (▪), moderate (), light () and negative (□) stained. Dark stained represents fibres which are glycogen filled, and negative stained represents fibres which are glycogen depleted.

Figure 3. Changes with concentric exercise in GLUT4 content and glucose transport in giant sarcolemmal vesicles from eccentric and control muscle

Bars show means ±s.e.m. of 7 observations. , percentage change from resting to post muscle biopsies in vesicle GLUT4 content; , percentage change in vesicle glucose transport.

Figure 4. Total glycerol release in eccentric and control thigh during step 1 and step 2 of the two-legged concentric exercise

Each bar shows mean ±s.e.m. of 7 observations, for values from the eccentric thigh that had performed eccentric exercise 2 days prior to the concentric exercise (▪) and values from the contralateral control thigh (□). Glycerol release was measured at rest, and at 10, 20 and 25 min during step 1 (lighter exercise) and step 2 (heavier exercise) of the two-legged concentric exercise, and on each step the total release was calculated from these values. * Significantly (P < 0.05) different from the control thigh at the same exercise step.