Seven healthy males ranging from 2430 years old volunteered

Seven healthy males ranging from 24-30 years old volunteered for a study on the use of fuel by exercising skeletal muscle. The subjects exercised on a stationary bicycle at a workload designed to elicit 80% of maximum capacity. Muscle biopsies were obtained at rest and after 5 min of exercise.

Rest

5 min Exercise

Phosphocreatine*

97.7±2.2

56.0±5.0

Creatine*

35.5±2.5

77.1±4.0

Glycogen*

405.3±16.7

345.0±22.4

Lactate*

4.4±0.5

56.4±6.5

Pyruvate*

0.18±0.03

0.63±0.03

Relative Muscle Oxygen consumption

3±1

205±15

Relative TCA cycle flux

0.04±0.01

2.69±0.20

*Values are means ± standard error (SE) in mmol/kg dry weight

Discuss which metabolic sources generate ATP for skeletal muscle contraction.

Describe the principal functions of the TCA cycle.

The student on the bike exercises so that the rate of the TCA cycle (and oxygen consumption) increases dramatically. Discuss how strenuous exercise results in increased TCA flux.

The student on the stationary bike exercises to exhaustion. During this time, the level of lactate in the blood increases. From your knowledge of the TCA cycle how do you explain the increase of lactate from the exercising muscle even though the flux through the TCA cycle is increased during exercise?

Solution

1). In resting state, muscles acquire ATP by the oxidative phosphorylation of glucose. During excessive muscular activity such as exercise, the oxygen consumption of muscles increase, which causes oxygen debt. During this condition, the muscles generate ATP by lactate fermentation (pyruvic acid is converted into lactic acid) or by creatinine phosphate breakdown. Accumulation of fatty acid causes fatigue.