Article

ATP and heat production in human skeletal muscle during dynamic exercise: higher efficiency of anaerobic than aerobic ATP resynthesis.

Institute of Exercise and Sports Sciences, August Krogh Institute, Department of Human Physiology, University of Copenhagen, Denmark.
The Journal of Physiology (impact factor: 4.72). 05/2003; 549(Pt 1):255-69. DOI:10.1113/jphysiol.2002.035089 pp.255-69
Source: PubMed

ABSTRACT The aim of the present study was to simultaneously examine skeletal muscle heat production and ATP turnover in humans during dynamic exercise with marked differences in aerobic metabolism. This was done to test the hypothesis that efficiency is higher in anaerobic than aerobic ATP resynthesis. Six healthy male subjects performed 90 s of low intensity knee-extensor exercise with (OCC) and without thigh occlusion (CON-LI) as well as 90 s of high intensity exercise (CON-HI) that continued from the CON-LI bout. Muscle heat production was determined by continuous measurements of muscle heat accumulation and heat release to the blood. Muscle ATP production was quantified by repeated measurements of thigh oxygen uptake as well as blood and muscle metabolite changes. All temperatures of the thigh were equalized to approximately 37 degrees C prior to exercise by a water-perfused heating cuff. Oxygen uptake accounted for 80 +/- 2 and 59 +/- 4 %, respectively, of the total ATP resynthesis in CON-LI and CON-HI, whereas it was negligible in OCC. The rise in muscle temperature was lower (P < 0.05) in OCC than CON-LI (0.32 +/- 0.04 vs. 0.37 +/- 0.03 degrees C). The mean rate of heat production was also lower (P < 0.05) in OCC than CON-LI (36 +/- 4 vs. 57 +/- 4 J s-1). Mechanical efficiency was 52 +/- 4 % after 15 s of OCC and remained constant, whereas it decreased (P < 0.05) from 56 +/- 5 to 32 +/- 3 % during CON-LI. During CON-HI, mechanical efficiency transiently increased (P < 0.05) to 47 +/- 4 %, after which it decreased (P < 0.05) to 36 +/- 3 % at the end of CON-HI. Assuming a fully coupled mitochondrial respiration, the ATP turnover per unit of work was calculated to be unaltered during OCC (approximately 20 mmol ATP kJ-1), whereas it increased (P < 0.05) from 21 +/- 4 to 29 +/- 3 mmol ATP kJ-1 during CON-LI and further (P < 0.05) to 37 +/- 3 mmol ATP kJ-1 during CON-HI. The present data confirm the hypothesis that heat loss is lower in anaerobic ATP resynthesis than in oxidative phosphorylation and can in part explain the finding that efficiency declines markedly during dynamic exercise. In addition, the rate of ATP turnover apparently increases during constant load low intensity exercise. Alternatively, mitochondrial efficiency is lowered as exercise progresses, since ATP turnover was unaltered during the ischaemic exercise bout.

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Keywords

aerobic ATP resynthesis
 
ATP turnover
 
CON-LI bout
 
coupled mitochondrial respiration
 
dynamic exercise
 
heat production
 
intensity exercise
 
ischaemic exercise bout
 
low intensity knee-extensor exercise
 
mean rate
 
Mechanical efficiency
 
mechanical efficiency transiently
 
mitochondrial efficiency
 
Muscle ATP production
 
muscle heat accumulation
 
Muscle heat production
 
muscle metabolite changes
 
muscle temperature
 
skeletal muscle heat production
 
water-perfused heating cuff