A comparison of skeletal muscle oxygenation and fuel use in sustained continuous and intermittent exercise |
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Authors: | Michael A Christmass Brian Dawson Paola Passeretto Peter G Arthur |
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Institution: | Department of Biochemistry, The University of Western Australia, Nedlands 6907, Australia e-mail: mxmass@cyllene.uwa.edu.au Tel.: +61-8-9380-2361, Fax: +61-8-9380-1025, AU Department of Human Movement, The University of Western Australia, Nedlands 6907, Australia, AU
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Abstract: | In this study we compared substrate oxidation and muscle oxygen availability during sustained intermittent intense and continuous submaximal exercise with similar overall (i.e. work and recovery) oxygen consumption (V˙O2). Physically active subjects (n?=?7) completed 90?min of an intermittent intense (12?s work:18?s recovery) and a continuous submaximal treadmill running protocol on separate days. In another experiment (n?=?5) we compared oxygen availability in the vastus lateralis muscle between these two exercise protocols using near-infrared spectroscopy. Initially, overall V˙O2 (i.e. work and recovery) was matched, and from 37.5?min to 67.5?min of exercise was similar, although slightly higher during continuous exercise (8%; P?0.05). Energy expenditure was constant (22.5–90?min of exercise) and was not different in intermittent intense 0.81 (0.01)?kJ?·?min?1?·?kg?1] and continuous submaximal 0.85 (0.01)?kJ?·?min?1?·?kg?1] exercise. Overall exercise intensity, represented as a proportion of peak aerobic power (V˙O2peak), was 68.1 (2.5)% V˙O2peak and 71.8 (1.8)% V˙O2peak for intermittent and continuous exercise protocols, respectively. Fat oxidation was almost 3 times lower (P?0.05) and carbohydrate oxidation was approximately 1.2 times higher (P?0.05) during intermittent compared to continuous exercise, despite the same overall energy expenditure. Capillary plasma lactate was constant from 15 to 90?min of exercise, and pyruvate was constant from 15 to 75?min, although both were higher (P?0.0001, lactate; P?0.001, pyruvate) during intermittent 5.05 (0.28)?mM, 200 (7)?μM, respectively] compared to continuous exercise 2.41 (0.10)?mM, 114 (4)?μM, respectively]. There was no difference between protocols for either plasma glycerol or non-esterified fatty acids. The decrease in muscle oxygenation during work periods of intermittent exercise resulted in a lower nadir oxygenation 54.62 (0.41)%] compared to continuous exercise 58.82 (0.21)%, P?0.001]. The decline in oxygenation was correlated with treadmill speed (r?=?0.72; P?0.05). These results show a difference in substrate utilisation and muscle oxygen availability during sustained intermittent intense and continuous submaximal exercise, despite a similar overall V˙O2 and identical energy expenditure. |
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