A comparison of skeletal muscle oxygenation and fuel use in sustained continuous and intermittent exercise

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 (VO2). 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 VO(2) (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 x min(-1). kg(-1)] and continuous submaximal [0.85 (0.01) kJ x min(-1) x kg(-1)] exercise. Overall exercise intensity, represented as a proportion of peak aerobic power (VO2(peak)), was 68.1 (2.5)% VO2(peak) and 71.8 (1.8)% VO2(peak) 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) microM, respectively] compared to continuous exercise [2.41 (0.10) mM, 114 (4) microM, 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 VO(2) and identical energy expenditure.

Measurement and Physiological Relevance of the Maximal Lipid Oxidation Rate During Exercise (LIPOXmax)

“…The theoretical concern was that, when exercise is performed above the lactate threshold, there is an extra CO 2 production which can be assumed to interfere with the calculations (MacRae et al, 1995). In fact, below 75% of the VO 2max , this increase in CO 2 has no measurable effect on calorimetric calculations (Romijn et al, 1992), so that these calculations predict closely oxidation rates measured by stable isotope labeling (Christmass et al, 1999). Clearly, even at high intensity exercise, respiratory gases are mostly the reflect of the balance of substrate oxidation.…”

Effects of swimming on metabolic recovery from anoxia in the painted turtle

“…Mammals use primarily fats during continuous, low intensity exercise and carbohydrates during high intensity exercise (Christmass et al, 1999). In rainbow trout, fuel use is speed-and temperature-dependent, with fats being the favored substrate at warmer temperatures and at lower speeds (Kieffer et al, 1998).…”

Comparison between continuous and intermittent submaximal exercise at the intensity of maximal fat oxidation

“…Although in continuous and intermittent exercise practices done with equal oxygen consumption, a difference wasn't figured out in total energy expenditure, there was a difference at the rates of used substrate, it was determined that in spite of the continuous exercise practice, in intermittent exercise practice fat oxidation rate was almost less then three times, despite this CHO oxidation rate displayed 1,5 times higher (Christmass et al, 1999). In another research, it was reported that although similar hormonal changes were seen in both moderate aerobic exercises applied in two sections and at once with an hour period, repetitive exercise applied in two sections proved clearer high fat oxidation than exercise applied at once (Goto et al, 2007).…”