Abstract
Interval training (IT), consisting of alternated periods of high and low intensity exercise, has been proposed as a strategy to induce more marked biological adaptations than continuous exercise training (CT). The purpose of this study was to assess the effects of IT and CT with equivalent total energy expenditure on capillary skeletal and cardiac muscles in rats. Wistar rats ran on a treadmill for 30 min per day with no slope (0%), 4 times/week for 13 weeks. CT has constant load of 70% max; IT has cycles of 90% max for 1 min followed by 1 min at 50% max. CT and IT increased endurance and muscle oxidative capacity and attenuated body weight gain to a similar extent (P > 0.05). In addition, CT and IT similarly increased functional capillary density of skeletal muscle (CT: 30.6 ± 11.7%; IT: 28.7 ± 11.9%) and the capillary-to-fiber ratio in skeletal muscle (CT: 28.7 ± 14.4%; IT: 40.1 ± 17.2%) and in the left ventricle (CT: 57.3 ± 53.1%; IT: 54.3 ± 40.5%). In conclusion, at equivalent total work volumes, interval exercise training induced similar functional and structural alterations in the microcirculation of skeletal muscle and myocardium in healthy rats compared to continuous exercise training.
Highlights
Regular practice of moderate aerobic exercise is widely recognized to reduce cardiovascular risk [1]
The maximal velocity achieved in the treadmill endurance test was significantly higher (P < 0.05) in the trained animals than in the sedentary group (SED) animals (Table 1); the observed increase in velocity was similar for the continuous exercise training (CT) and interval training (IT) groups at both six and 13 weeks of training
The most important novel findings of the present study are as follows: (1) CT and IT increased exercise endurance and muscle oxidative capacity and attenuated body weight gain to the same extent; (2) CT and IT increased functional and structural alterations in the microcirculation of locomotor skeletal muscle and of the myocardium of rats. These results suggest that IT mode is equivalent to CT in increasing exercise capacity and in inducing microvascular adaptations in both skeletal and cardiac muscles, when total training volume is matched supporting the concept that total energy expenditure, and not exercise intensity per se, is the major physiological stimulus, at least for chronic changes in skeletal and myocardium microcirculation
Summary
Regular practice of moderate aerobic exercise is widely recognized to reduce cardiovascular risk [1]. Since acute exercise is the most important stimulus for increasing myocardial demand, it is not surprising that major structural and functional adaptations occur in the heart consequent to chronic regular exercise training. These adaptations include higher efficiency in myocardial substrate utilization and energetic [2] and enhanced antioxidative stress capacity [3], both potentially involved with the protection against ischemia/reperfusion myocardial damage [3] and infarction [4] developed after exercise training. That is, capillary growth, and vascularization along with altered regulation of coronary blood flow are well-known features of physiological adaptations to chronic exercise and have been extensively revised [5,6,7]. The balance between metabolic demand and oxygen delivery is maintained along the weeks of training by a dynamic and stepwise combination of early angiogenesis followed by an increase in small and larger arterioles, in part as a consequence of capillaries developing into small arterioles [8]
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