Physiological adaptations to interval training and the role of exercise intensity

Abstract

Interval exercise typically involves repeated bouts of relatively intense exercise interspersed by short periods of recovery. A common classification scheme subdivides this method into high-intensity interval training (HIIT; 'near maximal' efforts) and sprint interval training (SIT; 'supramaximal' efforts). Both forms of interval training induce the classic physiological adaptations characteristic of moderate-intensity continuous training (MICT) such as increased aerobic capacity (V̇O2 max ) and mitochondrial content. This brief review considers the role of exercise intensity in mediating physiological adaptations to training, with a focus on the capacity for aerobic energy metabolism. With respect to skeletal muscle adaptations, cellular stress and the resultant metabolic signals for mitochondrial biogenesis depend largely on exercise intensity, with limited work suggesting that increases in mitochondrial content are superior after HIIT compared to MICT, at least when matched-work comparisons are made within the same individual. It is well established that SIT increases mitochondrial content to a similar extent to MICT despite a reduced exercise volume. At the whole-body level, V̇O2 max is generally increased more by HIIT than MICT for a given training volume, whereas SIT and MICT similarly improve V̇O2 max despite differences in training volume. There is less evidence available regarding the role of exercise intensity in mediating changes in skeletal muscle capillary density, maximum stroke volume and cardiac output, and blood volume. Furthermore, the interactions between intensity and duration and frequency have not been thoroughly explored. While interval training is clearly a potent stimulus for physiological remodelling in humans, the integrative response to this type of exercise warrants further attention, especially in comparison to traditional endurance training.

Sweat Rate Measurements After High Intensity Interval Training Using Body Weight

“…2 In that way, it is possible to consider that with higher sweating rates, the body mass will be smaller after the practice of exercise. 26,27 Regarding the difference between sessions HIIT and moderate, the intensity (all out) used at HIIT´s session can explain the results found in this study. Consequently, it is possible to consider that although the human body has a limitation to take advantage of the energy for movement (20%), about 80% of the energy is wasted in the form of heat 27 being proportional to higher intensities.…”

Impact of cardiac rehabilitation and exercise training programs in coronary heart disease

“…HIIT protocols consist of shorter high-intensity intervals (75%-95% of maximal effort) interrupted by periods of rest. 46 The effects of ET intensity and interval training are elaborated below.…”

“…46 Increased mitochondrial content in muscle promotes fat oxidation preferentially over carbohydrate oxidation. 66 This adaptation decreases lactate as a byproduct and permits a longer duration of ET at increased aerobic capacity.…”

The Effects of Two Weeks of Arm Crank Sprint Interval Training in Men with Chronic Spinal Cord Injury

“…Contemporary performance research typically considers a 1% improvement as the least meaningful improvement for events lasting 30 sec or less [18], indicating that our findings represent almost certain improvements in performance that were consistent across all subjects. While the increased in aerobic power are most likely tied to improved motor unit recruitment [11], the greater overall work capacity would improve overall upper extremity power, an important fitness component for wheelchair propulsion and activities of daily living [19][20][21][22]. For example, loss of upper extremity strength and power significantly increases one's risk for premature mortality [21], and strength and power have a profound influence on one's ability to perform activities of daily living and wheelchair propulsion [19,22].…”

“…Earnest [9] hypothesized that High-Intensity Interval (HIT), using efforts at > 80% VO 2 Peak , may offer a more powerful stimulus improving insulin sensitivity than moderate aerobic exercise, relating specifically to the aerobic metabolic processes (e.g., aerobic glycolysis, beta oxidation, and mitochondrial biogenesis). Similarly, Sprint Interval Training (SIT), which uses repeated "supramaximal" sprints above VO 2 [11], has also been studied extensively. For example, results by Gibala and others [12][13][14] have shown the powerful endurance-like impact that SIT has on oxidative capacity and metabolic function, while [13] showed that six weeks of SIT produced similar improvements in lipid levels, carbohydrate oxidation, and mitochondrial biogenesis compared to endurance training encompassing ten-times the total work expenditure (225 kJ vs. 2250 kJ).…”