High-intensity interval training workouts typically include short bursts of intense exercise alternating with relief breaks of varying lengths. The workouts include a limitless variety of exercises, including body weight movements, powerlifting, plyometrics, sprints and heavy rope drills.
It is known in the fitness industry that HIIT is a time-efficient way to:
- Improve the health of recreational exercisers.
- Boost the performance of competitive athletes.
- Provide the benefits of continuous-endurance training with fewer workouts.
Research on high-intensity interval training showed that healthy young and older men and women can improve cardiorespiratory fitness (VO2max) 4%-46% in training periods lasting 2-15 weeks and appears to induce rather rapid changes in VO2max. VO2 max is considered the body’s upper limit for consuming, distributing and using of oxygen for energy production. Commonly called maximal aerobic capacity, VO2max is a good predictor of exercise performance.
The current scientific explanation for this increase in VO2max from a HIIT program is that it causes and increase in stroke volume (volume of blood pumped by the heart per beat), which happens chiefly because the heart muscle’s contractility increases at near-maximal exertion. Researchers add that HIIT increases mitochondrial biogenesis (ability to make more ATP increases), which readily translates into improved cardiovascular capacity at any level of exercise intensity.
Low VO2max is predictive of cardiovascular fatalities and all-cause mortality. Data from another study clearly showed that in comparison with men and women of low fitness, people who were moderately or highly fit, regardless of whether they were sick or healthy, smokers or nonsmokers, had normative or elevated cholesterol levels, or were obese or normal-weight, seemed to have enhanced protection from factors associated with causing cardiovascular disease.
Additionally, researchers reviewed studies that assessed the benefits of moderate versus vigorous physical activity, as well as clinical investigations that trained subjects at different intensities. All of these studies found vigorous exercise intensity was more beneficial in improving one or more risk factors for coronary heart disease. Thus, HIIT should be considered a most advantageous method for counteracting the effects of cardiovascular disease, the number-one cause of death throughout the world.
Insulin sensitivity which describes the ability of the body’s cells to take up or metabolize glucose, typically increases during and after exercise. Studies found that insulin sensitivity can improve by 23% -58% over the course of 2-16 weeks of HIIT. The mechanism for this improvement appears to be well documented: Exercising muscle contractions can stimulate glucose shuttle transporters to take up glucose into the working muscle from the blood, whether insulin is available or not.
Researchers also said HIIT improves HDL cholesterol after a minimum of 8 weeks of training. The scientists suggest that a moderate decrease in body fat needs to accompany HIIT for improvements in total cholesterol, LDL cholesterol and blood triglycerides to occur.
Authors reported that consistent HIIT for up to 10 weeks has not shown any measurable effects on resting blood pressure in people with hypertension. The researchers concluded that people with elevated blood pressure (and not on hypertension medicine) need at least 12 weeks of HIIT training to see an appreciable reduction in systolic and diastolic blood pressure.
Because of the nature of high-intensity exercise, it’s effectiveness for burning fat has been closely examined. Studies have shown that fat oxidation, or fat burning, was significantly higher and carbohydrate oxidation (burning) significantly lower after 6 weeks of high-intensity interval training.
The striking surge in epinephrine and norepinephrine from HIIT training may be a catalyst for improving fat loss. Both of these fight-or-flight hormones have been shown to drive lipolysis (fat break down) and are largely responsible for the release of fat from both subcutaneous and intramuscular fat stores for use as fuel during exercise. HIIT may have the potential to specifically lower abdominal fat stores, which have been implicated as the unhealthy fat depots in the human body.
Another metabolic benefit of HIIT is excess post-exercise oxygen consumption (EPOC). After an exercise session, oxygen consumption and thus, caloric expenditure, remains elevated as the working muscle cells restore physiological and metabolic factors in the cell to pre-exercise levels. That translates into higher and longer calorie burning after exercise has stopped.
Researchers say it appears that notable changes in body weight/percent body fat requires at least 12 weeks of HIIT, however, assessing changing people’s body composition depends on a weight management program that finds an optimum mix of exercise, dietary intake and behavior changes.
The most common benefit from HIIT and certainly highly significant is the improvement in VO2max linked to enhanced protection from heart disease. Perhaps equally important are HIIT’s dramatic acute and chronic effects on improving insulin sensitivity.
The effects of HIIT on visceral fat and subcutaneous fat loss are encouraging, and the impact HIIT has on reducing systolic and diastolic blood pressure (when elevated) and improving HDL cholesterol is promising. The evidence is in, and it appears that HIIT is the metabolic health effects winner!Resource: IDEA Fitness Journal