Mitochondria, which are the energy centers of the cells, are essential for good health. Earlier studies have reported that exercise produces new mitochondria and improves the function of old mitochondria. Mitochondrial changes caused by a single session of exercise produce signals that may result in beneficial changes in the cells, preventing chronic disease.
The researchers aimed to determine whether the intensity of a workout affects mitochondrial response. To do this, the researchers recruited eight young adults to perform in cycling workouts of different intensities: moderate-intensity, consisting of 30 minutes of continuous exercise at 50 percent peak effort; HIIT consisting of five, four-minute cycling sessions at 75 percent peak effort with one minute rest interval; four 30-second sessions of sprint cycling at maximum effort, each separated by 4.5 minutes of rest.
The team measured the amount of energy the participants spent on every workout and compared changes in the mitochondria of the participants' thigh muscles before and after every exercise session.
The results showed that changes in the levels of hydrogen peroxide in various parts of the mitochondria occurred after exercise. Hydrogen peroxide is a type of molecule that plays a role in cell signaling called reactive oxygen species that contains oxygen and hydrogen. The levels were at an amount enough to promote cell responses that benefit metabolic function, while too much reactive oxygen species can cause damage to the cells.
The researchers also discovered that fewer minutes of higher-intensity exercise provided similar mitochondrial changes compared to a longer moderate-intensity exercise. Only a total of two minutes of sprint interval exercise was enough to cause the same effects as 30 minutes of continuous moderate-intensity aerobic exercise. (Related: Condensed exercise: High intensity workouts in less time will get you toned before the holidays.)
"This suggests that exercise may be prescribed according to individual preferences while still generating similar signals known to confer beneficial metabolic adaptions," said the researchers.
The researchers concluded that their findings contribute to the understanding of how exercise can be used to boost metabolism in the general population.
High-intensity interval exercise is composed of short bursts of high-intensity aerobic exercise alternating with short recovery periods. It can be done on a bike, treadmill, within a group training session, or however you can to reach the desired intensity.
Most studies report that two to 12 weeks of high-intensity training can provide significant health and fitness benefits in people new to exercise. High-intensity exercise can improve aerobic fitness and lower blood pressure, bad cholesterol, and insulin resistance of people at risk of heart disease, diabetes, and stroke, and people new to exercise. These effects are the same or even greater than continuous moderate intensity exercise. These benefits all occurred at a lower time commitment than that of the current exercise guidelines.
Interval training also offers a more effective exercise for a given time compared to continuous exercise. Short recovery periods enable people to exercise at a high intensity for longer, providing a greater stimulus for adaptation and better training effects.
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