Researchers still haven’t figured out exactly why HIIT works to improve aerobic fitness more than continuous types of exercise. But one key hypothesis, has to do with the heart’s ability to pump blood. One measure for blood pumping is something called stroke volume, or the volume of blood that comes out when the heart contracts. And a major determinant of VO2 max is stroke volume. “The maximum amount of blood that comes out of the heart is improved by exercise training,” said Gibala, “and there’s evidence that when you do interval exercise training, the stroke volume increases even more.”
What is HIIT?
HIIT workouts generally combine short bursts of intense exercise with periods of rest or lower-intensity exercise. At fitness studios and online, these workouts often mix aerobic and resistance training.