What does high-intensity interval training primarily improve?

High-intensity interval training (HIIT) is designed to push individuals to exert maximum effort during short bursts of activity, followed by rest or low-intensity recovery periods. This training method primarily improves cardiovascular fitness and anaerobic capacity due to the nature of the intense, intermittent effort required.

During HIIT, the heart rate increases significantly, enhancing the efficiency of the cardiovascular system in delivering oxygen to working muscles and removing carbon dioxide. This leads to adaptations that improve overall cardiovascular health, including increased stroke volume, improved blood flow, and better oxygen utilization.

Simultaneously, because HIIT incorporates high-intensity efforts that often exceed the steady-state aerobic exercise levels, it also enhances anaerobic capacity. This is the ability to perform quick, intense bursts of activity without relying solely on aerobic metabolism. Consequently, training in this manner results in adaptations that allow the body to increase power and performance during high-intensity activities.

In contrast, other options do not encapsulate the primary adaptations resulting from HIIT. While options like improvements in muscle hypertrophy, flexibility, and overall endurance may occur with other forms of training or under specific conditions, they do not capture the essence of what high-intensity interval training specifically targets.