The primary benefit of high-intensity interval training (HIIT) is its efficiency in promoting fat loss and improving cardiovascular fitness in a shorter amount of time. HIIT involves alternating between intense bursts of activity and fixed periods of less-intense exercise or complete rest. This method maximizes calorie burn and increases the body's metabolic rate even after the workout is finished, known as the EPOC effect (Excess Post-exercise Oxygen Consumption). HIIT has also been shown to have positive effects on muscle retention and overall fitness levels.