Which of the following is a key benefit of high-intensity interval training (HIIT)?

High-intensity interval training (HIIT) is particularly beneficial because it effectively improves cardiovascular fitness while also maximizing calorie burn within a shorter workout duration. This is primarily due to the alternating periods of intense exercise followed by short recovery phases. The high intensity elevates the heart rate significantly, leading to enhanced cardiovascular endurance over time. Additionally, the afterburn effect (excess post-exercise oxygen consumption, or EPOC) means that the body continues to burn calories even after the workout is finished. This makes HIIT a time-efficient and effective training approach for individuals seeking to achieve fitness goals quickly, whether that's fat loss, improved endurance, or overall health.

Other options mention benefits that either don't align with the core purpose of HIIT or are misleading. While flexibility is a crucial aspect of fitness, it is not the main focus of HIIT. Moreover, HIIT incorporates elements of strength training but is not solely centered on building muscle strength; it encompasses various types of movements that can improve aerobic and anaerobic fitness simultaneously. Lastly, while HIIT workouts can often be done with minimal or no equipment, many variations do utilize tools like weights or resistance bands to increase intensity, making equipment optional but not a defining characteristic.