What type of training alternates between different activities or levels of exertion?

Interval training is a method that involves alternating periods of high-intensity effort with lower-intensity recovery or rest periods. This approach allows for a variation in exertion levels, which has been shown to improve cardiovascular fitness, increase calorie burn, and enhance overall workout efficiency. During interval training, individuals can switch between different exercises or levels of intensity, providing a dynamic workout that can adapt to different fitness levels and goals.

In contrast, plyometrics focuses on explosive movements, while circuit training consists of completing a series of exercises in succession with minimal rest. Resistance training is primarily concerned with building strength through weights or resistance, without the specific focus on varying intensity or alternating between different activities. Thus, the nature of interval training makes it the most appropriate answer for the given question.