Fartlek training is primarily associated with which principle of exercise?

Fartlek training is primarily associated with speed variation because it incorporates a mix of different paces throughout a workout. The term "fartlek" is Swedish for "speed play," and this training method is designed to enhance both aerobic and anaerobic fitness by alternating between slower and faster running segments. This variability in pace helps to improve speed, endurance, and the body's ability to recover quickly from bursts of high-intensity effort.

While endurance training is an aspect of fartlek training, the primary emphasis lies in the fluctuation of speeds rather than maintaining a steady pace for long distances. Strength training focuses on building muscle power and size, which is not the main objective of fartlek. Flexibility training centers on improving the range of motion in joints and muscles, which is also not the focus of fartlek training.