The FITT principle is a set of rules that dictates the frequency, intensity, type and time of exercise, while the Sport principle applies to the specificity, progression, overload, reversibility and tedium. The principles are similar, but the Sport principle goes into greater detail about the specific strategies to use during a workout.
Sport Fitness Advisor explains that a major element found in both the Sport and FITT plans is frequency. Frequency of exercise involves not only how often it is necessary to work out, but also how to space out certain exercises for maximum effectiveness. The intensity and type of exercise are also covered by both principles, but the Sport principle puts more emphasis on specificity.
USA Triathlon explains that specificity training focuses on a certain skill or set of skills that need to be honed in order to achieve a specific goal. On the other hand, FITT training is far more general and applies to general aerobic and strength training regimens. Sport training is ideal for short-term use for those who need to train for a specific event such as a marathon or triathlon. By alternating between the Sport and FITT principles, athletes can avoid platueaing and can maintain a highly effective all-purpose fitness routine.