Answer:
A.muscular endurance principle
Step-by-step explanation:
Muscle endurance training is nothing more than working the muscle strength endurance for long periods of time, followed by a decrease in the intensity of the training. That is, training the muscle's ability to withstand the load longer, resisting more repetitions of a given exercise, and then lowering that load, similar to what is happening in Sam's training.
Resistance training determines continuous repetition of the same movement, which causes decreased fatigue and muscle definition to occur due to strengthening of the worked muscle.
By doing such training our body will be prepared for stronger and longer workouts and this will happen for both aerobic and weight activities.