Final answer:
A client should be working at an RPE of 3-4 during Phase 1, which is the aerobic-base training phase, of the ACE IFT Model. This is a low-intensity phase designed to build an aerobic foundation, especially for beginners or those returning to exercise.
Step-by-step explanation:
During which cardiorespiratory training phase of the ACE IFT Model should a client be working at an RPE of 3-4? The correct answer is A. Phase 1. The Aerobics and Fitness Association of America (ACE) Integrated Fitness Training (IFT) Model is a comprehensive system designed to ensure a safe and effective fitness training program that adjusts to the unique needs of the individual.
Phase 1, also known as the Aerobic-base training phase, focuses on building an aerobic foundation and is recommended for individuals who are new to exercise or returning to exercise after a long break. During this phase, workouts should be at a low intensity, which corresponds to an RPE of 3-4 on the Rated Perceived Exertion scale. This allows for developing cardiovascular endurance without overly stressing the body.