What type of training utilizes machines and weights with varying amounts of resistance?

The correct answer is variable resistance training, which refers to a method that employs machines and weights that adjust the resistance based on the position of the limbs or the specific exercise being performed. This type of training is designed to provide differing levels of resistance at different points during the exercise, effectively matching the muscle's strength curve and allowing for a more efficient workout.

Variable resistance training often incorporates devices such as specialized machines or elastic bands that change tension throughout the range of motion. This form of training is beneficial because it can help individuals maximize muscle engagement, improve strength, and potentially reduce the risk of injury by allowing for a more natural movement pattern.

In contrast, constant resistance training maintains the same level of resistance throughout the exercise, which may not align with the natural strength profile of a muscle during its entire range of motion. Isometric training focuses on muscle contractions without any movement, meaning that the muscles exert force without changing length, which does not utilize machines or weights for varied resistance. Bodyweight training relies on the individual's own weight as resistance, not on machines or weights to provide variation. Thus, the only option that matches the description of utilizing machines and weights with varying amounts of resistance is variable resistance training.