Final Answer:
The method of resistance training that creates a consistent stress on muscles throughout the range of motion is variable-resistance machines. (Option A)
Step-by-step explanation:
The term "variable-resistance machines" implies equipment that adjusts resistance according to the user's strength curve, ensuring a consistent challenge to muscles across the entire range of motion. Unlike fixed-resistance machines, which maintain a constant resistance level, or free weights, which may experience gravitational variations, variable-resistance machines adapt to the biomechanics of the movement. This adaptability enhances muscle engagement throughout the exercise, promoting more comprehensive strength development.
Option A is the answer, as variable-resistance machines align with the specified criteria of creating consistent stress on muscles throughout the range of motion, distinguishing them from fixed-resistance machines, free weights, and plyometrics.