International Sports Sciences Association (ISSA) Bodybuilding Practice Test

The intensity range of 65% to 85% of one-repetition maximum (1 RM) is widely regarded as the optimal range for maximizing muscle hypertrophy. This is because lifting within this range strikes a balance between sufficient load and volume, enabling the muscle fibers to experience enough tension and metabolic stress required for growth.

When working at intensities of 65% to 85% of 1 RM, athletes can perform a moderate to high number of repetitions—generally between six to twelve—allowing them to achieve both mechanical tension and metabolic fatigue, which are key drivers of muscle hypertrophy.

Furthermore, this intensity range is effective in promoting the recruitment of fast-twitch muscle fibers, which have a greater potential for growth compared to slow-twitch fibers. The combination of lifting heavy enough to stress the muscles while also allowing for multiple repetitions creates an ideal scenario for muscle adaptation and growth.

In contrast, the other intensity ranges listed are generally less effective for hypertrophy. The lower ranges (like 50% to 60% or 25% to 40% of 1 RM) do not provide the necessary overload, while the very high range (90% to 100% of 1 RM) typically focuses on building