The wide prediction intervals for muscle fiber hypertrophy (–0.71 to 1.28 for type I and –0.28 to 0.88 for type II) indicate that future studies on low-load versus high-load resistance training may find effects ranging from large benefit of one load to large benefit of the other, meaning current evidence is insufficient to guide training recommendations for muscle fiber growth.

When lifting light weights until exhaustion, the body first uses small muscle fibers that don't tire quickly. As those fibers get tired, the body starts using larger muscle fibers that were not needed at first. This forces all muscle fibers to work, no matter how heavy the weight is. When all fibers are activated, they experience similar levels of stress and chemical signals that cause them to grow. This is why both light and heavy weights can lead to similar muscle growth, but the exact outcome varies because not everyone fatigues the same way or recruits fibers identically.