When comparing full range of motion resistance training to lengthened partial range of motion resistance training, observed differences in muscle hypertrophy may be confounded by variations in the location of peak resistance along the joint angle spectrum, thereby complicating the ability to isolate the independent effect of muscle length on hypertrophy.

Study: Lengthened partial repetitions elicit similar muscular adaptations as full range of motion repetitions during resistance training in trained individuals

The study found that lifting weights through a partial range (stretched position) and full range gave the same muscle growth, even though the resistance felt different at the top or bottom. This supports the idea that it’s hard to tell if muscle length alone causes differences — because other factors like where the weight feels heaviest might be messing with the results.

Study: Muscle hypertrophy from partial repetition at long vs. short muscle length: A systematic review and meta-analysis

This study looked at whether doing partial lifts with muscles stretched (long length) vs. shortened (short length) makes muscles grow differently — and it found that muscle length itself matters, not just where the weight feels heaviest. So yes, it supports the idea that peak resistance isn't the only thing causing growth differences.

Study: Which ROMs Lead to Rome? A Systematic Review of the Effects of Range of Motion on Muscle Hypertrophy

The study found that where you stop or start your exercise matters more than just how far you stretch the muscle — meaning it’s not just muscle length causing growth, but where the hardest part of the lift happens.

Study: The interplay between muscle length, range of motion, and exercise selection: a review

The study says that when you train with a full range of motion, you might see more muscle growth—but that’s probably because the weights feel heavier at the stretched position, not just because the muscle is longer. So it’s hard to tell if length or resistance is the real reason.