New lifters get stronger at leg extensions by doing squats, but experienced lifters need to do leg extensions to get better at them.

The study found that when beginners train one hamstring exercise, they get stronger at a different hamstring exercise too — even if their muscles don’t grow much. This means their brains and nerves got better at coordinating the movement, not just their muscles getting bigger — which supports the idea that beginners can improve across exercises without training them directly.

People who only did squats got just as strong at leg extensions as people who only did leg extensions — meaning squats helped with the isolation move too, even though they weren’t training it directly. This supports the idea that compound moves can boost isolation move performance in beginners.