Training the hamstring muscle with exercises that stretch it fully increases the size of its connective tissue structures more than exercises that do not stretch it as much.

We analyzed the available evidence and found that training the hamstring with exercises that fully stretch the muscle may lead to greater increases in the size of its connective tissue, specifically the biceps femoris aponeurosis, compared to exercises that don’t stretch it as much [1]. This is based on one assertion supported by 55.0 studies or observations, with no contradictory findings in our current review. The biceps femoris aponeurosis is a sheet of connective tissue that connects the muscle to the bone and helps transfer force. When a muscle is stretched under load — like during lengthened state eccentric training — this tissue may adapt by growing larger over time. Nordic hamstring curls, while effective for strengthening, don’t always stretch the muscle to its fullest possible length, especially in the early phase of the movement. In contrast, exercises that emphasize a deep, controlled stretch — such as sliding leg curls or Romanian deadlifts with a full range — may place more mechanical stress on the aponeurosis, potentially encouraging more tissue growth. What we’ve found so far leans toward the idea that full-length eccentric training could be more effective for increasing aponeurosis size than Nordic curls alone. However, this conclusion is based on a single assertion with no direct comparison between the two training methods in the data we’ve reviewed. We don’t have studies that directly measure and compare aponeurosis size changes after Nordic curls versus other lengthened eccentric exercises. For now, if your goal is to potentially increase the size of your hamstring’s connective tissue, focusing on movements that allow the muscle to stretch fully under tension — like slow, controlled eccentric phases — may be worth considering. But more direct comparisons are needed to understand how these two approaches stack up against each other.