Although none of it comes easily, some muscles aren’t that difficult to develop. As any weight room regular can tell you, calves and forearms rank among the most challenging groups. But because everyone’s built a little different, hamstrings might be a challenge for some. If that’s a weak spot, you’re sure to appreciate the findings of a study published in the Journal of Strength and Conditioning Research.

Scientists measured the muscle activation of 12 experienced male weight lifters as they performed a single rep using resistance equal to 85% of 1RM. Exercises included leg curls, good mornings, glute-ham raises and the Romanian deadlift. The deadlifts and the glute-ham raise were best for activating hamstrings.

True Strength Moment: Even though hamstring activity was maximized during these two exercises, you shouldn’t neglect the rest. In fact, you might even want to add Olympic pulls and kettlebell swings to the list. Learn the right way to perform all of these movements before working them into your leg day routine.