You should exhale when a 90-degree angle is formed at your knees. If you really want to give your hamstrings a good workout, hold this flexed position for 1 or 2 seconds. Return to the starting position in a controlled manner, and repeat the exercise for your desired number of repetitions. If your goal is muscle size and strength, shoot for completing 8-10 repetitions per set. If you just want some tone, or are more interested in muscle endurance, lighten the weight and perform 12-15.
The following are a couple workout tips you can use to really get the most out of this leg exercise.
Are your hamstrings tight? This might make it hard for you to start this exercise with straight legs. Here’s what you can do. Lean back in the seat as much as you possibly can. This gives your upper hamstrings some slack, or breathing room. You’ll get a much stronger hamstring contraction if you sit up straight as you bend your knees, because this helps to maintain the tightness in your upper hamstrings.