The hamstrings are actually a group of three muscles -- the biceps femoris, semitendinosus and semimembranosus -- which run down the back of your upper thigh. Because they originate up over the top of your hip and then insert down below your knee joint, the hamstrings are involved in movement at your hips and at your knees. When you do exercises that force your hamstrings to concentrically contract, you’re calling on them to contract while they shorten.
Concentric Contractions
Most strength-training exercises involve both a concentric and eccentric contraction. The concentric contraction is when your hamstrings are shortening, and the eccentric contraction is when your hamstrings are lengthening. For example, in the common hamstring curl exercise, when you bend your knees and pull the leg pad to the back of your legs, your hamstrings are shortening or squeezing together; therefore, this is the concentric component of the exercise. When you control the straightening of your legs back to starting position, it’s your hamstrings that are handling the work, but this time they’re lengthening, or stretching, in an eccentric contraction.
Lying Leg Curls
The lying leg curl exercise, which focuses on the concentric responsibilities of the hamstrings, is done on a weight machine in the gym. The machine places you in a face-down lying position with your knees and lower legs hanging off the edge. Place your calves firmly against the leg pad. While you grip the handles to help keep you on the bench, bend your knees, bringing your calves, and thus the leg pad, up to meet your butt. This section of the exercise forces your hamstrings to work concentrically. Slowly extend your knees to return the leg pad to the starting position.
Standing Leg Curls
Standing leg curls accentuate and place more emphasis on the hamstrings working concentrically. Stand on a leg lever machine, facing the weight stack. Stand on one leg with the other leg positioned against a lever pad that’s set firmly against the calf. Contract your hamstrings concentrically to bend your knee to pull the leg pad up toward your butt, and then straighten your knee to control the pad back down.
Seated Leg Curls
The seated leg curl exercise is similar to lying and standing leg curls, but is done on a machine that places you in a seated position. You start with your legs extended out in front of you and resting atop a leg pad that’s set under your calves, and then you contract your hamstrings concentrically to pull the pad toward the back of your legs. Pull the pad back as far as you can and then slowly straighten your legs to return to starting position.
Eccentric Hamstring Exercises
Many of the hamstring strength-training exercises other than the leg curl options focus on working the hamstrings eccentrically. This means they place more emphasis on the hamstrings stretching or lengthening during the exercise. Examples include the glute-ham raise, straight-leg deadlift and good mornings. Each of these exercises begin with the eccentric contraction of the hamstrings.
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Writer Bio
Kim Nunley has been screenwriting and working as an online health and fitness writer since 2005. She’s had multiple short screenplays produced and her feature scripts have placed at the Austin Film Festival. Prior to writing full-time, she worked as a strength coach, athletic coach and college instructor. She holds a master's degree in kinesiology from California State University, Fullerton.