The Effects of Plyometrics on Hamstring Length

Plyometrics are used to strengthen the hamstrings and increase neuromuscular properties effective for maximizing athletic performance. They are exercises that require your muscles to change rapidly from a shortened state of contraction to an elongated contraction. In a prepared hamstring, these exercises will increase the overall function, including length and strength. However, in a cold hamstring, these exercises will leave the muscles at risk for strain.

  1. Physiology

    • During plyometrics, the hamstrings are challenged to shift quickly from a state of eccentric to concentric contraction. This tests the hamstrings to generate the highest amount of force at their greatest length. During the eccentric contraction phase, the hamstrings are forced to contract as they lengthen. This activates the stretch reflex, which causes the hamstrings to store energy. During the concentric phase of contraction, the hamstrings contract as they shorten, utilizing the stored energy for power. The transition between the two contractions is called the amortization phase. To maximize your plyometric workout, decrease your amortization time by increasing your speed.

    Lunge Jumps

    • Before you start a plyometric workout, jog for at least 15 minutes to increase the blood flow to your hamstrings. Perform a lunge on your right side, so your right knee is bent to 90 degrees directly over your ankle. As you prepare to jump, your hamstrings are in an eccentric, or lengthened contraction. When you jump in the air and switch your feet, your hamstrings transition into a concentric, or shortened contraction. Land with your left foot forward in a lunge position. Your hamstrings then return to an eccentric contraction. Repeat quickly back and forth for 15 to 30 seconds.

    Box Jumps

    • Place your feet shoulder-width apart on the floor. Bend your knees and hinge forward at your hips. In this position your hamstrings are forced into an eccentric contraction. As you lift up into the jump, your hips extend and your hamstrings shift into a concentric contraction. When you land on the box or step, the hamstrings return to an eccentric contraction. Jump backward onto the floor, and your hamstring move through the concentric phase and back into the eccentric phase. Perform the box jumps for 15 to 30 seconds. Start on a low step and progressively increase the height.

    Semi Contractions

    • Although lunge and box jumps move your hamstrings through obvious eccentric and concentric phases, the hamstrings are not fully engaged in either contraction. Since the hamstrings extend the hips and flex the knees, to fully eccentrically contract the hamstrings, the knees would have to be completely straight. Since you cannot prepare a jump with straight knees, your hamstrings settle into a partial eccentric contraction. To fully concentrically contract your hamstrings, you would have to bend your knees in midair and drive your heels to your butt. This can be a little tricky, so the hamstrings will often settle into a partial concentric contraction.