- Assume a face down lying position on a leg curl bench (angled bench is preferred).
- The knees should be beyond the far edge of the bench and the resistance rollers should be adjusted so that they rest against the back of the lower shin.
- Hold onto the grips usually situated by the head or onto the sides of the bench.
- The head should rest on the bench, on the side or on the chin.
- When ready, inhale and hold your breath as you bend the knees to raise the resistance rollers (shins).
- In the finish position the shins should be perpendicular to the thigh or slightly beyond.
- Exhale as you return to the original position under control.
- Execution should be at a moderate rate of speed.
- The toes should remain in line with the shins as you execute the exercise. This means the hamstring muscles are in good balance and that they provide greater lateral stability to the knee for greater protection against injury.
- If your foot turns out as you do the exercise, it means the biceps femoris is most powerful. Do the exercise with the toes in to balance the strength of the muscles.
- If the foot naturally turns inward as you do the exercise it means the semimembranosus and semitendinosus are most powerful. Do the exercise with the feet pointed outward to balance the muscular development.
- To strengthen the hamstrings in its action at the hip joint and at the knee joint you must do the glute-ham-gatroc raise on the Yessis Machine or Glute-Ham Developer. In this exercise you first contract the hamstring muscles with shortening of the muscles and the upper tendon and then execute knee flexion to contract (shorten) the lower tendons and hamstring muscle to produce a “double” maximal contraction.
- Your knees should extend beyond the edge of the bench when doing the exercise to allow for free movement. If the knee is on the bench, tremendous pressure can build up under the knee cap which can cause injury.
- The angled bench is preferred as it situates the hips up higher and places the upper end of the hamstrings on stretch. If you use a flat bench there is a tendency to hyperextend the spine to get the hips higher, which may create problems in the lumbar spine. To prevent this, place a rolled-up towel, cushion or inclined wedge under the hips. However do not raise the hips so high that it creates excessive curvature in the lumbar spine.
- Rate of execution is important. If you do the movement very slowly it becomes too difficult to stabilize the knee and you may stress the tendons and ligaments of the knees. When the weight is heavy, a burst of energy to get the movement started is permissible.
- Be sure to return to the full straight leg position before repeating. Stopping short of the full range will create muscle tightness, preventing you from having fully extended legs when doing leg extensions and when standing and walking.
- The hamstrings must be balanced to stabilize the knee joint. Since the knee is an unstable joint the stronger the tendons and ligaments are that surround the joint the greater its stability and the less chance of injury.
- Do not have someone hold the hips down to prevent the hips from rising if using a flat bench. The hips rising is a natural action of the body to place this two-jointed muscle in position for a stronger contraction.
MUSCLES INVOLVED The hamstring muscle group is composed of the semimembranosus, semitendinosus and biceps femoris muscles. They are two-jointed muscles having an action at both the hip and knee joints. The largest is the biceps femoris which has two heads at the upper end. Both heads act as a prime mover for knee joint flexion and outward rotation of the shin at the knee. At the knee joint the tendon crosses the outside of the knee and is known as the lateral hamstring. The semitendinous and the semimembranosus are long slim muscles. Their tendon of insertion is on the inner side of the knee joint and they are known as the medial hamstrings. Not only are they prime muscles for knee flexion but also inward rotation of the shin. The muscle bulk of the semitendinous is in the upper half of the thigh while the muscle mass for the semimembranosus is lower so that the two muscles form a cylindrical mass.
MUSCLE/JOINT ACTION In the lying leg curl the hamstrings perform knee joint flexion. In this action the back of the lower leg (the shin) moves toward the posterior thigh. All three muscles are involved in this action.
SPORTS USES A major role of the knee curl exercise is in bodybuilding, since this exercise is needed for development of the middle posterior thigh.
It is not very important in execution of most sports skills since the prime action of the hamstrings is usually at the hip joint were it is very important in extending the leg in running and jumping. Knee curls do little assist in this action since they do not affect the upper tendons and their attachments to the hip bone and muscles.
Knee joint flexion is important in some sports such as back kicks in soccer and in different wrestling moves. Aerialists use this action a great deal whenever hanging from the knees on the trapeze. In running the hamstrings fold the shin under the thigh as the leg is brought forward during the push-off action.