You would be hard-pressed to find a commercial gym that does not have leg curl machines. For over a half a century these machines have become one of the most popular ways to strengthen the hamstrings, especially for athletes. Let’s take a closer look at what these machines do and why they can be a valuable exercise for anyone seeking to improve athletic and physical fitness.
The basic functions of the hamstrings are to flex the knee, extend the hips, and rotate the foot outward and inward. In athletics, the hamstrings play a key role in deceleration. One way to test this claim is to run up a steep hill and walk down slowly for several repetitions. The following day you will feel the effects of this workout in your quads. A few days later repeat the experiment, but this time walk up the hill slowly and run down it. The following day you will feel it in your hamstrings.
From an anatomical perspective, the hamstrings consist of the semimembranosus, semitendinosus, and biceps femoris. The biceps femoris, often referred to as simply the leg biceps, has two heads, the long head and the short head. There are also several other muscles that assist in knee flexion (sartorius, gracilis and gastrocnemius) and hip extension (glutes and erector spinae).
Applying this anatomy background to workout design, a complete program for hamstring development requires that you should perform exercises that work both hip extension and knee flexion. An example of a hip extension exercise is the Romanian deadlift, a knee flexion exercise would be a leg curl, and an example of an exercise that works both functions is the glute-ham-gastroc raise. For this discussion, let’s focus on leg curls.
The three basic types of leg curls are prone, standing, and kneeling. Each has their advantage. For example, the prone leg curl is believed to emphasize the biceps femoris whereas the seated leg curls emphasize the semitendinosus and semimembranosus; and seated leg curl machine would also be more comfortable for those with certain lower back conditions and women who are pregnant. Rather than trying to determine which machine is best, it would be better to rotate among these exercises. For example, you might perform the prone leg curl for two weeks, followed by the standing leg curl, and then the kneeling leg curl. For variety, you can also vary foot position.
Because the hamstrings are involved in rotating the foot, you should perform hamstring curls with the feet pointed outward and also with the feet pointed inward. If there is a structural imbalance, then one exercise should be preferred over the other. For example, if you tend to walk with your feet turning away from the body (lateral rotation) excessively, you should focus on leg curls with your feet pointed inward (medial rotation).
To create the highest level of muscle tension on the hamstrings, it’s best to start with your toes pulled towards the body as you lift the weight and point them away from the body as you lower it. The reason is that you can lift more weight when the toes are pulled back because the gastrocnemius (a calf muscle) assists in the movement. When you point the toes away from you as you lower the weight, the gastrocnemius is less involved, increasing the tension on the hamstrings. Another way to increase muscle tension is to raise the weight with both legs and lower it with one leg, which increases the work of the muscles eccentrically.
Although a variety of repetition protocols is best for complete development of the hamstrings, for athletic performance heavier weights should be emphasized. In sports performed at high speeds, a high level of muscle tension is needed to effectively deal with sudden stops and changes in direction. When you consider that an estimated 70 percent of ACL injuries are non-contact injuries, it’s apparent that strength training for the hamstrings should be a priority in sports such as soccer that have a high percentage of ACL injuries, especially in women.
The importance of eccentric strength for the hamstrings was demonstrated in a major published in 2012 on Danish football players. The study involved 942 soccer players, divided into a control group and an experimental group, and lasted 10 weeks.
The experimental group performed a hamstring exercise called the Nordic curl, which can be described as a leg curl performed so that the feet are anchored, and the upper body moves. The exercise creates a high level of tension on the muscles eccentrically as you lower your torso. The results? At the end of the season, 52 injuries were reported in the control group, whereas the athletes performing the Nordic curl only had 15 injuries.
The hamstrings often don’t get much attention in most workout programs, but they are an important muscle group to focus on for athletes and the general fitness population. Leg curls have been shown to be an effective way to train the hamstrings, so be certain to include them in your workouts on a regular basis.