Many trainees decide their hamstring development is lacking. They increase their sets of traditional leg curls—usually with marginal results. Seated leg curls are often the next exercise to be added or substituted.
The seated leg curl is a better choice because the hamstring muscles cross two joints and must be stretched at both joints to recruit the hamstring muscles maximally. The two joints are the hip and the knee. The traditional leg curl, which is performed while lying facedown, allows the knee to bend and straighten but keeps the hip straight—hip extension—which removes the stretch on the hamstrings. That’s the reason equipment manufacturers started putting a mild bend in the leg curl bench—to allow a little bit more recruitment of the hamstring.
During a seated leg curl the hip is bent at 90 degrees—hip flexion—and the knee can bend and straighten. That gives you a much greater stretch on the hamstrings, which will help them fire better. If you wish to train your hamstrings with a machine, this is the most effective one. Romanian deadlifts, stiff-legged deadlifts, hyperextensions and glute\ham raises are all more effective hamstring exercises—but that’s separate topic.
There is a problem that’s relatively common among veteran trainees that the seated leg curl can aggravate. Disk injuries in the lower back can aggravate nerve roots as they exit the spine. The two lowest nerves are the most commonly affected—labeled L5 and S1. They exit the spine and travel underneath the gluteus maximus, down the back of the thigh between the hamstring muscles and down the lower leg to the foot. When the hamstrings are stretched, the L5 and S1 nerve roots are stretched as well. If you have a disk problem that’s affecting one of those nerve roots, or both, this type of exercise will make the problem worse.
Many trainees think they are helping themselves to recover from this back problem by strengthening and stretching the hamstrings. Those remedies are helpful for uncomplicated, mechanical low-back pain, but that does not apply while the nerves are inflamed. Inflamed nerves should not be stretched, as it will make the nerve symptoms—which may include pain, numbness, tingling and weakness—increase.
The small fibers within the nerve are very fragile as they regenerate after an injury. They also regenerate very slowly, and it’s a long way from your low back to your foot. Regeneration can take 18 months and sometimes more. Powerful contractions of muscles can damage the regenerating fibers. Powerful contractions would include heavy weight training. As noted above, stretching can also aggravate these nerves. The seated leg curl provides both an inappropriate stretch for the regenerating L5 and S1 nerves and an equally inappropriate powerful contraction of the hamstring muscles.
As you can see, not every exercise is a good idea for every trainee. To make if further complicated, not every exercise that you like is the right choice at a given point in time. You will need to be informed by a spine specialist, which can be a spine surgeon, chiropractor—especially a board-certified sportsmedicine chiropractor—or a specialist in physical medicine and rehabilitation. Don’t try to diagnose yourself.
Aside from the nerves, you have to be careful about the knee itself. The knee is braced so firmly in the seated leg curl, you have to make sure you don’t allow the weight to rise too fast and hyperextend your knee. If you already have problems with the medial or lateral meniscus, which are C-shaped cartilage cushions in your knee, or the anterior cruciate ligament, a.k.a. ACL, the hyperextension may cause further trauma and harm to the knee. Allow the weight to rise in a controlled manner.
The seated leg curl is a good exercise when performed by the right trainee at the right time.
Train smart, then train hard.
Editor’s note: Visit www.SoftTissueCenter.com for reprints of Horrigan’s past Sportsmedicine columns that have appeared in IRON MAN. You can order the books, Strength, Conditioning and Injury Prevention for Hockey by Joseph Horrigan, D.C., and E.J. “Doc” Kreis, D.A., and the 7-Minute Rotator Cuff Solution by Horrigan and Jerry Robinson from Home Gym Warehouse, (800) 447-0008 or at www.Home-Gym.com.