Leg extensions are exercises usually done with a lever machine in a gym. You sit on a padded seat and raise a padded bar with your lower legs. The exercise works mainly the quadriceps muscles of the front of the thigh -- the rectus femoris and the vastus muscles.

Technically, this is an "open chain kinetic" exercise to distinguish it from "closed chain kinetic exercises" such as squats. The difference is that the body part being exercised is anchored with the squat (feet on ground), and free to move with the leg extension (padded bar moves) -- thus the chain of movement is "open" in the leg extension.

This is where a relatively passionate debate has arisen in the strength, conditioning and rehabilitation communities with regard to the safety of leg extension exercises. Critics say that open chain exercises like the leg extension can damage the knees, and that even full depth squatting is safer. Many trainers seem to have gone along with the loudest voices, that is, that leg extensions are dangerous.

From reading quite a few opinions on this, including quite a few scientific and biomedical opinions, my position is somewhere in between. Mind you, this is not sitting on the fence, this is a considered opinion that leg extensions can be used safely with a few precautions. And the precautions are:

• If you have a knee/thigh to be rehabilitated, be guided by a qualified physical therapist or strength and conditioning coach who specializes in weight training rehabilitation. (Don't be surprised if they say to avoid the leg extension machine . . . but not all will.)
• Don't lift heavy: this is not the machine to be trying out for a maximum lift (1RM), or even low-rep, high-load strength conditioning.
• Don't do more than around 3 sets of 8 to 12 reps. You don't need to do any so-called endurance sets with high repetitions on the leg extension machine.
• Don't use the leg extension exercise exclusively for quadriceps development. Feel free to include it in a program, for variety if you wish, that also includes squats for lower-body conditioning.

1. Tagesson, S., Oberg, B., Good, L., and Kvist, J. (2007). A comprehensive rehabilitation program with quadriceps strengthening in closed versus open kinetic chain exercise in patients with anterior cruciate ligament deficiency: a randomized clinical trial evaluating dynamic tibial translation and muscle function. Am J Sp. Med. 36(2): 298–307.
2. Cohen, Z.A., Roglic, H., Grelsamer, R.P., Henry, J.H., Levine, W.N., Mow, V.C., and Ateshian, G.A. (2001). Patellofemoral stresses during open and closed kinetic chain exercises. Am. J. Sp. Med. 29(4): 480.
3. Fleming, B.C., Oksendahl, H., and Beynnon, B.D. (2005). Open-or closed-kinetic chain exercises after anterior cruciate ligament reconstruction? Exerc. Sport Sci. Rev. 33(3): 134–140.
4. Morrissey, M.C., Drechsler, W.I., Morrissey, D., Knight, P.R., Armstrong, P.W., and McAuliffe, T.B. (2002). Effects of distally fixated versus nondistally fixated leg extensor resistance training on knee pain in the early period after anterior cruciate ligament reconstruction. Phys. Ther. 82(1): 35–43.

From the first week of January this site at About.com Weight Training has almost doubled the number of page views it usually receives. I thought to myself: "wow, I must have got a few more incoming links from some big sites that boosted the search engine pointers. Or, maybe I got sent visitors directly by a few links from other sites with large readerships." The last indeed was true, but it could not account for a doubling of page visits.

In the end, it looks like it might just be the New Year's Resolution crowd. Not that there's anything wrong with making a resolution to get fit, lose weight and tune up. We can all do with a tune-up after Christmas. And I hope the site has helped those who did come looking for good information.

However, Tom Venuto, well-known bodybuilder and weight loss expert and former manager of fitness clubs said in a recent newsletter and blog that most of the signups in January were gone within a few months. For most people, the resolution only lasts until the "hard yards" are required. Don't let that be you.

I'd love all those visitors that came to About.com Weight Training in January to keep on visiting the site because they have continued to take an interest in fitness and weight training. There's a lot of you out there, so aim high and keep going.

Although there are potentially hundreds of exercises with barbells, dumbbells, kettlebells, machines and even bodyweight exercises to choose from for training the legs and lower body, I have some favorites that I suggest will work well for just about everyone.

It's a shame to see trainers, mostly young men, spend most of their time on pecs, shoulders, biceps and triceps and pay little attention to the legs and butt, lower back and abs -- the posterior chain.

I've put together a list of a dozen lower-body exercises that will provide a very strong lower body workout, either in a full body or split system.

• Best Lower Body Weight Training Exercises

I received a question the other day about how to develop the chest muscles so that they fill out the gap toward the sternum (breastbone). The inquirer apparently had good definition of the pectoralis major, the main chest muscle, but a fair separation from the sternum.

My feeling was that this is likely to be genetic and therefore not trainable. (The perfect abs tend to be inherited as well.) Even so, I thought that perhaps some squeezing action might improve the definition of the inside part of the muscle, and therefore I suggested these exercises to try:

• Close-grip bench press
• Pec deck flyes
• Cable crossover/standing flyes

I would welcome opinions from the bodybuilding community.