"Running on one leg is purely anecdotal." That's what someone told me after reading a recent article of mine. This immediately got me to thinking about how we got to this whole "functional training" thing to begin with.

The reality is that ideas like "you only run on one leg at a time" aren't anecdotal. It's a basic undisputable fact. Have you ever seen someone running on two legs at a time?

Figure 1: This guy runs on two legs at a time. It's really called jumping. Bunnies don't run, they jump.

Running, by definition, is a single leg action, really a series of bounds. This is why vertical jumps correlate so highly to speed. Running is simply a series of horizontal bounds.

In the early 1990s, when people like Vern Gambetta and Gary Gray began to point out simple anatomical lessons to me, all I could do was listen. Guys like Gray and Gambetta basically said that our approach of conventional double leg training was flawed, that our sagittal plane dominated world wasn't realistic. Heresy or science? Think about it.

Strength training has been and still is primarily sagittal plane and double limb. However, we've used single limb training for upper body stuff for years and raved about its superiority. We call it dumbbell training. Dumbbell bench presses and incline presses are widely accepted, as are dumbbell rows. However, unilateral lower body training was frowned upon. Step-ups? Lunges? Those are exercises for girls, right?

My reaction back in 1990 was, "What do you mean, do single leg exercises? What about squats and deadlifts?" The idea that single leg squats or lunges done with only bodyweight might be beneficial to athletes or to those looking to gain more muscle mass was initially as foreign and abhorrent to me as it was to many of you.

Bodyweight? Are you kidding? Come on, pile on the plates! Don't show me your single leg squat; tell me how much you squat!

Unfortunately for those who think that, training really comes down to two things: anatomy and physics. Our knowledge of physics hasn't changed greatly over the last few decades, but our knowledge of what we now call "functional anatomy" really has. The concepts presented in functional anatomy are what led me to functional training.

I often describe functional training as the application of functional anatomy to training. The truth is I'm a little embarrassed that I'm forever stuck with the "functional guy" label. People see the cover of my book and never read it. It's the classic case of judging a book by the cover. Don't people always tell us not to do that?

Okay, what does this have to do with the average T-Nation reader? The reality is it has a lot to do with the average T-Nation reader. Single limb training is a logical outgrowth of what we now know about functional anatomy. It'll promote greater muscle growth and greater muscle strength because it works more muscles. Knowing the way the body works allows us to develop and utilize exercises that work not just prime movers, but stabilizers and neutralizers.

Understand, I'm not anti-bilateral exercise; I'm simply pro uni-lateral exercise. Until recently, my athletes performed Olympic lifts almost every day. This is a double leg activity designed to work power. In addition, we'll perform front squats at least once per week.

However, that doesn't negate the case for single leg exercise either for performance or for muscle gain. The anatomical evidence for single leg exercise is still overwhelming. As a result, my athletes and personal training clients do lots of single leg exercises.

When looking at the anterior chain we see what's called the lateral sub-system. The lateral sub-system consists of the gluteus medius, the adductors, and the quadratus lumborum.

When we stand on one leg, as in a one leg squat, we engage three muscles that we don't use in a two leg squat. I know some will say we use the adductors because the knees move apart in the descent, but this isn't the same. The key to the lateral sub-system is that we engage these additional muscles in their normal role of stabilizers, not as movers.

In addition, in any single leg exercise, bodyweight becomes a more significant part of the resistance. Voila, functional training: training the muscles that we're using in the way that we use them. Bottom line: this doesn't happen in any version of the double leg squat.

In a conventional double leg squat, we simply strengthen the prime movers and neglect the stabilizers. Using the car analogy, we get a bigger engine, but maybe bad tires.

Now, I know many readers will say, "We've done it this way for years and it works." Well, here's where I disagree. We've done it this way for years, but I'm not so sure it works all that well. People have been squatting for years but very few athletes squat properly. Go into any weightroom in America and I guarantee you'll see more bad squatters than good ones.

As for the "it works" part, again I'm not so sure. If what we were doing worked so well, why do we have so many ACL tears and so many bad backs? I truly believe that single leg training is the best way to prevent knee injuries and the best way to train around a back problem. Double leg training may create double leg strength, but double leg training doesn't have the additional preventative value of single leg training.

My other problem: double leg strength doesn't correlate to single leg strength. I can't tell you how many athletes I've seen that can squat in excess of 500 pounds yet can't do a single leg squat. The reality is that they lack "functional strength."

Very little in life or sport is done with two feet on the ground. In fact, rowing is the only sport where both legs work simultaneously. In life, it rarely happens. Single leg training breaks down the same as double leg training; we have knee dominant and hip dominant exercises.

Anterior Chain or Knee Dominant Single Leg Training

All of the squat variations fall under the category of anterior chain or knee dominant single leg exercises. Lunges, step-ups, split squats, rear foot elevated split squats (Bulgarians, as much as I hate the term) and true one leg squats (pistols, another name I don't like) are all examples of knee dominant single leg exercises.

The great part about these exercises is that it's really hard to make them into glute or lower back exercises. Not true with the old back squat. The really beneficial (and really difficult) knee-dominant single leg exercises are what we call single leg unsupported.

Static, unsupported single leg exercises consist of single leg movements done on one leg with no movement forward or back (see video above).

To further explain, a lunge would be dynamic as the center of gravity moves forward and back. It's supported, as the non-working foot is in contact with the ground.

In an unsupported single leg exercise, the non-working extremity isn't allowed to touch the ground or any other object such as a bench. The only true static unsupported exercises are variations of one leg squats. These may be referred to as pistols, one leg squats, balance squats, or step-downs in various texts.

The One Leg Squat: A true static unsupported exercise

Until recently, I didn't feel it was necessary to distinguish between a static unsupported exercise and a static supported exercise. Strength and conditioning coach Karen Wood convinced me otherwise. Wood's rational was that there was limited functional carryover from the single leg supported category to the single leg unsupported category. In other words, performance of exercises like split squats or one leg bench squats (Bulgarian lunges in the literature) didn't seem to carry over to performance in a true one leg squat.

More and more evidence points to the relationship of the hip rotators and the glute medius to overuse knee problems. In static supported exercises (Bulgarians, split squats) the hip rotators and glute medius don't take an active role in stabilizing the femur. In true static unsupported exercises, the hip rotators and glute medius must actively work to prevent internal rotation of the femur.

The exercises are essentially tri-planar as the movement may be sagittal, but the stabilizers must prevent movement in the frontal and transverse plane. Any static unsupported exercise automatically becomes a tri-planar movement as the stabilizers work as what we call anti-rotators.

The bottom line is, more muscles work in an unsupported one leg squat. Either way, if you're looking for assistance exercises to work more muscle and improve performance, forget extensions and leg presses and add in some one leg squat variations. I'll bet you that if you don't know where your glute medius is today, you will after your first day of one leg squats!

Posterior Chain or Hip Dominant Single Leg Training

The interesting thing about hip dominant single leg training is that it's in fact not only single limb, but single joint. For years we've heard the gurus (and that often included me) say that single joint exercises are a waste of time. We advocated multi-joint movements as they gave us the most "bang for the buck."

Over time, I've realized that it's not about how many joints work as it is about how many muscles work. The "no single joint exercises" mantra may be an oversimplification. I may dislike a lateral raise or a leg extension because it isolates a single muscle in a non-functional manner, but I love one leg straight leg deadlifts

In truth, a one leg straight leg deadlift is a single joint exercise. What makes it better than a leg extension or a leg curl? The number of muscles working. It's not about the number of joints that are moving; it's about the combined action of moving a joint in one plane while stabilizing in two others.

In the one leg straight leg deadlift, the action is a sagittal plane hip hinge. However, the spinal erectors, lower traps, and rhomboids must work to stabilize the spine and the scapula. The hip rotators and pelvic stabilizers work to keep the pelvis moving in the sagittal plane.

What appears to be a relatively simple single joint exercise is actually an extremely complex exercise in muscle synergy that incorporates a huge amount of muscle. In addition, one leg straight leg deadlifts provide great stress to the glutes and hamstrings while providing 50% less back stress. Another great selling point.

The same can be said for the slideboard leg curl. Once again we have a single joint action. In fact, biomechanically, some would claim that it's the same action as a prone machine leg curl. However, as they say in the NFL, upon further review, the slideboard leg curl becomes a far superior exercise.

Why? Because the glutes and hamstrings must work together to hold the hip in extension while the hamstring works alone to flex the knee. The slideboard leg curl in effect forces the hamstring to work from both ends in its two joint function as a synergist of hip extension and a prime mover in knee flexion.

Wrap-Up

Sound complicated? I guess it is. It's clearly not as simple as "single joint is bad, multi joint is good." But if you're an athlete training to improve performance, an athlete trying to reduce injury potential, or a bodybuilder looking to stress some little used muscles, give one leg squats, one leg straight leg deadlifts, and slideboard leg curls a try!