Stop training like a kangaroo.
Kangaroos are cool. I mean, they can stand on their tail. And then kick you. While standing on their tail.
I took this video at Caversham Wildlife Park in Perth, Western Australia in May 2019.
Look at how their feet always move in unison, like a broad jump after broad jump.
What I mean is, our movement is distinct from marsupials. Most human movements, especially most sports movements, involve alternating actions of one leg then the other. Our training should mimic our unilateral nature especially if our goal is peak sports performance (which is the primary goal of my programs and the athletes I work with) but even if our main goal is to be strong and stay healthy.
Today I’m focusing on unilateral leg training, but Roman has written about why you need to be doing unilateral chest work for hypertrophy.
For a whole host of reasons, it should be the other way around.
When you stand on one leg, why don’t you fall? Yes, your major muscle groups like your quads and hamstrings isometrically contract to take on the brunt of the strength demands, but many other muscles keep you falling over like freshly cut timber.
If a meathead falls trying to balance on one leg, does it make a sound? Yes, probably a quite loud grunt.
These muscles—often called “stabilizer” muscles—like the side glutes and groin muscles, among others, work to… um… stabilize the frontal and transverse planes. Sparing you an anatomy lesson, understand that single-leg strength and stability require more muscles than a more stable two-leg stance. These muscles perform a similar role while running, jogging, and even walking. So, by prioritizing unilateral training, you’re preparing your body for the movements that sport (and real-life) require.
In sports, rarely if ever are both legs on the ground at the same time. For optimal performance, we should train our lower body the way it’s going to need to perform: one leg at a time.
In theory, this can prevent injuries. Ankles, for example, will be more prepared to absorb force while running and cutting if they’ve been trained under load without the support of another leg, support that wouldn’t exist in a sports context. However, I couldn’t find any research comparing injury rates between unilateral and bilateral leg training.
Really, all research comparing sports performance outcomes between single-leg and traditional bilateral training is still in its infancy. A 2018 study showed unilateral squats led to increased bar speed, and therefore a higher rate of force development (a fancy phrase for power) compared to bilateral squats (1). Another study on rugby players comparing a bilateral back squat to a unilateral rear-foot-elevated split squat found them exercises equal in efficacy for sprint and change of direction performance (2).
However, even if they’re equal in their efficacy, other data point to other upsides for unilateral training.
The strength of your legs individually is actually way stronger than your two legs together.
Don’t let that statement put your brain in a blender.
A phenomenon known as bilateral deficit explains that the sum of our strength on each of our legs is way stronger than the strength of our two legs working in unison (3). The strength of leg A + leg B is greater than the two legs performed together. And, it’s not a slight difference. In slow contractions (like typical weightlifting speeds) it’s as high as 20% (4) and in rapid contractions (like sports) it’s as much as 45% (5). The difference in rapid contractions, going back to the study that showed increased bar speed, supports that, especially for athletics, unilateral training is more effective, where power and rate of force development win out over raw strength.
Why this substantial strength difference exists isn’t completely proven, but the current prevailing theory is that each leg is wired by the nervous system to contract independently of the other. Walking and running movements we do all day long our whole lives more closely align with single-leg training. Our brains have learned to “wire” one leg at a time and training bilaterally goes against this natural neural wiring.
Regardless of the process for why, ignoring bilateral deficit is handicapping your strength gains.
This, for me, was hard to accept. Why don’t powerlifters or weightlifters use more single-leg training? Well, their competition is a bilateral movement, whether a squat or a deadlift. So, it makes sense they primarily train in that fashion. Bilateral training matches their bilateral demands.
In sports, bilateral training continues to be the norm because the origins or strength and conditioning arose out of powerlifting. The first strength coach in the NFL Alvin Roy was a weightlifting coach. Over the course of decades, those traditions simply haven’t changed. Now, a predominant bilateral lower body training program may be a result of the classic “this is how we’ve always done it approach” rather than an examination of what’s needed for peak performance.
Yet, even if you brush both of these aside–bilateral squats still improve performance and strength– there is an undeniable advantage to unilateral training: safety.
All right, I know I’m not the only one who has hurt their back doing heavy back squats. And, it’s not that there’s anything inherently wrong with back squats. Well, actually there is. It puts a lot of weight on your spine. If you don’t have near-perfect form and posture, the spinal loads will lead to excess stress on the low back.
Thinking about the posture of athletes (I speak from my experience with mostly hockey players, but it applies to most team sports), we have tight hip flexors, weak abs, a tight, overpowering low back, and rounded shoulders. When you set up for a back squat, you bring your tight shoulders behind you. Without enough shoulder external rotation, you will need help from other joints to reach back. Most likely, your back will arch so you can get your hands behind. Now you’re lifting a heavy load with your spine outside of ideal alignment.
At best, this makes the exercise a low back exercise instead of a leg exercise, which defeats the purpose. At worst, it causes a debilitating injury.
Heavy spinal loading has always been controversial. It has been associated with all kinds of not-fun stuff, from a greater likelihood of spondylosis (6) to compression of vertebral discs (7) to degeneration of your low back (8). And if your low back is sore after back squatting, you don’t need me to tell you this.
While we can’t say for certain that spinal loading is inherently bad and that there aren’t ways to do it safely, it’s risky. And if we can minimize those risks and find an equally effective approach, that’s an easy decision.
Why add unnecessary risk when we can get a better training effect (more specific to the sport and no bilateral deficit) from single-leg training?
Single-leg training avoids all these pitfalls and they’re much easier to load appropriately with less weight.
Unilateral leg exercises are not a cure-all, of course. And, a lot of the research on the performance side isn’t conclusive. Although, even if unilateral training isn’t more effective for increasing performance, it’s definitely safer. And unless you’re training for elite-level athletics, trading off a bit of performance for safety is the right decision (although more and more high-performance programs are moving towards unilateral leg training).
This is not to say there’s anything wrong with bilateral squatting. Squats are normal, they’re natural, they’re still a fundamental movement pattern. Goblet squats, front squats, squat jumps, zercher squats (no, wait these are dumb), and even back squats have a place in some programs. My programs are not void of bilateral training. But, as the main lift for building strength and power, they’re not the best option.
Onto the fun part. Okay, so what unilateral exercises should replace the main bilateral lifts in your program?
Enter: The Rear-Foot Elevated Split Squat.
Yes, yes, this isn’t a purely unilateral squat. The back leg supports balance and bears some of the weight. Which, on one hand, defeats some of the purposes of single-leg training that I, you know, just spent a whole article defending. Rather, I ascribe this as the king because it’s, in all practicality, the best I’ve found for force development. While single-leg squats without back leg support have a huge place, if we’re talking about what’s the easiest to do safely and effectively, the RFE split squat seems to work best because it’s just enough support so balance isn’t the limiting factor, while still maximizing the single-leg benefits.
These are often called Bulgarian split squats, but I’m trying to get away from non-descriptive exercise names (the Turkish get-up will have to stay). Roman disagrees with me on this, as for some reason he doesn’t object to misattributing exercise names to countries, but whatever. This is my article, so RFE split squat it is. For these, the first progression is goblet-style, then suitcase-style. Once you can hold 80-90lb dumbbells in each hand, you can move on to the ultimate strength-building lower body exercise: Safety bar RFE split squats.
When I worked with a division one hockey team, players did up to 535 lbs (that is not a typo).
And, every player who was a sophomore or older lifted at least 400 lbs on each leg. While this is an extreme example, and most of these athletes will make a living playing professional hockey after college, it still highlights all three of the main points: the movement suits the needs of their sport better, they’re able to truly maximally load their legs, they can load heavy weight without postural compensations common in bilateral squats (especially back squats), and avoid excessive spinal loading.
In order to get the same training effect with a bilateral variation, this athlete would need to put–if you say the back leg helped 20% (It could be less or more, but it’s a decent estimate) then they would need around 800 lbs in a bilateral squat to get the same training effect. That would be reckless and stupid.
Even this much weight on their back is only done twice in their entire year cycle (it’s a special occasion so we had to film it). Most of their RFE days are spent on a wide range of the force-velocity curve (I’ve only seen Eric after he lost his hair, so this is a blast from the past) with bands, lower weights, and higher velocities more suited to hockey.
There are many more single-leg exercises I program, from skater squats to lateral squats, to 1-leg bench squats, and they all have some unique benefits. I’ll save the full index of single-leg exercises for another article.
The one change you can make right now, especially if you have trouble with squatting, is to switch your back squat for a split squat in your program (especially useful for home workouts). Once you master the split squat, then move to the RFE split squat.
Happy split squatting.