By Carl Valle
The gloves are off! After a few years of holding my tongue, I’m now challenging the idea that single leg exercises are magical. Nor are they better than double leg options. Single leg exercises can be a great alternative to conventional two-legged counterparts. But they do have some unique problems, and it’s just as important to know these as it is the risks and limitations posed by bilateral exercises.
In this article, I offer a fair and balanced overview of the real differences, not the superficial fluff most blogs use to distract you. I have not invented an exercise or a piece of equipment that will encourage a trend or adoption of a movement pattern, so I am not biased. Without a dog in the fight, I can list pros and cons of the exercises and let you, the reader, decide on what is best for your program.
The Agendas Behind the Single Leg Training Craze
Conventional two-legged or bilateral exercise options like squats and Olympic lifts have been around a long time and have become standardized. Thus everyone in the iron game is familiar what good numbers look like. While a 1-rep max score is not a golden ticket to greatness in sport, it is a strong indication of how a program is working.
When coaches struggle to get results objectively, their safest bet is to create a smoke screen and reduce the possibility of an objective comparison that comes from testing or similar evaluations. By resetting the standard with a fresh set of exercises, a coach can hide from comparisons by starting the process over and literally rewriting the “record books” that show what is strong and what needs work.
Selling of Exercises
The selling of exercises also happens, especially new ones that surface when coaches get bored with teaching the tried and true. I’m a fan of anything innovative and welcome change, but only when the change improves results. Read the writing on single leg training–it’s as if one is committing a crime by performing power cleans and front squats with two legs. Education, an open market with little regulation, is ravenous for trends and sexy ideas. Even if everyone on social media claims they are polishing the basics and working on foundations, we tend to see coaches trying the new stuff with far more gusto than patiently ensuring athletes are doing what has worked for years.
New Products Create New Business
The equipment market is thirsty for new product ideas, and new exercises mean new business opportunities. I’m not against capitalism and want everyone to succeed. Don’t blame the companies trying to support coaches who want new or better tools, blame the industry as a whole. Remember the whole unstable surface fad of the late 1990s and early 2000s? How many single leg pioneers led us astray then and now want the same trust from us on single leg methodology? If they sold you exercises on unstable pads, they’re now likely selling you the promise of getting better with one leg. Unilateral training is essential, but it’s not special since sport already occurs on one leg. Excessive redundancy isn’t winning Super Bowls and world cups alone.
As you can see, we have an underlying problem on the business end of the industry that is influencing how we train, be it employment opportunities or selling education and equipment. Science and practice should be driving these decisions. The only way to solve this problem is to dive into the hard science and demand the same of anyone who attacks the safe and effective techniques that have worked in the past and still work today.
Is the Bilateral Deficit an Argument Worth Having Still?
I am a huge fan of single leg exercises, find them extremely valuable, and consider them indispensable. The argument that they are better than double leg exercises, however, shows a bad mentality. It’s rare that an exercise solves every problem and that an either-or situation exists.
When exercises are compared, electromyography data on a group of muscles is usually used as evidence to proclaim what is better and what is not. However, an exercise should be evaluated comprehensively, not distilled to a simple binary decision based on muscle activation alone. EMG is relatively easy; other joint evaluation measures are much more difficult.
Most proponents of single leg training are the functional training gurus who use the visual appearance of exercises as their hallmarks to success rather than the outcomes of entire training systems. Saying that “because we run one foot at a time” is the most overused and oversimplified argument as to why an exercise is a superior or better option.
Just because one makes a rhetorical question that is difficult to win against in a debate doesn’t mean their athletes are winning more on the field. Overloading one leg does indeed happen on the field and the track. Doesn’t adding more exercises that load one leg cut a path to overuse syndromes and pattern overload the same gurus warn us about?Function is not defined by how an exercise looks, it’s the results from what the exercise does. Click To Tweet
Again function is not represented by how an exercise looks; it’s represented by the results from what the exercise does. Take a look at the wonderful arguments from the researchers in hamstring health on the Nordic exercise. Although the kinematic motion of a Nordic exercise does not mimic running, the exercise causes structural and neuromuscular adaptations that certainly work, and there’s research to back this up.
After a decade, the coaching field still has trouble understanding bilateral deficit. Coaches often use the concept, most of the time embarrassingly incorrectly, to claim that single leg exercises are superior. The bilateral deficit is not a perfect rationale for the neurological differences between single and double leg actions. Based on a quick online search, the definition of the bilateral deficit is as follows:
“The bilateral limb deficit (BLD) phenomenon is the difference in maximal or near maximal force generating capacity of muscles when they are contracted alone or in combination with the contralateral muscles. A deficit occurs when the summed unilateral force is greater than the bilateral force. The BLD has been observed by a number of researchers in both upper and lower limbs, in isometric and in dynamic contractions. The underlying cause of the deficit remains unknown.”
I’ve blogged a half dozen times about how we should think of the bilateral deficit–it’s a phenomenon that we should train or augment, and it’s something we have naturally. When someone has a deficit, usually the normal response is to close it, not increase it. In sport, double leg actions do occur, and training bilateral facilitation is a benefit when trying to encourage elite adaptations. Lateralization, in fact, is never really discussed. And while these concepts are still emerging, we need to see how the nervous system provides performance enhancement.
“To understand plyometric training intensity further, concepts such as the bilateral deficit, bilateral facilitation, and lateralization must be considered.”
Most of the research explains the differences among these and why they happen scientifically. Taking the leap that one is absolutely superior is guru speak. Talking in absolutes is very powerful, and one can sound godlike doing so, but in sport science and coaching this is a dangerous avenue.
The Science on Single Leg Versus Double Leg Training for Performance
I’ve posted a huge number of articles that include single leg exercises for both strength and plyometric activities, so my suggestions on when to not use single leg options should be seen as unbiased. Single leg exercises make sense when they are the right option, not the “best” option. It’s not semantics; sometimes an exercise is too specific or too demanding, even if the research shows it “works” in a study. Coaches look for the best tools when what we actually want are the right tools for our athletes.
A great example of when results are too good to be true was the recent study comparing single and double leg exercises performed with plyometrics. At first glance, I was salivating at the results. But when I read the full article, I realized the subjects were not athletes, just poorly underpowered volunteers.
Another study about six years ago showed that both unilateral and bilateral exercises produced very similar performance results after three months of training. What was cool was that the researchers looked at how the interventions trended over each phase of training, giving insight on what may work quickly and what may potentially last longer.
Back Squats and Split Squats
The real controversy causing friction in the strength and conditioning community is over barbells and squatting. When Michael Boyle killed-off back squatting, he knew what he was doing. He took advantage of the fact that when all else is equal, a team sport athlete who converts to a single leg or “single plus” exercise won’t change much.
Boyle converted a lot of people to his split squat option. But so far nothing has surfaced in any training facility that screams that moving toward split squatting is a game changer. I’ve previously cited the study on academy rugby athletes that compared squats to split squats where the data showed similar results, not dramatically different results.
A clever study on potentiation used light or no load split squats for potentiation with lower level rugby players. A split squat, not a true single leg exercise but darn close to it, improved jump performance after doing it. This does not mean bilateral squats would not do the same since they certainly do help. Instead, it shows how the nervous system is very fluid and malleable to help performance.
My issue with the science is that unilateral versus bilateral exercises are easy to study with plyometrics because single leg hops and double leg jumps are very obvious to implement.
Lunges and Split Squats
With exercises that are not purely one or two-legged, things get messy. Examples are lunges and split squats. While primarily one-legged, they are double leg supported so they can be loaded heavier and create specific stimuli to the neuromuscular system.
My question to everyone who does single leg training is that, if potentiation sees some transfer, what about training effects that create 50-inch vertical jump monsters? The recent NFL combine record holder in the vertical jump didn’t lose half a foot because he needed additional single leg squats with a heavy vest and dumbbells. It’s likely he was doing something that worked enough for him.
The balance component of exercises is important but sometimes overrated. For example, the airplane exercise with pelvic control is interesting on paper but doesn’t have much bite. Many balance exercises actually decrease propulsion or their intended stabilizer recruitment. That’s because stabilization is sometimes about raw strength to overcome sway or instability, not about circus tricks. Even some single leg exercises that look impressive don’t require skills that can be useful for other exercises including bilateral options, like pistols.
Science supports the inclusion of single leg exercises, but nothing in the literature clearly places a crown on the head of unilateral training.
When do Single Leg Exercises Help with Injuries?
Single leg exercises help reduce injuries and recover from them very well but are not saviors of sport. It’s noteworthy that in early levels of training, single leg exercises do a great job with overload since the strength-to-bodyweight ratio is rather poor for most beginners. As the athlete progresses, the ratio usually goes from less than body weight to multiple times bodyweight. Eccentric strength helps with both knee integrity and soft tissue resilience; single leg training may not always be the best solution for extreme rates or loads here.
Based on injury prevention data, we see only one bilateral leg movement that acts as a strong intervention to injury–the Nordic hamstring exercise. No other individual exercise intervention is as robust as the Nordic. Single leg options for the Nordic are too demanding because overload is high with just bilateral recruitment. Thus single leg options are not yet shown to be the superior option.
Training is holistic and is about entire strategy, not one exercise. Based on research studying warm-ups, some programs with a combination of single and double leg exercises have performance and injury reduction benefits. The FIFA 11+ program is a cornucopia of exercises, including many noteworthy single leg exercises, and is linked to reducing ACL injuries. Unfortunately, based on a recent comparison study, when the FIFA 11+ was compared to a rather conservative and dated dynamic warm-up, the program didn’t help athletes prepare for performance.
So the science points out that there is something there for injury reduction, but it looks like it’s about the entire recipe rather than just one ingredient.
What are Reasonable Risks with Single Leg Exercises?
Single leg exercises are not golden options without sin, meaning the same pros and cons exist with these movements as with bilateral options. A common scare tactic is to highlight the risk of spinal injuries with squatting or other two-legged lifts. True, the spine is under load when more weight rests on the shoulders, but the fuzzy math arguments that accompany the bilateral deficit creates a lot of confusion between barbell total load and relative risk.
Asymmetrical loading of the spine isn’t a huge problem, but it does play a factor. Believing that half the barbell is half the strain, however, is not true. And because the bilateral deficit argument is used to push a single leg exercise agenda, the proponents must address the fact that as one becomes more effective with single leg training, the deficit grows as does the load on the spine.As we improve with single training, both the bilateral deficit and spinal load grow. Click To Tweet
Other anatomical risks exist with any exercise. Knees, hips, and ankle joints are all part of the equation when appraising exercise risk. In my experience, single leg jumps pose more risk than bilateral options. If an exercise allows for the acceptance of more stress in the equation, then the tradeoff must be accepting more risk of injury. How many coaches feel confident letting their kids jump off a picnic table in the summer but would cringe if an athlete jumped off and landed on one foot? The human animal is designed to run and jump, but tendons and ligaments have limits.
The “single leg is functional” crowd includes many who are experts in stability until the going gets tough. Suddenly stabilizing the spine in training disappears and they focus on “sparing the spine.”
By reducing the frequency of bilateral lifts, I did find some small but noticeable decreases in discomfort. This was earlier in my career and turned out to be a red herring. I was less experienced in coaching and loading, and that result was due to a programming error, not exercise selection.
Looking at the peer-reviewed research, we see that squats, cleans, and some pulling exercises do put stress on the spine. But consider this: where have all of the core programs gone that helped solve spinal stability. How did coaches train spinal stability with exercises, such as the back or front squat?
Most studies can only look at observational trends unless an exercise movement has a clear mechanism of acute injury. This is why there’s little research on injuries with new exercises. Some coaches are threatened by single leg hip thrusts and Bulgarian split squats. If they wanted to be more productive, they would put their time and energy into the lumbar spine and hip joint risks. These two exercises are rather safe, but to claim they are not without any risk shows biased thinking.
The Hidden Problems with Single Leg Exercises
Single leg training is just like any other part of training, it has principles that must be adhered to and doesn’t get a free pass on science or logic. Coaching is an art, but even art students have parameters to follow to become great.
Single leg exercises have similar and unique challenges that are not found with bilateral training. I’ll cover the common denominators and then discuss the unique problems that are less commonly talked about in the single leg circles. Again, most of this is a review, but I have a fresh angle that will be worth the time to read.
Progressive overload is still progressive overload, and eventually the same ceiling will be hit with single leg exercises that bilateral lifts meet. Risk always find its way in when athletes need more demanding challenges.
A hidden problem with single leg training is blinded by the obvious–adding more weight to the bar. Some protocols add more reps. While this works to a point, heavy training is not going to escape strength and conditioning no matter what form it comes in. Single leg or double leg, overload requires more load. If 250 kg squats are risky to the spine, eventually the 180 kg split squat will become risky even if we add more reps and keep the load the same. Fatigue is like Father Time or the Grim Reaper, they eventually find you!Single leg exercises involve compromising positions and eventually require more load. Click To Tweet
Single leg exercises have compromising positions as well. Dumping a split squat or step-up is not easy like back squats and front squats, for example. Dropping a bar in the front or back with a split squat is like having a dull guillotine falling on the support or balance leg. And while split squats have considerably less load, the total rep count is doubled, thus adding extra fatigue to muscles that may not respond well to exhaustion.
In addition to extra work put on overlapping muscles of the torso and low back, grips fail, and there are often limits on the ability to share equipment like weighted vests. Even if we wanted athletes to share their sweat with teammates, germs and illness could hinder performance. Single leg training isn’t a perfect utopia. Carefully ponder the logistical issues and whether the training effects are worth the challenges and risks.
Liberate Yourself and Make Your Own Path
If you skipped ahead through this article for suggestions of how much or which single leg or double leg exercises to do, you missed the point. The key to prescribing exercises is making the right choices–not hunt for the best exercises from someone else. I encourage coaches to share their top exercises and why, but only to engage in exchanging ideas. It’s not supposed to be a top-down approach where we’re told what to do based on another’s experience or perceived expertise.