Single-Legged and Semi-Functional?

About six years ago, strength coach Mike Boyle started a controversy that touched every aspect of the strength and conditioning community, from internet forums to the leadership of the NSCA. In its most aggressive form, the premise was this: lifters should abandon bilateral lower body lifts in favor of unilateral and semi-unilateral exercises. His main reasons were that these lifts weren’t specific to sports and that they were unnecessarily risky to athletes (Boyle). He had already excised deadlifts from his programming, so at the time of his announcement, he mainly targeted the back squat and to a lesser degree front squats and Olympic lifts.

He cited coach Vern Gambetta and mobility theorist Gray Cook as two forbearers, though Gambetta was never as polarized as Boyle, and Cook spends most of his time on the periphery of performance training. Boyle was clearly in the driver’s seat here and this is why I’m focusing on his remarks specifically. It should be said that his most attention-grabbing statements didn’t jive with the nuances of his thinking: Boyle primarily worked with hockey players and the odd mechanics of skating, and this sport informed much of his reasoning. For example, his Olympic lifters seemed to have kept the front squat in their programming. As we’ll touch on later, his thinking has involved since this time.

Boyle’s articles and taped clinics ran rampant within the strength community and ultimately became a likely factor in him being uninvited to an NSCA speaking event. (His frequent criticism of the NSCA didn’t help either.) Years later, the controversy has died down, though Boyle remains a fixture in North American strength and conditioning and his many missives are readily available online.

I write this now, years after the precipitating events, because I feel that there wasn’t much measured, research-backed response to his positions from any party. In fact, Boyle’s work (and perhaps Cook’s even more) has led to a much greater body of unilateral research being conducted. So consider this article a retrospective exercise in antagonism where we frame the debate around a hypothetical lifting regiment that uses only the following unilateral and semi-unilateral exercises (and similar lifts) frequently espoused by Boyle:

• Conventional split squats
• The Bulgarian squat (called the rear foot elevated split squat in Boyle’s work)
• Lunge variations
• Single-leg squats
• Single-leg deadlifts

Sport Specificity?

Single leg proponents have two tracks with sport specificity. First, their movements have more resemblance to sporting movements. Second, the single-leg movements develop the same qualities as bilateral movements (and just as well) while adding new qualities that bilateral movements lack. The first is pretty easy to dismiss. Sure, a flat-footed squat doesn’t look much like a long jump. But if just looking like a competition event mattered much at all, all those lovely lifts where one foot is propped on a bench or you’re standing on one leg holding on to a cable pulley (for a minute or more at a time) fail by the same standard. When the vast majority of an athlete’s time is spent practicing the actual sport, there isn’t much to be gained by matching strength exercises to sporting movements. This isn’t to say that there aren't any benefits to matching training to sporting actions, but it’s far more complex than simply stating that running is one-legged, therefore our training should be likewise.

LISTEN How Mike Boyle Became a Coach of Influence

The second line of reasoning has its own faults. While I do believe that there is benefit to having some similarity in neural patterns between training and sport, the sports that benefit most from weight training are ones that rely on power development. Most single-legged movements are lacking in their ability to promote power though. Why? These lifts are unstable to a degree that controlled, even slow descents and ascents are required, which is antithetical to power development. Even the athletes who master these lifts to the point where they can be performed rapidly are still devoting a large portion of their neural resources to stabilizer muscles. This is only worsened by stepping on benches or soft-touching Airex pads.

The retort would be that this stabilization is its own sport-specific benefit. I’d counter that the major forms of human locomotion are inherently stable in normal, healthy individuals. We have the basic hardware and wiring to stay upright on unbroken terrain. If this weren’t the case, most sports would look like they’re being played on undulating waterbeds.

Not only are our forms of travel stable, but they increase in stability as speed increases. The reason for this is that instability during gait is a result of contact with the ground. The longer contact with the ground is maintained, the greater potential for instability. The faster you walk, jog or sprint, the less contact your feet make with the ground. If you look at EMG results of sprinting, the prime movers really are the prime movers: gluteus maximus, hamstrings, hip flexors/quads and calves. They’re by far the most active muscles not only during contact with the ground but immediately prior to contact to allow for a strong elastic response (4). The minor portions of the glutes, the abductors and adductors, and other supportive muscles aren’t as involved. Now, it is true that the hamstrings and glutes are the key players in many unilateral movements, but in recognizing this, we return to the earlier problem—the difficulty in producing power.

So these exercises don’t prepare the torso for intense loading, and they don’t have a great impact on power production. It may seem that endurance running might then be a good fit, though the most exciting research in this field lately has been on improving movement efficiency through high loads and power outputs.

Safer in the Gym?

Boyle cited improving safety (particularly the reduction of lower back pain) as a prime motivator for abandoning bilateral leg lifts. His detractors had a habit of pointing out technique deficiencies in Boyle’s athletes that may have led to these problems (including spine curvature during heavy unilateral lifts).

This is largely the realm of anecdote and opinion versus anecdote and opinion, so it isn't very helpful to either side. Experience informs us that lifting injuries are usually the result of bad form, high intensity, unmanaged fatigue or poor exercise selection. These all fall on the lifter and/or the lifter’s coach, not the lifts themselves. If you round your back during a barbell squat, you’ll probably do the same with a pistol. If you overarch on a good morning, you’ll do the same on a Bulgarian squat. If anything, it’s easier to achieve an extreme, structurally stressful joint angle in most unilateral exercises than their bilateral cousins.

The lightened load of a unilateral lift is cited as a benefit to spine health, but this misses the point. It isn't the load on the back that matters as much as the muscular response to the load. It’s impossible for a barbell on your back to directly compress your spine—the bar would roll off as your posture straightened. Instead, the spinal erectors and other muscles that contract to stiffen the spine cause the actual compression. This is how an unloaded hyperextension exercise like the prone Superman causes so much compressive force on the spine. One recent study comparing barbell squats and Bulgarian squats (called pitchers’ squats in the article) supported this fact when it found similar levels of erector activity in the two lifts (7), though this finding isn’t universal.

In the big picture, a lunge or step-up will be easier on the back than a heavy squat or deadlift, but don’t throw caution to the wind. Boyle makes particular reference to this factor improving with taller athletes, and here I think he has a great point. A relatively slender, six foot, five inch basketball player has a markedly different (and more difficult) squatting action than people of shorter stature. An upright Bulgarian squat or lunge variation could be a back saver.

I’ll also argue that the multidirectional instability of most single-legged lifts is a risk factor for acute injuries. For example, loaded lunge and split squat variations are capable of having lateral movement failures (i.e. tipping over). I haven’t experienced this myself, but it seems like dumping the bar becomes a riskier prospect in this situation.

Explosive variations of single-leg exercises are probably harder on the body than bilateral ones, as any advantage from reduced load is offset by the smaller impact area and greater instability (14). Knee safety in these exercises is likely a product of strong quad/calf bracing (11), two areas a general regimen of unstable unilateral training struggles with.

Injuries on the Field

The changes in direction so common in gridiron football are often used as backing for USSL training, particularly with running backs and the number of injuries they suffer to knee ligaments. I’ll address the mode of play first and then the injuries.

Successful offensive football is built on the philosophy of “one cut and go.” One of the most common rushing plays in football is the wide zone play. The back takes the hand off, runs toward one of his offensive tackles, makes a quick cut and accelerates into the open field. That’s about six straight ahead steps at a moderate sprint, one moderate change in direction and then a burst of four or five steps before a secondary defender arrives. Nearly all the back’s motion is linear, and the one cut is a fairly mild change of a few degrees made at a less-than-breakneck pace. In fact, the action of the cut isn’t nearly as important as reading which way to cut and timing it right so that the defense is out of position. Just looking at the simple math of footsteps indicates that not focusing on power exercises means not preparing the athlete for the most common demand of the sport. The same metrics can define most popular sports.

Regarding injuries, gluteal and hamstring strength are continually found to be key muscular factors for injury prevention. In fact, the human gluteus maximus might be the muscle most evolved for upright locomotion at all speeds (1). Since single-leg work can involve significant glute activity, it can be part of a successful prehabilitation/rehabilitation program for knee injuries. However, activity isn’t enough. The glutes (and other muscles) have to absorb and disperse force to prevent injury, which is why explosive jumping techniques are a cornerstone of modern injury prevention. They also have to compete with the adductor muscles (8), which are also strengthened by many popular single-leg exercises. This might suggest that bridge/hip thrust style exercises and single joint hip exercises would be a more effective choice for preventing knee injuries than anything flamingo-esque.

Regarding the hamstrings, the stiffness of these muscles is important for their role in preventing knee injury, though some of the best results in improving this field have come with work involving glute ham raises and even leg curl machines (2). Also likely important are the calves (11) in jumping activities. As far as the prime movers’ ability to protect themselves from strain, that’s as much a feature of the muscle’s tendon thickness and exposure to eccentric loading (5).

Admittedly, much of the above is theory. In real world interventions, the most success has been had not with weight room activities but with pre-practice warm ups. The Santa Monica Sports Medicine Foundation’s Prevent Injury and Enhance Performance (PEP) program has had good initial results in large-scale testing (6) but is far from the only such program that’s been put through the paces. Single-legged work in the weight room could help set the stage for programs like these, though that’s speculative.

Regarding knee injuries that do happen, most are well beyond what a cautious one-legged Romanian deadlift can protect against. Trauma can occur without reactive muscles having time to protect the joints. One current orthopedic focus is on the rotational capacity of the knee joint, which is largely determined by ligament tension and joint structure (10).

Returning to the idea of pre-practice warm ups, perhaps the most effective use of single-legged work is in enhancing and preserving mobility. For example, Bulgarian squats are effective at improving movement and limiting pain associated with hip flexor issues. I’m of the mind that loaded lifts don’t provide much more benefit than unloaded lifts, though I admit I only have my opinion and personal experience to back this up.

Hypertrophy

Implied in Boyle’s broadest comments is that lifters seeking hypertrophy could benefit from the lifts he describes. I could see this being useful in untrained lifters or as a novel stimulus for experienced athletes, though not effective as a dominant mode of training. There seems to be a theoretical contradiction here, as two of the best predictors for a lifting session’s hypertrophic effectiveness are the degree of mechanical stretch that the muscles endured (9) and the level of mechanical fatigue reached. In unilateral lifts, the stabilizers are fatigued but rarely stretched. At the same time, the prime movers are often stretched but won’t fatigue before the stabilizers. As an example for the first point, most trainees seeking to add inner thigh mass would be better served by wide box squats that elongate the adductors. Addressing the second point, elitefts™ team member John Meadows prescribes Bulgarian squats but often following targeted single-joint exercises and with the lifter braced against a bench or squat rack (13).

Bonus: The Bilateral Strength Deficit

Here’s a factoid that most lifters have experienced firsthand: most people are stronger curling dumbbells one arm at a time than they are curling them simultaneously. This is an example of the bilateral strength deficit in action. The deficit is clear in simple, stable exercises such as various curls and extensions where the prime mover is always the weakest link and the largest beneficiary of the training stimulus and the double-limb movement mimics the single-limb version. The venerable leg extension machine appears routinely in related research.

Using this concept to say that a unilateral dumbbell lift is superior to a bilateral barbell lift though is nutty. A pistol squat is nothing like a barbell squat. Heck, most people position their legs different when switching from two-legged to single-legged leg presses. It’s an apples-and-oranges fallacy by any measure. Failing to add in the effects of increased balance demands on unilateral lifts only worsens the fallacy.

MORE Elitefts™ Multi-Level Single Leg Squat Progressions

What This Leaves Us

As you probably already thought, intelligent application is the key to making use of these lifts. Coach Boyle has backed away from his absolutist stance and now includes kettlebells and trap deadlifts with his athletes. I actually applaud him for his antithetical take, especially because the health of his athletes was a top motivator for him.

Given what we know and where the research is leading, we can come up with some recommendations. Lifters are probably best served to incorporate these exercises as body weight/light weight warm ups, with more serious inclusion for planned deloads and as responses to back or hip injuries. Other athletes, particularly running/jumping athletes, might stand to gain more from these lifts due to their greater degree of neural similarity to their sport skills, though there isn’t much to indicate that they should form the core of a strength training program. The same advice for deloads and back injuries applies here as with lifters, though more regard for taller trainees strikes me as very reasonable. Body aesthetes should use these lifts as they do every lift—as targeted tools to be manipulated however needed.

References

1. Bartlett J (2014) Activity and Functions of the Human Gluteal Muscles in walking, running, sprinting, and climbing. American Journal of Physical Anthropology 153(124–31).
2. Blackburn J, Norcross M (2014). The effects of isometric and isotonic training on hamstring stiffness and anterior cruciate ligament loading mechanisms. Journal of Electromyography and Kinesiology 98–103.
3. Boyle M (n.d.). Retrieved: March 2015. From: Functional Strength Coach 3 at http://www.functionalstrengthcoach3.com/squats.html.
4. Chumanov E, Heiderscheit B, Theyln D (2007) The effect of speed and influence of individual muscles on hamstring. Journal of Biomechanics 3555–62.
5. Fiorentino N (2014) Musculotendon variability influences tissue strains experienced by the biceps femoris long head muscle during high-speed running. Journal of Biomechanics 3325–33.
6. Gilchrist J, Mandelbaum B, Melancon H, Ryan G, Silvers H, Griffin L, et al (2008) A Randomized Controlled Trial to Prevent Noncontact Anterior Cruciate Ligament Injury in Female Collegiate Soccer Players. The American Journal of Sports Medicine 1476–83.
7. Jones EA (2012) Effects of unilateral and bilateral lower-body heavy resistance exercise on muscle activity and testosterone responses. The Journal of Strength and Conditioning Research 1094–100.
8. Mauntel T (2013) The effects of lower extremity muscle activation and passive range of motion on single leg squat performance. Journal of Strength and Conditioning Research 1813–23.
9. McMahon G, Morse C, Burden A, Winwood K, Onambele G (2014) Muscular adaptations and insulin-like growth factor-1 responses to resistance training are stretch-mediated. Muscle and Nerve 108–119.
10. Mokhtarzadeh H, et al (2015) Restrained tibial rotation may prevent ACL injury during landing at different flexion angles. The Knee 22:(24–9).
11. Morgan K (2014). Elevated gastrocnemius forces compensate for decreased hamstrings forces during the weight-acceptance phase of single-leg jump landing: implications for anterior cruciate ligament injury risk. Journal of Biomechanics 3295–302.
12. Osteras H (2013) A 12-week medical exercise therapy program leads to significant improvement in knee function after degenerative meniscectomy: A randomized controlled trial with one year follow-up. Journal of Bodywork and Movement Therapies, 374–82.
13. Tate D (2014) Retrieved from: http://asp.elitefts.com/qa/training-logs.asp?qid=208022.
14. Yeow C, Lee P, Goh J (2011) An investigation of lower extremity energy dissipation strategies during single-leg and double-leg landing based on sagittal and frontal plane biomechanics. Human Movement Science 624–35.