Ask anyone what the best exercise is to build leg strength and power and you’re bound to hear traditional (bilateral-2 legged) back squats. However, new research supports employing unilateral or single leg squats as a primary lift in your training cycles.
 
Unilateral exercises enable you to address strength imbalances between your dominant and non-dominant side and To examine this topic in closer detail, let’s look at some of the key research studies that support this training along with strength coaches who use these lifts on a daily basis with their athletes to maximize the development of strength and power.
 
Perils of Asymmetry

Asymmetrical strength of the lower extremities increases injury risk and can impact athletic performance in any sport. With Olympic lifting, you might see this in the athlete who subtly shifts their center of gravity to favor one leg over another as they drive out of the bottom of the squat position, increasing the risk for low back, hip and knee injuries. In a sport like soccer, many athletes favor their dominant leg for shooting setting the stage for both hamstring and anterior cruciate ligament injuries. R. J. Shephard and P.O. Astrand report that “athletes with greater than 10 percent difference in quadriceps and hamstring strength between the right and left sides” are at increased risk for injury, while the soccer player able to shoot with both feet has far more chances to score than one who only uses their dominant foot. In regards to athletic performance, the weightlifter that possesses relatively equal bi-lateral limb strength can “drive out of the hole with both sides in a challenging lift,” says strength coach Kevin Carr of Movement as Medicine.
 
Strength and Power Research

Sports performance coach Eric Cressey once commented on his blog that “most athletes are quad-dominant.” However, athletic performance requires more than just knee extension. Success on the weightlifting platform or on the field requires multiple movements at the hip joint (extension, external rotation and adduction) along with knee flexion.
 
Your glutes and the hamstrings are the primary muscles responsible for these movements. Glute training expert Bret Contreras recently posted on his blog that these are the muscles that power “sprinting, jumping, landing, climbing, throwing, striking, swinging, turning, cutting from side to side, squatting, bending, lunging, cleaning, and snatching.” So while, everyone needs need strong quads, it shouldn’t be at the expense of your glutes and hamstrings.
 
The primary single leg squat exercise used in the research is the Bulgarian split squat, also referred to as the rear foot elevated split squat or the pitcher’s squat. Kevin McCurdy and researchers compared the electromyography (EMG) activity in the gluteus medius, hamstrings, and quadriceps when performing a traditional back squat and the rear foot elevated split squat in eleven female athletes. EMG activity was recorded as the athletes completed three reps using 85 percent of their measured three-repetition maximum for both lifts. After analyzing the data, McCurdy found significantly higher mean and peak EMG amplitudes and therefore muscle activation in the rear foot elevated split squat versus the bilateral squat when performed at the same relative intensity. While the EMG activity registered for the quadriceps is still higher than any other muscle during both lifts, the rear foot elevated split squat enables you to work on squatting while placing additional emphasis on the glutes and hamstrings, resulting in increased strength, power and stability. “Rear foot elevated split squats benefits transfer to the field in improved performance and decreased injury risk,” adds Kevin McCurdy, Associate Professor in the Department of Department of Health and Human Performance at Texas State University.
 
Another study by McCurdy and researchers compared the effect of short term unilateral versus bilateral lower body resistance training on measures of strength and power in thirty-eight untrained men and women. All subjects lifted weights two times a week for eight weeks initially starting with three sets of 15 repetitions at 50 percent of predicted 1RM and working up to six sets of five repetitions at 87percent of predicted 1RM by the end. Plyometric Exercises were initiated at the start of the third week and continued on to the end of the study. Subjects began with three sets of five reps and progressed to three sets of 15 reps by the end of the program. The exercises used by both groups are listed in the table below. See table 1 in the article PDF.
 
What they found at the end of the study was that all the subjects significantly improved in all of the outcomes measures (traditional back squats 1RM, vertical jump and the Magaria-Kalamen stair climb test, used to assess changes in muscle power). There was no significant difference between the results on the outcome measures between groups (unilateral versus bilateral). The researchers concluded “that unilateral and bilateral (training) are equally effective for early phase improvements,” of muscle strength and power in trained men and women. While this study shows that unilateral squats can improve strength and power in untrained individuals, what are the effects of unilateral training in experienced lifters?
 
Speirs and researchers examined this question in an article published in the Journal of Strength and Conditioning Research in February of 2016. In the study, they assigned eighteen rugby players who were also experienced weight lifters to either a bilateral or unilateral training group. Both groups then trained the lower extremities for five weeks using either the back squat or the rear foot elevated split squat. See table 2 (in the PDF)  for volume and intensity progressions. All the subjects significantly improved their performance in three of the four outcome measures (1 Repetition Maximum, 40-meter sprint time and change of direction speed).
 
There was no significant change in any of the subjects 10-meter sprint time. The researchers attributed this to the short duration of the training cycle. More importantly however, the researchers concluded that both training modalities “appear equally effective in improving lower body strength, sprinting speed (at 40 meters) and CODS (change of direction speed).” Unfortunately, there are no studies in the literature that examine the impact of unilateral training on Olympic lifting or powerlifting outcomes. However, the principle of specificity still holds true: “if the movement patterns are similar, strength and power will transfer,” wrote Dr. McCurdy.
 
Strength Coach Views
 
Kevin Carr of Movement as Medicine and Steve Hartman, Sports Performance Coach at Bellarmine University, regularly use rear foot elevated split squats in their training. “All my athletes no matter how much experience they have with weightlifting start with rear foot elevated split squats,” says Hartman. “It’s low risk, high reward training that gets my athletes bigger, stronger and faster.” Kevin Carr is quick to agree. “Unilateral work enables you to teach the athlete how to drive out of both sides, maximizing the amount of work each leg can do,” he says.
 
Both of these gentlemen primarily train individuals in which the goal is to use weight lifting to improve performance on the field not necessarily inside the weight room. But, what about those athletes who compete on the weightlifting platform? “Single leg lift variations should be part of your training because they support bilateral training,” says Carr. Looking at my earlier example of the Olympic lifter who shifts their center of gravity to favor the dominant leg--even if they don’t injure themselves, shifting their center of gravity also increases the chances of a failed lift. Since improvements in single leg strength transfer to bilateral lifts after a short cycle of rear foot elevated split squats, when you get caught down in the hole in a lift instead of shifting your weight to the dominant side, you can stay centered and power up and out using both legs.
 
Trying it Out

Coaches, athletes, and weekend warriors are always trying to better performance whether it’s a new drill, workload progression or a new exercise, this is one that’s worth a try. The research tells us that Bulgarian split squats improve strength, power and athletic performance. Renowned trainers like Kevin Carr, Steve Hartman, Mike Boyle, Eric Cressey, Bret Contreras and even our own Greg Everett have all used this exercise in their programming to improve their athlete’s performance. So next time you’re at the white board drawing out programs, work a few sets of these into your workouts. Like Steve said “they’re low risk, high reward,” so what do you have to lose?
 
Catalyst Athletics’ video on how to perform Bulgarian split squats is available here.