This is a Short History and Explanation of the Bulgarian Split Squat
If youve never done a BSS, also known as Rear Foot Elevated Split Squat...they are HARD.
Bulgarian Split Squats were popularized by a now famous strength and conditioning coach, Mike Boyle, this was in the late 2000s.
Mike had a background in powerlifting, and like many coaches who grew up during the 1980s, the barbell lifts reigned supreme. Squat, bench press, deadlift, power clean. That these movements were mandatory in athletic training was considered unquestionable.
Mike used these lifts for years himself, and over the course of his Strength coach career, he eventually ended up training Hockey Players.
Particular to the Squat, Mike noticed over the years that heavy squatting seemed to have an a very high injury rate. And Hockey players are notorious for having very high wear and tear on their hips.
Mike questioned whether having his players back squat was a wise decision. Back squats are hard on the hips, hard on the spine, and heavy squatting is fatiguing.
So Mike made a decision then in the early 2000s that was unthinkable, he stopped having his athletes back squat.
He switched to what we now call single leg squats, with his preferred version being the Rear Foot Elevated Split Squat, now popularly referred to as the Bulgarian Split Squat.
What was the result?
Everyone got stronger.
Everyone got faster.
Everyone built muscle.
There was no loss in performance anywhere, of any kind. The single leg squats worked so well that Boyle questioned whether bilateral training was necessary at all beyond a bigger level.
When Boyle published his observations and insights, they were not well received.
To say he was “trolled” was an understatement. The internet of 2023 is actually much tamer than the late 2000s. This was before the era of political correctness, wokeness, and censorship.
Boyle was called every conceivable name you could think of, his masculinity was questioned, and endless articles were written about how REAL MEN SQUAT.
Despite this, Boyle did not care.
He continued to publish articles on single leg squats and unilateral training, and by the end of 2010s, the industry attitude had changed completely
The Powerlifting Era ended as people realized heavy, constant maximal lifting DOES lead to injury
Powerlifting is still as popular as its ever been, but the orthodoxy of squat bench and deadlift no longer existed.
The Effectiveness of Bulgarian Split Squats was Undeniable
The scientific research backed up what many coaches and trainers had noticed.
Today the BSS (Bulgarian Split Squat) has become a standard exercise in most personal trainers and coaches repertoire.
Ironically, the one factor that has kept it from being mainstreamed to the public is simply because they are HARD
And now we finally get to the topic of this post, which is the Bilateral deficit.
The bilateral deficit is a phenomenon that Mike Boyle noticed over a decade ago when he was having his athletes do BSS.
When we do a typical bodyweight squat, each leg is lifting 50% of our weight.
On a BSS though, the weight distribution is about 70/30 to 75/25 working leg to non working leg.
So a 200lb man doing a bodyweight squat, each leg is lifting approximately 100lbs.
But with a BSS, the working leg is now lifting 140-150lbs.
Thats 40-50% greater than a regular bodyweight squat.
To get that same load on a back squat, you would need a barbell loaded to about 90-100lbs.
200lbs man + 100lb barbell=300lbs/2
=150lbs per leg
A barbell loading with 100lbs is not considered heavy, but consider the difference in loading.
This was the bilateral deficit breakthrough
When Boyle did the math, he realized you could use 40% less weight compared to back squat, but get the SAME level of load on the working leg.
A BSS with your only bodyweight is the same as you using a barbell with a quarter on each side.
What happens if you do a BSS with 100lbs in added weight? Like holding two 50lb dumbbells?
Again, we will use our 200lb man example.
200lbs+100lbs=300lbs X 0.75
=225lbs
How much would you need to back squat to get that level of loading on each leg?
You would need 250lbs on a barbell
200lbs+250lbs=450/2
=225lbs per leg.
It does not stop there though. Boyle also realized that you could load the BSS with FAR more weight than people would assume.
Here is an athlete with barbell loaded to 225, doing a BSS
Here is an athlete with 300lbs in added weight doing a set of 10 reps
Here is an athlete with a barbell loading with 315 lbs, doing a BSS
Here is an athlete with barbell loaded to 425, doing a BSS
These are insane levels of Single Leg Strength
Just the 225lb BSS is equivalent to squatting 400lbs, the 300lb is equivalent to squatting 500+, and the 425 would require an equivalent back squat of 700lbs.
But here the Bilateral Deficit Phenomenon
Their individual leg strength was much greater than their spine would ever allow. Those athletes could NOT squat that much weight on a back squat. Hypothetically their LEGS are strong enough, but the limiting factor is not their leg strength
It is their SPINE.
Everyone knows this. Its why we can always leg press more than we can squat. Take the torso out as the limiting factor, and human legs can handle some crazy weights.
But whereas leg pressing has limited functional transfer over to athletics, bulgarian squats DO.
This is what made Mike Boyle so passionate about Single leg squats. You build nearly imhuman leg strength, with far less weight, in a far safer manner, that doesnt beat up or breakdown the body
This is why the Bulgarian Split Squat is one of the primaru exercises I recommend and include in many of my programs
Now you know.
Get the AJAC Guide to Leg Training while you are here.