Bilateral vs. Unilateral Squatting

Several of you who follow me are aware of the debate between Coach Mike Boyle and me.

If you aren’t familiar with the debate, I will give you a bit of the background. Coach Boyle’s take is that all bilateral squatting is both unsafe and ineffective for improving athletic performance. He concludes that the compressive load on the spine is dangerous, and that the spine isn’t designed for compressive forces. He also concludes that unilateral is superior because sports are played unilaterally. Specificity is king, making unilateral the best choice.

My take is that both bilateral squats (front squat and back squat) and unilateral squats (split squats and lunges) are great choices for improving athletic performance and for stabilizing the body to prevent injuries.



This debate has prompted me to take a closer look at the research on this subject. Before I go into my findings and my thoughts on the topic, I want to say that I respect what Coach Boyle has accomplished and contributed to our industry. I have actually paid for two of his seminars, so I am in no way saying that he is a bad coach. That would be a foolish assumption on my part. I am simply disagreeing with him on this one issue. We agree on so many topics like:

  • Sport specific training should be left to the sport coach.
  • Box squatting can be dangerous – especially the bouncing and rolling box squats.
  • Cleans are awesome for power production.

With that being said, let’s take a look at what I found.

Point #1: Bilateral Deficit

Let me first explain what the bilateral deficit really is. If you test out your one-repetition maximum unilaterally and add the right max to the left max, the two combined will normally be about 10% more than your bilateral maximum. There are a lot of theories as to why that is, but the data is really inconclusive.

The two main theories are:

  1. We are wired to be unilateral creatures because we walk around our entire life unilaterally.
  2. When we perform a movement unilaterally, we are able to counterbalance or shift around to find a mechanical advantage. An example is when you perform a preacher curl with one arm; you will naturally contort your body a bit to bang out a couple of more repetitions. Obviously when you perform a movement bilaterally you are in a fixed position making counterbalance much harder.

I am going to go with the cause as just a neurological response from all of the normal day-to-day unilateral movement we all do naturally. Coach Boyle uses this finding to say the body performs better when using unilateral movements. He goes on to say the body shuts down neurologically when performing bilateral movements. However, the research doesn’t agree with him.

The research will show that athletes will narrow the bilateral deficit after performing bilateral movements for a length of time. A lot of studies show athletes eliminating the deficit altogether, and a few show bilateral facilitation (bilateral outperforming the sum of the unilateral movements). Regardless, what does any of this have to do with performance?

So far the only study performed on the bilateral deficit regarding athletic performance showed that athletes with little or no bilateral deficit were able to produce more force against the blocks at the start of a sprint. So once again, this is a great point to use both in your training. Clearly this is the stance taken by most coaches.

The other studies performed on unilateral and bilateral squats in athletic performance showed that both worked about the same regarding actions like sprints, vertical leaps, and broad jumps. Once again, the finding didn’t surprise me. This just showed that either option is fine. However, I still have to lean toward performing both due to the one study showing a smaller bilateral deficit contributing to more force into the blocks in a sprint.

Point #2: Building Back Strength

Then I brought up a point that hasn’t been discussed that often. Coach Boyle said the limiting factor in a lot of squats is the back and not the legs. I would agree that is true with most, but there are a lot of athletes who lose squats due to leg strength. I’d say 70% of people lose big squats due to back strength, which brought me to my point.

The fact that the spinal erectors must overcome a major spinal flexor moment during squats and even more in the front squat means that you are increasing the strength of your back when squatting. The load is at least 40% less in the unilateral squat, so the back is only forced to adapt to this light load. If you are a competitive football player or rugby player, you are going to need that back strength.

Here’s a crazy finding: an average defensive back in the NFL weighing 199 pounds and running a 4.56 40-yard dash is capable of producing 1600 pounds of tackling force. If you are building monsters capable of this kind of force, you better build monster backs capable of withstanding 1600 pounds of force.

Obviously even with trap bar deadlifts, the spinal flexor moment is great – but it is reduced because of the proximity to the center of the body. The farther up the spine that you move a bar will increase the spinal flexor moment. When you perform a front squat, the spinal flexor moment is even bigger because now the bar is in front of the body and ever farther away from an intervertebral joint in the spine. If you want monster athletes, use monster movements.



After combing through the research and interviewing the experts, the result is a guide that will refine your technique and boost your squat in a safe and effective manner.

Specificity and Safety

At the end of the day, specificity will always win. If you are creating athletes who sprint, run, and cut, you should perform unilateral work specific to those movements. However, unlike the popular opinion of the unilateral crowd, not all sport is performed unilaterally. Just look at vertical leap, broad jump, the start of a sprint, athletic stance, batting, a wrestling throw, the start of a swim race, and so many jumps during volleyball. Once again, using both seems to be the answer.

To date there is no research on bilateral deficit as it pertains to risk of injury. Boyle simply references anecdotal data that several of his guys either got hurt bilaterally squatting or bilateral squatting was irritating the backs of his athletes. My data would say something much different. We haven’t noticed that squatting irritates anyone’s back. However, there are two cases on our team where athletes had prior injuries that didn’t allow them to back squat or squat as much. In one case, we simply performed front squats. In the other case, we performed unilateral squats once or twice per week and performed bilateral squatting two to three times.

Before I participated in the debate, I actually called Dr. Stuart McGill. Here were a few of my takeaways. First, here is Dr. McGill’s quote:

“Everything in biology has its tipping point. Below that tipping point everything is anabolic. Everything above that point is catabolic and damaging. This goes for unilateral squatting, bilateral squatting, and pretty much every lift.”

So either movement can be helpful or damaging based on the load and the particular athlete.

Dr. McGill and I agree that bad movement patterns can also get an athlete hurt regardless of load. If you notice a lot of knee valgus or anterior pelvic tilt while performing bilateral squats, you are probably going to get hurt. If you use a wide split stance during a unilateral squat, you are going to mess with the pelvic ring and cause SI joint pain. The takeaway is to find a good coach, learn the movement, and only load functional movement patterns.

All the research points to the back squat being one of the safest movements you can perform. When you are trying to build your absolute strength in those first two to three years, bilateral squats performed heavy are great. Once you reach that threshold of squatting around twice your bodyweight, you might want to consider specificity. At that point, based on these findings, I would focus on one day of velocity based training for the bilateral movements, one day of bilateral based movement for absolute strength, and one day of unilateral movements for hypertrophy and strength.

It might look like this:

Day 1

Unilateral squats – 5×5

Day 2

Velocity based back squat

Day 3

Front squat maximum effort
Unilateral squats – 3 x 8 each leg


I would like to say one more thing in defense of Coach Boyle. He coaches 1,000 athletes per year. He has to design a system to fit his athletes in their culture to get the most results. I think he has done a great job. His athletes are performing, so that’s all that needs to be said. (Of course I believe my athletes are performing even better, but I’m a little biased.)

Feel free to do your own research. I used two really great sources that led me to my research:

  1. “The Whole is Less than the Sum of the Whole” by Greg Nuckols in his online research review MASS
  2. “How to Squat: the Definitive Guide” also by Greg Nuckols

Yes, I am a Greg Nuckols fan mainly because he was one of my interns and powerlifters several years ago. He’s become quite amazing at diving into research and presenting his results in a way that is easily digested by coaches like me. I highly encourage all of you to check him out.

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