Monday 24 August 2015

Double vs Single Leg Squat – The Verdict Is In!

“You don’t play sports on 2 legs, so why should you train on 2 legs?” This argument is often used by those who are proponents of single leg training. For decades strength coaches have used the traditional bilateral (2 leg) squat to build strength and improve athletic performance. However the last several years, there have been coaches who have moved away from bilateral squats claiming the superiority of unilateral (1 leg at a time) training. Usually their augments were based on logic, observation and personal experience. However, now we have decent study to get to the bottom of this debate. It’s time to put opinions aside and look at what really matters – results.
Recently the NSCA (National Strength & Condition Association) released a study that compared unilateral squat (i.e. a rear elevated split squat – I’ll refer to this as the Bulgarian Split squat – not because it is from Bulgaria, but it just sounds way cooler!) and a bilateral squat (i.e. traditional squat done with a barbell on your back and two feet on the ground).

Study Reference: 
Speirs, D.E., Bennet, M., Finn, C.V., Turner, A.P. Unilateral vs bilateral squat training for strength, sprints and agility in academy rugby players. Journal of Strength & Conditioning Research. 2015. Published Ahead of Print.

The subjects were 18 healthy rugby players (wow – I didn’t think there were any healthy rugby players) with at least one year of resistance training. The subjects were divided into either a bilateral-only group or a unilateral-only group. Each group was tested on their 10 meter sprint, 40 meter sprint, pro-agility (, and 1RM (1 rep max) back squat and Bulgarian split squat. Each group trained two times per week for 5 weeks.

The results showed no real difference between the two groups. Neither group make significant improvement in the 10m. Both got faster in the 40m sprint and the pro-agility with a very slight advantage to the unilateral group. As far as strength goes, both groups got stronger on both the Bulgarian split squat and the back squat.

  • Small sample size – it would have been nice if they used more subjects
  • Short duration – 5 weeks is good, but it would be interesting to see if after a longer time there was a clearer advantage to one of the lifts.
  • 3 week instructional period was used to get good at the lifts 
  • They did research the hard way by actually testing, training and re-testing the subjects. Many researchers take the easy way out and look at things like EMG muscle activation, joint angles, force plates, hormones, blood work etc. While these are helpful things for a greater understanding of why something works, it leaves coaches hanging as to what actually delivers better results in the real world?
  • Previous research sited in the introduction section of the article used untrained subjects. This study used trained individuals. This helps to negate the “newbie effect” (i.e. pretty much anything works for beginners).
  • The split squat is not a true single-leg exercise. Some coaches have used the argument that you can do way more weight on one leg than two legs. They call this the bilateral deficit. While this does exist, it is over-stated when using a Bulgarian Split Squat because the back leg contributes significantly. As an experiment, I weighed myself on the ground and was 205lbs. Then got into the Bulgarian split squat position with a scale under my front foot and at the bottom I weighed 140lbs (previous research cited in the study found this to be 85%). If you want to compare bilateral and unilateral strength with the legs, you need to do a bilateral squat and a single leg squat – each to the exact same depth. 
  • With my curiosity peaked, I wonder about other benefits of these exercises. Would one be better than the other for fat loss? What about hypertrophy? 

Real World Application
How do you define functional training?
Functional training is not necessarily picking the exercises that look most like the activity. It is training in a way that effectively transfers over to improvement in work, sport and other real-life activities. If you have a good measure of your sport/work/life performance then you can pick exercises based on results that improve that real-life performance – this is a functional exercise!

You have options
You don’t have to be dogmatic and draw a line in the sand. Since both exercises improved performance, they can both be valuable parts of a complete training program as each has its own unique advantages. Ideally do both 1 and 2 leg exercises in your training if you can safely and effectively do so.  

Advantages of bilateral squats
  • There is lots of academic research and real-world evidence showing that traditional squats help athletes run faster, jump higher and improve sport performance
  • There is more required of the trunk stabilizers and thus you teach and strengthen your trunk muscles to effectively transfer force from the legs – very functional
  • If done with a full range of motion, they are great for maintaining an fundamental movement pattern as well as good lower body mobility 
  • They build mental toughness. The squat is a brutal exercise that strengthen mind and body.
  • There is something special about standing there with a heavy barbell on your back that wants to crush you. This is a survival threat that your body takes seriously and will respond to.
  • The squat allows you to spread the knees out and go deeper than the Bulgarian split squat. This allows you to pass through that high compression spot at 90deg of knee flexion instead of stopping and reversing direction at that spot. I can’t prove it yet, but I believe this places less stress on the knees.
  • The Bulgarian split squat places an eccentric load on the back leg. This can lead to a lot of DOMS (delayed onset muscle soreness) which can hinder athletic performance.

Advantages of Bulgarian Split Squats
  • Looks more like sports. This is important for the principle of specificity and getting a good transfer of training effect.
  • Allows you to work the hips and trunk differently than when you have both legs on the ground to help stabilize each other.
  • Less low back stress as you are able to stay completely upright with your torso. I have used them as a replacement for athletes who are not able to do traditional squats due to previous back injuries. 
  • May be easier to identify and correct left-to-right asymmetries
  • Provides a dynamic stretch to the back thigh (rectus femoris) which is a commonly stiff muscle
  • Gives you a reason to write “Bulgarian” in your training log – how cool is that!
  • While not statistically significant, there was in this study a very slight performance advantage to the Bulgarian split squat group

This is just one study
Always remember that research doesn't "prove" anything. This is just one study. Hopefully it will create new questions and more research will be done to give us an even clearer understanding of the relationship between unilateral and bilateral squats.

Why are you doing the leg exercise you are doing? For athletes (and those not competing in powerlifting), you don’t have to do a traditional barbell back squat. If you are an athlete, your goal of leg training is to get stronger legs so you can put more force into the ground. Ultimately if an exercise does not beat up your joints, but allows you to progressively add weight and gets you to your goals, then you have yourself a great exercise!

How about you? Which squat do you prefer? Please leave your comments below or on my Facebook Page.

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