The value of using bilateral or unilateral exercises with strength training is one of those topics that has been greatly debated in recent years. There is one school of thought believing it is preferable to predominately use bilateral heavy exercises like the bench press, squats and deadlifts where maximum load can be lifted. And the other school of thought believing it is more beneficial to use single limb exercises that try to even out imbalance and asymmetry. There are pros and cons to using both types of exercises and I fall somewhere in the middle and often use a combination of both types of training depending on the person and the situation in front of me. I always believed the unilateral exercises were more for rehab and core stability and the bigger bilateral exercise the preferred choice for sports and increasing serious muscle and strength. Once again I was proven wrong and this article we explain exactly how unilateral exercises provide greater strength gains than many realize.

Unilateral vs Bilateral Training

Before jumping right into this concept to clarify what unilateral means, it means using "one side" or "one limb" such as a one-arm dumbbell row or a single leg squat. Bilateral means using both arms or both legs, like a barbell bench press or squat. The picture above shows an example of a single leg deadlift versus a traditional deadlift.

Even though both types of movement will work the same muscle groups they are very different in terms of the benefit to the body. Most of us will find bilateral movements much easier to complete, however, perform poorly with unilateral movements, even though the same muscle groups are involved! Why? The main reason is there is significant more neural and brain connections to be made with unilateral training, as the less dominant side of the body struggles to do execute movement by itself. It is not strength that is lacking but more the coordination, stability, timing, and fine motor control that makes the movements efficient.

This does not mean bilateral training is not useful, for it provides many things that unilateral training cannot. The question is not really which is better, but WHEN to use each method to achieve your desired result. As I said earlier I always thought the single limb stuff was for rehab, but this is not the case as the strength gains from these exercises is much greater than you think.

This something that makes no sense for how can a more complex exercise where many things that can go wrong can increase strength more effectively than the simpler bilateral exercise? To understand this paradox we need to learn about what is known as the "bilateral limb deficit phenomenon".

The Bilateral Limb Deficit Phenomenon

This is a concept that has gained a lot of attention from many researchers in recent times and is something I noted myself many years ago during my own workouts and also with some clients who could do amazing things with one arm or one leg. I remember being able to easily complete 8-10 reps with a single arm dumbbell chest press using 32.5kg or 35kg but struggle to complete a bilateral exercise with only 30kg! I never understood exactly why this happened until years later after reading many complex books, journals, and completing various courses on injury and movement.

The definition of this is as follows.

“When the sum of torque (force) generated by each limb (individually) in the unilateral condition is greater than that generated by both limbs simultaneously (bilateral condition), it is termed the bilateral limb deficit”.  To clarify, this means that the sum of weight lifted by both limbs individually is greater than that of the same weighted exercise done by both limbs simultaneously.

In simple language this means that a person is able to squat more than half of what they can on two legs. We are actually stronger with one foot on the ground than with two if you divide the total weight lifted by two for the bilateral exercise.

Some of the world's leading sport coaches like Mike Boyle have also found this to be true and completely changed their training styles to accommodate this. Here is a quote from Mike Boyle's book "Functional Training For Sports" which features on the front cover (see below) the rear foot elevated split squat.

"Every athlete we train can do the rear-foot-elevated split squat with significantly more than half what they can do in a back squat. In fact when we tested both front squats and rear-foot-elevated split squats, many of our athletes could split squat and  front squat with the same weight! I know it seems impossible, but its not." - Mike Boyle

This all sounds great but is this only relevant to sporting athletes who have great skills and a strong base of movement to begin with. What about beginners or people with back pain for example? Surely the more complex movements like a single leg deadlift or single leg squat would be much weaker and not provide anywhere near as much strength as the more simple squat or deadlift? I used to use a lot of single leg work in my rehab programs for knee, hip and back injuries but more as a way to enhance stability and movement skill. Once that was established I always believed it was better to progress to the bilateral exercises for the "real strength" stuff.

Once again I was wrong and this is has been proven to be the exact opposite even with injury.

Who better to refer to for an answer on this than the world's leading researcher on back pain Dr Stuart McGill. Here is an extract from a lecture he provided to Stanford University several years ago where he was debating with Gray Cook the value of the FMS as a corrective exercise method. You can get this video lecture by going to OTP Books. I highly recommend getting this DVD series as it provides some amazing information and insights into functional training from two of the greatest minds in the health and fitness industry.

Here is an extract from this video series that stood out to me.

Question: My question is for Stuart McGill. For low back pain, would you do unilateral exercises with people with pelvic dysfunction? Or never?

Stuart McGill: To me, there’s no such thing as never. The answer is always “it depends.”

I wouldn’t be able to answer that question until I had the person in front of me, but then I would provoke the pelvis and determine whether that’s a pain generator or not. If it was, I would define the pain triggers very precisely in terms of motions, postures, loads, vector directions, magnitudes and duration. Only then can I design a program of what the person can do without bringing on those pain triggers.

I certainly hope I didn’t give the impression that I’m against unilateral loading or similar work. You may have seen the paper we published last year, which is about the first analysis on bilateral and unilateral load carriage—the farmer’s walk versus the suitcase carry. We measured the World’s Strongest Man competitors with the Super Yoke, where they got under a yoke and walked with the weights on each side.

I learned such a valuable lesson. When an athlete picks up a heavy load, the force comes up the leg, but in order to allow leg swing, the force has to shear across the pelvis and up the spine.

We measured the winning strongman. Believe it or not, he had 500 Newton Meters of strength of hip abduction. I could lie on his leg on the side and he would just pop me up into the air. His strength was mind-blowing. Then we measured him with the Super Yoke. Remember, he had 500 Newton Meters of strength to hold his hip there and hold his pelvis up through hip abduction to allow a leg swing. When we measured World Class level, we showed that he needed 750 Newton Meters. He did something that was impossible—he did something he did not have the strength to do.

Where did the strength come from?

It came from the quadratus lumborum on the other side. The obliques assisted in lifting and keeping the pelvic platform level to allow a leg swing. That’s the type of information we learn when we work with the world’s best.

Now let’s go to the world’s worst. Let’s consider a child who has a paralyzed QL. What’s the gait pattern? Would you see the paralyzed QL on this side? The hips can’t keep up. That’s just a little demonstration of the lessons you learn.

For a football player, the ability to do the job is not limited by pull or press strength—it’s limited by being able to hold the pelvic platform up on one leg, plant, externally rotate and go. The best way to enhance that is a suitcase carry. How many people have you seen do that in the weight room? The suitcase carry is the number one way to do it. It’s a unilateral exercise. Don’t do too much. Do perfect quality. Make it count. Get rid of the music. Work like hell and go have a beer." - Dr Stuart McGill

I am sure you would agree that is some very compelling evidence. I have learned a great deal from Dr Stuart McGill over the years and this is one of the things many years ago that stuck in my mind and really began to change the way I approached program design. You can read more about other things I learned in the article we published last year - Big Lessons About Back Pain I Learned From Dr McGill

And if after all that you still don't believe, go and test it in the gym yourself and see what happens. Many young males who tell me how much they can leg press or bench press disregard this information and cannot comprehend how a lighter load can make you stronger. It seems crazy to think a 60kg single leg deadlift is better than a 100kg traditional deadlift but as we just explained this is the reality.

I cannot tell you how many guys I have seen who can leg press over 400kg but barely move on a lunge or single leg squat with their own body-weight! See article - What Is Better The Leg Press Or The Squat?
They have an illusion of strength for the machine is doing most of the work for them.

Single Leg Exercises Relate More To Sports & How We Really Move

The next thing to consider is how similar to "real life" movement is bilateral versus unilateral exercises? In particular for sports.

Firstly let's look at bilateral exercises. How many sports can you think of where the athletes spend most of the time jumping and landing on two legs at the same time? Hardly any if at any all. Even running involves one leg on the ground at a time while the other leg swings through in the air. I cannot think of any sport other than rowing where two legs push at the same time constantly. Again this is not to say the bilateral exercises are not needed or a waste of time, this is just to make the point that if you only train with two feet and two arm exercises but compete in an entirely different fashion you may not be reaching your potential as an athlete.

Single leg strength is essential for the development of speed, balance and injury prevention for almost ALL the lower limb injuries seen in sports occur in a single leg stance or single leg landing. Of all the sporting injuries to gain a lot of attention in recent times is the dreaded ACL tear which is known as a season ending injury. The mechanism behind this injury is faulty single leg change of direction and single leg landing techniques. Strength from bilateral movement has little to no influence in preventing these injuries. There is two articles you can read below with more detail on this specific injury.

• What To Do If You Tear Your ACL?
• 5 Critical Things You Need Before Returning To Sport Following ACL Injury

But it is not just the knee that can be injured from poor single leg strength.

The feet/ankle and also the hip/lower back can be exposed to serious problems. Piriformis syndrome for example is a very common injury we come across that will have all types of pain and dysfunction with single leg stance movements. Correcting this dysfunction for good can ONLY be achieved with single leg movements. (see article - How To Get Rid OF The Pain In The Butt)

Single leg strength is specific and cannot be developed through double leg exercises as the role of the pelvic stabilizers and glutes are significantly different. The gluteus medius in particular is vital to the single leg stance and it is important to understand how this muscle works in order to correct it.

There is three distinct heads of the gluteus medius muscle that perform a unique role as the body moves:

1. The posterior fibers - These fibers contract at early stance phase to lock the ball into the hip socket. The posterior fibres therefore essentially perform a stabilising or compressing function for the hip joint.
2. The middle/anterior fibers - These run in a vertical direction, help to initiate hip abduction, this is where the clam comes in which is then completed by a hip flexor muscle known as the TFL. The glutes work in tandem with TFL in stabilising the pelvis on the femur, to prevent the other side dropping down.
3. The anterior fibers - These allow the femur to internally rotate in relation to the hip joint at mid-to-end stance phase. This is essential for pelvic rotation, so that the opposite side leg can swing forward during gait. The anterior fibres perform this role with TFL.

The exercise that performs these three key functions is single leg squats and single leg deadlifts. These exercise demand your glutes to stabilize the hip, act as a hip rotator, and lock the head of the femur into the socket, creating a very tight and stable hip joint during gait. This prevents the ball and socket joint from rattling around during walking and running. I also suggest to read our article How To Use The Single Leg Squat As An Assessment Tool to help guide you on finding your weaknesses.

You can read more about glute strengthening in the article How To Strengthen Your Glutes and below we have provided a FREE checklist you can download to help you.

The problems we see with single leg exercises such as foot stability and hip function are hidden with two leg exercises like the squat and deadlift. Don't get me wrong the squat and deadlift are fantastic and essential for building the base and movement skill needed to execute many movements. They just will not correct the underlying problem that affects how you move.

Anyone with pain will know exactly how difficult it is to perform a single leg movement. The bilateral one may not have any pain but it will be most likely compensating by adding a lateral shift away from the pain. The danger of continuing to use a bilateral exercise is you may enhance the compensation and create more pain or worse still new injuries! This is why we prefer to work in rehab with single leg or single are movements as early as we can. We may use the bilateral versions to begin with to help encourage the timing but addressing the stability and weakness will only be addressed in unilateral movement.

Single Arm Exercises And The Slings

We have established the value of single leg exercises but what about the upper body? Once again I have found many people are stuck in the mindset of the traditional training of heavy bilateral exercises like the bench press and think this is on the only way to increase muscle size and strength. However as we discussed with the single leg movement in sports where rarely do players jump and land off two feet we see similar things with the upper body. In many sports you will see mainly single arm movements used. Eg Throwing in baseball and cricket, serving in tennis, or lay-ups, jump-shooting, and dribbling in basketball.

The timing is of more importance to the body for efficient movement and development of power and it is via effective use of the slings that we enhance this timing and motor control.

The body really is a complex system made up of many chains known as myofacial slings. These slings, when they are working well, help us move efficiently, produce more force, and create more speed. There is 4 slings and they all share a common theme, unilateral movement!

Watch the video below to see these slings in action.

When there is a weak link in the chain most people don’t address the chains, but target specific muscles by using isolated exercises. Not only is this ineffective it can actually further enhance the existing faulty timing and muscle imbalance! Isolated exercises can be useful but there must be a method of gradually progressing to the integrated stage to make any long-lasting change.

My Favourite Unilateral Exercises

There is so many exercises and it is impossible to list them all. But here is a list of some of my favourite unilateral exercises in no particular order.

Single Leg Strength Exercises

As discussed earlier these are great for improving foot, knee, and hip stability. Glute strength and core control is massive with these exercises and are critical for anyone with injuries in the lower limbs.

Single Leg Hopping Drills

A progression from the strength and stability exercises that have a higher degree of speed and braking forces demanded of them.

Single Arm Strength Pushing Exercises

Single Arm Pulling Exercises

The pulling movement is unique in that you can use this to also develop the posterior sling and glute strength. One of the easiest exercises to complete but also one of the most effective.

Don't Forget About Bilateral Exercises

Now all this information makes it seem like you can drop all of the bilateral movements. But this is not the case for many of these are vital in setting the foundation for the more complex movements. Squats, deadlifts, push-ups, chin-ups and rows are all excellent exercises to develop strength and skills needed for the more complex movements to come. In some situations these may be the much better choice.

For example a push-up is a very effective way to learn scapula control and increase serratus anterior strength more so than a single arm dumbbell.

I will often spend  more time with bilateral leg exercises in the beginning with new clients for these are much easier to learn and require little coordination or stability. However, once I have established these are at an acceptable standard I will begin to progress to the more challenging unilateral exercises like single deadlifts before progressing back to loaded bilateral deadlifts.

For detailed explanations and pictures of exercises make sure you get a copy of our FREE Functional Training report below. And for a ton of workouts featuring these exercises and more grab a copy of the Little Black Book of Training Secrets.

Summary

It is amazing the things you learn when you have been around long enough and open minded to new and better ways to train. Sometimes things that just don't seem logical like the fact you can lift more with one leg than two and your mind tells you that you are wrong, so it is great when a scientist like Dr McGill confirms your thinking. I hope this article gives you some relief that you can build great strength from exercises many still regard as "fluffy stuff" or not true strength training. If you are injured these exercises will always address the imbalance and asymmetry in your body that is causing your pain. Bilateral exercises will tend to find ways to compensate but a unilateral one will not allow you to. You are forced to find a way to improve your stability to move and it is for this reason we use these so much.

For more ideas and information on specific topics I may not have covered in detail be sure to check out our INDEX PAGE on the website that has over 300 of our best articles. These are all sorted into categories for quick reference so you can find what you are after more easily. You can also subscribe to our FREE fortnightly newsletter by clicking here.

If you do need specific help with your exercise program please feel free to reach out to me for help and we can set you up with your individualised program.

About The Author

Nick Jack is owner of No Regrets Personal Training and has over 15 years’ experience as a qualified Personal Trainer, Level 2 Rehabilitation trainer, CHEK practitioner, and Level 2 Sports conditioning Coach. Based in Melbourne Australia he specializes in providing solutions to injury and health problems for people of all ages using the latest methods of assessing movement and corrective exercise.

References:

• Movement - By Gray Cook
• Corrective Exercise Solutions - by Evan Osar
• Athletes Acceleration Speed Training & Game Like Speed - by Lee Taft
• Diagnosis & Treatment Of Movement Impairment Syndromes - By Shirley Sahrman
• Low Back Disorders - by Stuart McGill
• Knee Injuries In Athletes - by Sports Injury Bulletin
• The ACL Solution - by Robert G Marx
• Understanding & Preventing Non-Contact ACL Injuries - American Orthopaedic Society For Sports Medicine
• Anatomy Trains - by Thomas Meyers
• Motor Learning and Performance - By Richard A Schmidt and Timothy D Lee
• Assessment & Treatment Of Muscle Imbalance - By Vladimir Janda
• How To Eat, Move & Be Healthy by Paul Chek
• Scientific Core Conditioning Correspondence Course - By Paul Chek
• Advanced Program Design - By Paul Chek
• Twist Conditioning Sports Strength - By Peter Twist
• Twist Conditioning Sports Movement - By Peter Twist
• Twist Conditioning Sports Balance - By Peter Twist