11 min read

How to Approach Single-Limb Resistance Training

A lot of human movement happens on one leg or with one arm. Here's how to approach training one limb at a time.
How to Approach Single-Limb Resistance Training

AKA Unilateral Training

This is basically the opposite of bilateral training.

Bilateral = Two Limbs (at the same time).

Unilateral = One Limb (at the same time).

As of June 2020, I’m taking a swell group of people through phase 2 of my better scientific seven-minute workout protocol over on Daily Training Session (for free by the way).

And we’ve transitioned into one of the most logical progressions a person can ever use to make something more challenging.

Put more stress on one limb at a time.

Bilateral Training is ‘Biased’

When you do bilateral training, you’re generally at your most stable, so it’s a great starting point for most people. You have a solid base of support and the balance requirements are trivial. It’s easier to learn.

A bilateral push-up is the standard push-up for a reason. And few people will ever take the time to learn how to do a single-arm push-up because it’s considerably harder.

However standard an exercise may be, this does not inherently make it better. Bilateral exercises make it difficult (next to impossible) to determine if one side is considerably stronger or weaker than another.

Sometimes there are dead give-aways like weight shifting, or one limb is playing catch-up but you can’t address these limitations and stick to the bilateral training.

Furthermore, because powerlifting and Olympic lifting are sports in-and-of-themselves a lot of people will bias towards these big compound bilateral lifts for the sake of efficiency or popularity.

Unless you’re competing in one of those sports, there is minimal need to focus your attention on the Big-3 or the Clean & Jerk or Snatch.

A lot of human physical activity happens one limb a time.

Sprinting is done one leg at a time. Change of direction. Shotput, javelin, throwing a baseball, serving in tennis or squash are all single limb activities. Jumping in basketball is often done off one leg. Etc…etc…

You could argue the majority of human activity is initiated by a single limb so why do so many people train two at a time?

Well some of that comes down to time efficiency. It is more time efficient to do your 30 seconds of bench, than two 30 second sets of a single arm press.

However, with modern time efficiency techniques like paired set training this should be a non-factor really.

Another bit of it comes down to equipment. You can dump 1-2k into a power rack, a barbell, a set of plates and a bench for your own pretty awesome garage gym.

Although I’d say if you’re only training the big-3 with that equipment, you likely also suffer from a lack of imagination. And you can get almost as much done with heavy adjustable dumbbells and a bench (which is cheaper).

The more obvious reasons are familiarity and popularity. Especially amongst men. Monday is ‘International Bench Day’ and as a strength coach I can’t tell you how many times I’ve been asked the question, ‘whaddya bench?’

There are a few big bilateral movements that have become the test of your masculinity or gym prowess. But it’s macho B.S. posturing, that you don’t have to listen to or follow.

Major Benefits to Unilateral Training

Not ‘pure’ unilateral, but getting there…

You’ll never lift the absolute maximum weights that you can lift with two limbs, on one limb. If the absolute load on the bar is what matters most to you, then you’ll want most of your training to be bilateral.

That much should be obvious, but let’s do a little math.

A lot of trainees hit inflection points with movements like the squat or deadlift that yield more stress on the back (especially low-back) and less stress on the legs. It can become a problem.

Tell me if this happens to you. You spend most of the year working up to a heavy set of squats and the only thing you feel during the exercise is your back.

✋ That’s me.

And yes, I could plug away and trying to add 5, 10, 20 lbs to the bar each and every year, what would be the point? To keep training my low back?

I don’t plan on competing in Powerlifting, nor Olympic Lifting, I’m in my 30’s, I just want to look the part and be able to coach other people on resistance training.

I care more about my vertical jump height than my squat numbers and I’m not trying to prove my manliness.

“Ben was squatting (half-squatting really) 600 lbs in his prime. Based on his performance, was their really a need to try for more? Would that be worth the risk?”~ Charlie Francis (Ben Johnson’s Coach – Paraphrased)

The magic number on the back squat has historically been around the very low 300’s for me. Which isn’t a mind-boggling squat by any means but it’s decent for a 6’1″ (186 cm) male with fairly long limbs.

However, I can also work up a Rear-Foot Elevated Split-Squat  (AKA Bulgarian Split-Squat) up into the 200-250 lbs range, without feeling my back at all. If you assume the majority of the stress is on my front leg and we multiple by two, suddenly my back squat looks a lot more impressive.

200 x 2 = 400 lbs  |  250 x 2 = 500 lbs

I’m not sure I’d ever be capable of back squatting those numbers, no matter how hard I tried. Yet with a few phases of planned unilateral activity, I can get there comfortably on mostly one leg.

And the stress is felt predominantly on my legs, rather than my back.

And it’s not just free weight lifts either. I’ve noticed the same thing on the leg press (my back also hurts eventually with heavy bilateral loads). I strain more (not necessarily my back) on a lot of bilateral machine lifts, with no real way to know if that stress is being applied where I want it.

The Bilateral Deficit

It’s worth mentioning that this phenomenon has a specific name. It’s called the bilateral deficit.

In effect, there is a deficit between the unilateral load a person can tolerate  that when multiplied by two will often exceed their ability in a similar bilateral movement.

There is a bunch of research on this but the gist of it is that most people can end up stronger using one limb at a time. So long as you add the numbers up.

Most of the time I can work someone up to a fairly heavy squat (let’s say 300 lbs for 5 reps), halve that number (150 lbs) and make that same person attempt a lunge or rear foot elevated squat with the new weight. The person then executes that weight for 15-20 reps!

A big jump, it happens all the time, and the bilateral deficit is the phenomenon that explains it.

Enter Unilateral Training

Let’s say you’ve also maxed out your ability to squat heavy weights comfortably. It’s also likely your back will give out before your legs.

Rather than keep training into pain or severe discomfort, why not split the load in two and switch to a lunge variation?

Takes stress off the spine and puts more weight onto one leg at a time. It’s a win-win.

If the safety of training bench press on your own has become compromised or you don’t have the right equipment to ensure safety while doing it.

A single-arm press can go a long way towards creating pressing stress in a far safer environment. Two hands can offer assistance for half the typical weight.

Your mileage might vary, and maybe squats or deadlifts are the bee’s knees for your legs and hamstrings. I’m not saying, don’t squat, deadlift or bench, I do, most of my clients do.

I’m saying don’t be dogmatic in your approach. You don’t have to do it all the time if you don’t plan to compete.

Mix in periodic unilateral training because it works wonders for anyone who doesn’t care to compete in powerlifting.

It can address equipment limitations, stagnant progress, fix left/right imbalances and cure training boredom.

Unilateral training is an easy progression in almost any circumstance.

The point being, unilateral training has a lot of potential benefits and you should always strongly consider integrating it into your routine.

How to Do It

Now that I’ve sold you on the idea…

There is a natural tendency for people to always start their training sets with their dominant arm or leg. It’s often an unconscious action, that’s why that limb is the ‘dominant’ one.

You don’t have to think about writing with your right hand, you simply do.

You have to consciously override this tendency to make the best use of unilateral training.

Or you will overdevelop your dominant side at the expense of your non-dominant side.

Ideally, you start any unilateral training with your weaker (often non-dominant) limb.

Then you match the stronger side to the same number of repetitions with the same load.

The side you can do more repetitions with, at the same weight in this instance is your dominant side.

i.e. if you complete 18 reps on the split squat on your left side, stop at 18 reps on your right side. If you can’t do 18 reps on your right side, that means your left side is stronger and you should start with your right side next time.

Let’s take a look at how that plays out.

Example 1:

You do a lunge on the left side for 10 repetitions (to technical failure). You take your break and then do your lunge on the right side but you can only do 7 reps with the same weight.

It’s easy not to think too much about that. Afterall Darren is always telling you to take every set to technical failure.

The next set it’s easy to forget that your right side is actually weaker and you keep training like this.

If you keep doing this, the gap in strength from one side to the other will likely only grow. Soon you can do 15 reps on the left side and only 10 on the right.

This is less than ideal. We don’t have nearly enough research on it, but it’s reasonable to assume that the bigger that strength gap from side to side, the greater the potential for injury.

*I’ll make a quick note about the ‘strength gap’ and ‘appropriate imbalances’ before my summary.

Most people are right-handed so I do typically prescribe the left side first, but that doesn’t let you off the hook so easily. If you’re left-handed or feel stronger on your left side then switch the order accordingly.

Most of us are right-handed but that doesn’t mean we’ll naturally be better at every lift on the right side.

I’m right-handed, but this generally translates as my left leg is stronger in a unilateral position. My left arm is stronger pulling (believe it or not) and my right arm is stronger pushing/throwing.

These are some quirks of human-handedness and coordination.

Believe it or not, this does happen. More often than you’d think.

You will have to experiment to determine what side is actually weaker and then match your performance to that weaker side on your stronger side.

Example 2:

How it should go down…

You do a lunge on the right side for 10 reps (again to technical failure). You didn’t even think about it, you’re right-handed, so you just did it.

You rest and then do the lunge on your left side. You stop on your left side at 10 reps, despite not reaching technical failure. Surprise, the left leg is actually your stronger leg in this exercise!

And I want to zero in on that last part of the sentence. My right leg is not my weaker leg in all unilateral movements. It’s movement-specific. My right arm is stronger in certain positions pulling, even if most of the time I can do more reps with the same weight on my left.

The effect is not universal and likely will need to be adjusted on a case-by-case (or exercise-by-exercise) basis.

Yes, in this example you’re might not be training the dominant arm or leg to technical failure. You might then assume the training effect is going to suck. It won’t because you’re prioritizing your joint health and complete development.

And it won’t because you’re going to keep a more appropriate balance between your two sides.

An Appropriate ‘Strength Gap’ or Side-to-Side Imbalance

There is a human bias towards symmetry that I want to address before I wrap this up.

Most people favour symmetry, if only unconsciously. Research suggests that we find human beings more attractive when they have symmetrical face features (and muscular features).

The whole point of bodybuilding is to achieve as much symmetry as possible, but your body will never perfectly be symmetrical.

This is a fact, your heart is more to one side, your liver the other, your left lung is bigger, there is a hole in your diaphragm on that left side. Assymetry is everywhere in the body.

I’m not saying you can’t strive for it in your training, but it’s unreasonable to expect your limbs to be perfectly balanced in ability.

It’s extremely rare, no matter how you train single-limb movements, for you to achieve strength (or hypertrophy) symmetry or parity.

The overwhelming majority of the time, you’ll always have one limb stronger than the other in any given unilateral movement. And you should get used to this.

However, when is it acceptable and when is it out of control?

Typically I like to see a difference in side-to-side ability with the same weight of about 2 reps or less. I’d say this is about as symmetrical as most people will ever get in most lifts.

However, at least one study suggests that ~4 repetitions off absolute failure (~3 off technical failure) will yield a pretty similar result in muscle growth (AKA ‘hypertrophy’) and by extension likely strength.

This leads me to believe that a strength gap of 2-4 reps is likely not a big issue for most people. i.e. the injury potential is still relatively low.

The approach I advocate for should manage such a discrepancy rather well.

Anything consistently over 5 reps difference from side to side may warrant more aggressive unilateral training protocols. Such as training the weaker side with more volume.

For example, if you can do 15 lunges on the left side and only 10 on the right side, you may want to consider training the right side for 3 sets to every 2 sets you do on the left side. Perhaps even more aggressively, you could do a 2:1 ratio if the imbalance is really large.

Yes, the only way to know if your imbalance is that large is to train both sides to technical failure or even absolute failure. I know I said you shouldn’t train single-limb movements like that, but this isn’t training, it’s assessment. They are totally different things.

Assessing your pure ability once and a while might be worth it. I’d simply advise you to do this no more than every few weeks, likely only once a month, possibly every two or three months. And only keep doing that if an assessment comes back at 5 reps or greater.

Anything smaller than that, can be managed with the method I recommend.

Wrapping Up

The tl;dr is that unilateral or single-limb training is a very effective way to train and warrants doing at least periodically in any training program.

I always recommend that you start any single-limbed sets with the side that is weaker in the movement. Then match that number of repetitions with the stronger side.

This will prevent an even larger strength gap from side to side down the road.

The side that you can do the most repetitions with the same weight, is your stronger side (duh?). This isn’t always obvious based on your dominant handed-ness though.

That being said, if you suspect that your strength from side-to-side is wildly different (greater than or equal to about 5 reps difference) you should assess the difference.

Then consider doing more volume on the far weaker side in your training program, or at least, a phase of that training program.

The closer to 5 the imbalance is, consider doing a 4:3 or 3:2 ratio of work for your weaker:stronger side. If you’re significantly beyond that, you could consider being more aggressive at a 2:1 or even 3:1 training ratio (week:strong).

One to three months of consistent unilateral training in this fashion, should be sufficient in bringing that strength gap back into the 2-4 repetitions of difference.

At this point, you can go back to my recommended approach of training the weak-side first and matching the strong-side with the same number of sets (volume) for each side.

Enjoy yourselves out there! Don't forget to ask questions if you have them in the comments. 👇