Recently, a lot of well-respected strength coaches started declaring that single leg (unilateral) lower body exercises are superior to double leg (bilateral) lower body exercises.
In other words, the claim is that leg exercises involving one leg at a time (i.e. split squats) are superior to leg exercises that require you to train both legs simultaneously (i.e. barbell squats).
Is this assertion true? Well, before we start to blindly “drink the Kool-Aid”, let’s take a closer look.
We will start by examining the “big three” reasons why the single leg proponents wouldn’t dare step into a squat rack (the forth reason, of course, is the fear of embarrassment from unveiling their shameful lack of strength!).
Then I will follow each of their claims with my personal opinion, which is based on 20 years of “in-the-trenches” training and coaching:
Claimed Benefit #1- Unilateral leg training makes you more athletic. When you are playing your sport, you are rarely on both feet at the same time. Instead, you are more commonly on one foot at a time. Therefore, it is more sports specific to train on one leg.
The Truth- The only activity that is “sports specific” is playing your specific sport. Period! I can assure you that no amount of lunges will turn the waterboy into the team captain. In the weight room, your only goals are to get stronger, more powerful, structurally balanced, and in some cases, bigger.
Claimed Benefit #2- Unilateral leg training is safer than bilateral training.
The Truth- I agree that unilateral leg training can be safer in some ways. Typically, single leg exercises cause less spinal compression.
This is because less loading is utilized with unilateral movements; thus, less compression on the spine is created when performing these exercises.
Also, when your legs are split, a more upright torso can be maintained, therefore decreasing stress in the lower back.
There is a flipside to this “safety” issue, however. Although the spine may be exposed to a reduced stress, the knees and hip flexors can suffer far more.
I’ve witnessed torn hip flexors from doing lunge/split squat type movements as well as various knee injuries from front lunges, pistols, and many other unilateral movements.
A good rule of thumb is this: if a particular exercise decreases stress in an area of the body that is involved in that movement pattern, then another joint involved may receive an even greater amount of stress.
Claimed Benefit #3- Unilateral leg training balances any strength disparities between the left and right leg.
The Truth- If one leg is stronger than the other, it makes perfect sense to train one leg at a time.
In theory, by doing this, you will force the weaker leg to do equal work with the stronger leg, thus balancing out the strength discrepancy. Unfortunately, this “weak side rule” rarely balances anything.
In most cases, strength imbalances are caused by genetic factors or are nerve flow related. If genetics are causing a disproportion in your strength levels, there is nothing you can do except be aware of it and don’t push much beyond the weaker side’s capacity.
If your strength issue is caused by nerve impingement or decreased nerve flow, go to a healthcare professional and have the problem addressed.
I have seen good soft tissue practitioners work wonders at freeing up nerve flow, allowing strength to return to the weaker side.
Well, those are the big reasons why the single leg movement is gaining considerable momentum in the industry lately. As you can see from my rebuttals, I disagree with the pundits once again!
However, this doesn’t mean that I don’t prescribe single leg exercises for my clients. It just means I don’t find them to be superior to bilateral movements. Here is how single leg exercises fit into my routines:
For assistance work- After knocking off a big lift (i.e. squats, deads, etc), I find single leg exercises to be great for supplementary work. Just be sure to emphasize a big lift first, especially if your goals are size and strength.
2) For individuals who are more concerned with fitness then strength- Some people don’t care about getting big and strong; they just want to be in great shape.
These people simply don’t need to take the time to dedicate themselves to learning how to do big lifts properly and safely. In these cases, unilateral movements (which are generally easier to perform) will provide an adequate training stimulus for these trainees to accomplish their goals.
3) For inflexible individuals- If you are too tight to pick an implement off the ground or lack the mobility to squat down to at least a parallel position without rounding your spine, you should (for your own safety) be sentenced to a life of single leg movements until you develop the necessary flexibility.
Even if you fall into my previous “fitness enthusiast” category, it would still be well worth your time and effort to develop an optimal level of flexibility. Get to it!
4) For those with pre-existing back injuries- For individuals with disk issues (i.e. herniations, bulges, degenerations, etc.), risk-to-reward should be considered before including any movements into their training routine. Since unilateral leg exercises have the potential to stress the lumbar spine less than bilateral leg movements do, they get the edge for individuals with back injuries.
I hope this clears up the all of the confusion on this topic: single leg exercises have their place, but in most cases, they should not be the nuts and bolts of your strength training routine.
Dedicated to your success,