The bilateral deficit is a phenomenon where the total force production of a bilateral lift (i.e. a squat, deadlift) will not be greater than the sum of individual efforts of a single limb.
Example would be of a squat vs. a unilateral type squat variation
A) Bilateral Squat Max = 400 lbs
B) Rear Foot Elevated Split Squat = The sum of each leg would be greater than 400lbs.
Now, from what I have heard or read from various strength coaches is that yes, the research is a little cloudy because this is done with exercises such as leg extensions & elbow flexion/extensions. In some ways you must have some faith or assume that this would be true of other multi-joint/functional exercises. So does that mean we should abandon all double leg lifts? Absolutely not, but I think there is just an awesome carryover once athletes can do unilateral work instead of double leg work. How many times can you see someone lifting really heavy weight in gyms with proper form? The last thing you want to do is neglect form for external loading (and I would say that form on heavy bilateral lifts is usually when form is compromised). I would also ask you to think about what do we tend to utilize more of in our daily lives? Bilateral or unilateral movements. Easily unilateral. This concept has been around for a couple of years now with guys like Mike Boyle, Kevin Neeld, Eric Cressey & Mike Robertson etc. (a ton of others). This is not to say that bilateral training is stupid at all. Goals also play an important role. If your goal is to lift heavy weight in the deadlift or squat, well then you better believe you need to lift heavy in the squat or deadlift! The cool thing about single leg training is that it offers…
- More force production from MORE muscles – more bang from your buck (superior for athletics)
- Small base of support increases great proprioceptive input (think balance)
- Grip can lower the spinal loading: so switching things up like front squats or unilateral exercises that utilize a front squat grip can help decrease this. More long term health possibly?
While I do believe that unilateral movements mimic the movements associated with life and sport, I do love some bilateral lifts. Especially the Double KB Front Squat. Even so, who does not love pulling a heavy deadlift or driving up a heavy squat? I know that hitting a personal best is a great feeling. It may be wise for people and athletes to rethink that hitting a PR for the sake of a PR immediately indicates a great thing. Again, it depends on the goals of that person. Helping these populations move better and reducing the risk of injury should be the #1 goal followed by the others they may have. Does a lineman who squats 500 (legitimately) guarantee that his on field performance will be better than the other lineman who may squat 400lbs? Not necessarily. Move better.