It is well known that humans typically express limb dominance on one side of their body in comparison to the other. Asymmetries occur in multiple fashions such as movement competency, mobility, strength and power differentials. It is extremely unlikely that one will ever reach outright kinematic or morphological symmetry, however, striving for the smallest differential possible is paramount.
WHY IS SYMMETRY IMPORTANT?
Maintaining equal morphology between opposing limbs often contributes to higher levels of general strength and fitness.
That being said, individuals assume that aesthetic symmetry automatically equals health and wellness without considering other factors. What must also be considered is neurological efficiency, mobility and power. Motor control and power output are typically greater on one side of the body than the other in all humans. Often, we choose to perform tasks such as writing, cooking and brushing our teeth with the side that feels best.
In athletics, it is no different as we throw, kick and hit with the side we can coordinate more efficiently with. Problems arise when we attempt to perform these tasks with our opposing "weaker" side. What happens is we aim to produce a force or action that we are uncapable of doing on one side and we compensate in dangerous ways. Our joints may get put in to positions that are unsafe because we lack mobility on that side, our muscles may become strained because they are introduced to forces they are unfamiliar with or other parts of our body may attempt to absorb force they are not capable of because our movement pattern is so deficient.
A perfect example of this is a skier who makes multiple race type-turns down the slope. Perhaps they are capable of making a hard-left turn and pushing off their right ski in proper alignment every time, but what about when they turn right? Hypothetically speaking, if they lacked proper ankle mobility and had a 15 percent power differential in their left leg, then they could run into some problems. Sure, they may execute that turn, but over time it is likely that their movement is compromised, and their lower back, hips and knees are paying the price with every right turn they make. Injuries occur at this level all the time, both chronic and traumatic, often the former leading to the latter.
WHAT SHOULD YOU DO?
As previously mentioned, no matter what you do it is extremely unlikely that you will become perfectly symmetrical.
Your first step should always be to achieve symmetrical mobility within each opposing joint. This will ensure you at least have the proper muscle and joint ranges of motion to complete tasks on both sides of your body.
One caveat to this is extremely specialized athletes such as baseball pitchers. Most likely they will never reach the level of maximum abduction and external rotation in their non-throwing arm in comparison to their throwing arm, nor should they strive for this. That being said, mobility should always come first.
Get your movement patterns assessed via a professional using tests such as the Functional Movement Screen. This will let you know where some errors may be occurring in your gross movement patterns. Next, test the performance of each side of your body. Can you jump higher on one leg than the other? Can you carry equal amounts of weight in both hands? Simple tests such as these can help, but if you really want to get specific, then you can find a professional that can use equipment to test peak power output via force plates. You are at a high risk for injury if there is a 10 percent or greater discrepancy between one side and the other.
Finally, once you have examined all these factors, adjust your programming accordingly. This might mean incorporating heavy doses of unilateral work, dynamic balance training, plyometrics and much more.
Above all else, train safe and keep moving in the most effective manner possible.