Imagine sitting in a rowboat with two people. The two people are a small child and an NFL athlete. They are sitting beside each other, and both are pulling on their own oar. They are in perfect synchronicity. Their form is identical, yet the boat keeps traveling in circles. After a month of paddling, both oarsmen have grown stronger, but the boat keeps making circles. Obviously the NFL athlete can generate more force than the child, and, unless the child grows in strength, comparable to the footballer, the boat will continue to circle.
What if, instead, we were discussing the strength differences in a person’s arms rather than two different sized rowers? Can you see the same outcome occurring? Most people have a dominant arm. It’s kind of like “Beauty and the Beast.” One hand is responsible for fine, beautiful motor skills (cursive writing, artwork, etc.) while the other hand is the brute that opens the jam jars.
Now consider grabbing a barbell or fixed handles of a circuit machine. What is the likelihood that both limbs will generate the same amount of force? Have you ever performed a bench press and noticed the bar tipping slightly toward the stronger side? The weaker side gets a little higher to shift the weight away from it. What about performing a pull-up? If you look closely, you will most likely find a person pulling toward one arm more than another or one shoulder creeping higher. Any time we move an object with both hands, or both legs, we unconsciously sacrifice a balance of strength for sheer force production.
Bench press, leg curl, leg extension, barbell curl, deadlift, kettlebell swing, pull up, push up, leg press, and the squat is all bilateral movements (both sides working at the same time). This does not mean they are bad exercises. There is no such thing as a bad exercise. It all depends upon the body performing the movement. If, like almost everyone in this country, you have subtle imbalances and distortions to your resting posture, and your gym routine is only comprised of bilateral exercises, expect to reinforce muscular imbalances, postural distortions, compensatory movements, and structural weakening. The likelihood of sustaining an injury is just a matter of time.
There should be a good reason for performing each exercise in your workout. You just need to ask why is it you are performing it. You may want to consider incorporating exercises which help to balance the body more. Perform single arm or leg exercises. Perhaps focus a little more attention on the weaker side. Try and move the arms in an alternating fashion or in opposing directions. Vary your movements often. These are simple suggestions which may provide long-term insurance against the side effects of bilateral movements.