Most of us figure since we've paid for our time at the gym, we might as well try and work out every single muscle we can during our sessions. Maybe you should re-think that strategy; Unilateral exercise, which is working one limb at a time, offers some surprising muscle-building benefits. For starters:
It corrects strength imbalances
If you have a strength deficit—that is, if one side of your body is weaker than the other—you’ll discover it here, and you can work to correct it by making your weaker side work harder.
It improves athletic performance
Sports almost never require you to simultaneously work both arms or both feet equally hard, so unilateral exercise more directly applies to athletic training.
It works more intensely
A limb working unilaterally often has more than half the strength of both limbs working together. That’s because when you work a pair of limbs together, a protective mechanism called the bilateral deficit shuts down some of your motor units (combinations of nerve cells and muscle fibers) to keep you from getting hurt during the heaviest lifts. When you work with one limb at a time, however, the deficit doesn’t kick in, so you can work the muscles in each limb more intensely.
So if you’ve maxed out the available weight on your leg curl when using both legs, try it with one leg at a time. (Start with your left leg if you’re right-handed, and vice versa.) Even if you haven’t maxed out, it’s a good idea to work unilateral exercises into your program from time to time.
It will give you positive results from negative contractions
A physiological phenomenon that’s somewhat better known than the bilateral deficit is the fact that your muscles are about 40 percent stronger when lowering a weight than when raising it. So, returning to the example of the leg curl, try lifting the weight with both legs but lowering it with one leg. That will give you a more potent muscle-building stimulus than would lowering with both legs.
It improves your balance
Unilateral exercise also changes the balance component of a movement. That’s why a one-legged squat or deadlift is much harder than you’d expect—you might not be able to do these with any weight other than your own body weight. So you improve your balance and coordination as well as your strength.