Unilateral (one-sided) training is often the ugly step child of many workout routines, especially for the bigger muscles. When was the last time you did 1 arm dumbbell chest presses? Or a 1 leg weighted deadlift? (This is one of the best butt exercises ). I think many people don't utilize single sided exercises because it takes more time to complete. One could argue that one side is mostly resting when the other is working, so you can switch sides without a rest period and finish in the same time. Besides, I always feel like I am wasting my time resting in between sets when I could be working.
Now here is where it gets really interesting, research has shown there is something called a "bilateral deficit" present in many people. Meaning, the total amount of weight the right and left limbs can lift is less than the total sum for the individual limbs combined. Furthermore integrated muscle tests (using EMGs) suggest the prime movers in bilateral work are less active!
Bilateral Deficit Example
2 Arm Barbell Curl: 90lbs. (90lbs. total)
1 Arm Dumbbell Curl 50lbs. (100lbs. total)
Studies show some trained individuals are immune to the bilateral deficit and most Olympic weight lifters have a bilateral increase in strength (probably due to the specificity principle - all their lifts are bilateral) . There is, however, an argument to be made that unilateral training is better than bilateral work. Before you go down that muddy road, you need to ask yourself what does "better" mean and will unilateral workouts meet my specific goals. If you are like most people, you will benefit more from a hybrid training style integrating both modalities. In certain situations unilateral work may be needed to correct imbalances and strengthen weak links.
Sources1. Journal of Applied Physiology :Contralateral Effects
2. Journal Of Applied Physiology: Training With Unilateral Resistance
3. Appl Physiol Nutr Metab: Greater Bilateral Deficit
4. Clinical Neurophysiology
5. Maximal voluntary force of bilateral and unilateral leg extension
Doug Joachim - NYC www.JoachimsTraining.com