When we perform an exercise with one arm or leg instead of using both it is call “unilateral” training. Training with one arm/leg and training with in them in tandem both have advantages.
The standing bicep curl will be my example for this article. I have some choices. I can train my biceps unilaterally with a dumbbell in each hand and curl them one at a time or curl both at the same time. When I train with both arms together I also have the option to use bars.
If I decide to curl them one at a time and alternate each arm I benefit by being able to use a heavier weight. If one bicep is flexing all available oxygen and blood can be sent to that area to perform the curl instead of both biceps sharing, thus allowing more weight to be moved per arm. Also, if I alternated curls between my two arms one bicep gets to rest while the other works. Another benefit of unilateral training is the added core involvement. When weight on only one side of the body is being moved the core is engaged to counter balance.
Sounds pretty good right? Well there are benefits of using both arms/legs to perform exercises. If building strength or muscle size is your goal you still want to include lifts with both arms/legs. This is because, for obvious reasons, the body is moving more total weight at once. In the end the body will adapt when the most weight is being moved. Your workouts will also be quicker when both limbs are exercising at once.
The verdict: Body parts should be trained with both styles to build a strong body.