Here is a very important article for you!
New research from Edith Cowan University (ECU) has revealed that training one arm can improve strength and decrease muscle loss in the other arm — without even moving it.
The findings could help to address the muscle wastage and loss of strength often experienced in an immobilized arm, such as after injury, by using eccentric exercise on the opposing arm.
In eccentric exercises, the contracting muscle is lengthening, such as when lowering a dumbbell in bicep curls, sitting on a chair slowly or walking downstairs. Previous research has shown these exercises are more effective at growing muscle than concentric exercises, in which muscle are shortening such as when lifting a dumbbell or walking up stairs.
Full article - https://scitechdaily.com/new-research-reveals-exercising-one-arm-has-twice-the-benefits/