Muscle Adaptations

Strength training in particular can result in not only the expected increase in muscle size (hypertrophy), but also rewires the brain-to-muscle connection. This enables the brain to fire muscles faster and the different components of the muscle fire in closer unison allowing you to increase force without even increasing your muscle size. This adaptation actually happens first before your muscles get bigger. (Hughes et al.)

Amazingly, even training just one side of the body (I.e. one side is injured and you can't move it) can result in a significant increase in strength in the non-trained limb! (Hughes et al.)