@Francesco I am sorry I am just getting to your question. Short answer yes, but it's complicated. I will try to unravel it here so that it becomes a little clearer. Strength is a skill or an attribute, depending on how you look at it. It is synthesized from:
- Quality and, up to a certain point, size of the muscle fibers
- The central nervous system (CNS)
- The cardiovascuar system
- The activation of specific kinetic chains in the body
Boxers and martial artists habitually use shadow boxing as part of their training to help develop upper body power for powerful combat moves. So yes, it will help build up the strength and speed of shoulders, biceps and upper back and, depending on how you move your body, lower back...