Unbalanced arms

my mom once joked to me that when i pitch in competitive varsity levels, by the time i graduate i’ll have a chuck norris right arm and a toothpick left arm. But as i’m going through my sophomore year i think she’s getting a bit more serious on this, and i was just wondering if this is an actual legitimate issue. (long-tossing with right arm, pitching bullpens, etc etc)

your throwing arm is going to develop some imbalances, though probably not in terms of size.

You’ll likely begin to develop GIRD (glenohumeral internal rotation deficit) which basically means the back of your shoulder capsule is going to get tight and you’ll need to start stretching it out using the sleeper stretch.
http://danblewett.com/2009/06/the-sleeper-stretch-essential-to-shoulder-health/

You’ll need to make sure your external rotators are strong (do tubing, etc)

Other arm care to improve scap function includes blackburns exercises

http://danblewett.com/2010/11/how-to-properly-perform-blackburn-exercises/

Your mom is intuitively right that overhead throwing creates imbalances over time, but you wont end up with a chuck norris arm from throwing a 5 oz baseball. The imbalances are more flexibility and mobility related.

You may already have imbalances just within the throwing arm. If you are not balanced front (biceps) to back (triceps) then you have an imbalance. It’s quite common for the tricep to not have as much mass and the bicep. Triceps are decelerators and if they’re out of balance, then you’ll either not accelerate as much as you capable of or you’ll risk injury.

So, balance left to right is important but so is front to back.