Why is Pitching Arm Weaker than Non-Pitching Arm

The fatigue comes from using muscles in ways that he doesn't typically use them. That should lessen as he does the exercises more.

I can't explain the strength difference unless something else is going on in the arm. Do the lifts get painful or does he just run out of strength?

My son is a RHP just coming off of a couple months of physical therapy due to tendonitis. Working with him in the gym I have not noticed any difference in strength from one side to the other.

When you talk about the lifts with 20 lbs - are you talking about just normal curls?

He just runs out of strength, no associated pain. Yes, normal curls. Thanks

I don't think the weight itself would be an issue for someone of his size, so it's probably just an unusual motion that his body will get used to.

At the beginning of his rehab, my son was doing one set of 20 lb curls, then quickly moved up to 2 sets. Then the weight was increased 5 lbs at a time to the 35lbs he is currently doing.  His therapist told him that there wouldn't really be much benefit for him to go higher than that.

If you haven't done so, you should look into one of the specific strength/conditioning  programs designed for pitchers.  There are some exercises that pitchers need to do that you don't usually see in a strength program.  There are a couple of programs that are advertisers here.

Thanks Rob T. I will look into those programs. I agree, if the strength differential from pitching arm to non-pitching arm were 1 to 2, I wouldn't think that is significant enough to be overly concerned. However, a differential of 1 to 4 is perplexing.

It is a little perplexing.  Hopefully something that resolves itself.

One thing to keep in mind that may be a factor... Just because you can do more reps with one arm does not necessarily mean the other arm is weaker - it just doesn't have the same endurance.  I would be willing to bet that on a single curl there wouldn't be much difference in the max weight that either arm could do. However when you introduce repetitions you add endurance to the equation.  For whatever reason, his left arm has much better endurance in sustained activity. However I would be willing to bet if you were to throw a baseball (or do some sort of "explosive" activity) with both arms - the right arm would last longer.

Sort of like training for sprinting vs training for a marathon.  Both activities use primarily the same muscles, but use them differently. 

It is odd that your dominant arm would be that far behind in that type of exercise. 

OK, this is a longshot but...  I have had a few instances where weakness in one arm was the result of spinal misalignment/ slight nerve impingement.  A good chiropractic visit or two took care of it.

I wouldn't worry about it, your son isn't an athlete yet, see how he's doing after a 12-16 week SAQ training program.  If it's a good program he should be fairly well balanced.  Since he's a pitcher he should start a pitching prehab routine (like a throwers 10 program) to help prevent throwing problems from starting.