Not knowing all of the answers to all of the questions that I would ask you face to face, I would most likely start by regressing your upper body resistance training program. And I would really only do this to an extreme if the imbalance was causing discomfort and/or dysfunction. The weaker arm would dictate the load and rep range for both sides in all exercises.
Yes, this would slow down progress for the strong side. But that is the point. It may be that this would never resolve completely. That is possible, even likely. But in the case of dysfunctional imbalance, not proceeding accordingly will result in continued dysfunction and eventual injury.
Unilateral training, including the weaker parts of the range of motion. Partial reps just through the weakest or most difficult part of the ROM will also help. This can be done after the full ROM exercise is completed.
I’ve found that one extra set on the weaker side is a good gradual way to get it to catch up. More than that can sometimes lead to other imbalances. Also using the weaker or non-dominant side for daily activities can help too.
The answer here can be as simple as exercising the limbs individually. For example I have more strength in my left leg than in my right due to injuries. Because of this I do one leg balance exercises, squats, lunges, ankle/foot work on each leg separately. I also do more repetitions on the weaker side. I would do the same for your arms, just know that they may never equally balance out.
Best to you,
Hi Marie Chris,
the one thing I would suggest to have checked is whether the difference may be the result of neurological problems. If the client has not athletic background that could account for a significant size difference between left and right, the it is a possibility that the muscles do not get as much neurological input.
Is there also a significant difference in strength?