It is difficult to answer this question without photos and an examination. In my experience with armlift patients, they tend to benefit from exercise and weight training before and after surgery. Usually any loss in fat is improved by the gain in muscle mass. This typically results in a more toned and contoured arm even in women. I would encourage you to continue with your eercise regimen. Your arms should do well. Congratulations!
Congratulations on having undergone the arm lifting surgery; hopefully, you will be very pleased with the results of the procedure. Generally speaking, building muscle mass will help improve the appearance of the arms. However, I would not expect significant skin “retraction” for most patients. Whether the skin will “sag” will depend on how much weight loss occurs. Again, generally speaking, it is best to undergo arm lifting surgery ( and any other type of body contouring surgery) when patients have achieved a long-term stable weight. Doing so improves the safety of the operation, the outcome of the operation, and helps decrease chances that additional surgery will be necessary in the event of additional weight loss that occurs after the procedure. Best wishes.