My arms were weak after but I had a bilateral mastectomy and tissue expander inserted so the chest wall muscles were cut. A lumpectomy wouldn't be like that. I had pushing and pulling issues initially but it quickly improved with the exercise. You will most likely be a bit numb under your arm from sentinal node biopsy and sore but your arms certainly won't be useless. The exercises help strengthen quickly and ensure scarring doesn't restrict movement. If a full node clearance I'm sure the recovery would be slower but that most likely wouldn't be happening this surgery unless they believe you have positive nodes already and they would have told you this if they thought that. You will feel so much better obce the surgery is done and you know the rest of your treatment plan. X