When they did my mastectomy, they took out the lymph nodes on both sides. I was warned not to lift more than 5 lbs. ever, for the rest of my life. I got the surgery just prior to becoming a grandmother, and wanted it out of the way, so I could hold my grandchild. My doctor was very well aware of the situation.
I began doing exercises to build the muscles. In fact, I had to return to his office when I began "cording". I thought he was going to enroll me in physical therapy, and they would break the cords, but he was against it. He told me to slow down some with my exercising, and do more isometrics. I did, and it paid off big time. I can lift a 50 lb. feed bag for a short period, which amazes my doctor.
I thought I was doing good, but hit a snag the first time I tried to use my pistol. I could NOT pull the slide, or hold it in position for long. That uses other muscles than just lifting weight. It took me about 6 weeks, until I could hold the weight steady, and work the slide well. I worked with an empty pistol, holding it in position, then pulling the slide. Next, came building the muscles to hold, and pump my shotgun. My rifle presented the biggest challenge, but in time, I got the muscles built up for that too.
My doctor still says I should do a specialized video, on how to rebuild the muscle groups in the arms, after the type of surgery I had. He swears I did a better job on my own, than going to physical therapy have done for me, and no one has really come up with a decent method of retraining, and building up the remaining muscles to to the workload, the way I did.