alxra

Unless you use 10lbs max on the various machines, a workout on weights in the gym is going to lean more toward an anaerobic workout, and I gather you are trying to get a longer, aerobic workout in while your knee heels.

If you do swim you need to start out with some workouts designed to warm up your shoulders, and protect and loosen the muscles, ligaments/tendons around your rotator cuff(s). I would first consult the surgeon who performed your shoulder surgery. If he/she gives you the thumbs up on swimming, then go swim a lap or two ONLY, and let your shoulder rest a day to see how it reacts. Make sure you use a pull buoy (see pic below) so your legs will float and you won't kick. If you don't feel pain, and your shoulder recovers, then follow this for the next few workouts:

Go to the the pool, and make sure you stretch your upper body and core muscles for a significant amount of time before swimming. Use a pull buoy, and start with very slow exaggerated freestyle strokes. The way to get to a slow exaggerated stroke is by 1st swimming a couple of normal laps, and count your strokes for each lap. If it took you 20 strokes for one lap (once across the pool), then try to finish the next few laps using only 16 strokes per lap. Then try to complete the next few laps using only 14 strokes per lap, and so on. This will really warm up your shoulder joints and may give a good work out up to this point - depending on how good a swimmer your are. Once you reach your benchmark minimum strokes/lap, use that as a reference and swim 4X200 slow, easy and exaggerated. If your not tired, repeat the interval slow, easy and exaggerated. Again, it's really going to depend on how good a swimmer you are/were. After a few weeks of this workout, and if your shoulder is reacting normally, then you could move on to some longer distance swimming and normal interval training in the pool.

If you can't do freestyle because of your shoulder, then try breaststroke and follow the same procedure described above.