You may want to try adding drag, using hand paddles or flippers for a more intense workout. Also, you will want to do mainly sprint sets as short (as 25 yards) for the majority of your workout. Obviously, your yardage and pool time will decrease, but your muscles should increase due to the added load on the muscles. Just be careful with your joints. If you want to bulk up, the best way is through weights. Also, it is extremely important that you eat enough protein if you are trying to add muscle.
Hook'em
Blue
I agree with Blue; weights and sprints. Use all four strokes; Fly is great for shoulder, back and abd strength. *** develops good arm strength. While backstroke is only good for rest during 400 IM :p .
Use paddles with caution. A good abd workout is to do underwater butterfly kick with arms out in front of you, or do the butterfly kick on your back.
