Last month while on the trainer it suddenly hit me that I could be doing some simple weight training at the same time. I stopped lifting 2 years ago and while I like the trade off from more swimming and biking, my arms definitely are less than they used to be.
Found an old dumbbell in the garage and sure enough, it works just fine.
Every 15 minutes, I go through a cycle of curls, tri extension and over head extension, one arm at a time while still pedaling. While it is not a heavy dumbbell, and it is easy the first couple of sets, it gets a lot harder by the 10th set. It also helps break up the monotony.
If I am missing something and this is a bad thing let me know. If not try it.