Thank you for your question. I see that you have been taking the
Tysabri since March, and just noticed tremors a few weeks ago.
Hand tremors are a possible side effect of Tysabri - not one of the most common side effects, but frequent enough to make their list. Hand tremors can also be a symptom of MS. Either way, hand tremors are much more annoying (I personally spill a lot of food) than they are serious.
The best general advice I can give for exercise with MS is to exercise regularly, but be kind to yourself. Aim for 3-4 days a week, so you have time to recover, and don't try to do extra hard workouts because you want to get better faster. Give yourself time; try to think of what workout you would recommend if a good friend of yours had MS - swimming, bicycling, walking,
yoga (not the power stuff). Avoid workouts that use the words "boot camp". Regular exercise 3 times a week for 30 minutes, enough to get your heart beating faster and speed up your breathing, will help get you feeling better and stronger. And not feeling like Godzilla beat you up afterwards.
I hope I have answered your question. I wish you all the best, and if you have any further questions I will be happy to help.