From what I understand he has never stopped exercising all together, minus when he had heart surgery.
As of 1yr ago his routine was lifting 3days wk moderate weight very high reps...no more heavy lifting because of the heart problems, doctors orders apparently. Also some sort of cardio 5-6 days wk either by way of stationary bike for 45min or tennis with Franco.
Now it's not surprising that he got a bit out of shape since being governor, the job has a pretty crazy schedule, and it would be very difficult to stick with even this very light routine of his extremely consistently. Hopefully for his sake he has been able to manage his time a little better to ensure he gets his training in and that's why he is starting to look a little better.
By the way, that pic is freakin weird