The View. It's hard not to feel motivated when you're looking at a spectacular vista like this. And don't forget the view next to the pool. The perfect weather make bikinis and swim trunks much more abundant, not to mention more interesting.
The Weather. Year-round weather that ranges from mid-70s to low-90s makes working out more palatable. Plus, the weather brings out a desire for less clothing, which makes you want to make the effort to workout.
The Abundance of Things to Do
There are a lot of outdoor activities to keep you moving if working out in the gym isn't your thing. Whether you choose to go zip lining through the jungle canopy, golfing on one of the many golf courses, kayaking on a river, surfing in the ocean, or just taking your best friend--4-legged or otherwise--for a long walk on the beach, you won't run out of active things to do.
Don't worry if your body isn't bathing suit ready, Panama can help fix that. Almost every Westerner I know loses weight here. Maybe it's because the weather promotes a more active lifestyle. Maybe it's because the food is fresher and you're eating fewer preservatives. Maybe it's because you have less stress in your life. Whatever the reason, Panama is the best place to implement a realistic workout regimen that you'll actually enjoy. And if nothing else, you'll enjoy the view when you watch other people workout.