Out-side the box, personal experience: Any exercise will do.
- Raquet-ball: Only one hand gets much work, but gets your whole body moving and blood circulating. This game works well because it is intense. (wear eye protection, it really is necessary)
- Moving rocks: There are lots of large rocks on our property and I move them around to make walls or steps or what-not. This is more of an all day sort of thing.
- Hammer-drill: Concrete screws require a hole to be pre-drilled. This I find to be the most helpful. It is also satisfactory because it's not going anywhere, almost no matter how much weight you put on it. (assuming you have good concrete or blocks). The hammer-drill required to pre-drill the hole creates a vibration that tends to strengthen the body parts involved.
After any of these activities, my piano skill is improved.
The general concept is, over-use is really just that you are under-using the rest of your body. The human body has tremendous capacity, but is often never used due to the comforts we provide ourselves with (air-conditioning, TV, computer).