For an athlete like Watt, the most important type of exercises (not practical to list them all) are those that maintain flexibility and increase the strength of his large back muscles and the entire realm of abdominal core muscles. At this stage, Watt will be performing the same exercises that he has been all along, but now with incremental increases the load placed on of these muscles. Otisbean may be able to comment on this further.
As far as the chronology summary of Watt's back injury. He was dealing with a significant back issue since at least last October (most likely on a lesser scale very much longer than that). The typical epidural regimen was undoubtedly instituted along with intense muscular rehab. In the course of his rehab, he re-injured his back.........attempt at further rehab was unsuccessful leading to his microdiscectomy on July 20.
The first thing to do is re establish motor control of the musculature around the spine. I had a minor knee surgery several years ago and it took me a couple weeks to be able to activate my quads properly. With regards to the spine, there is an intrinsic stabilization system consisting of deeper core muscles that needs to be developed, the diaphragm, pelvic floor muscles, the transverse abdominus, and the multifidus. These muscle provide segemental stability to the spine and help create inter abdominal pressure to provide support for the spine. If these muscles don't work properly other muscles have to help and you end up with compensation patterns which will lead to injury.
Once the muscles activate properly, you have to begin to re build their endurance. Many low back injuries occur because fatigue. If you think of the spine as a fishing pole with a bowling ball (your head) attached to it, there's no way the fishing pole can hold the bowling ball upright. However, if you take a large number of support cables (your core muscles) and run them up and down the fishing pole, you can stabilize the bowling ball with no problem. If you cut a support cable, it fails to properly support the fishing pole and it can buckle. As your core musculature fatigues, it can fail to properly support the spine and the spine can buckle. Rebuilding the endurance of the supporting muscles is really important. You would begin with isometric exercises such as planks, side bridges, bird dogs and pall of presses. Once you have a high level of endurance in stationary exercises, you can begin to work on spinal stabilization in a dynamic environment with loaded carries and unbalanced lifting (think of a standing single arm chest press utilizing a cable weight system)- again focusing on endurance over load.
After muscular endurance is re established, you can begin to rebuild strength. The exercises would be similar you would simply increase the loading. Once strength has been re-established, you can start to re-introduce power work - med ball throws and catches where the core muscles have to rapidly turn on to provide instantaneous support.
It would also be very important to make sure he has proper range of motion in his lower extremities so that he has proper movement patterns. When athletes can't move properly through the ankles and hips, they tend to compensate by flexing/bending their spine - which causes major problems
The thing I worry about, has enough time passed since his surgery to allow this process to happen? For JJs sake and for all us fans sake, I hope so. I want nothing more than to see him back to his old self again