Why 又 is used there instead of 再? In this dialogue:


  A: 现在恢复得怎么样了？
  B: 没问题了，又可以爬山了。


Why is 又 used there and not 再?  

As far as I know (I might be wrong), both 再 and 又 are used for describing recurring actions, but 又 refers to actions that took place in the past and 再 refers to future actions. So in the example, 可以爬山 (I can climb mountains) seems a future event (needs to go to a mountain first).
In my opinion, 


再 foresees the future, as  in 再见.
又 emphasis 'once more', as in "又可以爬山了"