Keep up the good work bro,

If you've injured your knee and it's playing up I suggest using a exercise bike, running on the treadmill can cause stress on the joints and if you've damaged it in the past it would only bring it back with vengeance.

If you have time try this out; when you wake up in the morning, before you have any thing to eat go outside and just walk for an hour, get yourself a audible book and just take a moderate paced walk. It really does work wonders.