If you are able to run (my wife has bad ankles so she can't do what I do)
This is what I did, while wearing a 40 lb weight vest. You don't need the vest though.
I did a nice light jog for around 3-5 minutes. Followed by this;
Set the treadmill to a high speed (literally as fast as you can sprint) for 30 seconds, turn it down and walk for 10 seconds. Do this for 8 sets.
By doing this 30 sec sprint, 10 sec walk, 30 sec sprint 10 sec walk etc, you'll have ran for the equivalent of 60 minutes.
This also increases your endurance, strength, and speed.
Once you do a week of this, do 3 days of intervals with the hills. Alternate level, and hills and by the third week, you'll be so amazed at the results.
I was able to run 4-5 miles after, with no issues (with that 40 pound weight vest as well).