Originally Posted by LABARINTH

if it is your legs that are exhausted then you can always do different cardio for 40 minutes. Say 20 minutes of running and 20 minutes of swimming (but it would be hard to do back to back). If it is your whole body that is exhausted I'm sorry there really isn't much for you to do. You're going to just have to push yourself for the next 2 weeks until you get used to it. Your body will eventually adapt. For example, my wife is training for a half marathon and she has started going to wrestling with me. So on some days she runs for an hour or more straight and then has to shower, get dressed, and go wrestle a few hours later. It kicked her ass for a while but her body is used to it now.