5 minutes of HIIT isn't going to be the end of your muscle building, Jake I would suggest throwing that in somewhere in the middle of your run, instead of at the end, though. Make it part of your run every couple of days and work it in, then you can still enjoy a cool down.

Change is good. Some moderate cardio a little longer one day, a short HIIT session on a different day - keeps the body from getting complacent.

Nat