Report Off days in Running Tips Posted November 7, 2017 On my days off from C25K, I have been power walking on the treadmill at a brisk pace for me about 4mph. As my c25k mileage is picking up I have found my knees getting really “tired” I don’t feel like I’ve injured them but rather just overuse soreness. Is it a bad idea to be power walking like this on the days off? Should I try a different exercise for the off days instead of walking which is using the same muscles as running??