you don't have to do running hiit only. crosstraining is important to give the joint impacts a rest and work supportive muscles that get less work during a run. I do several different exercises for hiit but the one that is most brutal is cycling intervals at 100% 30 secs on and 30 off. of allthe hiit that one makes me burn like a SOB. now if it its got to be running based then do uphill sprints. it will build more strength than running flats.
Sent from my HTC T-Bolt.
Sent from my HTC T-Bolt.