I've read throught the interval posts and h.i.i.t posts and have gotten mysel a little confused. Age 60, resting heart is approx. 87. Mayo clinic site says my training heart zone is 112-136. Can get my heart up to 140-150 after one minute on treadmill (max walking plus elevation). I've been doing this for a few weeks and can really feel the benefits. During the slow interval I decrease the evlevation and speed. I feel ready to repeat the fast interval when my h.r. is 120, 125 or so. Adjusting the elevation and the speed during the "slower" interval affects the length of time to get down to 125 bpm. Is there an "optimal" or recommeded recovery time to shoot for? Zero elevation and very, very slow walk gets the HR down quickest. By manipulating the intensity (speed and elevation) during the recovery/slow interval I can get to 125 in 2, 3, 4, or 5 minutes, which is recommended?