well, used to jog a lot for my cardio but in attempts to get better results, i'm varying up my cario with stair-climbing and bike-riding. however, since it's been literally years since i've done either, my legs burn like hell when doing them even at 140bpm.
now, supposedly when you get that bad burn like that you're pushing past your anaerobic threshold, yet my hr averages about 135-142bpm while i'm doing it, which would seem well within a reasonable range for aerobic cardio. during jogging, i can bring my cardio up to 150-160 easy and my legs don't really burn much at all. so, just wondering if since i'm getting that bad burn i might be pushing into the anaerobic state and burning muscle protein or if i'll still be burning fat despite the severe burn and my legs will simply adjust?