You spend at least 3 times as long going up the hill as you do going down it, and a reasonably fit person will be putting out the equivalent heat of an 800w-100

You spend at least 3 times as long going up the hill as you do going down it, and a reasonably fit person will be putting out the equivalent heat of an 800w-1000w heater during that period. This makes wearing protective gear impossible. If you look at downhill mountain biking the gear worn is very different. That’s the reason!