Strawburger wrote:I guess it may be unsafe if it's up at your max HR for an extended period but others can shed some light on that one.
It's unsafe if one has an underlying heart disease or other related condition that decompensates during the extreme exertion. Otherwise there's no particular harm done by hitting and sustaining at the HRmax, and in any case, the duration will be self-limited by one's physical and mental condition.
The simplest way to hit it is to sustainably climb a 10% hill and push hard. HRmax would only come when one starts to make that deep dying man's breath breathing pattern. Otherwise an intravenous injection of a suitable dose of adrenalin can also hit it while one lies in bed.