I’m 92kg +/-, 187cm. Run 2x a week 6.5km like clockwork, plus extra fitness 2-3x a week. So heavy guy. I do about one 1/2 marathon a year and train up to 15km. Heart sits at 180-185 by the end. The 18km is definitely a hump where it’s not aerobic fitness but feels like need to push through a mental wall. I don’t think I have the physique for a full marathon without proper preparation but may try next year.