What makes you believe that a species that evolved from persistence hunters is “not designed” for hard aerobic exercise?
Isn't the idea behind persistence hunting that it's long-term, low effort aerobic exercise? That is, our ancestors were good at maintaining low-speed pursuit for long distances, but not so great at sprinting after prey.
Sprinting is anaerobic.
Someone more athletic or fitter than you wouldn’t mouth breath at the level of activity you mouth breath at. Their capacity is higher.
So? Hard aerobic exercise is hard. A fitter person will just be faster.
well I just meant it could be an area for improvement. It is possible to work your way to being more capable with just nasal breathing. Or sometimes you just have to be conscious you are mouth breathing and you'll be able to revert to nasal breathing. I didn't say you should never mouth breathe or somehow you are inferior to a super athlete.