here is more on exercise-level and risk of AMS ..AND.. not just mild AMS but also its complications, even at a modest altitude.
"In 1943 British physiologist and physician Griffith Pugh evaluated military ski trainees at ‘The Cedars’ Mountain Warfare Training Centre at a moderate altitude of 6,890ft (2,100 m) in Lebanon. The tallest peak climbed was Cornet es Saouda 10,095 ft (3,077m). Pugh found that after only a few days of hard ski-mountaineering two men had dilated hearts on physical examination, the total rising to 10 of 33 after two weeks."
The dilated hearts refers to the sequence of small oxygen pressure decrease, pulmonary hypertension, right ventricle overload, and high altitude pulmonary edema (HAPE)- the most common complication of AMS. Some of his recruits (and all populations) were HAPE- prone. In 1943, the understanding of altitude illness was limited, and Pugh was way ahead of the curve.
