Why is staying under 4% dangerous? I don't see an explanation in your reply rustychain. If you lower your bf superslow and your body won't get into starvation, where the risk then? And staying at 4% is eating statusquo kcalories, i don't see the harm there actually
At bf's that low you are risking organ damage.
You need at least 3% bf to cushion the organs. There is no way that if someone actually got to 4% (and I mean a true 4%, not internet 4%), they could hold it for more than several hours (think bodybuilders) without suffering a severe performance drop.
Cyclists at 4%..not gunna happen.
4% is doable, it just has to be done very slowly. There is always that weight at which a person has trouble dropping below. Most cyclists know about what that weight is. For example, I am 6'3" or 190.5 cm and have a hard time dropping below 175 lbs or 79 kg. I can do it, it is just harder to stay down there without constant vigilance of what goes in the ol' pie hole. At that point, 1000 calorie per day (2 lb per week) weight loss is no longer healthy and a 500 cal per day (1 lb per week) weight loss should be done. Of course when I wrestled in high school, I just starved myself but got down to a flotation measured 4%. I was able to do 2.5 hour brutal practices with only a single 1 min break for water. The lack of body fat certainly did not hurt my endurance or power.
Elite Nordic skiers are another group of endurance athletes with crazy low bf %. You don't see too many of those guys with a spare tire....