“His theory has been discredited by current research. High performance (efforts above 75% of VO2 max) require carbs after no more than 30mins.”
I think that he found the same, hitting a wall as he called it, where the brain is being protected. But like you say, 75% is top-notch.
But I generally target my posts to the other 99.9998% of the country.
Most US adults over 55 cannot walk 2 miles.