Wow, you folks are cruel ! LOL !! I can only speak to my experience back in 1976.
I went to Lackland after being on the swim team in High School the last two years. I weighed 169 lbs at 6' tall. After the food and PT I weighed 195 and it was all muscle.
On Black Flag days we did the whole PT regiment under shade of what were, at that time, the newer training squadron buildings.
For the over weight and "un-motivated" there were Motivational Flights. These poor dudes would run in place while assembled and run every place they went on base. Needless to say a portion washed out but several persevered.
Interesting now is that none of the branches have any bragging rights these days as the entry requirement standards have been so lowered and diluted that post basic training wash outs are now the rule rather than the exception.
Spent 12 years of my career working on these. Three years at RAF Woodbridge U.K. Nine years at Grissom AFB, IN.