When any 'averages' are used the average may not be a good indicator of health. Should we all be more athletic and how would that change the average? Go back to the 1950's when most people walked or cycled to work and many more than today had manual jobs, and the population average was a lot fitter/healthier. I know my Father was a lot stronger than I am.
An amusing story (but with worrying consequences).... 26 years ago when our Daughter was a babe, one of the mothers in the 'group' said "my Daughter is doing really well she's in the 95th percentile so was close to getting to 100!" She was concerned because our Daughter was just under 50th percentile, poor child! Her Daughter was pretty huge.
Our Daughter works in NHS mental health, and saw a huge baby recently. It became apparent the healthcare professionals do not explain to mothers that they aren't in a test or competition where 100% is the goal like an exam at school, but 50% or thereabout is 'ideal'. The hundredth percentile is made up of the heaviest 1% of the 'population. The mothers didn't study statistics at school, and IMHO medics often don't explain many conditions or symptoms in language the 'average' (here we go again) public understand.
If this 100% carries on and skews the average then each generation will get more and more obese.