The body mass index is a little clunky as a measure, but for those with knee and back problem, it should  be your 1st port of call.  Do you have  a healthy Body mass index?
click here and check
If not and you are  active, think on this. “Active” normally means 10,000 steps a day. If you are 10kg over weight  thats  10 x10,0000 that 100,000 kilos extra than your body  expected  . Weightlifters brace and prepare!
If you are inactive and slumping in your chair thats a lot of deadweight pressing on knackered  back and bum muscles.
“Dude, loose some weight!”
If you  have an ok weight, well thats ok. Go you. Thats not the problem!
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