Angelina i may have misunderstood. i never wore thighbands on days when i had sports lessons, only on days when i didn't. this may have been a bit of a double standard on my father's part, but we didn't know a better solution. i never did sports with thighbands.
In my family we had a solution for that. The envelope system.
My father gave me a closed and signed envelope to school in which there was the key. 15 minutes before sports class he sent me something I have to write on the closed envelope and send him a picture. Then I was allowed to open the envelope and get the keys to remove the tightbands. Then I placed the keys in another envelope and signed this envelope with what he has sent me and my name and send him a picture. I have done this at the school toilet during the break before sports class.
After sports class I had to bring the tightbands back in place and send him a picture of the closed locks with the envelope on the picture.
It sounds more complicated then it was. It worked fine as long as I had sport classes.