I agree that the PE classes in junior high and high school were run very differently in the 1970s than that they would be today. For one thing, our PE teachers closely supervised the locker rooms while we were changing and showering and it had nothing to do with them being perverts. It had everything to do with running a tight ship and not allowing horseplay and requiring showers for everyone of us every class period, no exceptions. Our PE teachers were also the coaches for the school teams so for those of us who played sports they saw us in the locker rooms then too. They were strict about our PE uniforms, strict about our exercises, strict about conduct in the locker rooms and in class, and strict about showering. But I didn't think that they were unfair.
They were probably stricter in junior high and our freshman year in high school about PE uniforms, conduct, and showering than they were once we were sophomores and older in high school. By that time, we knew what their expectations and rules were and we had been made to be compliant for several years by the time we were sophomores that they didn't have to watch us every second. Which isn't to say that they weren't present or enforce the same rules. But they knew that we knew that we had to shower after every PE class so they didn't bother to watch us that closely. The way the locker rooms were arranged,, the PE teacher had an office with a big glass window that looked out into the locker room and had a direct view into the showers. After PE class, we went back into the locker room, stripped down, went into the showers, grabbed a towel and dried off, got dressed and headed off to our next class. In the early years of junior high and freshman year of high school, the PE teacher stood outside the showers to make sure that everyone went in, showered, and got a towel on the way back to get dressed. By sophomore year, the PE teacher went into his office that looked into the locker room and did paperwork or something and just kept an eye on us to watch for fights or horseplay that he thought was dangerous or behavior against the rules. Even with the PE teacher close by, we did things that we weren't supposed to do and caught hell if we got caught.
As for forced nudity, of course there was. For those of us on sports teams especially if the PE teacher who was also our coach wanted to tell us something in PE, he either came out of his office and spoke to us while we were undressing or totally undressed or he called our names and we went to his office immediately in whatever clothing or lack of clothing we were in when he called for us. We knew better than to keep a coach waiting while we showered or got dressed. My best example of that was when three of us boys were stripping down after PE and the coach called our names from his office in the locker room. We didn't hesitate. We immediately went to his office and were worried that we were in trouble or something. We weren't in trouble it turned out. But there were the three of us, one or two of us nude and at least one of us in a jockstrap only as that was what I was stripped down to when he called my name. He told us whatever he had to tell us and we hurried back into the locker room to go to the showers. Didn't think anything of it. It just wasn't a big deal as he saw us nude or nearly nude all the time.