The engine is weak and the RPM changes frequently
Well that would make me tense up as well !!!
I've noticed a similar problem myself a few times on flights when I started my hour building e.g. if it was very bumpy. A few times on some of my more "memorable" flights, I've ended up holding the yolk in a death grip and then felt a dull, faint muscular pain a few hours after the flight.
I've not noticed it over the last few flights, probably because I'm becoming more relaxed in my flying.
I also agree that, after flying a 172, a 150/152 feels very light and 'skittish' and that might well make the problem worse.