Interesting observations on curls.
I tore my left bicep (somehow. I can't remember the exact circumstance, just a big bloody bruise), and stopped doing any type of curls for about 6 weeks. Ended up with pain through both elbows if I tried to fully straighten them that went away shortly after curling again.
My right arm- tore the pects, anterior delts, and bicep after developing benchpressitis from workin out like bro. Exacerbated the anterior rotation of the humerus by blowin up the biceps- cause chiks dig big guns.
So now I just treat them as an accessory type thing and I'm no longer interested in having biceps that look like fake baseball titties.
Never cared much for leg extensions. I've always been quad dominant anyways, so there was never much need.