As a matter of fact, yeah, we worked that a lot. I never used it in competition, I never used any shady technique in any competition, ever, honest. But I've sure cracked a few people with that forearm strike in other aspects of my life. Works pretty darn good.
Joe was notorious for throwing that "ridge arm" as he frequently called it. I try to avoid the PC arguments of what's proper and what's not, but please keep in mind that Martial competitions were completely different than what they would later become and certainly what they are today.
In the following clip you can get a pretty good look at one of them in slo mo starting at the 3:40 mark, and again, in much clearer detail starting at the 6:10 mark.
I remember that particular competition very well, it was the first time any kind of Martial fighting was on prime time, network TV. It was my birthday and that's a pretty nice present for a young Karate man. It was rerun again, again on prime time, the week after Christmas. We were driving down to Fort Lauderdale, stopped and got a motel room in Maryland, watched it again, checked out and continued our trip.
Joe used to teach that technique in self defense class. One of the things he used to do with it was - after the hit with the inside forearm, he would immediately cup the back of your neck with his palm and yank you forward, down or to the side, into a knee, a sweep, an elbow, an uppercut or various other things. I still use all of them to this day. Especially that "ridge hand". Oh, I smiled so wide when I typed that.