I read in a book about a guy who subbosedly could grab a beam like a four by four from underneath, a thumb on side, and the fingers on the other. He would then do one-handed pull-ups.
I’ve been trying to do this for years. I have a good grip, and can do the pull-up part on a normal bar, but I’ve never been able to muster a grip that could grab a beam and hang on from underneath (I’m two hundred pounds.)
Is this even possible withing the constraints of human physiology? I’ beginning to think not.
I have watched climbers step up to the steel door jams/frames like one finds in commercial buildings, and with the middle finger of both hands hooked over the half inch or so lip on the wall above the door, do seemingly endless pull-ups. Some of us might have the ability, or have experienced a grip about the forearm that could not be removed, even one finger or the thumb at a time. One handed pull-ups are not a real issue, other than the sharing of some of the muscles that come into play with the grip. I have seen exercises done that specifically develop the strength of the opposing ability of the thumb.
Given the appropriate texture of wood and moistness of skin, coupled with a significant strength of grip, I believe it can be done.
When you can merge the thumb hole with the finger holes on a bowling ball, Grasshopper, you will have arrived. Diddling a loved one, from that day forth, will require attention to detail.
Perhaps some medium-sized to smaller people could devellop the strength and technique, but not by simple means like squeezing a tenis ball a few minutes each day. I imagine you’d either have to have a very strong grip to start with and/or spend a lot of time (obsesivly?)develloping it and keeping the rest of your body as light as possible. I say smaller people because of the scaling deal. As you get bigger, your strength does increase but not proportionaly to your mass. There are several other things that factor into a person’s strength, but in general a smaller person will be able to swing/lift their own body weight around easier than a bigger person; one reason you never see a 6’6" 230lb gymnast performing an iron cross.
I know a guy who I have climbed with in the past who can do the type of pull-ups that you described. He can also do a couple one finger, as well as many one armed pull-ups. He’s an excellent rock climber, stands about 5’9" and weighs 110#. So body habitus does play a role, I believe.