I’ve written a handful (get it?) of posts on elements of hanging and swinging to support the Mouse Hands to Monkey Arms section of my book Move Your DNA. Recommended reading order is Hanging and Swinging 101, Hanging and Hand Skin, Upper Body Terrain, and Upper Body Texture. These posts have been updated November 2018 for easier use.
For most, the reason we exercise is to adapt/change the tissues of our body. There are system-wide or whole-body adaptations to movement and there are local ones. Doing bicep curls won't make your legs stronger and vice versa. We can have a few strong areas and not be strong all over; we can still have an Achilles' heel. A weak spot. Missing scales on a dragon’s left breast plate that are easily penetrated by an arrow shot by one Bilbo Baggins. But this post isn't me (or you, if you got that last reference) being a fantasy nerd, it’s about skin. And not just any skin, but weak skin.
There are many visual signs you can read that give you insight into how you use your body and calluses are one of them. A lack of hand calluses is a sign of a lack of loading them. What story do your hands tell about your lifelong habits?
When it comes to closing the upper-body strength gap, what gets in most people’s way is the weakness of their skin. Skin does not have muscle, but it actively thickens over time in response to different types of loading. Skin can adapt to pressure, but it also adapts to tension.
Tension on the skin occurs when one tissue (in this case, the skin) is pulled in opposing directions. Consider the palm of your hand while hanging:
You can see that the hand, sliding (even slightly) around the bar creates a shear force on the palm. But if you take a closer look at the layers of skin, the shear force is really between the topmost and subsequent layers of the skin:
When you take super-unloaded skin (that's skin that hasn't done a lick of work in its entire life) and load your body weight onto it, this shear force can rip the skin. Viola! You've just made either a flesh wound or a blister. These are both signs that you tried to jump the skin-strength gap a little quickly. Ideally your skin would have been gently loaded throughout a lifetime, when you weighed less and "hung around" more frequently.
Callused skin is actually an area of stronger skin, an area that has better circulation than non-callused areas and is a necessary part of the kinetic chain when it comes to movement. But wait! You thought that a callus was something that was unhealthy, right? When you get a little callus, because of repeated friction (like a corn on your toe or a tiny area of callus on the sole of your foot), this small patch of “health” becomes like a rock in a shoe (or a pea under a mattress if you’re a princess). Ideally, calluses should be developed widely -- across the entire palmar surfaces of the hands and feet. We need strength in these tissues to really optimize the whole-body strength actions of both the upper and lower body.
And, now that you know how skin works, you can probably answer this reader’s question about his feet:
I'm trying to spend more time walking barefoot, but my feet are sooooo sensitive. Every little pebble, rock, or pillbug is a problem for me. The muscles of my feet don't mind going barefoot, but it's torture to the skin. It's like The Princess and the Pea, but with walking instead of sleeping.
When I was a kid, I went barefoot all the time, even spending a year in Borneo without a pair of shoes. I remember being barefoot without issues until 12 or 13, then it's a blur... What has happened to me? How can I get that back?
What has happened to you is this: your skin has atrophied since those barefoot in Borneo days of yesteryear. Just like your body does not maintain unused muscle, the body will let skin atrophy if the skin itself is not loaded. My guess is the last 20-something years of keeping the foot skin tension and traction-free means that even with the arms, legs and torso of a god, it appears you literally have the foot-skin of a little wuss.
But why take my word for it when you could take my book’s word for it instead? Here’s a swiped paragraph (because I’m too lazy to write it out again...):
“The optimal way for getting super-regenerating skin would be to allow our foot to interact with natural surfaces outside of the shoe over a lifetime, prompting a slow adaptation in foot skin thickness over that lifetime, giving us a much better ability to cope with the sensations caused by walking barefoot.” - from Simple Steps to Foot Pain Relief.
Familiar with "a bed of nails"? I won't explain how it works (you can read about it here), but basically the lack of a full-footed callus means everything you step on creates a higher amount of pressure. Everything you step on acts like a single nail.
If you were as callused as you would be for your weight, abundant natural movement in a natural environment, everything you stepped on wouldn't hurt as much because you'd be distributing the pressure of what you stepped on over the entire surface of your foot.
Now for those of you who email me, sending pictures of your blisters and jacked up feet following "the time you thought it would be fun to go barefoot for a 5K with minimal training," here's the skinny on surfaces:
I am a much bigger fan of natural surfaces when it comes to bare feet because the skin often takes a much greater beating on man-made stuff. This doesn't have to do with the hardness of the surface, but how a surface is connected to itself. Natural surfaces are not fused. The top layers move freely over the lower layers. So when you're walking or running and push back to move forward, there is much less shear force on the skin because a tiny portion of the top layer of the ground moves back with the foot.
Man-made surfaces are firmly connected throughout and increase the tension and shear on the skin. And, when the surface is porous, like asphalt, it can act like teeth grabbing into the skin. Not an ideal place to begin barefoot movement habits.
So how to build calluses? Obviously, use your hands more, but also, vary the grip (the shape) of what you're grasping as well as the texture of what you're grasping (or walking on) to move more of your skin. This will keep you from only moving tiny parts of your hand (or foot) skin!
In case you were wondering why these pictures are so crappy? I only had one hand to draw them with.
And in case you were wondering if I lead a glamorous life? I was pantsed by my 18-month old while drawing pictures with one hand.