Grandpa Burnham was showing me the pink scar across his palm. "I can't work in the shop right now. The doctors had to sort out the nerves in my hand." I was in high school in the 70's and Grandpa was telling me about his carpal tunnel surgery. Unfortunately, a lot of woodworkers face the same health problem today. It might result directly from our woodshop work, or it might be something we get from other exposures that ends up aggravated by hobbies like woodworking. In college I studied industrial ergonomics and then worked in factories to redesign jobs that hurt people. As I think of Grandpa rubbing his palm and wanting to get back to his woodshop to finish up some projects, I wish I could have shared some of these tips with him to avoid the pain and frustration he experienced.

Our hands are an incredible part of the body. Biomechanically there are 27 degrees of freedom (different ways the hand can move) in the hand/wrist. Think what that means in woodworking - you grasp tools, pick up boards, manipulate parts, open jars, point and poke and touch. A large part of your woodworking skill comes from careful, precise, coordination of hand/wrist motions - broadly called manual dexterity. Through repetition and practice of fine motor tasks, your brain develops efficient neural pathways that enable dexterous performance. Woodworking is a craft that helps you develop manual dexterity (dental schools like to see woodworking as a leisure activity on your application).

Figure 1. Marquetry uses many of the 27 degrees of freedom in your hand/wrist for precise freehand cutting.

Part of your amazing hand is the sense of touch. There are two kinds of nerves to detect warm/cool and four types of mechano-receptors to detect vibration and pressure. I love the name - Pacinian corpuscle - that's one of the ones that detects vibration. When you touch something this complex web of specialized sensors in your skin collects reams of data about how much and how fast and where. All this information goes to your brain where more amazing stuff happens to sort out the data and generate information about what you are touching. Close your eyes and touch that piece of wood in front of you. Your brain is telling you something about warm/cool, rough/smooth, soft/hard, sticky/slippery. Studies show that people can detect surface differences in the nanometer range (that's small) and we can detect temperature differences of about 1 degree C. The apprentice hands the master a board and asks, "Is this good enough?" A pass of the master's hand and the answer is back to the bench for more scraping.

Figure 2. Is that joint flush? Is the surface smooth?

Our nerves are more than just data collectors. They are wired into a feedback loop with nerve sensors in our muscles and joints. When you pick up your marking knife you grip it lightly in a pinch grip. You know how hard you need to squeeze, and you know how hard you are squeezing. Your brain, muscles, and touch sensors are firing away in a coordinated dance to effortlessly glide the knife along the line. But then you reach over to pick up a #7 bench plane and your handgrip immediately dials up to 10 lbs. The touch sensors in the palm of your hand are now measuring how hard you are pushing the plane into the wood and how hard the wood is pushing back. The adjustment from precise and delicate to firm and strong is effortless.

But, to quote a certain band from the 70's, touch is, "more than a feeling." Close your eyes and pass your hands over something soft like perhaps a Christmas sweater. You can easily describe the sensations along the dimensions of smooth/rough, hard/soft, sticky/slippery, warm/cool. But your brain goes further. It connects that neurophysical sensory input to emotional responses. Maybe memories of happy times or family or just an inner sense of comfort. Warm-soft-fuzzy generally creates a favorable emotional response. There is a whole line of research on how people emotionally react to the touch of wood. This is important for product design - is a glossy varnished surface perceived as more "pleasurable" than a plastic laminate surface? Is an open-grained wood like oak perceived as more "natural" than something like maple sanded to 400 grit? The kinds of emotional descriptors that researchers test include adjectives like, "thrilling", "uncomfortable", "irritating", and "calming".

Our hands are one of the most important ways we engage with the world around us. We touch, we feel, we hold. We change the world when we put our hands on it and the world changes us through our hands. The woodshop is a particularly potent smorgasbord of somatosensory (touch) delight. When most of us step into a shop and see an old tool - we reach out and touch it. When we see a wooden object made by another - we pick it up and touch it. Inspired, we pick up a board, grasp a tool, and begin to create. If you could see all the sensory activity while you work, it would be a glorious lightning storm coursing through your hands and head. But your brain sorts out all those exciting impulses and simply says, "a little more to the left" and, "this is joy." Take a new look at your hands.

Things I Wish I Could Have Told Grandpa Burnham

Carpal Tunnel Syndrome (CTS) is a cumulative trauma disorder that results from various combinations of: poor hand/wrist posture, hand/arm vibration, forceful grips, and repetitive activities. It is also influenced by a host of personal factors such as body mass, hormonal levels, and age/gender. One of the challenges in addressing CTS is that one person may suffer from it while a co-worker, using the same tools and methods, never has a problem. The basic etiology of CTS is that something causes swelling in the tendons that pass through the wrist (the carpal tunnel). Swelling pinches the nerves and you lose your sense of touch. It becomes a self-driven cycle of inflammation, pain, pinching, more swelling. All that said, there are a few key woodworking task factors to keep in mind to minimize your risk of CTS.

a) Never use your hand, particularly the palm of your hand, as a hammer. We all do this, thumping on a misaligned board with the palm of our hand. This kind of impact can lead to inflammation and swelling that may trigger the development of CTS.

b) Watch out for forceful grips. Objects that are slippery, handgrips that are too big or too small, things you have to pick up by pinching instead of grasping - all these things tend to cause us to squeeze tighter, putting more strain on the tendons of the hand. Gloves are a mixed solution. Some gloves may give you better grip, but poorly fitting gloves can just make it harder to grasp things and make it worse.

c) Keep your wrist in a neutral posture as much as possible. The tendons passing through the tunnel slide easier when they can just slip back and forth through the tendon sheaths. If they have to go around a bend because your wrist is bent, that adds friction and strain. Neutral posture for your wrist is like a handshake position - thumb up, palm pointing straight ahead. Think of a plane tote. Your neutral grip is a "pistol-grip" with whatever you are holding onto (like a plane tote), at an angle of about 25-30 degrees from the vertical.

Figure 3. Think about how the height of your work affects keeping your wrist straight.

d) Minimize extended hand-arm vibration exposure. In my shop doing custom furniture, the biggest vibration exposure comes from random orbit sanders. Other shops might use more pneumatic tools or reciprocating tools that can also create other vibration issues. To minimize vibration exposure, limit your time with the tool and try to have as loose of a grip as possible. There are special gloves that can help buffer vibration if you have a serious job exposure.

e) Reduce exposure to highly repetitive gripping, twisting, and pinching. Grandpa Burnham made mini- scrapers out of old hacksaw blades. When he was shaping the body of a violin he would repeatedly pinch and push on those tiny blades. If you think about it, in the course of an hour, he was pinching hundreds of times. Classic risk factor for CTS.

f) Be aware of your whole exposure. CTS is a cumulative trauma disorder. Your body doesn't know the difference between work hours or recreation. If you work in your shop and then go play video games, or spend hours typing on a computer, you will accumulate more stress and strain on your body.

g) Finally, listen to your body. If you have any nerve symptoms (tingling, numbness) or if you feel like your hands are sore or tired after a stressful bout in the shop - take a break. Continuing until you can't stand it any more isn't a good plan. There are non-surgical interventions to help break the cycle of inflammation if you catch the injury early enough. Be kind to your hands, enjoy your shopwork!

References

Bhatta et al. 2017. Sensory and Emotional Perception of Wooden Surfaces through Fingertip Touch.
Front. Psychol., 13 March 2017 https://doi.org/10.3389/fpsyg.2017.00367

Sennett, R. 2008. The Hand, Chapter 5. In: The Craftsman. Yale University Press. 315 p.

Bob Rummer lives in Colorado and is a part-time woodworker. He can be reached directly via email at rummersohne@gmail.com. You can see his shop and some of his work at www.JRummerSons.com.

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