The goal of the BatWerk exercise app (Android / iOS) is to keep you healthy, happy and productive without requiring you to overhaul your life. This is a series of blog posts that talks about the different aspects of an exercise app and how we're approaching them in BatWerk (Intro, How do muscles work, Pains, Maintaining the routine, How to play). Interested? How would you like to improve it?
Where does the pain come from? You know. The one that you get from wearing headphones all day. Or the one from sitting at your desk tapping away at the secrets of the universe. Or that one where you're thumbing your mobile for hours on end.
Pain
The initial thoughts I had around pain: Pain is a bunch of nerves firing pain signals and those getting carried up to the brain. Painkillers block the inflammation response without fixing the root cause. The nerves fire pain signals because they're activated in some way. Maybe there's something pressing on the nerve, maybe the nerve is under tension, maybe there's damage of some sort that's causing the nerve to fire.
Going from there, what could be pressing on the nerve? Holding your body in a painful position. Build-up of liquid that increases pressure on the nerve. Inflammation. Damage to the nerve.
Some causes are difficult to fix by yourself, but some are more feasible. Painful position? Change position. Find a good sleeping position. Static load on muscle that causes build-up of liquid (e.g. using a computer / phone for a few hours)? Take regular breaks, try to unlock the muscle by locating it with status query meditation, massage, and 10-15 minutes of varied moves. Throw in a painkiller to help reduce the inflammation. Wearing headphones and getting neck pain? Try earbuds. Pain on the sides of your head? Bring your display down so that you don't have to look up so much.
Wrists hurting after a day at the keyboard? Wear mittens. Set a timer to lock the screen every 15 minutes. Do pushups, curls and grips to strengthen your wrists and fingers. Move your fingers less when typing. Use a flat keyboard with minimal force required.
Prevention design
Doing the micro-exercises every half an hour over the work day has been a pretty good preventive measure. It makes me move often enough and with enough variety that I don't get as many static load lockups. Still happens sometimes though, especially when I zone into something for more than an hour, or keep working in a weird position for a while. The workout and the neck stretch set can help there but it's kind of tough to get yourself through 15 minutes of movement when your head is splitting and you just want to sleep.
What sometimes helps is the painkiller, movement and massage -combo. Block the pain to loosen up the muscle, then wash the dishes to shake them more, find out which neck muscle is hurting and massage that. It usually gets me far enough that I can fall asleep and rely on the sleep relaxation to fix stuff up.
The BatWerk moves contain a bunch of neck motions and core moves, twists and stretches because a major goal for the app is to act as a preventive painkiller. If your body doesn't lock up, it's not going to get lock up pains, right? Would love to make it even better, so let me know if you can help.
Deep pain
What we have above are high level features of sedentary office worker pain. Folk medicine. But what is actually happening on a deeper level when your wrist starts to hurt?
Okay, so, let's say that you have the initial twinge of pain from the median nerve inside your wrist getting squeezed. First you get the fast pain, which is followed a bit later by the dull pain. Fast pain is a signal from a pain receptor that travels along an A nerve fiber. Dull pain is a pain signal that travels on a C nerve fiber.
The difference in the speed of sharp pain and dull pain comes from the different nerve fiber types. The A fibers are myelinated - they're wrapped in an insulating sheath that helps nerve signals travel faster. The C fibers are smaller and don't have the myelin wrapper, so it takes a few seconds for the signal to reach the brain.
As the nerve signal leaves the pain site at the wrist, it travels up the median nerve to the brachial plexus in the shoulder, where it splits into the medial cord and the lateral cord. The cords then further split and merge into the five root nerves connected to the spinal segments.
The pain signal enters the spinal cord at the dorsal horn, which can change the intensity of the signal. If you're pre-occupied with something, the dorsal horn can block the pain from reaching your brain. Then when you stop doing whatever you were doing, you start feeling the pain.
From the spinal cord, the pain signal travels via the spinothalamic tract to the brain. And now you're in pain.
Sensors
Okay. Now we know the road pain travels. But what is it exactly?
Our sensory neurons detect changes in their neighborhood. There are sensors all around your body, for example on the skin and eyes, in your muscles, joints, organs and the digestive tract. These sensors are not only for pain, but are also responsible for sensory perception and your body sense (i.e. the position of your limbs relative to each other).
Different sensor neurons detect pressure changes, stretching, presence of chemicals, and temperature changes. The pain sensors are tuned to fire only when the stimuli exceeds a specific threshold. The threshold isn't fixed, and can change as a result to changes in the environment. For example, a gentle touch can be quite painful on an inflamed area.
As the sensor is stimulated, it builds up an electric potential. As it exceeds the threshold value, it sets off an action potential (a kind of wave of flipped polarity) down the nerve. Electric? Yeah, all your cells maintain -70mV voltage between the inside and outside of the cell. Messing with this voltage is what neurons use for internal messaging.
A neuron consists of a receiving end and transmitting end. The two ends of a neuron are connected by a cable called the axon. The receiving end sets off the action potential to tell the transmitting end to release neurotransmitter molecules. These are picked up by the receiving ends of the neurons next in the chain (which makes them more or less likely fire off their own action potentials). There are hundreds of different neurotransmitters, but each neuron usually releases only one kind. Pain sensors use glutamate? Noradrenaline?
Putting it all together, tissue damage causes immune cells to release cytokines and prostaglandins that create inflammation which releases histamines and other molecules that are picked up by nociceptors, making them more sensitive and turning the inflamed area painful to touch. The inflammation also leads to the production of lysophosphatidic acid and sphingosine-1-phosphate that directly activate TRPV1 high temperature nociceptors responsible for burning sensations, causing a voltage potential buildup that exceeds the nociceptor's threshold, making it fire an action potential to its A fiber and C fiber axon ends, where the change in voltage triggers the intake of calcium ions into the cell, which signals the axon to bring neurotransmitter vesicles to pores in the cell membrane and release the contained glutamate molecules into the synaptic cleft, where the dendrite of the next neuron picks them up and excites the neuron, making it propagate the signal. On reaching the spinal column, the dorsal horn attenuates the pain signal with GABA and noradrenaline neurotransmitters before forwarding it on along the spinothalamic tract to the brainstem and thalamus. And now you're feeling burning pain at the inflammation site and it's become sensitive to touch.
This feels like one of those "what happens when you click on a link"-explainers that ends up with an explanation of how to build an adder circuit out of transistors. Anyway, that was an educational journey.
Nociceptor Sensory Neuron-Immune Interactions in Pain and Inflammation https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5205568/
General Pathways of Pain Sensation and the Major Neurotransmitters Involved in Pain Regulation https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6121522/
Presynaptic Inhibition of Pain and Touch in the Spinal Cord: From Receptors to Circuits [PDF] https://www.mdpi.com/1422-0067/22/1/414/pdf
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