The next part of this module about the body is entitled Repetitive Strain. Now, repetitive strain is probably the most common cause of persistent pain and the development of chronic pain. And repetitive strain injuries occur not just in the workforce, but also at home. And in it's an injury due to strain of the muscles and joints from either repetitive tasks such as bracing the phone between your head and your shoulders. Or forceful exertion, such as lifting from the wait, waist. vibrations, for instance, equipment that's vibrating constantly underneath you. Or mechanical compression such as pressure on your shoulder from a back pack or a shoulder bag, or sustained or awkward positions like sitting forward in a, a computer over time or having your head forward. And many other types of sustained tension within the muscles. Now, in the occupational sense, it plays a significant role because it's a very common cause of worker compensation problems. And within this study, by Australia, found that these were the distributions of repetitive strain injuries at work. Shoulders 10%. upper, lower back is 38%, the most common. Knees were 12%, legs 7%, arms 28%, and neck 2%, so it's very common in all areas of the body, depending on the type of the repetitive strain. It's also called a number of other things from repetitive stress injury, to repetitive motion injuries, cumulative trauma disorder, occupational overuse injury, overuse syndrome, myofascial pain, and regional musculoskeletal disorder. well, let's first understand a little bit about how the muscles work to understand repetitive strain. So, there are two different muscle fiber types in general within the muscles and they are distributed, distributed throughout all of the skeletal muscles. There are the type one muscle fiber types, which are red, and, they're for postural. So, the other fiber types, type two, or white fibers are for strength, and every muscle has a distribution of both postural muscle fiber types and strengthening muscle fiber types. So, first of all, the muscle fiber types are red or slow twitch. These are characteristics and built up within marathon runners who after long, run for long periods of time, or people who are doing any type of repetitive work. They maintain a high postural muscle tone. They have high endurance. They don't fatigue out very easily. They're slow twitch. They don't respond quickly. And they use oxidative phosphorylation with high oxygen production, ATP, which is the metabolism, the fuel, for muscles. And increase in mitochondria and vascularity in the area. So, these are muscles that have to sustain in tension or contraction for a long period of time. Now, there are muscle fiber types two which are also termed white or fast twitch muscle fiber type. Now these are for large forces over brief periods of time. It's the strengthening muscles. And here is an example of a sprinter. And they have a significant high number of, of Type two muscle fiber types within their muscles. And this has low endurance. It cannot sustain holding it for very long. It's fast switch so it goes quickly. And it's anaerobic glycolysis, low oxygen, low mitochondria, but high lactic acid. So it immediately uses a fuel that's around the muscles. Now, all muscles are like chameleons. So, one muscle may have a distribution of both type and type two, type one and type two muscle fiber types. But if there is an increase demand from high forces over short periods of time, muscle fiber types will convert. They'll go from type one into type two. Now conversely, you'll also find that muscle fiber types two can convert to one when there is an increased demand from postural strain for longer periods of time. So, we need to understand this balance between type one and type two muscle fiber types when we're understanding repetitive strain. And they're always converting back and forth depending upon the strains placed on the muscle. So, the big question is really, who wins? Is it the type two slow postural muscle fiber types, or is it the type two fast, strong my muscle fibers types, but it depends really what you are doing with the muscle. So, what happens with repetitive strain? So, what muscle fiber types are you challenging the most? Which ones do you need the most of? Well, we found that several studies done by Larsson, Bengston, Bennett, Dennet and Fry and others have found that muscle fibers of type one or posture muscle fiber types compensates, but often loses in the end run. So, in this case, type two muscle fiber types will convert to type one. And this increased conversion is due to this repetitive postural strain that is placed on the muscle. Now, when this happens, it is like a slippery slope. Now you remember the concepts of wind-up, sensitization, hyperalgesia, these concepts play a role in this. And when you start with increasing type one muscle fiber types and you overstrain it, it's a slippery slope. That brings you in develop chronic pain. So, the mechanism from this conversion from acute to chronic pain occurs with all the peripheral and central risk factors that can play a role. So here's a a diagram that illustrates what happens when you have an original acute muscle injury. And then if you have a number of peripheral factors. Now this may be injury, posture, trauma, repetitive strain locally in the, in the tissue. And it's accelerated or supported by central factors such as inactivity, anxiety, depression, lack of sleep or continued repetitive strain. These will contribute to a cycle that occurs where you initially have sensitization of the peripheral muscle nociceptors. Then you have sensitization of the central processing. So, both of these start act, becoming activated. If it, if the sustained strain or repetitive strain continues, and then you have this convergence, facilitation, and broadening of the pain and, and more muscle strain. So that pain referral pattern broadens. So it's not just a localized pain in the head or the, the back but then it spreads over the whole back. The neck shoulders, and then you develop an increase in muscle strain as a result of the pain. You have high muscle tone, high muscle tension. You hold your muscles tight. You have a decrease in removal of those neurotransmitters or allergens in the area. And then the whole process of sensitization, wind-up and expansion of the reptor, receptor fields all increase the hyperalgesia in the area. And you have the development of chronic pain. And with all, each of these, we have to understand, go back to the whole concepts of cybernetics. These are cycles that are set up. And there are. An injury may start the pain cycle, but there's a number of contributing factors or risk factors that lead this cycle to continue. Including, tension due to pain, then inactivity to avoid the pain. You get weak muscles, you protect the muscles by tensing, you have poor posture to compensate for the pain. And then you have more muscle strain and, of course, more pain and this just continues the cycle over and over again with repetitive strain. And there's a lot of factors that lead the way. For instance here is you have jaw pain and headaches that result from clenching of the teeth. So, when you have pain, it's not unusual to clench your teeth, bring your teeth together. And here is the difference between patients who have jaw pain and temple headaches and those in the general population and you can see, just by self report, there is a significantly higher number of oral parafunctional habits in those patients with pain compared to the general population. Now in addition, neck pain has a number of risk factors, including awkward tensing computer posture that we all find ourselves in. Our bending or twisting our neck repeatedly to the one side, doing dictation and typing, or looking up and down for hours will do that also, specially someone who is staking things up and anybody who braces their phone, forceful arm movements where you're constantly, repeatedly, moving your arm. Holding your arm in a tense posture, any long durations of sitting is going to strain the neck also, twisting or bending of the trunk, and hand, arm vibrations can all play a role. And back pain is similar. Similar types of contributing factors that can play a role in a repetitive strain. Rotation or bending of the trunk or lifting repeatedly by bending at the waist. Heavy or physical workloads lack of exercise. High body mass index which means you have to make that much effort in order to move if you have a higher weight. Then prolonged sitting, just like neck pain, or standing, monotonous work plays a role too because it's doing the same thing over and over again. Any type of manual operations and whole body vibrations have all been identified within a variety of studies as risk factors that contribute to continued back pain. And then there is a significant number of occupational risk factors that can play a role also. For instance, poorly designed workstations, as you can see by this example right here, versus ones that are very nicely designed. If it's cluttered. If there's a cold setting, if there's an awkward posture to the work that you're doing, vibrating equipment around you, if you have no rest or stretch breaks to, to relax your muscles and move them into a different posture. And there is actually tripping on the equipment and cables will also lead to injuries and, and chronic pain, ultimately. And it's important to note that, that these factors, again, like the cybernetic cycles that we talked about in, in the second module is really, occurs short-term, and then if they continue over time, just like sensitization and wind-up. The body protects yourself, so the more strain that you have over a period of time, it's going to ramp up the pain, and you will ultimately develop, more pain, more pain areas, a chronic pain syndrome. As in the cycle where you have worry anxiety contributing to muscle tension and protective postures. Musculoskeletal strain, pain, poor sleep, diet, exercise, stress, and then the cycle continues, and ultimately will continue to a long-term cycle where you have poor understanding of the factors that are contributing or causing the pain, unsuccessful treatment, secondary gain, Catastrophizing, thinking the world is falling apart around you, feeling helpless, hopeless, just depression and that contributes to sleep problems and these cycles again. So, it just continues short-term. Any short-term change continues into the long-term. Thank you for your attention. [SOUND] [BLANK_AUDIO]
