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In which the Festive Turkey imparts some wisdom despite being dead. And cooked.

December 30, 2011

If Physics bored you to sleep in school, here’s a really good reason to have stayed awake: the principles of levers and forces. I’ve just spent the last four days lying on my back, unable to sit or stand, because in the Festive Roasting Rush I forgot those fundamental principles. I’ve also spent that time reflecting on pain, culture, folk wisdom, and the appalling state of Australian telly. Now that I can have my torso upright without excruciating  pain, I want to share some of my thoughts with you (not about Oz telly – it’s beyond redemption) over a series of posts.

First, to Physics, and how I hurt myself: with a 5 kilo turkey. A piffling weight to lift, you say – provided one keeps it close to one’s body. But what with the general cooking kerfuffle, the only clear space to baste the bastard was on top of the stove, which meant standing an open-oven-door’s-depth away from the stove, and lifting the turkey from below onto the stove top at pretty much full horizontal arm extension. I did that 6 times over the course of Christmas Eve day. A rough and dirty calculation makes that turkey a bit over 90 kilos of force – almost twice my entire body weight – each time I lifted it up, and each time I put it back in the oven. This is where remembering that Force = (Weight x Length-from-fulcrum) / Length-to-fulcrum BEFORE cooking would have come in handy and suggested clearing some bench space prior to basting so that the whole procedure avoided long lever action….

Now, the lifting-the-turkey fulcrum point is not at the shoulder joints – it’s in the area where a variety of muscles attach the arms to the spine. These include the muscles we’re all familiar with from gym weights training: traps, lats, rhomboids. It’s important to remember here that despite the pretty coloured diagrams you find on weights machines and in anatomy books, muscles do not work in isolation. Remember also that the spine is articuated (and therefore bendy) so to provide a stable fulcrum for lifting turkey-type loads, all of the extensor/postural muscles of the back have to participate, and to a certain extent, the diaphragm.

In an ideal body, each muscle in the whole ‘orchestra’ contributes its fair share, distributing load proportionately. There may be ideal bodies out there somewhere (although I think it’s pretty unlikely) – but mine is not one of them. So some of my muscles didn’t participate as much as they should have, and other muscles had to compensate by doing more than they’re capable of. It’s important not to interpret this as some muscles being weak, in need of some jolly-hockey-sticks strengthening discipline. What it means is that my nervous system didn’t coordinate muscular activation properly – a bit like the conductor forgetting to cue in the second violas.

In my case, the muscles which got hammered with overwork were a few small sections of the postural muscles close to the spine. As I’ve written before, this kind of injury doesn’t always present itself immediately as a pain experience, and in fact I didn’t notice a thing until the following day. I lifted my arms to pin my hair up, and, whammo. But more on acute pain in the next post.

Now, the reason I’ve painstaking detailed this fairly mundane sequence of events is because this sequence is exactly that: mundane. Long lever lifting is something that lots of folk do quite a lot of the time without thinking, and the injuries it can cause are the reasons why safe lifting practice is a standard part of OHS education. But I have never seen lever force equations or diagrams used to elucidate just WHY safe lifting techniques are important (eg that a light weight at the end of outstretched arms requires nearly 20 times force at the back). What seems to happen is that documentation like our National Code of Practice for the Prevention of Musculoskeletal Disorders from Performing Manual Tasks at Work (2007) simply lists ‘hazardous’ actions and postures. If one were to apply the term ‘hazardous’ to these actions in everyday life, it would pretty much rule out sport, housework, cooking, playing a musical instrument, gardening, having a pet, having children…. The problem with teaching people WHAT rather than HOW is that you end up with a whopping great list (over 7 pages in the Code, with diagrams) in the hope that all possibilities will be covered. They won’t, and people won’t remember the whole list either.

The Wisdom of the Festive Turkey: remember your high school Physics.

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