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I’d like to discuss a statement I put in the “Question for Kit” thread. This is the statement: "The evidence for this, as often quoted, is that under surgical anaesthesia, it is possible to put someone in a perfect split. As the anaesthesia wears off, the usual pattern of flexibility returns." I have started a new thread on this topic, because it seems to be diverging from the original query. I have heard the opening statement many times, and on querying it seems the information has come from people who should really know, such as orthopaedic surgeons. Please note that issue here is not whether the brain does or does not have some effect on flexibility; it is clear that it does, because we all know that voluntary relaxation can increase a stretch. Neither is the issue whether our normal pattern of muscular tightness is under the control of the brain: of course it is. If we were fully relaxed, we would not be able to stand up. Anaesthetics clearly abolish this pattern of muscle activation, and if we were anaesthetised while standing we would expect to fall over. In addition, some people carry more muscle tension than the minimum needed to stand up, and it quite reasonable to think that this also is driven by the brain, that it should disappear when we are anaesthetised, and reappear when we come out of the anaesthetic. Rather, is a question of how much flexibility, or lack of it, is driven by the brain – because a perfect split needs a very great deal of flexibility, far beyond the range of most people. If the opening statement was true, it would mean that the properties of muscle (or other associated tissue, such as connective tissue) would have NOTHING to do with flexibility (at least up to the range needed to give a full split). It would ALL be due to (1) neural reflexes, with (2) the ultimate limit set by joint properties. Because this conclusion is rather surprising (as well as going against a great deal of current exercise science), I thought I’d look into it further, to see where the evidence comes from. If indeed it is something reliable known to the medical world, then the information should be found in authoritative sources such as medical textbooks. So I did Google searches using different variants of the terms. However, although I found many references to the issue, they were all in exercise-related webpages, rather than in authoritative basic sources. Usually, it was just a throwaway statement, and never with a justification saying where the evidence had come from. However, there was one helpful comment in an article by Craig (yes, the same Craig who posts here; thank you Craig), in Aware Relaxed Connected1. It quoted an experiment by Robert Schleip2, who tested the effect of anaesthesia on flexibility, in patients who were about to undergo surgery on the knee. (1) Before and during anaesthesia, Schleip2 raised the arms of the supine patients, to see how high they would go. In 1 out of the 3 patients tested, before anaesthesia the arms could be passively taken right overhead and lie against the table – so no increase in range in this patient could be expected. In the other 2 patients, the arms did not lie flat against the table before anaesthesia, but did during anaesthesia. So anaesthesia increased the mobility of the shoulder joint in these two (though he did not quantify by how much). (2) He also dorsiflexed the feet of the patients. None of the 3 patients showed any noticeable increase in range; i.e. there was no sign that the calf muscle had become more extensible. So it seems that one joint (a complex one, where many factors will determine its mobility) could be affected by anaesthesia, but simple muscle length could not. I then searched the medical literature via Pubmed. I found only one paper that had addressed the issue “Neurophysiologic influences on hamstring flexibility: a pilot study”3. In this study, the hamstring flexibility of a healthy leg was assessed before during and after anaesthesia, in patients about to undergo surgery on the other knee. Averaged over all 11 subjects who had general surgical anaesthesia, there was NO change in the flexibility of the hamstring as a result of anaesthesia. Over the 3 patients who had spinal anaesthesia, there was a small increase in flexibility during anaesthesia (average change in popliteal angle 8.1 degrees – enough to allow the foot to move by another 5cm or so). Mean popliteal angles with hip held at 90 degrees were around 130 degrees – i.e. the subjects were not particularly flexible, either before or during anaesthesia – certainly nowhere near to doing a “full split”. The clear conclusion from this paper is that loss of central control has NO effect on hamstring flexibility, contra the opening statement. Spinal anaesthesia (which will also affect motor neurones and local spinal reflexes) has a small effect. In neither case does anaesthesia allow anything remotely near to a full split. My conclusion from this reading is that the opening statement is inaccurate. In people lying conscious on an operating table, the nervous system only has very minor effects on leg flexibility. When neural control is removed, there is only a very minor increase in leg flexibility. 1 Found at: http://awarerelaxedc...-motion-basics/ 2. Found at: http://www.somatics....ging-the-brain. Source: Talking To Fascia – Changing The Brain - Explorations of the Neuro-Myofascial Net by Robert Schleip. Rolf Lines March/April 1991: 3 Abstract found at: http://www.ncbi.nlm....pubmed/11753061 (the full text needs a subscription). Reference: Krabak BJ, Laskowski ER, Smith J, Stuart MJ, Wong GY. (2001). Neurophysiologic influences on hamstring flexibility: a pilot study. Clin J Sport Med. 11(4):241-246. (As far as I can tell, this study has not been followed up or repeated.)