Our brains depend on oxygen and the lower the level of oxygen the less alert we are and the less able we are to understand the dangers we are in. Although our muscles depend on oxygen there is another phenomenon that occurs when oxygen levels fall – the brain itself begin to shut down our muscles, making us move slower.
“Effect of graded hypoxia on supraspinal contributions to fatigue with unilateral knee-extensor contractions“ does not come trippingly off the tongue but this paper by Stuart Goodall Emma Z. Ross Lee M. Romer of the Centre for Sports Medicine and Human Performance, Brunel University and Chelsea School Research Centre, University of Brighton, give an insight into the way in which the brain seeks to protect muscles when oxygen levels are low.The researchers, who were replicating high-altitude atmospheric conditions, tests 11 healthy subject who breathed gases containing four different levels of oxygen: 21 per cent, normal atmospheric oxygen, 16 per cent, 13 per cent and 10 per cent. They found that the brain contributes 18 per cent to muscle fatigue with normal oxygen, 25 per cent for mild to moderate hypoxia and 54 per cent for severe hypoxia.
Note that this is not low-oxygen levels generating muscle fatigue, it is signals from the brain through the nervous system, possibly to prevent over-exertion in low-oxygen conditions which could damage the muscle.
New Scientist magazine quotes Dr. Ross: “Our findings provide the first direct evidence that when the human body is stressed beyond its normal limits, such as through exercise in a low-oxygen environment, the brain has an increased influence on our ability to use our muscles,” says Ross. “It could be an evolutionary mechanism to ensure we always have some capacity for movement.”
This effect will clearly reduce the ability to work safely in confined spaces and adds to the need to ensure that confined spaces are ventilated to ambient oxygen levels. It may also introduce a certain amount of warning options – if your muscles are starting to ache or the person you’re monitoring is moving slower than might be expected – then low oxygen may be the culprit and the space should be evacuated immediately.
Thanks to Jim Nicol of Newslink for tipping off MAC about this development.