Tuesday, 19 November 2013

The A - Z of Sports Vision - Sleep

The importance of a good night’s sleep is often underestimated in sport. Mah et al (2011) studied the effect of giving college basketball players an extended sleep (between about 80 and 110 extra minutes). They found that the players were able to sprint faster, and were 9% more accurate in their free throws. By contrast, Winter (2013) found that the higher the level sleepiness of a Major League Basketball player, the less likely he would still be in the league three seasons later. And all this has more to do with the eyes than you might think. Many with be familiar with the two light receptor cells in the eye – the rods and cones. But here’s another group of cells known as photoreceptive retinal ganglion (prg) cells. The existence of these cells had first been proposed in 1923 by a Harvard graduate called Clyde Keeler, who noticed that the pupils of mice reacted to light even when they had no rods and cones. The idea lay dormant until the 1990s, when Oxford Professor Russell Foster was studying circadian rhythms, the daily cycles of our bodies, which appeared to be related to light levels. It was known, for instance, that if people live in the dark for days on end, their circadian rhythms drift, so they might end up sleeping in the day rather than at night. In 1999 Foster found that mice who had eyes, but no rods and cones, kept the same circadian rhythms as sighted mice. Then, in 2002, Berson et al found that these prg cells contained a photosensitive pigment called melanopsin, showing that this was the mechanism that’s used to set our daily cycles, including our sleep cycles. This explains why there are some completely blind people who are able to tell whether or not a light is on in the room, even though they don’t know how they do it. When melanopsin is stimulated, we become more alert and wakeful. And it’s most stimulated by blue light. So if you want a really good night’s sleep, you need a dark room, but you can have some red light as this doesn’t stimulate melanopsin. Leaving your curtains slightly open may give enough blue light to get you going in the morning, so you can start preparing for your sporting endeavours of the day. David Donner