biology zoology blog benno meyer leg balance

Standing on One Leg is Comfortable

For some (I’m not pulling your Leg)

My children’s favourite character of Richard Scarry’s books was the one-legged “Lowly Worm”. When I was a kid there was no “Lowly Worm”, but I knew Maasai men often stood on one leg when resting from work or activity and I wondered if that wasn’t uncomfortable. Upon seeing photos of this unusual form of ‘relaxation’ and wanting to be a little different from others, I myself started standing on one leg when waiting for the bus or tram. Needless to say, I earned some peculiar looks from bystanders, who must have thought that I had hurt one of my legs. To be honest, it wasn’t a very comfortable resting position, but for some people (and not just the Maasai) and especially for birds it seemingly is.

Balancing on one leg is no easy task. Babies would say even standing on two legs isn’t exactly easy and if you are an adult on the unstable surface of a ship at sea you’d agree with the baby). People with the Uner-Tan syndrome cannot stand. To balance on one leg means to shift the body’s centre of mass, which involves appropriate muscle activations, the central nervous system to integrate, interpret and act upon information received from sensors like muscle spindles and stretch receptors in the muscle, as well as information from visual and vestibular systems in the head. The muscles most involved are known as the adductor longus and the gluteus medius and to activate them requires energy. Therefore, apart from being less stable (at least with regard to a human) and requiring energy, why would Maasai and some other people stand on one leg to relax? I do not know, but we can look at some birds that habitually rest and may even sleep standing on one leg. Storks, cranes, flamingos, and even ducks come to mind and one of the ideas is that they withdraw one leg to reduce heat loss when standing in cold water.

The problem with that theory is that storks and ducks may also stand on one leg when on dry land and the fact that flamingos do not often stand in very cold water (although it has been reported that they less often stand on one leg when it is warmer). Another idea, also related to saving energy, is that long-legged species withdraw one leg, because that reduces the need to pump blood through both of the long and outstretched appendages equally. Yet, this theory would not explain why short-legged species like ducks also often rest on one leg.

An interesting explanation has been suggested for wading birds like flamingos that have legs with special ankles, which are in a place of the leg where we’d expect the knees to be. A joint that can stabilize if not temporarily lock the joint that links foot and leg. The body posture of flamingos standing on one leg is so stable that the bird may even sleep in this position and actually save energy. Yet another idea why the birds stand on one leg suggests that the birds stand motionlessly on one leg to look like reeds or thin trees, thereby attracting food. Flamingos, however, feed on algae and tiny zooplankton, the latter having poor eyesight, avoiding shadows and being feeble swimmers. However, for herons and storks that feed on fish and frogs, this camouflage idea may have some merit. Amazingly flamingo cadavers could be made to stand stably on one leg which led Chang & Ting in a 2017 paper in the journal Biology Letters to the conclusion that “rather than to reduce muscle fatigue or heat loss, flamingos stand on one leg to reduce muscular energy expenditure”. Perhaps the Maasai seeing the flamingos of Lake Nakuru thought to copy their behaviour just like I copied the Maasai behaviour of standing on one leg.

© Dr V.B. Meyer-Rochow and, 2020.
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