Do animals exercise to keep fit? | Fitness February

As it is Fitness February, here’s an interesting question that Dr Lewis Halsey from the Department of Life Sciences talked about earlier last year at New Scientist Live in London.

Dr Lewis Halsey on stage at New Scientist Live

If humans want to get fit, we have to expend quite a bit of energy through exercise. In terms of our basic anatomy and physiology, the inner workings of our bodies are similar to other mammals. Given this, wouldn’t it make sense that animals need to exercise to stay fit, too?

Scientists have been working with humans for a long time to make athletes more physically fit and improve training techniques, and looking at their diets to have a fitness advantage over other athletes. In contrast, there is very little research into other animals and if they exercise to keep fit. However, we don’t expect to see unfit animals in the wild. In the wild environment, if you are out of shape, you won’t last long. If you are prey you’ll get caught; if a predator, you won’t be able to hunt successfully. Perhaps the wild environment is a large gym where animals naturally stay fit to survive in these environments.

An example of an animal that is not particularly active on a daily basis are Thomson’s gazelles that live on the plains of Africa. They spend most of their time standing, sitting or on the ground asleep or resting. The exercise they take is slowly walking and grazing on vegetation. However, if a gazelle is not in shape, it would be eaten by predators. But typically they are able to outrun their feline predators. The human equivalent of this type of speed endurance would be a 400m runner and they of course need to train very hard.

Adult animals exposed to physical exercise get more fit. In a research project, mosquito fish were in flowing water like a stream and another in a pond, so the ones in the stream had to constantly exercise. The fish who were in the flowing water environment had greater cardiovascular fitness.

One of the best studies on animal fitness involved researchers placing hamster wheels in the forest with cameras in place to monitor usage. A menagerie of animals went on the hamster wheels and used them, including mice, frogs and a slug! It is unclear why these animals did this, but it shows evidence that animals do have a voluntary interest to do exercise, over and above that which they get involuntary through their regular activities of finding food, walking, running or flying.

Some animals will change their body shape as their environment changes. Robins will gain weight before the winter comes to give them more chance to survive over the winter when there is no food. They also need to keep their weight balanced so that they don’t get attacked by predators.

Animals that don’t bother to exercise perhaps can’t spare the energy, or it’s the case that being physically fit isn’t a priority for that species. For example, the dormouse will gain weight before hibernation and they don’t do much exercise; they need to be fat not fit to stay alive. The polar bear also hibernates, but when they finish their hibernation they have to eat, and killing seals takes a lot of strength. Polar bears lose weight during their hibernation, but certain muscle groups stay large. In this sense, polar bears partially circumvent the need to exercise because they aren’t losing fitness in key aspects of their body during long periods when they are doing no activity at all.

Possibly, humans get fit in response to exercise, because we don’t need to know when we need to be fit or how fit we need to be. It is really possible for some animals to become very muscular without exercising. Over time, the risk of humans having predators has decreased, which could explain why humans need to exercise regularly to keep fit.

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