Unlike me, my dogs bound up hills as easily as they run on the flat. Does having four legs aid with climbing, or are the dogs just fitter than me?
Andrew Carothers
Edinburgh, UK
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The biologist and evolutionary theorist John Maynard Smith originally qualified and practised as an engineer, giving him unique insights into physical constraints on living organisms. His book, , devotes a section to examining how size affects the ability of animals to move uphill.
By considering the scaling effects of rate of metabolic heat loss, rate of oxygen supply and stresses on bones and muscles, he shows that the maximum power output of an animal should be roughly proportional to the square of its linear dimensions. However, the power needed to move uphill is proportional to the product of weight and vertical velocity. Equating power available to power needed, he concludes that vertical velocity should be inversely proportional to linear dimension. This is borne out by observation:can move uphill with almost as much ease as on the level, whereas climbing quickly exhausts horses and elephants can manage only a slow ascent. Since the number of legs doesn’t make any difference, humans must fall somewhere between dog and horse.
So if you are a fit and healthy person being chased by a large hungry bear, you should run up the nearest hill as fast as possible to escape. It isn’t a theory that I would care to put to the test myself, as I am over 80, and one factor that Smith didn’t take into account was the effect of ageing!
Steven Field
Via email
While dogs’ abilities to climb hills may be down to physiology, my experience of walking my 13-year-old collie cross makes me wonder if there are deeper considerations.
When walking on a slack lead, Mutley (at 20 kilograms) can decelerate from fast walking to zero instantaneously. This brings me (at 90 kg) to an immediate stop when the slack vanishes, causing a rebound backwards while the dog remains unmoved. According to Isaac Newton’s third law, the change in momentum should be shared by us, but this isn’t observed. My hound then appears to become infinitely massive and unmoveable. Perhaps a dollop of dark matter or a canine ability to harness dark energy is at play. Further investigation is required.
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