Backpack Physics: This Is Why Smaller Hikers Can Carry Heavier Loads

Michael Loccisano/Getty Images for Nickelodeon

Hikers are generally told the weight of the packs they carry should correspond to their own size.

Bigger people get heavier loads than smaller people.

Kansas State University physics professor Michael O’Shea noticed that some of his smaller students, on backpacking trips for Outward Bound, could comfortably carry a greater pack weight than the larger ones of similar fitness levels.

He thought the explanation might have something to do with the fact that hikers must haul not only their packs but also their own body weight.

He incorporated both of these variables into a model described this week in the journal The Physics Teacher published by the American Association of Physics Teachers.

“Online advice from several sources was somewhat misleading in suggesting that pack weight should be a certain percent of a person’s weight,” says O’Shea.

However, as the size of any animal increases, strength increases more slowly than body weight. This is the reason why tiny ants can carry a heavy load.

He combined this information with body scaling proportions obtained from other research to create a model matching his observations.

The resulting equation takes into account a hiker’s entire load, backpack plus body weight, and can be used to determine the maximum backpack weight for an individual of a given size.

“Overall strength of an individual does not determine how heavy a backpack a person can comfortably carry,” says O’Shea.

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