Physicist shows that smaller hikers can carry heavier loads

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vibramhead
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Physicist shows that smaller hikers can carry heavier loads

Post by vibramhead » October 22nd, 2014, 5:55 am

Turns out that, according to one physics professor, the smallest hiker in your group doesn't necessarily need to be carrying the lightest pack.
"Online advice from several sources was somewhat misleading in suggesting that pack weight should be a certain percent of a person's weight," said O'Shea. However, as the size of any animal increases, strength increases more slowly than body weight—the reason why tiny ants can carry a disproportionately heavy load compared to their weight.

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 the 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," said O'Shea.
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sprengers4jc
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Re: Physicist shows that smaller hikers can carry heavier lo

Post by sprengers4jc » October 22nd, 2014, 6:45 am

Great! We've been looking for an excuse for our 25 lb lab/beagle mix to finally 'carry her own weight' :lol: .
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texasbb
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Re: Physicist shows that smaller hikers can carry heavier lo

Post by texasbb » October 22nd, 2014, 7:27 am

This is no surprise to the trees among us. We've envied the sturdiness of you squats our whole lives. :)

mcds
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Re: Physicist shows that smaller hikers can carry heavier lo

Post by mcds » October 22nd, 2014, 2:09 pm

I know your comment was in jest, but it's not a matter of shorter people being more squat or stout. It's based on the long accepted finding that muscle strength is proportional to its cross-sectional area, not to its volume (weight). So even for two people with the same physique but different heights, the smaller person can carry a heavier pack than the taller person ... as a percentage of body weight.

This is bears out in the general observation that as a person grows and developes and becomes 50% heavier, their strength will not increase by 50%. It will increase by a significantly smaller percentage.

Imagine it this way. Consider a clay brick standing on end. Scale it up by a factor of two so that it is twice as high, twice as wide and twice as deep. Its weight will increase by a factor of 8, while its cross-section will increase only by a factor of 4.

Then there is a second factor. Conceptually, there is a muscle group that sets the limit for the amount weight a given person can carry in a given situation, for most people/situations its usually in the lower body, perhaps calf or thigh muscles. Lets say it is the thigh muscles. The thigh needs to carry not only the weight of the backpack, but also the weight of the of the hips, torso, arms and head.

The author, Michael O'Shea, professor of physics at Kansas State University, uses basic algebra to show (article) that due to these two factors, small people can not only carry a backpack that is a higher percentage of their body weight than a similarly physiqued taller person, but that there is a point in size disparity where the smaller person can carry a heavier pack (in absolute terms) than the large person, and that the tipping point is within the range of normal variation in adult body size.

Being more stout or squat amplifies this.

fwiw. tl;dr.

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texasbb
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Re: Physicist shows that smaller hikers can carry heavier lo

Post by texasbb » October 22nd, 2014, 2:50 pm

Actually, the jest of my post was not in the literal meaning of "squat," but its colloquial use to describe shorter people. Much like I used the word "tree." :) Few here would follow my allusion, though, since squats and trees refer to two platoons of the Ross Volunteers, a drill team in the Corps of Cadets at Texas A&M and the official honor guard of the Governor of Texas. I guess that's what happens when I think out loud.

Regardless, I was serious about tall folks not being surprised by this. In addition to the strength vs weight considerations that you explained lucidly, our long limbs also slow us down, rotational inertial being proportional to the square of the length. That's why you see relatively few tall sprinters. But you also see very few short ones, owing I'm sure to the limited progress they make on each stride. So you folks in the middle have it best. You have more clothing options, too. :P (BTW, in the Ross Volunteers, the middlings are known as meatballs.)

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retired jerry
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Re: Physicist shows that smaller hikers can carry heavier lo

Post by retired jerry » October 22nd, 2014, 2:58 pm

similarly, "squatter" people have an advantage staying warm in cold weather

skinnier people have an advantage staying cool in hot weather

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Sean Thomas
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Re: Physicist shows that smaller hikers can carry heavier lo

Post by Sean Thomas » October 23rd, 2014, 6:20 am

I knew it! I've always dreamed of being a squat middling-meatball eating flubbergaster :D


Looks like Jo is carrying my pack from now on too :!: :D

mcds
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Re: Physicist shows that smaller hikers can carry heavier lo

Post by mcds » October 23rd, 2014, 4:10 pm

texasbb - yeah, that did go right over my head. Guess I categorize as a squat meatball. Interesting about the legs and arms. Hadn't thought about that. I guess an infinitely long leg at rest would require an infinite amount of energy to start it swinging, and a leg of zero length wouldn't get one anywhere. Seems like there must be an optimal length given other factors.

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Re: Physicist shows that smaller hikers can carry heavier lo

Post by raven » October 23rd, 2014, 11:33 pm

I can assure you that longer legs (within the range of normal human variability) are an advantage when crossing tundra tussocks. Probably an advantage any time there is much ground clutter but plenty of headroom.

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Grannyhiker
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Re: Physicist shows that smaller hikers can carry heavier lo

Post by Grannyhiker » October 24th, 2014, 6:33 am

Obviously, this short, squat granny with bum knee was not included in this study!

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