The backpack weight a hiker is capable of carrying depends on several factors. These include the hiker’s weight, body mass index (BMI), fitness, and training. It can also depend on the terrain on which the hiker travels, e.g., off-trail or on-trail. However, online advice has tended to focus on the hiker’s weight and suggests that pack weight should be a certain percentage of the hiker’s weight. We developed a model of how the ability of a hiker to carry a backpack depends on the weight of the hiker. Modeling such real-life situations helps grab the attention of students in introductory physics. We have expanded on our earlier idea and present a more sophisticated model of an adult backpacker. In particular, we generalize our model for scaling of the human frame, and investigate how the ability to carry a backpack (within our model) varies with the form of scaling used.

1.
“Pack Weight is Relative,” http://www.backpacking.net/packwate.html; “How to Pack a Backpack,” http://www.wildbackpacker.com/backpacking-gear/backpacks/how-to-pack-a-backpack/, accessed July 12, 2015.
2.
Michael
O’Shea
, “
Backpack weight and the scaling of the human frame
,”
Phys. Teach.
52
,
479
481
(
Nov.
2014
).
3.
The scaling increases the human frame size without changing the proportion of weight in each body part; thus α, will not change as β is changed, provided the limiting body part does not change.
4.
We may write WC0 = αWh0 + Wbp0 and WC = αWh + Wbp. Now (Wh0)βWC0 = αWh0 + Wbp0 and (Wh)βWC = αWh + Wbp. Dividing the second equation by the first yields Eq. (4).
5.
Evidence for this comes from a scaling of muscle mass with body mass to the power 1.0, a scaling of surface area with body mass to the power 0.65, and a scaling of skeletal mass with body mass to the power 1.08.
See
I. P.
Herman
,
Physics of the Human Body
(
Springer-Verlag
,
Berlin
,
2007
), see Table 1.13 and references therein.
6.
The appendix can be viewed at TPT Online, https://doi.org/10.1119/1.5021432 under the Supplemental tab.

## Supplementary Material

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