'One pound on your foot is equivalent to five pounds on your back' Really?

Rough bounds of Moidart

Read anything on outdoor walking footwear and sooner or later you'll come across the mantra 'One pound on your foot is equivalent to five pounds on your back' and usually associated with the review of fabric boots or latterly trail shoes and adjectives including awesomeness and amazing. Coincidentally reading the blogs and posts by light footwear advocates, I'm aware of the attrition rate of foot injuries and ailments. Google : plantar fasciitis, achilles tendinitis, metatarsalgia ...

So is there any science behind the statement of increased footwear weight equivalent to increased backpack weight? There is indeed. A study report published in 1983 by the US Army Research Institute Environmental Medicine, titled "The energy cost and heart-rate response of trained and untrained subjects walking and running in shoes and boots" Bruce H. Jones, Michael M. Toner, William L. Daniels and Joseph J. Knapik.

It is an often cited report by advocates of light footwear, less so the actual summary and almost never the results or discussion.

The summary reads :
To determine the difference in the energy cost of walking and running in a lightweight athletic shoe and a heavier boot, fourteen male subjects (6 trained and 8 untrained) had their oxygen uptake (V O2) measured while walking and running on a treadmill. They wore each type of footwear, athletic shoes of the subjects' choice (average weight per pair = 616g), and leather military boots (average weight per pair = 1776g) at 3 walking speeds (4.0, 5.6 and 7.3 km ° h-I) and 3 running speeds (8.9 10.5 and 12.1 km h 1 ). The trials for running were repeated at the same three speeds with the subjects wearing shoes and these shoes plus lead weights. The weight of the shoes plus the lead weights was equal to the weight of the subjects' boots. The VO 2 values with boots were significantly (p< .05) higher (5.9 to 10.2 percent) at all speeds, except the slowest walk, 4.0 km/hr. Also, O2 with shoes plus lead weights were significantly (p < .05) higher than shoes alone. Weight alone appeared to account for 48-70% of the added energy cost of wearing boots. The relative energy cost (Va02, ml * kg - I min - ) of trained and untrained subjects were the same at all speeds, but heart rates for the untrained were significantly higher (p<.05) in both shoes and boots except at the slowest walking speed (4.0 km/hr ). These data indicate that energy expenditure is increased by wearing boots. A large portion of this increase may be attributed to weight of footwear. In addition, the increased energy cost of locomotion with boots appears to place a limiting stress on untrained subjects.

And in the discussion

"HR (heart rate) during boot trials were higher than shoe trials at all speeds except the slowest walk, 4.0 km/hr"
"The data from this study indicate that for an increment of weigh:.equal to 1.4% of body weight carried on the feet the average energy cost increased 8% or 5.7 times what one would have expected for the same weight carried on the torso (Soule and Goldman 1969). Most importantly, the energy cost is significantly increased by wearing boots rather than shoes for walking and running at speeds above 4.0 km / hr"

OK, but what about the ladies?

Ergonomics. Volume 29, Issue 3, 1986
The energy cost of women walking and running in shoes and boots. B H. Jones, J J. Knapik, W L. Daniels and M M. Toner

Abstract
The purpose of this study was to determine the difference in energy cost for women walking and running in shoes versus heavier boots. Seven subjects wore athletic shoes (mean weight = 514 ± 50g) and leather military boots (mean weight = 1371 ± 104g) at three walking speeds (4·0, 5·6 and 7·3km/hour) and two running speeds (8.9 and 10·5 km/hour). During each walking and running trial oxygen uptake ([Vdot]O2 ml kg−1 min−1) was measured. The [Vdot]O2 for women wearing boots were significantly higher (P < 0·05) than for shoes for both walking and running, with the exception of the slowest walking speed. The average increment in energy cost was 1·0% per 100-g increase in weight per pair of footwear. These results are similar to those reported for men from other studies which found increments in energy cost of 0·7 to 0·9% per 100-g increase in weight of footwear.

A vast expanse of wet peat bog and tussocks, Cambrian Mountains

The science points to 4.0 Km/hr as the point at which lighter footwear is significantly better for men and women, walking and running on a treadmill.  Strangely enough you don't read anywhere that there's an insignificant difference between light and heavy footwear below a walking speed of 4km/hr.  4.0 Km/hr (~2.48 mph) is a walking speed that in my opinion is an aspirational a very respectable speed for a landscape photographer in the hills, laden with the hill kit and photography gear. Throw in the wild camping kit and food, and 4 km/hr is probably only exceeded on a gentle descent with the car in sight. Come to think of it, for a 7 hours hill walking trip, with an hour for stops, that's a walk of 24 km at a sustained pace of 4 km/hr, I would speculate that there's a high percentage of hill walkers who walk at speeds less than 4 km/hr and/or stop for far longer than an hour. Walkers and backpackers maintaining walking/running speeds greater than 4 km/hr, could make an empirical and justified scientific case for lightweight footwear, for everyone else it seems dubious if 'one pound on your foot is 5 pounds on your back' actually applies, as the research data inconveniently point out the human body's biomechanics of leg muscles and tendons have an inherent energy tolerance threshold for footwear weight, that threshold is reached at a walking speed of 4 km/hr.

'one pound on your foot is 5 pounds on your back' is a memorable line though. Put 5 lb of weight into a backpack and lift it, yup you can feel it. It doesn't take a genius to work out that a pound of weight on the other foot is another 5 lbs of weight on your back, 10 lbs in total!  Pick up a pair of heavy boots and lighter boots, you can also discern the weight there too. It is odd though that when you put the heavy boots on your feet and walk around you soon forget the weight, the fit and comfort are more apparent and light boots when new are generally less stiff and 'comforting' than new heavy boots.

I can't find any research for temperatures/climate where breathability of the boot and its physiological effect is measured, but in hot conditions there's good empirical evidence to indicate a fabric allows better breathability and 'cooler' feet and are much preferable to 'hot' feet or better still even wear sandals.

Heather bashing on the Moelwyns

So away from people on the internet advocating light footwear for hill walking, what do people who actually work outdoors wear on their feet? Actually there's not that many professions requiring sustained exposure to hill terrain and elements day after day. Of those professions left, it has been my good fortune to meet gamekeepers and stalkers, in the hills and have a 'wee blether' about the land and weather, I've also taken the opportunity to enquire about clothing and footwear worn day in, day out on the hills and moor in all weather, contouring the slopes below ridge lines whilst stalking game across terrain that rarely sees walkers who aren't lost. The same boot names came up time and again. The boots aren't fabric and they are heavy, so they are never written about by backpackers and hill walkers, instead I'll write more about these boots in a future post.