Weight on your feet

In several books, including the soon to be published Smarter Backpacking, I have written that it is five times as energy consuming to carry something on your feet, compared to carry it on your back. This makes some people irritated, so I have collected some of the scientific articles that support this rule of thumb. Read and judge for yourself.

By Jörgen Johansson

I have written the following in Smarter Backpacking:
Carrying a weight on your feet takes five times more energy than carrying the same weight on your back. Thus, finding the lightest footwear that does the job has top priority for me.
...
Climbers preparing for the first ascent of Mount Everest in 1953 formulated a rule of thumb; one pound on your feet equals five pounds on your back. In other words, to move something attached to your feet requires five times the amount of energy that it takes to transport the same weight on your back. Since then quite a bit of research supports this rule of thumb. Depending on circumstances such as speed,slope and weight carried, there is of course variation.

All this feels intuitively right to me. Anyone who has walked with mud caked to their feet knows how heavy the strides become. For exercise purpose weight cuffs for wrists and ankles are sold. If they did not increase the strain on the body they would have no place.

My sources
I read my first American backpacking books in the 70's. A fact-filled bible was The Complete Walker by Colin Fletcher. In the third edition (1983) I could read (p 53):
Weigth is even more important on the feet than on the back. In his classic 1906 book, Camping and Woodcraft, Horace Kephart calcculated the results of wearing boots just one pount too heavy: "In ten miles, there are 21, 120 average paces. At one extra pound to the pace, the boots make you lift, in a ten-mile tramp, over ten tons more foot gear". In 1953 the successful Mount Everest expedition came to the conclusion that in terms of physical effort one pound on the feet is equivalent to five pounds on the back. A consensus of informed opinion now seems to support that assesment.

You will find the same wording in the latest version, The Complete Walker IV (2002) written by Fletcher and Chip Rawlins.

What could be be called the modern day standard bible of backpacking is The Backpacker's Handbook by Chris Townsend. Chris is one of the worlds most experienced long distance hikers, as well as a journalist that has tested hiking gear for decades. In the second and third editions (2005) of his book you can read (p. 39):

That lighter footwear is less tiring seems indisputable. The general estimate is that every pound on your feet equals 5 pounds on your back. If that's correct, and it certainly feels like it, then wearing 2-pound rather than 4-pound boots is like removing 10 pounds from your pack.

By the same author we also have The Advanced Backpacker (2001) in which Chris writes (s. 113-114):
The often quoted adage that a pound on your feet equals five on your back is true in its overall implications, even if the specific figures aren't necessarily accurate. I discovered that on the Pacific Crest Trail when I ended up carrying my 5-pound boots and hiking in my 17-ounce running shoes. Although I could feel the addition to my load, the boots were less tiring to carry on my back than to wear on my feet.


Scientific base
So far we see that the rule of thumb seems to be well established in backpacking literature. With a bit of help I have also managed to find a number of scientific articles on this subject. Not surprisingly these articles show a more varied picture than the rule of thumb. Otherwise it would not be a rule of thumb.

Below I have made short summaries of a number of these articles.

The energy cost and heart-rate response of trained and untrained subjects walking and running in shoes and boots by Bruce H Jones, Michael M. Toner, William L. Daniels och Joseph J. Knapik. US Army Research Institute of Environmental Medicine, Natick, Massachusetts, USA. Publicerad i Ergonomics1984, vol. 27, No.8, 805-902.

In the introduction the authors describe how differen studies have looked at energy cost for walking and running, but that few studies have taken the weight of the footwear into account. Examples of such studies are Catlin and Dresendorfer (1979), who have found that a weight difference of 350 grams (12 oz) on footwear increases energy consumption with 3.3%. Soule and Goldman (1969) have found that the energy cost is about 5 times greater if you carry a weight on your feet compared to carry it on your torso.


The authors of the current study mean that it can be expected that even small increases in weight on the feet should have considerable impact on the energy expenditure for both walking and running. Many professions like fire man, lumberjack, miner and soldier use heavy footwear and the job demands that you move about in these. But no studies have so far been made where energy cost for different weights of footwear ad different speeds That is the purpose of the current study.


Research method
Fourteen men, six trained and eight untrained was part of the experiment. There maximum oxygen uptake was measured using  a standardised method using Douglas bags. After this the energy cost was compared between walking and running in boths shoes and heavy boots. Finally the energy cost for running in shoes plus weights was measured. Running shoes and army boots were used. The average weight of the shoes was 616 grams, that of the boots was 1776 grams. The men walked on a treadmill with three different speeds; 4, 5,6 and 7,3 kilometers/hours.


The third part of the test was comparing the running shoes with boots by adding weights around the ankles so that the weight compared to that of the boots.


Results
The energy cost of wearing boots was significantly higher at all speeds except the lowest (4 km/h). The increase in oxygen uptake that could be attributed to wearing of boots compared to shoes varied from 5,9% to 10,2%, with an average of 8% in spite of the fact that the weight added by the boots was only 1,4% of the persons body weight.


The difference in running in shoes only compared to shoes plus ankle weights varied between 5,0-6,3%. Comparing shoes with weights and boots, 48-70% of the difference was due to the weight, leaving at least 30% unaccounted for. The hypthesis if the authors was that this unexplained extra energy cost due to wearing boots was because of biomechanical limitations like stiff soles and restricting uppers.


The conclusion was that the study supported the calculations from Soule and Goldman (1969) about energy cost for wearing a weight on your feet was 4,7-6,3 (depending on speed) times as big as carrying the same weight on your torso. This means that for trained and untrained persons walking and running i boots mean a considerable increase in energy expenditure compared to the same activities in running shoes.

Energy cost of backpacking in heavy boots by S. J. Legg and A. Mahanty, Army Personnel Research Establishment, Farnborugh, Hants, England. Publicerad i Ergonomics, 1986. Vol. 29, No. 3.
(This study has been frequently quoted in backpacking literature.) In the introduction the authors says that is well known that the weight of footwear can affect the energy cost for walking and running. References given are Hettinger och Miller (1958) and Strydom et al (1968). There is also a reference to Catlin and Dressendorfer (1979) having made studies of marathon runners on treadmills that show a 0,9% increase in energy expenditure for every 100 gram increase in shoe weight.


There is also a reference to the study refererred above by Jones et al (1984) where the result was a 0,7% increase for every 100 gram increase in shoe weight, this being the same as Martin (1984) has shown. Comparable results for women was 1,0% according to Jones et al (1986).
All these studies had been made without the test persons carrying any other weight except that on their feet. Normally, says Legg and Mahanty, use of heavy footwear is connected to carrying a pack. The purpose of their study was to study what increasing the weight of the footwear meant energy expenditure while backpacking.


Research method
Five young men took part of the test. Their maximum oxygen uptake was measured according to Taylor et al (1955) and this was then the base line for the test:


- No pack, military boots
- Pack and military boots. Pack weighing 35% of body weight (average 24,9 kilograms)
- Pack and military boots with weights. 30% of body weight was carried in the pack and the difference up to 35% was a lead weight taped to the boot upper, near the ankle.


Results
Carrying 5% of the body weight on the boots was significantly more strenous than carrying it on the back. It was calculated that a 100 gram extra on the shoes meant an increase in energy cost by 0,96%, meaning it was 6,4 times more energy consuming carrying this weight on the feet than in the pack.


It is concluded that the results are well in line with other studies (0,7-1,0% increase in energy cost per 100 grams in shoe weight). The final conclusion is that the therory of the relation between shoe weight and energy cost, earlier developed for walking and running without a pack can be expanded to include walking with a pack.

Physiological strain due to load carrying in heavy footwear av M. Holejwin, R. Heus och L. J. A. Wammes TNO Institute for Perception, Termal Physilogy Research Group, Soesterberg, Nederländerna publicerad i European Journal of Applied Physiology 1992 65:129-134.
In the introduction to this study the authors says that it is well known that walking with shoes leads to a 0,7-1,0% increase in energy cost per 100 gram weight added. Other studies are referred to, some of the above as well. However, most studies have been made with men, except Jones et al (1986), who found a value of 1,0% for women.


The authors mean that in order to do a just comparison both men and women should be tested in the same study. A theory is that women due to shorter legs have a higher frequency while walking than men an tend to increase their hiking speed by increasing the frequency rather than the lenght of the stride. This would in turn mean a comparatively higher energy cost for women if the shoes get heavier.


This and other question marks concerning the differences between men and women is the basis of the current study.


Research method
Five men and five women were tested. They were all physically active but did not take part of any formal training program. The maximum oxygen uptake was measured in order to compensate for individual differences. Everbody then walked on a horisontal treadmill for six minutes at the different speeds of 4, 5,25 and 6,5 kilometers per hour.This was done with the following loads:


- Barefoot without pack
- With either military boots or waist belt (12 kilograms)
- With both military boots and waist belt


The average weight for the boots worn by the women was 2,045 kilos/pair and by the men 2.370 kilos/pair.


Results
It was found that the weight of the footwear increased energy cost with 1,9-4,7 times compared to the same body weight, dependent on sex and speed. The lowest value was for women at 4 km/h, the highest for men at 6,5 km/h. It is also concluded that this is in agreement with earlier studies involving only men.
The increased energy cost is explained by the fact that if you walk at 6,5 km/h every foot has to be raised approximately 0,3 meters and then accelarated to twice the average body speed before the foot is slowed down to zero. It is also referred to Jones et al (1984) who claims that 30% of the increased energy expenditure is explained by stiff soles and limiting uppers. The authors also add that energy expenditure during backpacking is also influences by factors such as clothing, slope and surface. Pandolf et al (1977) has shown an equation including these effects which show that they lead to a considerable increase in energy cost.

My own summaries and conclusions
A common measurement in the studies is that each addition of 100 grams to your feet increased the energy cost with 0,7-1,0%. Personally I find this measurement hard to relate to. What does it all mean in real life?


Obviously the scientists also feel a need to communicate their results in a more practical way. All three papers summarized above do the same maths, they relate the increase in energy cost to carried weight. These are the results from the three articles:
- 4,7-6,3 times
- 6,4 times
- 1,9-4,7 times

One of the articles show that no increase in energy cost was seen at the lowest speed, 4, 0 km/h. However it was found at higher speeds. This is reported but the authors do not let this result influence their overall conclusion, which is that earlier findings of it being 4,7-6,3 times as energy consuming to carry something on your feet compared to carrying it on your back.

Since the scientist themselves do not let this difference at 4,0 km/h influence their conclusions that is good enough for me.

How exact is "five times as heavy"?

Looking at the above the question that should be asked is if we should revise our rule of thumb and instead say that it is 4,7 or 1,9 times more energy consuming to carry something on your feet than on your back.
Well, maybe. It can of course be stated that "it depends" on speed, slope, surface and other things that are pretty obvious to a hiker. So for a hike you do on a well graded trail, the decimal should probably end up in a different place than when you hike on a road or cross country on talus. 

And I have found no newer research that contradicts these findings. This is where science stands today.
None of the above scientists have made any great attempt to establish any other rule of thumb. By rule of thumb I mean some sort of average that could be applied in most situations and offer guidance without being totally misleading. I have no personal commitment to "5 times". I certainly did not make it up, nor did Colin Fletcher or Chris Townsend. What I find interesting is to reach as wide an audience as possible with this important piece of information. It certainly has a, scientifically proven, majore impact on how strenous your hike will be.

For some people this rule of thumb, or maybe any indication that weight on your feet is important, very controversial and I have in fact been accused of spreading myths by repeating this rule and publishing the studies above in Swedish last year. My answer was and is; you have seen my scientific articles supporting what I say, where are your studies contradicting these findings and this rule of thumb? I am still waiting.

One might speculate on why this question is, or has been, loaded. My guess is that it is a mixture of conservatism (everybody KNOWS that you need heavy shoes while you hike) and commercial interests (where should the heavy shoe industry go if everyone hiked in running shoes?). Note that heavy shoes usually means boots, but not always. Today you can find boots that are just as light as running shoes. But that is a different discussion.


So the main message is that you pay a very high price for heavy footwear. I want as many hikers as possible to be aware that they have a choice. Plenty of hikers have hiked along the Rocky Mountains and Andrew Skurka has circled Alaska in trail runners. You do not NEED heavy shoes or boots to hike cross country in demanding terrain. It is simply a matter of personal choice.

But in order for everyone to be able to make their choices I believe that information should be free and availble. Then it is up to everyone to choose. We all carry the weight of our own choices. And there are still people who believe the earth is flat. Fortunately they no longer have the power to stop others from claiming otherwise.
As I researched this area a couple of years ago I was in e-mail contact with Professor Stephen Legg, the author of one of the above articles and a man who did many other studies on the subject of footwear and transportation a couple of decades ago. I asked him:

Jörgen: My own conclusion is that the old adage, reputedly from the 1953 Everest expedition about 5 times is still a nice round number which adheres to available scientific findings and communicates that you pay a severe penalty for carrying weight in your feet. Exactly how heavy can vary and depends on a lot of factors.
Does this seem reasonable ?
Stephen Legg: I agree for practical purposes 5 times is a fair adage.

15 comments:

Andrew Wilson said...

I just hiked some 1600+km from Erfurt, Germany, to Rome, all of it in Crocs. And I loved the weight: my pair weighs 370 grams. I was told repeatedly by people along the way that it was impossible. The single most repeated question we got along the way when we told people we were going to Rome was "I hope you have sturdy shoes." There's something deeply ingrained in the European mind about sturdy shoes. Probably has something to do with tetanus. Well, Crocs are sufficient for most trail-like travel.

Lukas said...

Nice. I totaly agree. As a competing cross country runner I use lighter shoes on competitions than on training. Why? Less energy use is the main reason. When new hikingboots is needed I will think more of the weight for sure.

John Dourneen said...

Excellent, excellent article. It was a real pleasure to read such a well-researched piece. Thanks. I'm looking forward to your book. Where will one be able to order it?

It would seem, to draw another parallel, that the belief for the NEED for heavy boots, is a the backpacking equivalent of creationism. While evolution and lighter shoes are both just theories they are the best we have. Scientific 'truth' is, of course, merely the most expedient error.

That said, I wear fairly heavy boots at the moment, although they are soon to be retired. My reason? After rupturing my achilles (no walking at all for three months), I felt I NEEDED (that word again!) something that would support and, through the extra weight around the ankle, strengthen my weak joint. I've done a lot of hiking in them (approaching 1000km) and they have been faithful and hard wearing. Nonetheless, I'm relishing walking without 650g on each foot!

Phil said...

Chris,

Thanks for the documented info which supports what virtually every through hiker has learned from experience - lighter footware is the prefered choice.

Jörgen Johansson said...

Thank you. Still, many people get extremely vexed when you publish an article like that. It is a translation from Swedish and was published in 2009. It lead to endless debate on a forum, where many thought you should not be allowed to publish such inferior nonsense. You've proably read this piece:
http://www.fjaderlatt.se/2009/05/interview-chris-townsend-on-footwear.html
It was published around the same time an one comment was: "excentric Englishmen"
I thought that one was great in showing how the subject makes people emote. I'm sure you could write a thesis on why a small part of a reasonably peaceful hobby can be soo sensitive.

Jörgen Johansson said...

Forgot; the book should be available any day. You'll find it on Amazon, and co.uk seems to ship, while in US it is 'temporily out of stock'.
I hesitate to make a big show out of introducing it before I know it is readily available, especially since people might order it for Christmas and get disappointed if it does not show up. I have ordered a copy from Amazon.co.uk and been told it should arrive on Dec 23.
www.smarterbackpacking.com will let you know more. Look at this as a low key launching :-)

Lightening up... said...

Thank you Jörgen!

This is R-E-A-L-L-Y interesting! I will pass the information (i.e. link to this post) on some Finnish hiking discussion forums.

Inspired by this, I also did some searching thru multiple article data bases and found a lot of interesting articles, though mostly on pack weight and load distribution. Unfortunately I don't have the time to read them all for a while...

But for those of you who have also access to scientific full texts: Go and take the hobby to the next level. ;)

Jörgen Johansson said...

Lightening up,
I think it would be great if people with access to scientific databases would publish information they find there. For this article I had help from a friend with that kind of access. There are lots of interesting things to be found, mostly having to do with the military looking at ways of increasing mobility and range for infantry.
I have also heard of studies showing that east Africans are so good at long distance running because they have very slender/light bones in their feet and lower legs. Can someone find that kind of stuff it would be interesting. As well as studies on how using weighted cuffs around wrist and ankles affects muscles and energy expenditure.

Anonymous said...

East-Africans can run more efficient. There are several reasons for that. A few come to mind:

East-African runners have a short calf muscle and a long achilles. Now the achilles stores energy when the foot comes down and because their achilles is relative long, it can store more energy. This means that the runner has to generate less energy. So East-African runners can run longer distances using on the same amount of energy.

Also, their lower leg (beneath the knee) is relative light, which means that there is less mass to move while running. And the lower leg is the part that must be moved most during running. So less energy is required.

Your shoes are at the very end of the leg. So moving them, takes relative much energy. That's physics. The further away a mass is on a moving part, the more energy it takes to move it. So you can save energy by reducing the mass of that part. In this case: reduce the mass of the shoes.

English is not my first language, but I hope it was understandable...

sabi said...

Excellent read and collecting research - connecting different fields!

Add some biological things to the physics:
When having weight on your feet it is concentrical and excentrical muscle work with fast and energy-consuming leg muscles.

When having weight on your back it is mostly statical muscle work with low and energy saving back muscles.

Differences in the distribution of these low and fast twitch fibers are also part in the different energy efficiency in long distance runners. Good runners will rarely have bulky muscles like Arnold ;)

Joe Newton said...

Excellent article Jorgen. I will no doubt be pointing many 'non-believers' in the direction of this post. For me I needed to try hiking in lightweight footwear just once. It was a revelation.

Sarvi said...

Perhaps one of the reasons people get upset is that you alienate them by comparing them to flat earth-believers and other idiots. Stick to the science and skip the name-calling and ridicule, please. It would definitely help the cause.

Jörgen Johansson said...

Sarvi,
You're probably rigth. And I'm probably human...

Unknown said...

What if you have a weak ancle and twist it time and again?
And if you walk in very rocky/stony conditions?

Jörgen Johansson said...

If you have an ankle that is repeatedly twisted this is a medical condition that could benefit from talking to a physician.

If you are thinking of ankle support my advice is to separate this from the footwear. It is doubtful to say the least if high boots give much support, in spite of marketing claims and general supposition. Encyclopedic backpacking books like The Backpackers Handbook by Chris Townsend looks at this at lenght. More important for avoiding twisted ankles than high boots is the shape of the heel cup.

The number one solution for support would be sports tape. Many athletes with damaged ankles and other joints tape themselves routinely. I alway carry a couple of yards when I am hiking.

More permanent-ish solutions giving ankle support can be found in the link below and is further commented on in the book:
http://www.smarterbackpacking.com/search/label/Ankle%20support

In very rocky and stony conditions I have found light footwear that gives better precision when placing your feet and, mostly, a pair of hiking poles being the best ankle support. Fact is, since I started using poles and travelling light rocky terrain does not slow me down much, compared to what it used to.

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