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  1. #1
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    Default Myth or fact? Wt of boots = ?? lbs in pack.

    OK, I admit it. I am bored and felt like starting a "discussion".

    Subject: Is it a fact or a myth that for every pound of weight on your feet it equals a much larger weight in your pack.

    Background: I have seen folks claim numbers from a factor of 3 (this was thirty years ago) up to 6 (in the last couple of weeks). To clarify my understanding of this claim it would go something like this: if your boots weighed 3 lbs apiece then it is the equivalent of adding from 18 to 36 lbs (depending on your favorite factor from above) to your pack over going bare foot.

    Question: does anyone actually have scientific (sorry, I am an engineer) proof that some version of the above is true or false.

    My opinion: There is some truth to the claim, as experience has demonstrated that the heavier the shoe the more exhaustion one feels at the end of the day. However, experience has also convinced me that the claim is wildly exagerated. For example, when I was much younger I participated in a mountain climbing expedition to the wilds of Alaska. At the time I weighed a very ripped 145 lbs and carried a 110lb pack (camping and climbing equipment plus 21 days of food). As you can imagine there was no room for extra shoes so I (as did everyone else) wore my mountaineering boots. I don't know the actual weight of the boots but I am sure that they were at least 3 lbs each (I think 4 but we will go with 3). Nothing was light 30 years ago! By the figures above this works out to an equivalent of 18 to 36 extra lbs. Or 128 to 146 lbs equivalent. Though I could and did carry that pack all day long, over rough trailless terrain, I do not believe that I could have actually carried the equivalent of 128-146 lbs. The 110 lbs kicked my butt good.

    I have thought about this claim some and compared it to other examples I know of in mountaineering and extreme backcountry travel. I just do not believe it can be true. Other examples: in backcountry mountaineering and cross-artic or ant-artic travel it is not uncommon for people to carry 50 lb packs and pull 100+ lb sleds for long periods of time while wearing heavy footwear. Also, thirty years ago many long distance hikers (AT & PCT) carried 60 lb packs, wore heavy hiking boots and managed to do 20 mile days consistantly. I think these examples indicate that factors in the 5-6 lb range must be urban (rural??) legends vice fact.

    Anyway, does anyone want to throw in their $.02? No fighting now

    Wyo

  2. #2
    J.D.
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    Quote Originally Posted by Wyoming
    Question: does anyone actually have scientific (sorry, I am an engineer) proof that some version of the above is true or false. Wyo
    Interesting! 'Cause I have often wondered about those claims myself and I am NOT an engineer. Especially this winter. Age or something and my feet have been freezing/painful cold wearing sneakers. Keep looking at boots.

    Quote Originally Posted by Wyoming
    Also, thirty years ago many long distance hikers (AT & PCT) carried 60 lb packs, wore heavy hiking boots and managed to do 20 mile days consistantly. I think these examples indicate that factors in the 5-6 lb range must be urban (rural??) legends vice fact. Wyo
    In the '70's, I was very proud that I kept my pack under 60 pounds...<g>... And, yes, I did 20 mile days with heavy Vasque boots.

    I'm guessing that it "may" be an age-thing....? Factor in the enthusiasm of youth versus the treachery of age!
    Happy Trails,

    J.D.

  3. #3
    J.D.
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    Good Morning, Wyoming! Just noticed "Round Hill"....! I'm up here in Woodbridge, VA. We're neighbors!
    Happy Trails,

    J.D.

  4. #4

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    From an engineering standpoint, it takes slightly more work to move the boots than if they were in the pack. Taking a boot in my hand, if I wave it back and forth in front of me, it uses more energy than if I quietly hold it.

    Moving them quickly takes more energy and I have felt this difference when I have tried to jog in my leather hiking boots. That gets me tired very quickly.

    However, the 3X, 4X, 6X figures are different hikers ways of estimating how much harder it is for them to carry 4 extra pounds on their feet vs 4 extra pounds in their pack.

    I do know that the weight of a 1 inch diameter blister on a heel seems incredibly heavy and weighs down my whole day.

    My method has been to wear the lightest shoes that I am comfortable in. For winter and for this spring, that is an old fashoned pair of Vasque Sundowner boots, despite my allegiance to a lightweight/ultralight lifestyle and hiking style.
    Walk Well,
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  5. #5
    Registered Loser c.coyle's Avatar
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    Quote Originally Posted by Wyoming
    Subject: Is it a fact or a myth that for every pound of weight on your feet it equals a much larger weight in your pack. ...
    Question: does anyone actually have scientific (sorry, I am an engineer) proof that some version of the above is true or false.
    I, too, would like to see someone post a link or a reference to a credible source for this claim. It makes sense to wear the the lightest footwear you can, consistent with safety and comfort, but I am skeptical of the old 1=5 claim.

    Obviously, you lift your feet over and over while walking, but you don't pick them straight up and put them straight down. I have no scientific or engineering background, but forward momentum has to play a part.

  6. #6
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    My recollection is that this "rule of thumb" came from a study done by the U.S. Army, so SGT Rock may be able to shed a little light on its origins. I'm not sure about the actual ratio, but it's easy enough to prove that it has some validity. From a strictly physics (or engineering) standpoint it takes no actual work at all to move an object (such as your backpack) in a straight line, as long as you do not raise or lower it any. Your feet, on the other hand, must be raised, how ever many inches, every time you pick them up to step forward. I know it sounds a bit strange to say that you're not doing any "work" carrying your pack while walking on level ground, but that's how the laws of physics define it. Realistically, we have to expend energy to keep our packs suspended and to move them forward, along with the rest of our body. But it's not the same as lifting.
    kncats

  7. #7
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    Default Time to pick some nits

    While I agree that weight on the feet has greater impact per pound on the energy you expend while hiking than weight carried on your back, I've couple of nits to pick with some of this discussion.

    First,
    Quote Originally Posted by flyfisher
    From an engineering standpoint, it takes slightly more work to move the boots than if they were in the pack. Taking a boot in my hand, if I wave it back and forth in front of me, it uses more energy than if I quietly hold it.
    I think this analogy could use some tweeking. I think if you compare waving a boot in your hand to hiking, then holding the boot still would be comparable to standing still. In a fairer comparison, you would still be making the same motion with your arm, but the mass of the boot would be supported elsewhere (perhaps your shoulder or upper arm, so as to demonstrated the reduced energy required to do a similar task with the same mass involved).

    Second,
    Code:
    I know it sounds a bit strange to say that you're not doing any "work" carrying your pack while walking on level ground, but that's how the laws of physics define it.
    Close but not quite. You would not have done any work ONLY if you ended up in the same place as you started. If you walk on level ground you will not change your gravitational potential but you may still do work (in the physics sense of the word) if you finish in a new spot. Work = force*distance, but is independent of the path taken.

  8. #8
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    Where is that edit button when you need it? Those should have been "quote" tags instead of "code" tags.

  9. #9
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    Default A better example

    I hate to post twice in a row (so I REALLY don't like posting a third time) BUT, I think this might be a better example.

    Consider the milage you would get in your car if you drove around with 4 bags of concrete in your back seat. Probably pretty close to your normal mileage. Unless you drive something like a Geo Metro.

    Now consider what you happen if you took the concrete out of your back seat and filled your tires with it. Your mileage is toast.

    As c.coyle mentioned it is a matter of momentum (or inertia as engineers call it). More specifically it has to do with the mass moment of intertia (a measure of the distribution of mass throughout a volume).

    While this example had more to do with rotational inertial the same thing can be seen with linear motion if you just swing a sledge hammer the normal way (mass away from your hands) and then swing it backwards (holding it near the mass end and swinging the handle) and notice home much effort it takes for each way.

  10. #10
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    Quote Originally Posted by hiker5
    Work = force*distance, but is independent of the path taken.
    True, however, force=mass*acceleration. As long as you're moving at a constant speed there's no acceleration hence no work.

    Regardless, it's still a bit confusing to try and think and say that we're not doing any work. That's strictly a physical sciences definition of the word which my tired back doesn't really care about. But I think it does help to show that there's more of what we would normally think of as work involved in picking our feet up (with boots) and moving them forward all day.
    kncats

  11. #11
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    Quote Originally Posted by Wyoming
    OK, I admit it. I am bored and felt like starting a "discussion".

    Subject: Is it a fact or a myth that for every pound of weight on your feet it equals a much larger weight in your pack.

    Background: I have seen folks claim numbers from a factor of 3 (this was thirty years ago) up to 6 (in the last couple of weeks). To clarify my understanding of this claim it would go something like this: if your boots weighed 3 lbs apiece then it is the equivalent of adding from 18 to 36 lbs (depending on your favorite factor from above) to your pack over going bare foot.

    Question: does anyone actually have scientific (sorry, I am an engineer) proof that some version of the above is true or false.
    I think the mathematical model is too varied for anyone to have proven what the actual ratio is for hikers because we hike in varied conditions on a daily and hourly basis. On flat sidewalks, the difference is not going to be as much as when you are climbing up Mount Washington in NH because the biggest increase in work, or energy expended is when you lift your feet and likewise the difference will be even less when you are going down Blood Mountain in GA. For hikers, that means it is subjective because we are not always hiking the same terrain. I don't have a problem with the x5 rule... sounds about right to me.

    This same argument also applies to maximum pack weight or maximum daily mileage. It all depends on many factors, too many to make detailed analysis useful... so we resort to rules of thumb to come up with useful models and then adjust the rule of thumb when and if we find that it is no longer applicable. I'm an old engineer and at least that's the way I do it.

    Youngblood

  12. #12
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    Quote Originally Posted by kncats
    True, however, force=mass*acceleration. As long as you're moving at a constant speed there's no acceleration hence no work.
    I know you really aren't interested in the technicalities of the physics, but I can't help myself. For this to be true we would have to make some assumptions.

    -frictionless example (clearly not true, just see any of the chaffing threads )

    - you did not start the hike from rest

    - you did not end the hike at rest


    I think the force in this example would be the force that you impart on the ground to propel yourself with each step.

    I think we have covered all 3 of newtons laws of motion now.

  13. #13
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    I found reference to U.S. Army treadmill test in 1969 in an old magazine article: http://www.rockandice.com/gear/135%20Field%20Tested.pdf

    That says:

    "U.S. Army treadmill tests in 1969 found that an extra pound on the foot exacted the same energy output as an extra 3.5 to 5.25 pounds on the back. Similar tests published in Ergonomics in 1986 concluded that a pound on the foot equals 6.4 pounds on the back. Simply put, wearing a boot like La Sportiva’s Trango S (3 pounds 6 ounces for a pair of size 10.5, $225), which eliminates 1 to 1.5 pounds of weight, could be like tossing five to seven pounds from your pack."

    Can't find the actual tests, though.

  14. #14
    Yellow Jacket
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    Backpacker magazine had some sports medicine group (in CO?) do all kinds of test on various hiking/climbing superstars (flyin' brian, etc.) about 1.5 years ago. Besides listing various VO2 max levels for each person, they also listed that 1# on your feet is 6.2# on your back. Rather than the "common belief that 1# is 5# on your back".

    I think, too, they showed that an hour of walking with treking poles consumed 30-40% more calories than without.
    Yellow Jacket -- Words of Wisdom (tm) go here.

  15. #15
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    Quote Originally Posted by hiker5
    Now consider what you happen if you took the concrete out of your back seat and filled your tires with it. Your mileage is toast.
    It'd be closer to realistic if only 180 degrees of each tire were filled with concrete.
    Just hike.

  16. #16
    Registered Loser c.coyle's Avatar
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    Thumbs up Hiker Physics

    Quote Originally Posted by franklooper
    It'd be closer to realistic if only 180 degrees of each tire were filled with concrete.
    Sorry Frank. That had me howlin' for some reason. This is one of the best threads ever.

  17. #17
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    Default External Work != Internal Work

    Quote Originally Posted by TDale
    I found reference to U.S. Army treadmill test in 1969 in an old magazine article: http://www.rockandice.com/gear/135%20Field%20Tested.pdf

    That says:

    "U.S. Army treadmill tests in 1969 found that an extra pound on the foot exacted the same energy output as an extra 3.5 to 5.25 pounds on the back. Similar tests published in Ergonomics in 1986 concluded that a pound on the foot equals 6.4 pounds on the back. Simply put, wearing a boot like La Sportiva’s Trango S (3 pounds 6 ounces for a pair of size 10.5, $225), which eliminates 1 to 1.5 pounds of weight, could be like tossing five to seven pounds from your pack."

    Can't find the actual tests, though.
    ENERGY COST OF BACKPACKING IN HEAVY BOOTS.
    Legg, S. J. (Army Personnel Research Establishment, Farnborough, Engl); Mahanty, A.
    Source: Ergonomics, v 29, n 3, Mar, 1986, p 433-438
    ISSN: 0014-0139 CODEN: ERGOAX

    Abstract: Previous studies have investigated the oxygen cost (VO//2) of increasing boot weight during unloaded walking or running, and have shown that for each 100 g increase in weight of footwear there is a 0. 7-1. 0% increase in VO//2. In reality (except in athletic events) the use of heavy footwear is associated with load carriage, usually backpacking. We therefore investigated the effects of increasing boot weight by 5% of body weight on the VO//2 of backpacking a load amounting to 35% of the body-weight in five healthy young males who walked at 4. 5 km/hour (0% grade) on a motor-driven treadmill. The results indicated a mean increase of 0. 96% in VO//2 whilst backpacking for each 100-g increase in boot weight. In contrast the oxygen cost of increasing the backpack load was only 0. 15% indicating that it was 6. 4 times more expensive to carry weight on the feet as compared to the back.

    Quote Originally Posted by kncats
    True, however, force=mass*acceleration. As long as you're moving at a constant speed there's no acceleration hence no work.

    Regardless, it's still a bit confusing to try and think and say that we're not doing any work. That's strictly a physical sciences definition of the word which my tired back doesn't really care about. But I think it does help to show that there's more of what we would normally think of as work involved in picking our feet up (with boots) and moving them forward all day.
    I think that is the whole point. The physics definition of work dosen't apply to trying to figure out how much work is being done inside your body.

    I could push agaist a wall for an hour, not move it and have a physicist tell me that I haven't done any work. A physiologist could measure the metabolic energy spent pushing against the wall and tell me that I have, in fact, done a lot of work.

    Engineers would really like a mechanics type answer to this question. The big limitation to using biomechanics in a walking type of situation is that is that is walking is an extremely repetitive task (therefore dosen't take into consideration fatigue) and metabolic factors are going to be the limiting factor in terms of effort performed by the body.

    ERTW

  18. #18
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    Quote Originally Posted by TDale
    I found reference to U.S. Army treadmill test in 1969 in an old magazine article: http://www.rockandice.com/gear/135%20Field%20Tested.pdf

    That says:

    "U.S. Army treadmill tests in 1969 found that an extra pound on the foot exacted the same energy output as an extra 3.5 to 5.25 pounds on the back. Similar tests published in Ergonomics in 1986 concluded that a pound on the foot equals 6.4 pounds on the back. Simply put, wearing a boot like La Sportiva’s Trango S (3 pounds 6 ounces for a pair of size 10.5, $225), which eliminates 1 to 1.5 pounds of weight, could be like tossing five to seven pounds from your pack."

    Can't find the actual tests, though.
    This makes perfect sense. See, my 'cruit boots in 1985 didn't weight very much at all.In about 1989 the Army came out with a new design that cost about twice as much, and weighed about twice as much. Then just recently they started issuing another boot that costs about 25% more than the last pair of boots and weighs about 25% more two. Lesson - the military is one place where they will spend millions to figure something out then ignore their own advise. I better get out before boots cost $!50 a pair and weigh 5 pounds.
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  19. #19
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    Perhaps the key is that the original study was a TREADMILL test. On a treadmill the feet move all over the place while the back stays nearly stationary. While actually hiking, all that weight on the back is getting moved along the Trail, up and down hills.

    I bet that treadmill results are not the same as real life, giving an exagerated impact of boot weight.

    But I agree with Sarge, the military has made some pretty weird footwear choices.

  20. #20
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    Default Thanks All - very instructive

    Hey, I really appreciate the comments. I would have never guessed there were actual studies done that verified this.

    Perhaps the reason why there is something of a range in the results is that each person has a different bio-mechanical efficiency in how they stride? If you watch marathon runners you will notice that many of the very good ones seem to glide rather than run. Maybe it works the same way for hikers only in slow motion.

    We need a film of "flyin brian" to evaluate

    Wyo

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