Ultralighting: Pack Weight Vs Body Weight

[Burnsy]

I have run a heap of searches and read a heap of threads but I can find no real discussion on the above. In the Ultralight = Fad thread I found the following quote but there was no follow up discussion.

For active adults I'd argue that percentage of your body weight (in reference to your pack) is more relevant than total actual weight.

I think the pursuit of lighter gear relative to the environment you are in can only be a good thing for your body and while upgrading gear recently we have been looking at the weight of each item and taking into account when deciding on purchases. I do wonder though if some perspective has been lost or is everyone on here the same size and build While I understand that it is easy to categorise based on base weights and these weight classes generally define quite distinct changes in the design and style of the big 4, should there not be more consideration and discussion regarding the size of whoever is carrying them?

Being light is all well and good but a base weight of 5kg is not the the same when you compare a 190cm 90kg bloke with a feather weight like myself (64kgs wet). I expect for our next trip my total pack weight including water sits between 15 and 18kg or about 25% of my body mass and I know in the past it has been up around 25kgs (nearly 40%). When you think about it this is not really comparable to the same weight carried by a fit 90kg person - 15% of body mass.

Are there any discussions concerning what is a healthy weight to carry for a person as a percentage of body mass? There must be some sports science types around who can produce some facts and figures. Or perhaps some armed service personnel, you would think this type of thing would have been looked at by the army over the years. Does anyone know of any good reads on the subject?

[icefest]

You mean like this:
http://scitation.aip.org/content/aapt/j ... /1.4897584

[Burnsy]

Interesting read and goes against everything I assumed. Being small I assumed a big bloke could carry more, this study says I should be able to pretty much carry equal based on weight and more based on percentage. Kind of makes sense when you think that we are limited by our joints and structure and this should be pretty similar for all of us.
Thanks for the link.

[Burnsy]

This other link referenced within that above is a different yet slightly circular take on it, no science though.
http://www.backpacking.net/packwate.html

[stry]

Interesting read Icefest.

My observations and personal experience are more in line with burnsy's.

If build, which is most important, approximate age, and fitness are similar; the heavier person wins - absolutely no contest. I would go as far as to say that the opposing theory is entertaining brain exercise for someone, but has produced incorrect conclusions.

Note this is for weight carrying only. Climbing lightly laden and general bush agility, again lightly laden, favour the lighter person. Pushing through scrub does not.

I've got the scans, bills and xrays to support my view . Sample size of one, but observations of many.

[Bubbalouie]

This other link referenced within that above is a different yet slightly circular take on it, no science though.
http://www.backpacking.net/packwate.html

To be honest I agree with you a bit. People easily become overly fixated on numbers.

Ideally you should just aim for the lowest weight that is both safe and practical for your needs and destination. Once you've achieved that you can't go any lower any way so why keep looking at numbers.

Personally I am 193cm tall, most of my gear is the long+wide or larger size. For an overnight trip in moderate conditions I fit the ultralight criteria. If I'm going for longer my pack gains some redundancies and it doesn't take much and I'm no longer classified as ultralight. In practical terms I could only change 1 or 2 things to save weight without compromising function, the extra grand that would cost will save 300 grams and still wouldn't see me ultralight for a 5 day trip. However, I've found my current set up to be fairly comfortable and isn't missing things I need (might need?). Whilst I'm sure a few people would balk at a 200g med kit (a bandage suitable for snake bites alone comes in at 80g) or a spare set of trousers for trips over 4 days those few extra grams afford me greater peace of mind.

[Burnsy]

200 g for a med kit is light. Mine is 500 but I have spent enough time in the bush and attended to enough casualties to know I would personally rather carrying the extra than be left short if one of my family was injured. As you said though it is about your own ability and comfort both physically and mentally.

[slparker]

Icefest wrote:
You mean like this:
http://scitation.aip.org/content/aapt/j ... /1.4897584

Image

Interesting... makes sense and really all walkers should carry loads no more than a small guy can carry. When stooping, climbing or negotiating difficult terrain that '30% of bodyweight' carried by the 100kg guy suddenly creates a fair moment of force that is quite different to standing upright.
We'll never see small powerlifters - but they just lift in a vertical plane; but those same big bulky dudes carrying that muscle mass, plus another 40kg of packweight bent over and scrambling upa hill are doing it really tough - suddenly that 40g + torso weight is placed on a lever pivoting on the hips and I doubt that even that extra muscle strength could bear it easily.
Another way of looking at this is that muscles derive power from surface area (2-dimensions), proportionate weight is a factor of volume (3-dimensions). It means that bearable weight is not a linear relationship and it may be 30% of weight for a 60 kg person but only 15% of weight for a 120 kg person.....

[Bubbalouie]

Another way of looking at this is that muscles derive power from surface area (2-dimensions), proportionate weight is a factor of volume (3-dimensions). It means that bearable weight is not a linear relationship and it may be 30% of weight for a 60 kg person but only 15% of weight for a 120 kg person.....

+1

This is why you don't see olympic gymnasts that are 6+ feet tall.

In practical terms though I think conditioning is vastly more important than how tall you are. Being taller puts people at a slight mechanical disadvantage but it's easier to be conditioned to tolerate 15% than 20% simply as a side effect of being active (f=ma). So in an "unconditioned" state the active large person has an advantage over the active small person. However, with deliberate training and conditioning the person who's a hair under 6 feet tall will exceed the capabilities of some who's 6'6" (all other things being equal that is).

The point is, given deliberate conditioning the medium sized people have a distinct advantage. However, a normal active person (that isn't training to specifically increase load carrying ability) who is taller+heavier will have a natural advantage in total capacity (explaining Stry's observations), at least until they both start trying to maximise carrying capacity.

[madmacca]

I have run a heap of searches and read a heap of threads but I can find no real discussion on the above. In the Ultralight = Fad thread I found the following quote but there was no follow up discussion.

For active adults I'd argue that percentage of your body weight (in reference to your pack) is more relevant than total actual weight.

I think the pursuit of lighter gear relative to the environment you are in can only be a good thing for your body and while upgrading gear recently we have been looking at the weight of each item and taking into account when deciding on purchases. I do wonder though if some perspective has been lost or is everyone on here the same size and build While I understand that it is easy to categorise based on base weights and these weight classes generally define quite distinct changes in the design and style of the big 4, should there not be more consideration and discussion regarding the size of whoever is carrying them?

Being light is all well and good but a base weight of 5kg is not the the same when you compare a 190cm 90kg bloke with a feather weight like myself (64kgs wet). I expect for our next trip my total pack weight including water sits between 15 and 18kg or about 25% of my body mass and I know in the past it has been up around 25kgs (nearly 40%). When you think about it this is not really comparable to the same weight carried by a fit 90kg person - 15% of body mass.

Are there any discussions concerning what is a healthy weight to carry for a person as a percentage of body mass? There must be some sports science types around who can produce some facts and figures. Or perhaps some armed service personnel, you would think this type of thing would have been looked at by the army over the years. Does anyone know of any good reads on the subject?

I'm not sure whether there is any loss of perspective here. Whether you are 90 kg, or 64 kg, you are going to benefit from a lighter pack.

Of course, there is an argument that a bigger person requires a longer mat and sleeping bag, extra fabric in their clothes, etc. But if we are looking at base weights in the 4-7 kg range, then an extra 0.5 kg allowance for this would be generous.

The miltary expect their people to fight (ie. charge the mythical machine gun nest) with about 15 kg of gear. Expected marching weight is around 35 kg, but an infantry combat load-out is 50-55 kg. They accept that there is a performance drop off at these kind of weights, but figure that the increase in combat power (more equipment and ammunition) is worth the fatigue. In interpreting these figures, remember that we are talking about people who are young and extremely fit, and an organisation structured on pushing people to their limits. Carrying 50 kg is NOT enjoyable, and I bushwalk for pleasure. There is normally a slight adjustment for size - you don't give the heavy equipment (eg. radio, machine gun) to the smallest guy in the squad, but apart from that, everyone carries pretty much the same.

[Burnsy]

Found a little more on pack weights with studies carried out by a couple of armed forces all coming out around the same - 30% of bodyweight before performance is affected.

The write up is down the page a bit here:
http://bushwalkingnsw.org.au/clubsites/ ... _Packs.htm

[sunnyape]

I have run a heap of searches and read a heap of threads but I can find no real discussion on the above. In the Ultralight = Fad thread I found the following quote but there was no follow up discussion.

For active adults I'd argue that percentage of your body weight (in reference to your pack) is more relevant than total actual weight.

I'd agree with Bubbaloie regarding percentage. I've used the general rule of not exceeding 30% of my body weight for my total pack weight. Having a lighter total pack weight just means you can carry a higher percentage of food and go for longer periods. Or, having a lighter pack weight means you can carry the same amount of food and fatigue less over the same distance.

[Turfa]

Interesting question....and raises another point I have always wondered about.

When trying to reduce your pack weight, is there an equal benefit from reducing your body weight. For example, rather than spending hundreds of dollars on new lightweight gear to reduce your pack weight by 5kg, would you get the same benefit by simply losing 5kg of body weight (much cheaper, but no shiny new gear !!!)

The study in the link would seem to support that losing body weight is just as beneficial.

[forest]

When trying to reduce your pack weight, is there an equal benefit from reducing your body weight. For example, rather than spending hundreds of dollars on new lightweight gear to reduce your pack weight by 5kg, would you get the same benefit by simply losing 5kg of body weight (much cheaper, but no shiny new gear !!!)

Turfa your suggestion I don't like one bit. Gosh come on, we all like shinny new gear !!!
But it is valid and a point I'll often make to people, it's a touchy subject with many........

I've seen the same argument over the cycling game. People spend thousands more on the flashiest bike that might be 500g lighter than another costing a sensible amount.
And the rider does this all chasing weight so they can be "faster"...... Never mind the extra 20kg's there carry around there waist from all the indulgences at each end of the regular Saturday social ride. Gotta get fuelled up for the return ride.
But hey my bikes lighter than yours.

It raises an excellent point. One which I struggle with sometimes as I've a real sweet tooth.

[sunnyape]

Never mind the extra 20kg's there carry around there waist.

The English teacher groans and rolls THEIR eyes at what THEY read has been written THERE.

[South_Aussie_Hiker]

Don't get me started, sunnyape.

As for percentage weight, I'm a 60kg 6' tall male - I'm very skinny, but fit and strong.

I used to carry 20-22kg (35% body mass) for a week long trip. I could do it, but it used to kill the walking experience.

Now I carry around 14kg for the same duration trip (less than 25% of my body mass).

It just makes the walking so much more enjoyable.

[Bubbalouie]

Never mind the extra 20kg's there carry around there waist.

The English teacher groans and rolls THEIR eyes at what THEY read has been written THERE.

They're their there, everything will be Ok, theirs know problem hear your just making to much off this.

[Orion]

When trying to reduce your pack weight, is there an equal benefit from reducing your body weight. For example, rather than spending hundreds of dollars on new lightweight gear to reduce your pack weight by 5kg, would you get the same benefit by simply losing 5kg of body weight (much cheaper, but no shiny new gear !!!)

I don't think it's that simple.

For one thing the idea presupposes that all bodyweight is equivalent, e.g. muscle and bones versus excess body fat. If you have extra kg to lose then why not lose it? It isn't so easy for most people. And if you're already fit and at your fighting weight then additional loss might be counterproductive.

Also, a little excess fat, the "alpine belly", may allow you to carry less food on a walk as you slowly burn your on-board supply. Most people lose weight over the course of a long walk. But if you start out fit and lean you'd have to supply those kJs by carrying them on your back.

Another thing is that the body adapts to its own weight over time whereas loading up a big pack is an occasional stress. I think weight in the pack carries differently than weight on one's bones. In my own experience: I used to weigh less and carried a bigger pack. Now I'm heavier and carry a lighter pack and I can walk so much further.

I don't think it's a one to one trade-off, not even close.

[Bubbalouie]

When trying to reduce your pack weight, is there an equal benefit from reducing your body weight. For example, rather than spending hundreds of dollars on new lightweight gear to reduce your pack weight by 5kg, would you get the same benefit by simply losing 5kg of body weight (much cheaper, but no shiny new gear !!!)

I don't think it's that simple.

For one thing the idea presupposes that all bodyweight is equivalent, e.g. muscle and bones versus excess body fat. If you have extra kg to lose then why not lose it? It isn't so easy for most people. And if you're already fit and at your fighting weight then additional loss might be counterproductive.

Also, a little excess fat, the "alpine belly", may allow you to carry less food on a walk as you slowly burn your on-board supply. Most people lose weight over the course of a long walk. But if you start out fit and lean you'd have to supply those kJs by carrying them on your back.

Another thing is that the body adapts to its own weight over time whereas loading up a big pack is an occasional stress. I think weight in the pack carries differently than weight on one's bones. In my own experience: I used to weigh less and carried a bigger pack. Now I'm heavier and carry a lighter pack and I can walk so much further.

I don't think it's a one to one trade-off, not even close.

Agreed.

The original article based the load carrying capacity on the cross sectional area of muscle. So, if you get skinnier without getting shorter your load carrying capacity will decrease unless you only lose fat.

It's not so much heavier people that are at a disadvantage (kind of) the it's taller people, due to the square / cube problem.

Of course, if you're wearing size 48 trousers and are under 6 feet tall it is reasonable to suppose shedding a few kilos would do more good for your hiking than some lighter gear (not to mention all of the other health benefits when not hiking).

[Turfa]

Never mind the extra 20kg's there carry around there waist.

The English teacher groans and rolls THEIR eyes at what THEY read has been written THERE.

They're their there, everything will be Ok, theirs know problem hear your just making to much off this.

The English teacher explodes !!!!! ha ha ha , love it !

[madmacca]

Interesting question....and raises another point I have always wondered about.

When trying to reduce your pack weight, is there an equal benefit from reducing your body weight. For example, rather than spending hundreds of dollars on new lightweight gear to reduce your pack weight by 5kg, would you get the same benefit by simply losing 5kg of body weight (much cheaper, but no shiny new gear !!!)

The study in the link would seem to support that losing body weight is just as beneficial.

Taking 5kg off your pack is more beneficial in terms of effort and fatigue than 5 kg off your body.

5 kg of body fat will be fairly well distributed around your body, and won't really alter your centre of gravity. But 5kg on your back will have your upper body and core working harder to stay balanced, even while standing still. And at a guess, 2kg of that 5 will be on the legs, with 3 kg on the upper body. So loading on the spine will only be an extra 3 kg, not an extra 5 kg.

Not saying you wouldn'r benefit from losing 5 kg of body fat, just that there is less effort when it is PART of your body.

[Chezza]

You mean like this:
http://scitation.aip.org/content/aapt/j ... /1.4897584

That's a nice paper, which takes the exp(2/3) rule a bit further.

It is very limited in its scope though, so quite far from being able to produce useful results. Speed, distance, grade, fitness/conditioning, muscle types, joint geometry, injury, illness, altitude acclimatisation, and many other factors I'm sure will all skew the result quite significantly.

But the fact that most people who carry heavy loads for long distance on a regular/professional basis seem to be moderately built endurance athletes (my personal observation at any rate) lends credence to the results in the paper, "all other things being equal".

As for being ultralight, unless you're a trail runner I suspect if some people spent half as much time running and doing some basic conditioning as they seem to do counting grams, they would see more appreciable results in terms of comfort on trail

[Chezza]

Double post

[Turfa]

Not saying you wouldn'r benefit from losing 5 kg of body fat, just that there is less effort when it is PART of your body.

Agreed...the distribution is important...although at least you can put your pack down at the end of the day !

This also seems to be relevant to the concept of "cameling up" at a water source. Drinking as much water as you can and putting less in your bladder/bottles. It does seem easier to carry water internally rather than on your back

[forest]

Never mind the extra 20kg's there carry around there waist.

The English teacher groans and rolls THEIR eyes at what THEY read has been written THERE.

LOL. Thanks for your contribution to this thread sunnyape. That's cleared a few things up for me........ Now what was I only saying the other day about teachers....
(I'm a Mech. Engineer so like numbers more)

As for being ultralight, unless you're a trail runner

Oh NO....I'm double doomed.
Some good info in that link. It's all interesting.

[Turfa]

(I'm a Mech. Engineer so like numbers more)

Well, that also explains your love of shiny things !!!!!!!

Sad thing is, I too have to admit to being a Mech Eng. and one who thinks that the only thing wrong with titanium is that it isn't as shiny as stainless steel !

[wildlight]

Never mind the extra 20kg's there carry around there waist.

The English teacher groans and rolls THEIR eyes at what THEY read has been written THERE.

And when all is said and done, THEY'RE only words!

Cheers,

Wildlight

[neilmny]

Never mind the extra 20kg's there carry around there waist.

The English teacher groans and rolls THEIR eyes at what THEY read has been written THERE.

Wouldn't it be...........The English teachers groan and roll their eyes at what they read written there............