Tough question to ask.
There are many variables, eg. level of physical fitness and strength, level of mental preparedness and strength, correct fit of pack.
Whilst Franco's on legged suggestion is unsual, that may be the simplest answer. This is an issue I have contemplated deeply a few times due to OHS of clients. It's an issue that I am yet to see be accurately resolved. Work Safe have a variety of guidelines when it comes to lifting and carrying items, but it doesn't refer to wearing an item
http://www.worksafe.vic.gov.au/__data/assets/pdf_file/0020/9425/large_bulky_awkwardVs3.pdf . The Absolute maximum they state anyone should lift is 25kgs. It also emphasizes that the same repetitive action of carrying 10kg is of high risk too.
It's certainly not as simple as just a percentage of body weight, as that implies that the unfit, over weight person can carry more than the fit and healthy lighter weight person. A more accurate measure would be to use a eg. 7 divided your BMI to work out a percentage of body weight. A little more simply it would be 7 / BMI x Body Weight = Pack Weight.
There are a few issues still with this...
*What is the correct number eg. 5,6,7 or 8 etc. that who defines this number?
*The BMI is known to be somewhat inaccurate. For example many elite athletes would rank as being overweight due to them having muscle bulk. Heck, I almost count as overweight!
So despite all my contemplation there are only two thing I strongly promote to my clients:
* If you don't need it, don't carry it.
* Always use a friend when lifting and lowering your pack. The action of putting a pack on Solo is when you are most likely to injure your spine. Especially when you're feeling exhausted.
Also planning to camp at water sources where possible is important too.
phan_TOM wrote: No doubt some people would struggle with that much weight and others, like guides in the mountains chaperoning clients or doing food drops, can run up mountains all day long with 40kg and smile all the way.
Whilst I'd prefer to carry 15 kg instead of 30kg, I am quite used to carrying 30kg and it doesn't bother me.
As for my personal pack weight for work:
My pack empty weighs almost 4kgs. (WE Lost World)
First Aid and Coms probably weighs over 3kgs.
My main sleeping bag has 1kg of down, so I think it's about 1.6kgs
I sleep under a fly ~ 800grams
Sleeping mat ~ 800 grams
Often 2-3 L of water. It's not uncommon to carry more.
I'm at over 12kgs, and I haven't got any clothes, rain gear, food, fuel or stove yet
Stove is a Trangia, but I'm unlikely to carry this if I have the first aid too. I'm unsure how heavy 4-5 days worth of food is. It's pretty heavy as we need need to over cater a little to allow for some choice and spillage, and in case we need don't make it on time to the food drop etc.
Last trip I did was in a dry area. I regularly carried 4-5 L of water. The most I carried was 12 L of water.
All up I have no doubt that I was carrying over 30kgs after food drop and collection of water. We only were walking 10km though. But in soft sand and offtrack it still takes a while, even when it's flat.
In rare circumstances I have carried two complete packs for short sections (eg. up to 4 km). I expect that would have been a total of 40-45kg. Surprisingly though if you clip it the second pack on properly in front of you then it is really quite comfortable. The main issue with it is you can't see your feet.
Reading this forum makes me feel like I carry alot of weight.
Edit: I corrected Empty pack weight