Sunday, 5 February 2012

Slow, slow, quick, quick, slow

Whilst researching my most recent post, All Things Being Inequal, I found an interesting set of formulae and some data which had me reaching for a pencil and paper to play with the figures which turned out to have quite interesting results.

Let's start with a question: If you have to go and get something, should you walk slowly or walk quickly? The aim of the game is to minimise calorie loss. Let's assume you've got plenty of water and there would be no additional risks with any of the strategies.

Let's first determine the amount of calories that we burn walking in general. This largely depends on your weight (or more strictly mass), gait and conditions and of course, some combination of speed, distance and time. As your mass, gait and conditions will be the same for each case for this question, we can ignore them.

Within normal parameters of ability (ie. not dawdling or speed walking), it has been shown that  it doesn't really matter how hard you work, the calorie burn is associated with the distance you travel, rather than the actual speed. Put more simply, walk for twice as long at the same speed, you'll burn twice the number of calories. Walk twice as fast for the same time, you'll cover twice the distance and you'll burn twice the calories. Walk twice as fast for half the time, you'll cover the same distance and you'll burn the same number or calories.

Here's the  paper, The mass-specific energy cost of human walking is set by stature.

So, it would seem that it doesn't matter how fast you walk, you'll burn the same calories. However, in a genuine survival situation, one might consider advantages and disadvantages to either strategy. Walk slowly, and you're more likely to spot exciting foodstuffs and useful resources, however, you'll be away from camp for longer, which keeps you away from camp longer, which might include your signals. It's all well and good finding a patch of chanterelle, but if that means you can't light your signal fire when the chopper goes over, then that's a bit of a pain. Maybe consider additional signals on your normal walking routes? Maybe consider moving camp closer to regular resources?

A corollary to this are the considerations about walking up and down hill. If you're walking up hill, it takes more calories, if you're walking down hill, it takes less. This is because you're working against or helped by gravity respectively. Scrambling notwithstanding, it takes the same amount  of extra calories to walk up hill as the amount you save walking down. That is, assuming you are the same mass for each portion of the journey. So, if you're going to go and collect, say, wood, or water, then given no other choice, make sure you walk up hill to fetch it and down hill to get it back. Generally speaking, people will consider water as something they should walk down hill to find, but if you can walk up hill to get it as an alternative, then all the better. Something I've advised people to do on courses whilst collecting wood is to walk up hill to find it and roll it down hill back to camp.

Something that is quite interesting about the research, as the title suggests, is that it shows that calorie expenditure depends not only on mass and distance, but stride length. The longer your (normal) stride length, the less calories you expend over the same distance. This makes sense if you think about how much walking is associated with muscles and how much is associated with pivoting, but this leads to an interesting set of questions about who should go and get the water. Would it be the tall skinny guy, the short fat guy, the short skinny guy, the athlete, the older guy or the child? Well, so long as it's not me, I don't really mind.

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