Today I have walked 3,124 paces. yesterday I managed 6,442 and the day before 13,105.

How do I know this? I have a small, pillbox-sized gizmo clipped onto my belt, close to my right hip bone. It adds one to the count each time my foot falls. It's a pedometer.

If a pedophile is someone who loves children a little too much, does a pedometer count children?

Pedometers are the latest must-have gadget for those who wish to be seen to be healthy. Or so the marketing people would have you believe. Unusually, they might even be right this time.

A pedometer is a device that counts how many steps you have taken. Simple versions just count the number of steps. More complicated ones can translate the number of steps to a distance and then estimate the calories burned. (So that you know how many chocolate bars you need to eat to replenish the energy). They can have stopwatches, clocks, and things that tell you how fast you are going or how many minutes it takes to cover a certain distance. They can even sound an alarm when you reach a predetermined number of steps. The most advanced units can keep track of the number of paces taken on each day of the week or month and display statistical information on your activity over the last month. That's rather too much information for me, thank you very much.

They are cheap: basic models are usually less than £10 or $10 to buy. With the current health kick, there are plenty of offers about. You can even get them free (google for "free pedometer offer"), though you may find a company logo printed on the side. I bought mine through a promotion run in conjunction with a TV programme for about £5 including a lot of stickers and advice booklets.

I'm wearing it now. It's not complicated. Like most pedometers it is small and light, clipping unobtrusively onto a waistband or belt. The one I am wearing is fairly typical, it is about 4cm long, 1 cm thick and 2 cm deep. Mine has a hinge so that you can flip the lid down to see the read-out. Others have the read-out on the top surface, so you can just glance down to see the display.

if you really want to pay $50 or more, I'm sure there are people out there who will take your money, but there's no need to pay more than $10. More expensive models come complete with heart rate monitors and, for all I know, GPS systems that can work out *exactly* how far you travelled. I've seen a few recently that have a radio built in, so that you can listen to music whilst you jog. I have yet to see an iPod with a pedometer function or one with a USB connection so that you can upload the data to a spreadsheet, but I'm sure the day will come....

Whatever you pay, a pedometer will count paces, whether those paces are run, walked or jogged. Depending on the sensitivity of the pendulum within the gizmo, it may well count each time you stand up or sit down, or each time you step up or down a stair. It is unlikely to count each revolution of the pedals on a bicycle, at least, not with any accuracy or reliability.

While pedometers count the number of paces pretty accurately, the estimate of distance travelled is less reliable. In theory you can calibrate the gizmo with your pace length and it will then estimate the distance travelled by multiplying the number of steps by this single estimated pace length.

You tell the thing your pace length is 75cm, so after 1000 paces, you must have travelled 750m, right? Wrong!. Unfortunately, it's not that simple, because you don't always walk with the same step length.

Going from desk to desk in the office, or across to the coffee machine, I'm walking slowly and taking short steps. Maybe only 70cm or so.

When I'm walking serious distances, like from the station to home, I increase the step length quite a bit and can cover 85-90cm with each step.

There is even a difference between when I am walking briskly and walking very briskly. To speed up a tad, I subconsciously increase my step length, as well as increasing my strike rate.

When I jog, the pace length increases still further to over 100cm, and a full-out sprint gets the pace length up to over 120cm.

I've never seen a pedometer than can cope with this kind of variation in step length. Nevertheless, if you are using the pedometer as a training aid, in the run-up to a competitive distance event, it may be helpful to calibrate it with your average step length.

It's an aside, but an interesting one, A lot of people nowadays use their pedometer on a treadmill or running machine. The treadmill also measures distance travelled, but it is rare (according to the websites) for the pedometer distance to match the treadmill distance.

When going by foot for more than a kilometre or two, the step length tends to settle down to a more or less constant length so that variations in length from step to step become less significant. In an ideal world, then, you should be able to calibrate the pedometer by counting the number of steps taken in a measured distance. The ideal is to find a measured distance, such as a football field or a running track, and walk or run at your normal pace for a few minutes. Once in that rhythm, you use the pedometer to count the number of paces needed to cover a fixed distance. Simple maths will then give you the average step length, and you can feed this into the little electronic brain sitting on your waistband.

If you can use a long distance, such as a mile or a kilometre, the calibration will be more accurate. This is partly because you will be using your natural walking (or running) rhythm for most of the measured distance, and partly because the extended distance allows you to take some longer and some shorter strides, averaging the effect over a realistic distance. On the whole, a longer the measured distance will give a more accurate average step length.

Even so, multiplying up the average step length is never going to give an accurate readout of distance. Just remember that it is only an estimate. The estimate will be reasonably accurate (probably better than 10 per cent) if the distance was covered over even ground and at the same kind of pace as your calibration run. It is likely to be wildly inaccurate (up to 25 per cent wrong) if the distance was done at different speeds or in different walking styles or over uneven ground, where your pace length will vary considerably.

How it works

Word has it that Thomas Jefferson invented the pedometer a couple of hundred years ago, but things have moved on since then. Most pedometers nowadays are electronic devices, with batteries, LCD displays and electronic chips. It is possible to get non-battery pedometers that have a mechanical counter. These are heavier, more expensive and can be less reliable, but obviously, there is no need to replace the battery every year or so.

The electronic units all rely on the same basic mechanism. A small, weighted pendulum (about 5 or 10 mm long) swings as you walk, and each time it touches a sensor, makes a circuit. The electronics then increment the step count by one. In other models, the pendulum is magnetic and operates a reed switch which again, adds one to the step count. The important thing to know is that there is a pendulum inside the pedometer which has to move. This means the pedometer works best when it is fitted the correct way up. They are pretty forgiving things, so accurate set-up is not necessary. usually, you just clip it on in the obvious position and the thing works straight off.

Incidentally, the above paragraph should explain why pedometers don't really work for cyclists: the counter works when a pendulum is jogged by the impact of a footfall. When a cyclist pushes the pedals around, there's no impact to jog the pendulum, so no count increment.

You can buy GPS-based pedometers, but these are no longer really pedometers, but speed and distance devices for the serious athlete. They work using standard GPS technology to calculate distance travelled. Much more accurate and much more expensive than ordinary cheap and cheerful pedometers.

How to use

Duh! Clip it to your belt and start walking

The health sites recommend using one of these for a few days to see how far you really walk in a day. Most people will manage between 1,000 and 5,000 steps. I walk quite a lot, but I only manage about 7,000 steps per day, unless I choose to get off the train a couple of stops early and add another 5,000 steps (and 40 minutes) to my daily journey.

The target is about 10,000 steps per day, or about 6 km. A pedometer is one of the easiest ways to build exercise into a daily routine. By doing small things you can increase the count from 3,000 to 4,000. Another set of small things brings it up to 5,000. Walking up stairs; getting off the transport one stop earlier, taking a longer way around to the coffee bar. Simple things, which can easily be built into a daily routine.

Links, sources, further reading

  • http://sd.znet.com/~schester/grand_canyon/pedometer_accuracy.html
  • http://itotd.com/index.alt?ArticleID=368
  • experience

Pe*dom"e*ter (?), n. [Pedi-, pedo- + -meter: cf. F. p'edometre.] Mech.

An instrument for including the number of steps in walking, and so ascertaining the distance passed over. It is usually in the form of a watch; an oscillating weight by the motion of the body causes the index to advance a certain distance at each step.

 

© Webster 1913.

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