What is an Accelerometer Pedometer?

Robyn Clark

An accelerometer pedometer is one of several types of devices that count the number of steps taken by the wearer by registering or measuring vertical movement. Pedometers are excellent tools for tracking activity and for motivating users to increase their activity levels. Studies on pedometers have shown that their usage increases physical activity, decreases body mass index (BMI) and decreases blood pressure levels. Compared to other types of exercise equipment, pedometers are low-cost, reliable and easy to use.

Usage of a pedometer may increase a person's physical activity and decrease his or her blood pressure levels.
Usage of a pedometer may increase a person's physical activity and decrease his or her blood pressure levels.

The simplest types of pedometers are pendulum pedometers that have spring-based internal mechanisms. This design uses a horizontal lever arm suspended from a spring that moves up and down as the user’s hip accelerates when taking a step. The movement of the lever arm opens and closes an electrical circuit, which registers the step. Another similar mechanism uses a magnet at the end of the lever to trip a proximity switch that registers the step. Pendulum pedometers make a clicking sound as the lever arm moves and the steps are counted.

The internal mechanism of an accelerometer pedometer uses a piezoelectric crystal as part of a strain gauge that generates voltage in proportion to the vertical acceleration. This type of mechanism is more durable and will typically last longer than a spring mechanism. Accelerometer pedometers also offer a significant advantage in that they measure rather than simply register vertical movement, and they can measure the intensity of activity in addition to counting steps. Another advantage is that the mechanism of an accelerometer pedometer is silent and does not make a clicking sound while counting steps.

A pendulum pedometer must be kept in an upright vertical position for the spring mechanism to work properly, and it typically is worn clipped to a waistband. Tilting or wearing at an angle can affect the accuracy by as much as 25 percent or more, depending on the model. Accelerometer pedometers have been shown to be significantly more reliable and accurate. Depending on the model, they can be accurate within 1 percent. Pedometers with dual-accelerometer sensors are not sensitive to tilt and can be carried in a pocket or purse or worn on an ankle strap.

Simple pendulum pedometers can be very inexpensive and are often given away for free as part of exercise promotion and awareness programs. A more sophisticated accelerometer pedometer can cost more than $100 US Dollars and typically will have additional features, such as calculating distance and estimating the number of calories burned. The sensitivity of the internal device is another important factor when one is considering different models. Pedometers tend to overestimate step counts by counting other movements, such as the wearer shifting his or her body while seated. Higher-quality pedometers will include a routine that registers but does not record steps until a certain minimum threshold number of steps has been reached, which helps prevent over-counting.

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