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INTRODUCTION
Interest in accelerometers for the measurement of human motion both in the clinical and performance setting has grown in recent years due, in part, to their robust design and possibility for widespread application. With the growing interest and increasing use, validation of the accuracy and reliability of these devices needs to be more clearly established. Regardless, accelerometers exhibit the potential to surpass other biomechanic sensors in both the clinical and performance settings, and usher a new era of ergometric and biomechanic measurement.
ACCELEROMETERS
Although accelerometers have been used for decades to quantify human movement, recent advancements in miniaturization and memory storage have resulted in increased interest in their use as tools for biomechanical and physiological analysis (1, 6, 7, 10). Advantages of accelerometers over other biomechanical devices primarily lie the fact are that they are generally small and would offer limited restrictions to their anatomical placement and provide minimal impediment to movement. Therefore, they can be used as wearable biosensors to measure movement parameters, such as gait, in laboratory and real world situations without the limitations inherent to more immobile laboratory approaches such as force plate/camera systems. Many accelerometers are wireless and either send signals to a base station or collect data onboard for subsequent download, further enhancing their ability to be implemented in a variety of conditions.
Accelerometers: The device
Several types of commercially available accelerometers are used to monitor human movement: strain gages, piezoresistive, capacitative, piezoelectric as well as microelectromechanical systems (MEMS) (8),
F=-kx (equation 1)
where F = force, k = spring constant, x = spring displacement, and Newton's second law of motion
F=ma (equation 2)
m = mass and a = acceleration. The combination of these two formulas yields the resulting equation for acceleration:
a = (-kx) / m (equation 3)
which serves as the underlying principle whereby acceleration is determined that (7).
Microelectromechanical Systems (MEMS)
The use of MEMS technology recently has allowed for accelerometers to decrease in size while increasing accuracy. The way in which these function is analogous to a pendulum, oscillating back an forth between two pickups, and the speed at which it moves is calibrated to differing forces required to move it at this rate. This in turn is used to determine acceleration. The coupling...