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First published online January 19, 2006
Journal of Experimental Biology 209, iv (2006)
Copyright © 2006 The Company of Biologists Limited
doi: 10.1242/jeb.02072
Outside JEB |
WE GOT THE BEAT
Mount Holyoke College
ggillis{at}mtholyoke.edu
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My various, albeit thankfully limited, experiences with dancing, both as an observer and participant, always left me with the impression that people typically have their own rhythm and move to their own beat. Some folks tend to move faster than others, some slower and some... well let's just say that the movements of some of us might be harder to characterize. By contrast, such variation appears not to be characteristic of the rhythm or tempo of another, more common, type of human movement: walking. In fact, laboratory studies have shown that the cadence of human over-ground walking is quite consistent and that a stepping frequency of approximately 2 Hz is generally adopted. If you're like me, several questions come to mind upon learning this: (1) why 2 Hz and (2) are such results simply some artefact of studying walking in a laboratory? In a recent paper, Hamish MacDougall and Steven Moore of Mount Sinai School of Medicine provide possible answers to both of these questions by studying locomotor tempo under natural conditions.
Ten men and 10 women of varying age (22-62 years) and body mass (40-100 kg) were outfitted with a device that monitored linear accelerations of the head in three orthogonal directions (forward-backward, side-to-side and up-down). Previous studies have shown that vertical accelerations of the head map well onto patterns of stepping frequency during walking, thus the device could essentially measure a subject's movement tempo when used. The `activity monitor' was mounted onto a baseball hat worn by each of the subjects for 10 hours during his/her everyday activities. A subject could flag periods of particular types of activity via a button on the device and recorded information about activity types and times in a logbook.
Using fast Fourier transformation, power spectra of head accelerations from each subject could be calculated and analyzed. Despite the varied forms of activity within and among the subjects (e.g. walking, climbing stairs, riding a bike, attending dance class), there was an obvious dominant peak of vertical head movements at 2.0 Hz. Moreover, this result was always present, regardless of gender, age or body size. This value corresponds well with the previously published stepping frequency of 1.95 Hz observed during laboratory studies and illustrates that, in natural circumstances as well as in the lab, adult humans consistently adopt a specific locomotor cadence.
This is quite interesting in itself, but the questions of why an inherent
locomotor tempo might exist, and why at 2 Hz, remain open to some speculation.
The authors refer to the fact that locomotor energy cost is lowest at a
stepping frequency near 2 Hz, and this may be part of the answer. This
frequency might also reflect some inherent rhythmicity generated by our
central nervous system (e.g. a spinal central pattern generator) - humans
adopt a spontaneous frequency of finger tapping at 2 Hz as well. Finally, the
tempo may be related to the coordination of head and eye movements during
locomotion as the reflexes underlying such coordination display their optimal
response at 
2 Hz. Regardless, this work shows that there may well exist a
`common frequency' to human movement; which reminds me, the next time I go
dancing I'm going to bring a metronome and set it to 120 beats per minute to
keep up with everyone else.
References
MacDougall, H. G. and Moore, S. T. (2005).
Marching to the beat of the same drummer: the spontaneous tempo of human
locomotion. J. Appl. Physiol.
99,1164
-1173.
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