title: Biomechanical examination of the 'plateau phenomenon' in ActiGraph vertical activity counts.
abstract: This paper determines if the leveling off ('plateau/inverted-U' phenomenon) of vertical ActiGraph activity counts during running at higher speeds is attributable to the monitor's signal filtering and acceleration detection characteristics. Ten endurance-trained male participants (mean (SD) age = 28.2 (4.7) years) walked at 3, 5 and 7 km h(-1), and ran at 8, 10, 12, 14, 16, 18 and 20 km h(-1) on a force treadmill while wearing an ActiGraph GT3X monitor at the waist. Triaxial accelerations of the body's center of mass (CoM) and frequency content of these accelerations were computed from the force treadmill data. GT3X vertical activity counts demonstrated the expected 'plateau/inverted-U' phenomenon. In contrast, vertical CoM accelerations increased with increasing speed (1.32 ± 0.26 g at 10 km h(-1) and 1.68 ± 0.24 g at 20 km h(-1)). The dominant frequency in the CoM acceleration signals increased with running speed (14.8 ± 3.2 Hz at 10 km h(-1) and 24.8 ± 3.2 Hz at 20 km h(-1)) and lay beyond the ActiGraph band-pass filter (0.25 to 2.5 Hz) limits. In conclusion, CoM acceleration magnitudes during walking and running lie within the ActiGraph monitor's dynamic acceleration detecting capability. Acceleration signals of higher frequencies that are eliminated by the ActiGraph band-pass filter may be necessary to distinguish among exercise intensity at higher running speeds.
authors.affiliation: Department of Kinesiology, University of Massachusetts, Amherst, MA 01003, USA. djohn1@kin.umass.edu
authors.forename: Dinesh
authors.initials: D
authors.lastname: John
authors.forename: Ross
authors.initials: R
authors.lastname: Miller
authors.forename: Sarah
authors.initials: S
authors.lastname: Kozey-Keadle
authors.forename: Graham
authors.initials: G
authors.lastname: Caldwell
authors.forename: Patty
authors.initials: P
authors.lastname: Freedson
mesh_terms: D000054:Acceleration; D056044:Actigraphy / Q000379:methods*; D000328:Adult; D001696:Biomechanical Phenomena / Q000502:physiology; D005080:Exercise Test; D006615:Hip; D006801:Humans; D008297:Male; D008954:Models, Biological; D013997:Time Factors