C-26 Free Communication/Poster - Objective Measures: Accelerometry and Pedometry: JUNE 3, 2010 7:30 AM - 12:30 PM: ROOM: Hall C
Accelerometers are being widely used to quantify individuals' physical activity (PA) profiles. An important component of the PA assessment is the quantification of time spent in moderate-intensity or higher PA. This is typically performed with the use of absolute intensity thresholds.
PURPOSE: The primary purpose of this study was to determine the actual relative PA intensity, as a percentage of oxygen uptake reserve (VO2R), while meeting the absolute thresholds of 1953 activity counts/minute for moderate- and 5725 activity counts/minute for vigorous-intensity. This study also evaluated how much activity counts/minute variability existed between subjects at a VO2R of 40% and 60%.
METHODS: Twenty-eight individuals, 13 men (22.7±2.5 years), and 15 women (23.2±2.8 years), completed a maximal exercise test to determine their maximal heart rate (HRmax) and VO2. Six men and 4 women had VO2max considered high fit (≥ 80th%ile for age and gender) and 3 men and 5 women were considered low fit (≤ 20th%ile). On a separate day, subjects completed a submaximal exercise session, which was terminated when he/she reached 85% of HRmax. This exercise session included up to ten 5-minute stages, beginning at 1.5 mph followed by 2.0, 2.5, 3.0, 3.5, 4.0, 5.0, 6.0, 7.0 and 8.0 mph. Subjects' VO2, HR, and activity counts/minute (measured using ActiGraph GT1M; ActiGraph, Pensacola, FL) were recorded every minute during the exercise session.
RESULTS: Subjects' actual relative intensity at the absolute moderate- and vigorous-intensity thresholds of 1953 and 5725 activity counts/minute were 15±6% and 45±12% VO2R, respectively. The activity counts/minute ranged from 3340 to 8250 and from 5250 to 12364 when subjects achieved 40% and 60% VO2R, respectively. Intraclass correlations (ICC) between activity counts/minute determined by both VO2R and age-predicted HRR were significant (p<0.05) at both at moderate-intensity (ICC= 0.77) and at vigorous-intensity (ICC= 0.85).
CONCLUSION: The absolute intensity thresholds do not accurately represent the actual relative intensity for most individuals. These results emphasize the need for establishing a relative activity counts/minute threshold when using accelerometers to accurately determine an individual's time spent in moderate-intensity or higher PA.