Sarah L. Kozey

Accelerometer Output and MET Values of Common Physical Activities

PURPOSE This article 1) provides the calibration procedures and methods for metabolic and activity monitor data collection, 2) compares measured MET values to the MET values from the compendium of physical activities, and 3) examines the relationship between accelerometer output and METs for a range of physical activities. METHODS Participants (N = 277) completed 11 activities for 7 min each from a menu of 23 physical activities. Oxygen consumption (V O2) was measured using a portable metabolic system, and an accelerometer was worn. MET values were defined as measured METs (V O2/measured resting metabolic rate) and standard METs (V O2/3.5 mL.kg.min). For the total sample and by subgroup (age [young < 40 yr], sex, and body mass index [normal weight < 25 kg.m]), measured METs and standard METs were compared with the compendium, using 95% confidence intervals to determine statistical significance (alpha = 0.05). Average counts per minute for each activity and the linear association between counts per minute and METs are presented. RESULTS Compendium METs were different than measured METs for 17/21 activities (81%). The number of activities different than the compendium was similar between subgroups or when standard METs were used. The average counts for the activities ranged from 11 counts per minute (dishes) to 7490 counts per minute (treadmill: 2.23 m.s, 3%). The r between counts and METs was 0.65. CONCLUSIONS This study provides valuable information about data collection, metabolic responses, and accelerometer output for common physical activities in a diverse participant sample. The compendium should be updated with additional empirical data, and linear regression models are inappropriate for accurately predicting METs from accelerometer output.

Comparison of the ActiGraph 7164 and the ActiGraph GT1M during self-paced locomotion.

PURPOSE This study compared the ActiGraph accelerometer model 7164 (AM1) with the ActiGraph GT1M (AM2) during self-paced locomotion. METHODS Participants (n = 116, aged 18-73 yr, mean body mass index = 26.1 kg x m(-2)) walked at self-selected slow, medium, and fast speeds around an indoor circular hallway (0.47 km). Both activity monitors were attached to a belt secured to the hip and simultaneously collected data in 60-s epochs. To compare differences between monitors, the average difference (bias) in count output and steps output was computed at each speed. Time spent in different activity intensities (light, moderate, and vigorous) based on the cut points of Freedson et al. was compared for each minute. RESULTS The mean +/- SD walking speed was 0.7 +/- 0.22 m x s(-1) for the slow speed, 1.3 +/- 0.17 m x s(-1) for medium, and 2.1 +/- 0.61 m x s(-1) for fast speeds. Ninety-five percent confidence intervals (95% CI) were used to determine significance. Across all speeds, step output was significantly higher for the AM1 (bias = 19.8%, 95% CI = -23.2% to -16.4%) because of the large differences in step output at slow speed. The count output from AM2 was a significantly higher (2.7%, 95% CI = 0.8%-4.7%) than that from AM1. Overall, 96.1% of the minutes were classified into the same MET intensity category by both monitors. CONCLUSIONS The step output between models was not comparable at slow speeds, and comparisons of step data collected with both models should be interpreted with caution. The count output from AM2 was slightly but significantly higher than that from AM1 during the self-paced locomotion, but this difference did not result in meaningful differences in activity intensity classifications. Thus, data collected with AM1 should be comparable to AM2 across studies for estimating habitual activity levels.

Medical Hazards of Prolonged Sitting

Prolonged sitting is hazardous to one’s health. In 1700 Italy, Ramazini observed that sedentary tailors were not as healthy as active messengers (10). In the 1950s, the first epidemiological study using occupational activity to define sedentary and active behavior was conducted by Morris and colleagues (6). In this study, bus conductors who climbed approximately 600 stairs per day at work had half the number of heart attacks in comparison to bus drivers who spent 90% of their work time sitting. More recently, a wealth of evidence has arisen indicating that postural fixity (either sitting or standing) is undesirable from a health standpoint. A review article by Neville Owen, Ph.D., and colleagues (8) in this issue of Exercise and Sport Sciences Reviews reports on ‘‘Too Much Sitting: The Population-Health Science of Sedentary Behavior.’’ Their article expands on information presented in a lecture by Owen at the 2009 American College of Sports Medicine (ACSM) Annual Meeting and helps to strengthen the link between sedentary behavior and ill health. Their paper draws attention to several new findings: 1) Cross-sectional studies show that TV viewing is associated with obesity, diabetes, impaired glucose uptake, and insulin resistance. 2) These associations remain even after statistically adjusting for moderate-to-vigorous leisure time physical activity and waist circumference. 3) Accelerometer studies indicate that in adults, on average, 60% of waking hours are spent being sedentary (i.e., accelerometer values G100 counts per minute). 4) Individuals who meet the recommended levels of moderateto-vigorous physical activity and spend the majority of their waking hours in sedentary activities may have compromised health, compared with those who are sufficiently active and sit less.