Physical activity is known to reduce risks of heart disease and all-cause mortality,¹ as well as risks of colon, breast, and endometrial cancers.² Less is known, however, about whether physical activity reduces risk of other cancers, which, together, constitute 75% of incident cancers in the United States³ and 61% of cancers worldwide.⁴ Physical inactivity is highly prevalent, with an estimated 51% of people in the United States⁵ and 31% of people worldwide not attaining recommended physical activity levels.⁶ Any decrease in risk of cancer associated with physical activity may therefore be relevant to public health and cancer prevention efforts.

A primary barrier to elucidating the association between sedentary behavior (SB) and health outcomes is the lack of valid monitors to assess SB in a free-living environment. The purpose of this study was to examine the validity of commercially available monitors to assess SB. Twenty overweight (mean ± SD: body mass index = 33.7 ± 5.7 kg·m(-2)) inactive, office workers age 46.5 ± 10.7 yr were directly observed for two 6-h periods while wearing an activPAL (AP) and an ActiGraph GT3X (AG). During the second observation, participants were instructed to reduce sitting time. We assessed the validity of the commonly used cut point of 100 counts per minute (AG100) and several additional AG cut points for defining SB. We used direct observation (DO) using focal sampling with duration coding to record either sedentary (sitting/lying) or nonsedentary behavior. The accuracy and precision of the monitors and the sensitivity of the monitors to detect reductions in sitting time were assessed using mixed-model repeated-measures analyses. On average, the AP and the AG100 underestimated sitting time by 2.8% and 4.9%, respectively. The correlation between the AP and DO was R2 = 0.94, and the AG100 and DO sedentary minutes was R2 = 0.39. Only the AP was able to detect reductions in sitting time. The AG 150-counts-per-minute threshold demonstrated the lowest bias (1.8%) of the AG cut points. The AP was more precise and more sensitive to reductions in sitting time than the AG, and thus, studies designed to assess SB should consider using the AP. When the AG monitor is used, 150 counts per minute may be the most appropriate cut point to define SB.

Background: Moderate-to-vigorous–intensity physical activity is recommended to maintain and improve health, but the mortality benefits of light activ

IGraph GT3X (Actigraph, Pensacola, FL) for estimating measures of sedentary behavior: absolute number of breaks and break rate. Methods Thirteen participants completed two 10-h conditions. During the baseline condition, participants performed normal daily activity, and during the treatment condition, participants were asked to reduce and break up their sedentary time. In each condition, participants wore two ActiGraph GT3X monitors and one activPAL. The ActiGraph was tested using the low-frequency extension filter (AG-LFE) and the normal filter (AG-Norm). For both ActiGraph monitors, two count cut points to estimate sedentary time were examined: 100 and 150 counts per minute. Direct observation served as the criterion measure of total sedentary time, absolute number of breaks from sedentary time, and break rate (number of breaks per sedentary hour (brk·sed-h−1)). Results Break rate was the only metric sensitive to changes in behavior between baseline (5.1 [3.3–6.8] brk·sed-h−1) and treatment conditions (7.3 [4.7–9.8] brk·sed-h−1) (mean (95% confidence interval)). The activPAL produced valid estimates of all sedentary behavior measures and was sensitive to changes in break rate between conditions (baseline, 5.1 [2.8–7.1] brk·sed-h−1; treatment, 8.0 [5.8–10.2] brk·sed-h−1). In general, the AG-LFE and AG-Norm were not accurate in estimating break rate or the absolute number of breaks and were not sensitive to changes between conditions. Conclusion This study demonstrates the use of expressing breaks from sedentary time as a rate per sedentary hour, a metric specifically relevant to free-living behavior, and provides further evidence that the activPAL is a valid tool to measure components of sedentary behavior in free-living environments....

National guidelines for aerobic physical activity recommend adults should participate in at least 150 minutes per week of moderate intensity aerobic activity or 75 minutes per week of vigorous intensity activity or an equivalent combination of both.^1-3 Levels of physical activity equivalent to meeting this guideline have been associated with substantial health benefits, including reductions in all-cause,^4,5 cardiovascular disease (CVD)–related,^4,6 and cancer-related^4,7,8 mortality. However, most of the evidence on the mortality benefits of physical activity comes from studies that measure leisure-time physical activity (LTPA) at only 1 point, usually during midlife (eg, 40-60 years of age). To date, no study to our knowledge has taken a life course approach to examine how participation in physical activity throughout the different stages of adulthood may be associated with mortality risk.