These studies indicate that analysis of the data using 60-s epochs and a vertical magnitude cut-point < 200 cpm or using 30- or 60-s epochs with a machine learning algorithm provides the most valid estimates of SB .
Conclusions Few studies have examined the reliability and validity of accelerometers for measuring SB  in older adults .
Studies to date suggest that the criteria research ers use for classifying an epoch as sedentary instead of as non-wear time ( e.g. , the non-wear algorithm used ) may need to be different for older adults than for younger adults .
The required number of hours and days of wear for valid estimates of SB in older adults was not clear from studies to date .
Background The evidence showing the ill health effects of prolonged sedentary behaviour ( SB ) is growing .
Most studies of  SB in older adults have relied on self-report measures of SB .
However , SB is difficult for older adults to recall and objective measures that combine accelerometry with inclinometry are now available for more accurately assessing SB .
The aim of this systematic review was to assess the validity and reliability of these accelerometers for the assessment of  SB in older adults .
Reproducibility of Accelerometer-Assessed Physical Activity and Sedentary Time.
INTRODUCTION Accelerometers are used increasingly in large epidemiologic studies , but , given logistic and cost constraints , most studies are restricted to a single , 7-day accelerometer monitoring period . It is unknown how well a 7-day accelerometer monitoring period estimates longer-term patterns of behavior , which is critical for interpreting , and potentially improving , disease risk estimates in etiologic studies . METHODS A subset of participants from the Women 's Health Study ( N=209 ; mean age , 70.6 [ SD=5.7 ] years ) completed at least two 7-day accelerometer administrations ( ActiGraph GT3X+ ) within a period of 2 - 3 years . Monitor output was translated into total counts , steps , and time spent in sedentary , light-intensity , and moderate to vigorous-intensity activity ( MVPA ) and bouted-MVPA ( i.e. , 10-minute bouts ) . For each metric , intraclass correlations ( ICCs ) and 95 % CIs were calculated using linear-mixed models and adjusted for wear time , age , BMI , and season . The data were collected in 2011 - 2015 and analyzed in 2015 - 2016 . RESULTS The ICCs ranged from 0.67 ( 95 % CI=0.60 , 0.73 ) for bouted-MVPA to 0.82 ( 95 % CI=0.77 , 0.85 ) for total daily counts and were similar across age , BMI , and for less and more active women . For all metrics , classification accuracy within 1 quartile was > 90 % . CONCLUSIONS These data provide reassurance that a 7-day accelerometer- assessment protocol provides a reproducible ( and practical ) measure of physical activity and sedentary time . However , ICCs varied by metric ; therefore , future prospect i ve studies of chronic diseases might benefit from existing methods to adjust risk estimates for within-person variability in activity to get a better estimate of the true strength of association
These studies indicate that analysis of the data using 60-s epochs and a vertical magnitude cut-point < 200 cpm or using 30- or 60-s epochs with a machine learning algorithm provides the most valid estimates of SB .
Conclusions Few studies have examined the reliability and validity of accelerometers for measuring SB  in older adults .
Studies to date suggest that the criteria research ers use for classifying an epoch as sedentary instead of as non-wear time ( e.g. , the non-wear algorithm used ) may need to be different for older adults than for younger adults .
The required number of hours and days of wear for valid estimates of SB in older adults was not clear from studies to date .
Background The evidence showing the ill health effects of prolonged sedentary behaviour ( SB ) is growing .
Most studies of  SB in older adults have relied on self-report measures of SB .
However , SB is difficult for older adults to recall and objective measures that combine accelerometry with inclinometry are now available for more accurately assessing SB .
The aim of this systematic review was to assess the validity and reliability of these accelerometers for the assessment of  SB in older adults .