Why Are Children Different in Their Daily Sedentariness? An Approach Based on the Mixed-Effects Location Scale Model

The Relationship Between Physical Activity and Frailty Among U.S. Older Adults Based on Hourly Accelerometry Data

Background/Objectives

Accelerometry measures older adult (in)activity with high resolution. Most studies summarize activity over the entire wear time. We extend prior work by analyzing hourly activity data to determine how frailty and other characteristics relate to activity among older adults.

Methods

Using wrist accelerometry data collected from the National Social Life, Health and Aging Project (n = 651), a nationally-representative probability sample of older adults, we used mixed effects linear regression to model the logarithm of hourly counts per minute as a function of an adapted phenotypic frailty score, adjusting for demographic and health characteristics, season, day of week and time of day.

Results

Higher frailty scores were associated with modestly lower activity; each frailty point (0-4) corresponded to a 7% lower mean hourly counts per minute. Older age, more comorbidities, male gender, and higher BMI were also associated with lower activity, though the latter was not evident among frail respondents. After adjusting for differences associated with frailty and other covariates, a substantial amount of between-individual variability in activity remained, as well as within-individual variability across days.

Conclusion

Our findings indicate that frail elders, men, those who are older, overweight or have multiple comorbidities are most likely to have low activity. However, residual differences between individuals remain larger than the differences associated with frailty and other covariates. We suggest defining individual-specific activity goals and further research to identify the sources of between-individual variability to better understand how activity reflects health status and to permit the development of more effective interventions.

Patterns of objectively measured sedentary time in 10- to 12-year-old Belgian children: an observational study within the ENERGY-project

BACKGROUND

This study examined the frequency of and differences in sedentary bouts of different durations and the total time spent in sedentary bouts on a weekday, a weekend day, during school hours, during after-school hours and in the evening period in a sample of 10- to 12-year-old Belgian children.

METHODS

Accelerometer data were collected as part of the ENERGY-project in Belgium (n = 577, 10.9 ± 0.7 years, 53% girls) in 2011. Differences in total sedentary time, sedentary bouts of 2-5, 5-10, 10-20, 20-30 and ≥30 min and total time accumulated in those bouts were examined on a weekday, a weekend day, during school hours, during after-school hours and in the evening period, using multilevel analyses in MLwiN 2.22.

RESULTS

More than 60% of the participants' waking time was spent sedentary. Children typically engaged in short sedentary bouts of 2-5 and 5-10 min, which contributed almost 50% towards their total daily sedentary time. Although the differences were very small, children engaged in significantly fewer sedentary bouts of nearly all durations during after-school hours compared to during school hours and in the evening period. Children also engaged in significantly fewer sedentary bouts of 5-10, 10-20, and 20-30 min per hour on a weekend day than on a weekday.

CONCLUSIONS

Although primary school children spend more than 60% of their waking time sedentary, they generally engaged in short sedentary bouts. Children's sedentary bouts were slightly longer on weekdays, particularly during school hours and in the evening period, although the differences were very small. These results suggest that in this age group, interventions focusing on reducing total sedentary time rather than interrupting prolonged sedentary time are needed.