To make robust conclusions regarding the association between accelerometer-measured sedentary time and overweight and obesity among children, several gaps in the literature must be addressed. The purpose of this study was to examine associations between sedentary time, weekday sedentary time, weekend sedentary time, sedentary bouts, sedentary breaks, and BMI z-score among children and by low (bottom 50%) and high (top 50%) moderate- to vigorous-intensity physical activity (MVPA) participation. Results are based on 787 children aged 11 years living in Toronto, Canada. Children’s physical activity and sedentary time were objectively assessed using ActiGraph accelerometers in 2010/11. Height and weight were measured and BMI z-scores were calculated based on the World Health Organization growth standards. When participants were stratified into low and high MVPA groups, sedentary bouts of 5–9 (β = 0.22 [95% CI: 0.01, 0.43]) and 10–19 (0.30 [−0.05, 0.55]) minutes for total days were associated with BMI z-score in the low MVPA group only. Similar trends were observed with the weekday but not the weekend variables. Therefore, in addition to increasing MVPA, reducing time spent in 5- to 19-min sedentary bouts may have important implications for weight status particularly for children with lower MVPA participation during the week.
Valerie Carson, Michelle Stone and Guy Faulkner
Michelle R. Stone, Dale W. Esliger and Mark S. Tremblay
The purpose of this study was to determine the effects of age and leg length on the energy-expenditure predictions of five activity monitors. Participants (N = 86, ages 8–40 years) performed three progressive bouts of treadmill activity ranging from 4 to 12 km/hr. Differences between measured energy expenditure (VO2) and activity-monitor-predicted energy expenditure were assessed across five leg length categories to determine the influence of leg length. Accelerometer counts or pedometer steps along with age, weight, and leg length accounted for 85–94% of measured energy expenditure. The addition of age and leg length as predictor variables explained a larger amount of variance in energy expenditure across all speeds. Differences in leg length and age might affect activity-monitor validity and, therefore, should be controlled for when estimating physical activity energy expenditure.
Jordan M. Glenn, Michelle Gray, Jennifer L. Vincenzo and Matthew S. Stone
Muscular power decreases with age, and lower-body power relates to overall functional fitness; however, functional lower-body power has not been evaluated in late-middle-aged (LMA) populations.
To evaluate average and peak lower-body functional power and velocity among sedentary (SED), recreationally active (RA), and masters athlete (MA) LMA adults.
Participants were SED (n = 13, age = 59.3 ± 4.5 years), RA (n = 35, age = 59.6 ± 5.0 years), and MA (n = 26, age = 56.7 ± 5.4 years). Five sit-to-stand trials were completed to assess lower-body functional power. Average/peak power and velocity were calculated for each trial. Power was expressed relatively to account for participant body weight.
MA (13.44 ± 2.76 W/kg) had significantly (p < .01) greater peak power compared with SED (9.99 ± 2.70 W/ kg) and RA (9.93 ± 2.30 W/kg). Similar significant (p < .01) differences existed for peak velocity (SED = 1.02 ± 0.22 m/s, RA = 1.04 ± 0.22 m/s, MA = 1.25 ± 0.19 m/s). No differences existed for average power or velocity between groups.
Maintaining a competitively active lifestyle results in greater lower-body functional power in LMA adults and may support longitudinal functionality.