Calum Mattocks

Objective measurement of levels and patterns of physical activity

Objective: To measure the levels and patterns of physical activity, using accelerometers, of 11-year-old children participating in the Avon Longitudinal Study of Parents and Children (ALSPAC). Design: Cross-sectional analysis. Setting: ALSPAC is a birth cohort study located in the former county of Avon, in the southwest of England. This study used data collected when the children were 11 years old. Participants: 5595 children (2662 boys, 2933 girls). The children are the offspring of women recruited to a birth cohort study during 1991–2. The median age (95% CI) of the children is now 11.8 (11.6 to 11.9) years. Methods: Physical activity was measured over a maximum of 7 consecutive days using the MTI Actigraph accelerometer. Main outcome measures: Level and pattern of physical activity. Results: The median physical activity level was 580 counts/min. Boys were more active than girls (median (IQR) 644 (528–772) counts/min vs 529 (444–638) counts/min, respectively). Only 2.5% (95% CI 2.1% to 2.9%) of children (boys 5.1% (95% CI 4.3% to 6.0%), girls 0.4% (95% CI 0.2% to 0.7%) met current internationally recognised recommendations for physical activity. Children were most active in summer and least active in winter (difference = 108 counts/min). Both the mother and partner’s education level were inversely associated with activity level (p for trend <0.001 (both mother and partner)). The association was lost for mother’s education (p for trend = 0.07) and attenuated for partner’s education (p for trend = 0.02), after adjustment for age, sex, season, maternal age and social class. Conclusions: A large majority of children are insufficiently active, according to current recommended levels for health.

Objectively measured physical activity and fat mass in a large cohort of children

Background Previous studies have been unable to characterise the association between physical activity and obesity, possibly because most relied on inaccurate measures of physical activity and obesity. Methods and Findings We carried out a cross sectional analysis on 5,500 12-year-old children enrolled in the Avon Longitudinal Study of Parents and Children. Total physical activity and minutes of moderate and vigorous physical activity (MVPA) were measured using the Actigraph accelerometer. Fat mass and obesity (defined as the top decile of fat mass) were measured using the Lunar Prodigy dual x-ray emission absorptiometry scanner. We found strong negative associations between MVPA and fat mass that were unaltered after adjustment for total physical activity. We found a strong negative dose-response association between MVPA and obesity. The odds ratio for obesity in adjusted models between top and the bottom quintiles of minutes of MVPA was 0.03 (95% confidence interval [CI] 0.01–0.13, p-value for trend <0.0001) in boys and 0.36 (95% CI 0.17–0.74, p-value for trend = 0.006) in girls. Conclusions We demonstrated a strong graded inverse association between physical activity and obesity that was stronger in boys. Our data suggest that higher intensity physical activity may be more important than total activity.

Prospective associations between objective measures of physical activity and fat mass in 12-14 year old children: the Avon Longitudinal Study of Parents and Children (ALSPAC)

Objective To investigate associations between physical activity at age 12 and subsequent adiposity at age 14. Design Prospective birth cohort study with data collected between 2003 and 2007. Setting Original recruitment in 1991-2 of 14 541 pregnant women living in the former County of Avon (United Kingdom). Participants At age 12, 11 952 children were invited to attend the research clinic. Of these, 7159 attended, and 4150 (1964 boys, 2186 girls) provided sufficient data on exposure, outcome, and confounding variables. Main outcome measure Fat mass at age 14, measured by dual emission x ray absorptiometry, associated with physical activity at age 12, measured by accelerometry. Results Prospective associations of fat mass at age 14 (outcome) with physical activity at age 12 (exposure) were strong for both total activity (accelerometer counts/min) and for daily amount of moderate-vigorous physical activity (min/day). An extra 15 minutes of moderate-vigorous physical activity per day at age 12 was associated with lower fat mass at age 14 in boys (by 11.9% (95% confidence interval 9.5% to 14.3%)) and girls (by 9.8% (6.7% to 12.8%)). The proportion of physical activity due to moderate-vigorous physical activity was between 20% and 30% in boys and girls at the two ages. Conclusions Higher levels of physical activity, in particular activity of moderate to higher intensities, are prospectively associated with lower levels of fat mass in early adolescence. Interventions to raise levels of physical activity in children are likely to be important in the fight against obesity.

Calibration of an accelerometer during free-living activities in children

OBJECTIVE The aims of this study were to develop an equation to predict energy expenditure and to derive cut-points for moderate and vigorous physical activity intensity from the Actigraph accelerometer output in children aged 12 years. METHODS The children performed a series of activities (lying, sitting, slow walking, fast walking, hopscotch and jogging) while wearing an Actigraph and a portable metabolic unit. The sample was divided into a developmental and a validation group. Random intercepts models were used to develop a prediction equation in the developmental group. The equation was assessed in the validation group by calculating limits of agreement (actual minus predicted energy expenditure). Thresholds for moderate and vigorous activity were derived by refitting the energy expenditure model with VO2 as the outcome. RESULTS The developmental group comprised 163 children, while the validation group comprised 83 children. The equation, adjusted for age and gender, adequately predicted energy expenditure from accelerometer counts. Physical activity intensity cut-points were derived from resting VO2. The lower threshold for moderate intensity (four METs), adjusted for age and gender, was 3581 counts per minute. The lower threshold for vigorous activity (six METs) was 6130 counts per minute. CONCLUSION The prediction equation and the derived cut-points will help to better interpret the output of the Actigraph in children aged 12 years. The cut-point for moderate to vigorous physical activity is higher than that reported previously.

Sedentary Behavior and Obesity in a Large Cohort of Children

The purpose of this study was to examine the association between sedentary behavior and obesity among 12‐year‐old children, while adjusting for moderate‐to‐vigorous physical activity (MVPA) and other potential confounding variables. Cross‐sectional analyses were carried out with data from 5,434 children who participated in the Avon Longitudinal Study of Parents and Children (ALSPAC). Fat mass was derived using dual‐energy X‐ray emission absorptiometry, and height and weight measurements were used to calculate BMI (kg/m2). The children wore an accelerometer for 7 days. The cut points for sedentary behavior and MVPA were ≤199 and ≥3,600 counts per minute (cpm), respectively. Logistic regression analyses were performed to estimate odds ratios (ORs), adjusting for potential confounders of physical activity that included gender, social factors, early life factors, and maturation. The minimally adjusted association between sedentary behavior and obesity was positive, OR = 1.18 (1.08, 1.28). After adjusting for the series of potential confounders of physical activity the positive association remained, OR = 1.32 (1.14, 1.53). The crude association between 15 min of MVPA per day and obesity was negative, OR = 0.54 (0.48, 0.62). When 15 min of MVPA per day was additionally controlled for in the models, the positive associations between sedentary behavior and obesity were negated. Sedentary behavior was positively associated with obesity in the 12‐year‐old children, but this association was not independent of MVPA; low levels of MVPA among the sedentary children increased the odds of obesity. These findings support the importance of specifically engaging in MVPA during childhood to reduce the prevalence of obesity.

The contribution of active travel to children's physical activity levels: Cross-sectional results from the ALSPAC study

OBJECTIVE To assess the association between active travel to school and physical activity (PA) in a large population-based sample of 11-year old children. METHOD Cross-sectional analyses using data from the Avon Longitudinal Study of Parents and Children (Bristol, UK), collected in 2002-2004. The analyses include all children providing valid data on objectively measured PA (Actigraph accelerometer), and having parent-proxy reported data on travel mode (walk, cycle, public transport, car) and distance to school (N=4688). RESULTS 43.5% of children regularly walked or cycled to school (i.e. on every or most days). Compared with car travelers, walking to school was associated with 5.98 (95%CI: 3.82-8.14) more minutes of moderate-to-vigorous PA (MVPA) on weekdays in those living 0.5-1 miles from school, and with 9.77 (95%CI: 7.47-12.06) more minutes in those living at 1-5 miles. This equates to 24.6 to 40.2% of the average daily minutes of MVPA. Only modest differences were observed in those living <0.5 mile from school. CONCLUSION Children who regularly walk to school are more active during the week than those travelling by car, especially if the distance is >0.5 mile. Increasing participation in active travel might be a useful part of an overall strategy to increase population PA.

Habitual Levels of physical activity influence bone mass in 11-year-old children from the United Kingdom: findings from a large population-based cohort

We examined the influence of habitual levels of physical activity on bone mass in childhood by studying the relationship between accelerometer recordings and DXA parameters in 4457 11‐year‐old children. Physical activity was positively related to both BMD and bone size in fully adjusted models. However, further exploration revealed that this effect on bone size was modified by fat mass.

Physical Activity and Blood Pressure in Childhood. Findings From a Population-Based Study

The pathological processes associated with development of cardiovascular disease begin early in life. For example, elevated blood pressure (BP) can be seen in childhood and tracks into adulthood. The relationship between physical activity (PA) and BP in adults is well-established, but findings in children have been inconsistent, with few studies measuring PA mechanically. Children aged 11 to 12 years were recruited from the Avon Longitudinal Study of Parents and Children. 5505 had systolic and diastolic BP measurements, plus valid (at least 10 hours for at least 3 days) accelerometer measures of PA; total PA recorded as average counts per minute (cpm) over the period of valid recording, and minutes per day spent in moderate to vigorous PA (MVPA). Data on a number of possible confounders were also available. Small inverse associations were observed; for systolic BP, &bgr;=−0.44 (95% confidence interval −0.59, −0.28) mm Hg per 100 cpm, and &bgr;=−0.66 (95% CI −0.92, −0.39) mm Hg per 15 minutes/d MVPA, adjusting for child’s age and gender. After adjustment for potential confounders, associations were weakened but remained. When PA variables were modeled together, associations with total PA were only a little weaker, whereas those with MVPA were substantially reduced; for systolic BP, &bgr;=−0.42 (95% CI −0.71, −0.13) mm Hg per 100 cpm, and &bgr;=−0.03 (95% CI −0.54, 0.48) mm Hg per 15 minutes/d MVPA. In conclusion, higher levels of PA were associated with lower BP, and results suggested that the volume of activity may be more important than the intensity.

Early life determinants of physical activity in 11 to 12 year olds: cohort study

Objective To examine factors in early life (up to age 5 years) that are associated with objectively measured physical activity in 11-12 year olds. Design Prospective cohort study. Setting Avon longitudinal study of parents and children, United Kingdom. Participants Children aged 11-12 years from the Avon longitudinal study of parents and children. Main outcome measure Physical activity levels in counts per minute (cpm) and minutes of moderate to vigorous physical activity for seven days measured with a uniaxial actigraph accelerometer. Results Valid actigraph data, defined as at least three days of physical activity for at least 10 hours a day, were collected from 5451 children. Several factors were associated with physical activity at ages 11-12 years. Regression coefficients are compared with the baseline of “none” for categorical variables: maternal brisk walking during pregnancy (regression coefficient 5.0, 95% confidence interval −8.5 to 18.5; cpm for <1 h/wk and ≥2 h/wk of physical activity 17.7, 5.3 to 30.1), maternal swimming during pregnancy (21.5, 10.9 to 32.1 and cpm for <1 h/wk and ≥2 h/wk of physical activity 24.2, 7.8 to 40.7), parents’ physical activity when the child was aged 21 months (28.5, 15.2 to 41.8 and cpm of physical activity for either parent active and both parents active 33.5, 17.8 to 49.3), and parity assessed during pregnancy (2.9, −7.6 to 13.4 and cpm of physical activity for 1 and ≥2 parity 21.2, 7.1 to 35.3). Conclusions Few factors in early life predicted later physical activity in 11-12 year olds. Parents’ physical activity during pregnancy and early in the child’s life showed a modest association with physical activity of the child at age 11-12 years, suggesting that active parents tend to raise active children. Helping parents to increase their physical activity therefore may promote children’s activity.

A Prospective Study of Sedentary Behavior in a Large Cohort of Youth

PURPOSE The studys purpose was to describe longitudinal patterns of objectively measured sedentary behavior from age 12 to 16. METHODS Children participating in the Avon Longitudinal Study of Parents and Children wore accelerometers for 1 wk at ages 12, 14, and 16. Participants included boys (n = 2591) and girls (n = 2845) living in a single geographic location in the United Kingdom (Bristol). Total minutes per day spent in sedentary behavior and time spent in blocks of sedentary behavior lasting 10-19, 20-29, and ≥ 30 min are described. Growth curve models were used to determine the rate of change in sedentary behavior from age 12 to 16. RESULTS At age 12, the boys and girls, on average, were sedentary for 418.0 ± 67.7 and 436.6 ± 64.0 min·d(-1), respectively, and sedentary behavior increased over time to 468.0 ± 74.3 and 495.6 ± 68.9 min·d(-1) at age 14 and to 510.4 ± 76.6 and 525.4 ± 67.4 min·d(-1) at age 16. Growth curve analyses found that total sedentary behavior increased at a rate of 19.5 ± 0.7 and 22.8 ± 0.7 min·d(-1)·yr for the boys and girls, respectively. The absolute mean increase in total sedentary behavior (+92.4 and +88.8 min·d(-1) for the boys and girls, respectively) closely matched the mean decrease in light physical activity (-82.2 and -82.9 min·d(-1) for the boys and girls, respectively) from age 12 to 16. Time spent in continuous sedentary behavior lasting ≥ 30 min increased by 121% from age 12 to 16. CONCLUSIONS Sedentary behavior increased with age, at the expense of light physical activity. The increase in sedentary behavior lasting ≥ 30 min in duration contributed greatly to the increase in total sedentary behavior.