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Alex V. Rowlands

It is well known that physical activity is important for children’s current and future mental and physical health. Despite this, there appears to be a secular decline in children’s physical activity (Cameron et al. [2]; Dalene et al. [3]). Furthermore, (frustratingly) interventions aiming to increase children’s physical activity have limited success (Metcalf et al. [10]), demonstrating a need for more information on the amenability of activity levels to change.

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Alex V. Rowlands

Significant advances have been made in the measurement of physical activity in youth over the past decade. Monitors and protocols promote very high compliance, both night and day, and raw measures are available rather than “black box” counts. Consequently, many surveys and studies worldwide now assess children’s physical behaviors (physical activity, sedentary behavior, and sleep) objectively 24 hours a day, 7 days a week using accelerometers. The availability of raw acceleration data in many of these studies is both an opportunity and a challenge. The richness of the data lends itself to the continued development of innovative metrics, whereas the removal of proprietary outcomes offers considerable potential for comparability between data sets and harmonizing data. Using comparable physical activity outcomes could lead to improved precision and generalizability of recommendations for children’s present and future health. The author will discuss 2 strategies that he believes may help ensure comparability between studies and maximize the potential for data harmonization, thereby helping to capitalize on the growing body of accelerometer data describing children’s physical behaviors.

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Alex V. Rowlands

2016 has been an exciting year for research in physical activity, inactivity and health. Recognition of the importance of all physical behaviors (physical activity, sedentary time and sleep) across the 24-hr day continues to grow. Notable advances have included: applications of recent methodological innovations that account for the codependence of the behaviors in the finite 24-hr period showing that the balance of these behaviors is associated with health; methodological innovations focusing on the classification of behaviors and/or quantification of the 24-hr diurnal activity pattern; and a series of systematic reviews that helped provide the evidence base for the release of the innovative 24-hr movement guidelines earlier this year. This commentary focuses on just two of these papers: the first by Goldsmith and colleagues who demonstrate a new statistical method that exploits the time series nature of accelerometer data facilitating new insights into time-specific determinants of children’s activity patterns and associations with health; the second by Tremblay and colleagues who describe the evidence base for associations between each physical behavior and children’s health, the emerging evidence base for associations between the balance of behaviors and health, and development of the world’s first 24-hr movement guidelines.

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Alex V. Rowlands

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Alex V. Rowlands

Background:

The total activity volume performed is an overall measure that takes into account the frequency, intensity, and duration of activities performed. The importance of considering total activity volume is shown by recent studies indicating that light physical activity (LPA) and intermittent moderate-to-vigorous physical activity (MVPA) have health benefits. Accelerometer-derived total activity counts (TAC) per day from a waist-worn accelerometer can serve as a proxy for an individual’s total activity volume. The purpose of this study was to develop age- and gender-specific percentiles for daily TAC, minutes of MVPA, and minutes of LPA in U.S. youth ages 6-19 y.

Methods:

Data from the 2003-2006 NHANES waist-worn accelerometer component were used in this analysis. The sample was composed of youth aged 6-19 years with at least 4 d of ≥10 hr of accelerometer wear time (N = 3698). MVPA was defined using age specific cutpoints as the total number of minutes at ≥4 metabolic equivalents (METs) for youth 6-17 y or minutes with ≥2020 counts for youth 18-19 y. LPA was defined as the total number of minutes between 100 counts and the MVPA threshold. TAC/d, MVPA, and LPA were averaged across all valid days.

Results:

For males in the 50th percentile, the median activity level was 441,431 TAC/d, with 53 min/d of MVPA and 368 min/d of LPA. The median level of activity for females was 234,322 TAC/d, with 32 min/d of MVPA and 355 min/d of LPA.

Conclusion:

Population referenced TAC/d percentiles for U.S. youth ages 6-19 y provide a novel means of characterizing the total activity volume performed by children and adolescents.

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Danielle Lambrick, Alex Rowlands, Thomas Rowland and Roger Eston

Prior experience of fatiguing tasks is considered essential to establishing an optimal pacing strategy. This study examined the pacing behavior of inexperienced children during self-paced, 800 m running, both individually and within a competitive environment. Thirteen children (aged 9−11 y) completed a graded-exercise test to volitional exhaustion on a treadmill (laboratory trial), followed by three self-paced, individual 800 m time-trials (Trials 1−3) and one self-paced, competitive 800 m time-trial (Trial 4) on an outdoor athletics track. Ratings of perceived exertion (RPE) and heart rate (HR) were measured throughout all trials. Overall performance time improved from Trial 1−3 (250.1 ± 50.4 s & 242.4 ± 51.5 s, respectively, p < .017). The difference in overall performance time between Trials 3 and 4 (260.5 ± 54.2 s) was approaching significance (p = .06). The pacing strategy employed from the outset was consistent across all trials. These findings dispute the notion that an optimal pacing strategy is learned with exercise experience or training.

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Verity Booth, Alex Rowlands and James Dollman

Purpose: To assess trends in South Australian children’s physical activity between 1985 and 2003 and 2013 in the contexts of school active transport, organized sport, physical education, and school break times. Method: The 1985 Australian Health and Fitness Survey was administered in South Australian schools in 2004 (8 schools) and 2013 (9 schools) and was demographically matched to the 10 South Australian schools in the Australian Health and Fitness Survey. Ordinal logistic modeling was used to identify trends, stratified by older children (10–12 y) and early adolescent (13–15 y) subgroups. Results: School active transport generally declined for males and older female children (19 and 20 percentage points per decade, respectively), whereas early adolescent females increased in walking to school (11 percentage points per decade). School sport participation declined for early adolescents, and club sport participation declined in early adolescent females (23 percentage points per decade). Moderate to vigorous physical activity participation during school break times (particularly lunchtime) generally declined (16–26 percentage points per decade). Observed changes in most contexts occurred between 2004 and 2013. Conclusion: There was evidence of context-specific declines in children’s physical activity participation over this time span. Early adolescent females were the subgroup of most concern, experiencing declines in most contexts.

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Charlotte C. Benjamin, Alex Rowlands and Gaynor Parfitt

Past studies have shown the patterning of affective responses during a graded exercise test (GXT) in adult and male adolescent populations, but none have explored the patterns in adolescent girls or younger children. This study explored the patterning of affective responses during a GXT in adolescents and younger children. Forty-nine children (21 male and 28 female) aged between 8–14 years (10.8 ± 1.8 years) completed a GXT. Ventilatory threshold (VT) was identified. At the end of each incremental step, participants reported affective valence. Results revealed that affective valence assessed by the Feeling Scale (FS) significantly declined from the onset of exercise until the point of VT in the younger children, but remained relatively stable in the adolescents. Exercise above the VT brought about significant declines in affective valence regardless of age or sex, but the decrease was significantly greater in adolescents. Results suggest it may be preferable to prescribe lower exercise intensities (below VT) for children, compared with adolescents, to ensure a positive affective response.

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Charlotte L. Edwardson, Melanie Davies, Kamlesh Khunti, Thomas Yates and Alex V. Rowlands

Purpose: To compare steps counts recorded by consumer activity trackers when worn on the non-dominant and dominant wrist against a waist-worn pedometer during free-living. Methods: 30 participants wore six consumer wrist-worn physical activity trackers and a pedometer. On day 1, three trackers were worn on the non-dominant wrist (ND) and three on the dominant (D) wrist. On day 2 trackers were worn on the opposite wrist. On both days, a pedometer (New-Lifestyles NL-800) was worn at the waist. Mean absolute percent error (MAPE) and the Bland-Altman method assessed tracker agreement with the pedometer. Repeated measures ANOVA examined whether MAPEs were significantly different between wrist trackers (i.e., brand comparison) and between wrist location (i.e., non-dominant vs. dominant). Results: MAPEs were higher for the D wrist trackers. Five out of six trackers on the D wrist over-counted, while four out of six trackers on the ND wrist under-counted. MAPE errors were significant (p ≤ .001) between trackers but not across wrist location (p > .05). Fitbit Flex_ND, Mi Band_ND and D, Garmin Vivofit3_D and Jawbone UP24_D had a mean bias of <500 steps. 95% limits of agreement were narrowest for Mi Band_ND. Conclusions: Tracker agreement with the waist-worn pedometer varied widely but trackers on the ND wrist had better agreement. The Mi Band was the most comparable to the pedometer.

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Alex V. Rowlands, John M. Schuna Jr., Victoria H. Stiles and Catrine Tudor-Locke

Background:

Previous research has reported peak vertical acceleration and peak loading rate thresholds beneficial to bone mineral density (BMD). Such thresholds are difficult to translate into meaningful recommendations for physical activity. Cadence (steps/min) is a more readily interpretable measure of ambulatory activity.

Objective:

To examine relationships between cadence, peak vertical acceleration and peak loading rate during ambulation and identify the cadence associated with previously reported bone-beneficial thresholds for peak vertical acceleration (4.9 g) and peak loading rate (43 BW/s).

Methods:

Ten participants completed 8 trials each of: slow walking, brisk walking, slow running, and fast running. Acceleration data were captured using a GT3×+ accelerometer worn at the hip. Peak loading rate was collected via a force plate.

Results:

Strong relationships were identified between cadence and peak vertical acceleration (r = .96, P < .05) and peak loading rate (r = .98, P < .05). Regression analyses indicated cadences of 157 ± 12 steps/min (2.6 ± 0.2 steps/s) and 122 ± 10 steps/min (2.0 ± 0.2 steps/s) corresponded with the 4.9 g peak vertical acceleration and 43 BW/s peak loading rate thresholds, respectively.

Conclusions:

Cadences ≥ 2.0 to 2.6 steps/s equate to acceleration and loading rate thresholds related to bone health. Further research is needed to investigate whether the frequency of daily occurrences of this cadence is associated with BMD.