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  • Author: Samantha G. Fawkner x
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Samantha G. Fawkner and Neil Armstrong

The purpose of this study was to examine methods of assessing Critical Power (CP) with children. Eight boys and 9 girls (10.3 – 0.4 yrs) completed 3 cycle tests in one day, each at a different constant power output predicted to induce fatigue in 2 to 15 min. Time to exhaustion was recorded, and order of the tests was randomized, with 3 hours recovery between tests. The children repeated these tests and 2 additional tests with at least 24 hr recovery between each test. CP was determined using least squares linear regression analysis of the power — t−1 relationship, for the single day (CP1), the 5 tests from different days (CP2), and the repeated 3 tests from different days (CP3). The 95% limits of agreement (range of percentage differences) were −15.4 to 13.1% (CP1 v CP2), −16.8 to 13.5% (CP1 v CP3), and −8.4 to 6.7% (CP2 v CP3). CP is a robust measure even when only 3 tests are completed in a single day and may be used to provide a simple and useful parameter of exercise intensity for constant load exercise with children.

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Mhairi MacDonald, Samantha G. Fawkner and Ailsa Niven

Background:

It is currently not known how much walking should be advocated for good health in adolescent girls. The aim of this study was therefore to recommend health referenced standards for step defined physical activity relating to appropriate health criterion/indicators in a group of adolescent girls.

Method:

Two hundred and thirty adolescent girls aged between 12 to 15 years volunteered to take part in the study. Each participant undertook measurements (BMI, waist circumference, % body fat, and blood pressure) to define health status. Activity data were collected by pedometer and used to assess daily step counts and accumulated daily activity time over 7 consecutive days.

Results:

Individuals classified as ‘healthy’ did not take significantly more steps·day–1 nor spend more time in moderate intensity activity than individuals classified as at health risk or with poor health profiles.

Conclusion:

‘Healthy’ adolescent girls do not walk significantly more in term of steps·day–1 or time spent in activity than girls classified as ‘unhealthy.’ This could suggest that adolescent girls may not walk enough to stratify health and health related outcomes and as a result the data could not be used to inform an appropriate step guideline for this population.

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Mhairi J. MacDonald, Samantha G. Fawkner, Ailsa G. Niven and David Rowe

Background: Currently, it is not known how much walking should be advocated for good health in an adolescent population. Step count recommendations for minimum time in moderate-intensity activity have been translated predominantly from treadmill walking. Purpose: To compare the energy cost of walking on a treadmill with overground walking in adolescent girls. Methods: A total of 26 adolescent girls undertook resting metabolic measurements for individual determination of 1 metabolic equivalent using indirect calorimetry. Energy expenditure was subsequently assessed during treadmill and overground walking at slow, moderate, and fast walking speeds for 4 to 6 minutes. Treadmill step rates were matched overground using a metronome. Results: The energy cost of treadmill walking was found to be significantly greater than and not equivalent to overground walking at 133 steps per minute; (equivalent to the fast walking pace): V˙O2 3.90 (2.78–5.01), P < .001, mean absolute percentage error (MAPE) = 18.18%, and metabolic equivalent 0.77 (0.54–1.00), P < .001, MAPE = 18.16%. The oxygen cost per step (V˙O2 mL·step−1) was significantly greater and not equivalent on the treadmill at 120 and 133 steps per minute: 0.43 (0.12–0.56), P < .05, MAPE = 10.12% versus 1.40 (1.01–1.76), P < .001, MAPE = 17.64%, respectively. Conclusion: The results suggest that there is a difference in energy cost per step of walking on a treadmill and overground at the same step rate. This should be considered when utilizing the treadmill in energy expenditure studies. Studies which aim to provide step recommendations should focus on overground walking where most walking activity is adopted.

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Ailsa G. Niven, Samantha G. Fawkner, Ann-Marie Knowles and Claire Stephenson

This cross-sectional study examined the relationship between physical self-perceptions (PSPs), maturation, and physical activity and compared the strength of the relationships of biological and chronological age with PSPs in early adolescent girls (N = 208; mean age = 11.83 ± 0.39 years). Participants completed the Physical Activity Questionnaire for Older Children, the Children’s Physical Self-Perception Profile, and the Pubertal Development Scale. Results indicated that PSPs were significantly and moderately correlated with physical activity. There were no differences in physical activity between maturation stages. Girls who were in the early stages of maturation had significantly more positive perceptions of body attractiveness and physical self-worth than girls in the mid stages of maturation. There was no evidence of a relationship between PSPs and chronological age. This study provided further support for the relationship between PSPs and physical activity and the relationship between maturation and aspects of PSPs. In this age group, maturation does not appear to be related to physical activity or the PSPs most strongly influential on physical activity behavior.

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Samantha G. Fawkner, Neil Armstrong, David J. Childs and Joanne R. Welsman

The purpose of this study was to assess the reliability of the ventilatory threshold using visual analysis (TVent) and a computerised v-slope method (TV - slope) with children. Twenty-two children completed 2 ramp incremental cycling tests to voluntary exhaustion. Oxygen uptake (V̇O2) at TVent was derived independently by two observers using plots of V̇E/V̇CO2, V̇E/V̇O2, PETO2 and PETCO2, V̇E and RER as a function of time. V̇O2 at TV - slope was determined by both observers using linear regression analysis of the plot of V̇CO2 against V̇O2. A TV – slope was determined for each test, although a TVent could not be found by one of the observers in 7 of the 44 tests. Inter-observer reliability was slightly better for TV - slope, and both methods had similar test-retest coefficients of repeatability (0.19 and 0.22 L • min−1, TVent and TV - slope, respectively). Although TV slope may be the method of choice, investigators should consider the 95% limits of agreement when interpreting their data.

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Brynmor C. Breese, Craig A. Williams, Alan R. Barker, Joanne R. Welsman, Samantha G. Fawkner and Neil Armstrong

This study examined longitudinal changes in the pulmonary oxygen uptake (pV̇O2) kinetic response to heavy-intensity exercise in 14–16 yr old boys. Fourteen healthy boys (age 14.1 ± 0.2 yr) completed exercise testing on two occasions with a 2-yr interval. Each participant completed a minimum of three ‘step’ exercise transitions, from unloaded pedalling to a constant work rate corresponding to 40% of the difference between the pV̇O2 at the gas exchange threshold and peak pV̇O2 (Δ). Over the 2-yr period a significant increase in the phase II time constant (25 ± 5 vs. 30 ± 5 s; p = .002, ω 2 = 0.34), the relative amplitude of the pV̇O2 slow component (9 ± 5 vs. 13 ± 4%; p = .036, ω 2 = 0.14) and the pV̇O2 gain at end-exercise (11.6 ± 0.6 vs. 12.4 ± 0.7 mL·min−1·W−1; p < .001, ω 2 = 0.42) were observed. These data indicate that the control of oxidative phosphorylation in response to heavy-intensity cycling exercise is age-dependent in teenage boys.

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Brynmor C. Breese, Craig A. Williams, Alan R. Barker, Joanne R. Welsman, Samantha G. Fawkner and Neil Armstrong

This study examined longitudinal changes in the pulmonary oxygen uptake (pV̇O 2) kinetic response to heavy-intensity exercise in 14–16 yr old boys. Fourteen healthy boys (age 14.1 ± 0.2 yr) completed exercise testing on two occasions with a 2-yr interval. Each participant completed a minimum of three ‘step’ exercise transitions, from unloaded pedalling to a constant work rate corresponding to 40% of the difference between the pV̇O 2 at the gas exchange threshold and peak pV̇O 2 (40% Δ). Over the 2-yr period a significant increase in the phase II time constant (25 ± 5 vs. 30 ± 5 s; p = .002, ω2 = 0.34), the relative amplitude of the pV̇O 2 slow component (9 ± 5 vs. 13 ± 4%; p = .036, ω2 = 0.14) and the pV̇O 2 gain at end-exercise (11.6 ± 0.6 vs. 12.4 ± 0.7 mL·min−1·W−1; p < .001, ω2 = 0.42) were observed. These data indicate that the control of oxidative phosphorylation in response to heavy-intensity cycling exercise is age-dependent in teenage boys.