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Mark S. Tremblay

Background: Emerging research shows that the composition of movement behaviors throughout the day (physical activities, sedentary behaviors, sleep) is related to indicators of health, suggesting previous research that isolated single movement behaviors maybe incomplete, misleading, and/or unnecessarily constrained. Methods: This brief report summarizes evidence to support a 24-hour movement behavior paradigm and efforts to date by a variety of jurisdictions to consult, develop, release, promote, and study 24-hour movement guidelines. It also introduces and summarizes the accompanying series of articles related specifically to 24-hour movement guidelines for the early years. Results: Using robust and transparent processes, Canada, Australia, New Zealand, South Africa, and the World Health Organization have developed and released 24-hour movement guidelines for the early years: an integration of physical activity, sedentary behavior, and sleep. Other countries are exploring a similar approach and related research is expanding rapidly. Articles related to guideline development in South Africa, the United Kingdom, Australia, and by the World Health Organization are a part of this special series. Conclusions: A new paradigm employing 24-hour movement guidelines for the early years that combines recommendations for movement behaviors across the whole day is gaining momentum across the globe.

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Meghann Lloyd, Rachel C. Colley, and Mark S. Tremblay

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Diego Augusto Santos Silva, Katie E. Gunnell, and Mark Stephen Tremblay

Background: This study aimed to examine the factor structure of responses to the Portuguese version of questions related to screen time–based sedentary behavior among adolescents. Methods: This cross-sectional study with a sample of 1083 adolescents aged 14–19 years was conducted in Brazil. The sample was randomly divided into 2 groups for an exploratory factor analysis and for a confirmatory factor analysis. Screen time was investigated by a Portuguese version of questions about time sitting in front of television, computer, and video games on weekdays and weekends. Results: Scree plots showed 2 factors with eigenvalues above 1. One factor was formed by items about television and computer use, and the other factor was formed by items about video game use. The exploratory factor analysis with 2 factors resulted in factor loadings above .60. A second model with 1 factor was estimated and resulted in factor loadings above .55. A confirmatory factor analysis was estimated based on the 2-factor exploratory factor analysis and goodness-of-fit statistics were adequate. Confirmatory factor analysis with 1 factor had goodness-of-fit statistics adequate. Conclusions: The Portuguese language version of self-report screen time had 2 possible factor solutions, and items demonstrated good factor structure with reasonable reliability making it suitable for use in the future studies.

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Richard Larouche, Meghann Lloyd, Emily Knight, and Mark S. Tremblay

The current investigation assessed the impact of active school transportation (AST) on average daily step counts, body mass index (BMI) and waist circumference in 315 children in Grades 4–6 who participated to Cycle 2 of the Canadian Assessment of Physical Literacy (CAPL) pilot testing. T-tests revealed a significant association between AST and lower BMI values (18.7 ± 3.3 vs. 19.9 ± 3.8 kg/m2). The active commuters accumulated an average of 662 more steps per day, and their waist circumference was lower by an average of 3.1 cm, but these differences were not statistically significant. ANCOVA analyses controlling for age and step counts, found trends toward lower BMI and waist circumference values among the active commuters. These results suggest that AST may be a valid strategy to prevent childhood obesity; further research is needed to determine more precisely the impact of AST on body composition, and the direction of the relationship.

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Jennifer L. Copeland, Samuel Y. Chu, and Mark S. Tremblay

Women experience significant changes in endocrine function during aging. Decreasing levels of anabolic hormones may be associated with musculoskeletal atrophy and decrease in function that is observed in older women and, as a result, there has been an increase in the use of pharmacological hormone therapies. It is difficult to distinguish, however, between physiological changes that are truly age related and those that are associated with lifestyle factors such as physical activity participation. Some research has shown that circulating levels of anabolic hormones such as DHEA(S) and IGF-I in older women are related to physical activity, muscle function, and aerobic power. Exercise-intervention studies have generally shown that increasing age blunts the acute hormonal response to exercise, although this might be explained by a lower exercise intensity in older women. There have been relatively few studies that examine hormonal adaptations to exercise training. Physical activity might have an effect on hormone action as a result of changes in protein carriers and receptors, and future research needs to clarify the effect of age and exercise on these other components of the endocrine system. The value and safety of hormone supplements must be examined, especially when used in combination with an exercise program.

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Joey C. Eisenmann, P.T. Katzmarzyk, and Mark S. Tremblay

Background:

In recent years, it has been noted that children and youth are physically inactive, and physical activity levels have declined over the past decades. However, few empirical studies have been conducted to test this assumption. Therefore, the purpose of this study was to examine leisure-time physical activity levels among Canadian adolescents 12–19 years of age.

Methods:

Age, sex, geographic, and temporal trends in leisure-time physical activity energy expenditure (AEE) were examined using data from 5 national surveys conducted between 1981 and 1998. AEE was calculated from participants’ questionnaire responses on physical activity participation. General linear models were used to examine the differences in AEE across survey years, geographic regions, sexes, and age groups.

Results:

Males and 12–14-year-olds displayed greater AEE than females and 15–19-year-olds, respectively, and AEE was lowest in Quebec and highest in the West. AEE increased between the 1981 and 1988 surveys and has since remained relatively stable. The prevalence of subjects meeting the 12.6 kJ · kg−1 · d−1 (3 kcal · kg−1 · d−1) recommendation increased from 1981 to 1988. Since 1988, the prevalence of those meeting the 12.6 kJ · kg−1 · d−1 recommendation has decreased in 12–14 year old boys and remained relatively stable in the other groups. In 1998, about 45% of males and 35% of females met the 12.6 kJ · kg−1 · d−1 recommendation. In 1998, about 20% of 12–19-year-old males and 12–14-year-old females met the 25.1 kJ · kg−1 · d−1 (6 kcal · kg−1 · d−1) recommendation, while about 10% of 15–19-year-old females met this recommendation. In females, the prevalence of those meeting the 25.1 kJ · kg−1 · d−1 recommendation has remained relatively stable (about 10%) since 1981 except for an increase between 1996 and 1998 in 12–14-year-old girls. In males, a similar pattern, but not as dramatic, of that observed for the prevalence of those meeting the 12.6 kJ · kg−1 · d−1 emerged—that is, an increase between 1981 and 1988 and then a decrease in 12–14-year-old boys and a stable pattern in 15–19-year-old boys.

Conclusion:

Although self-reported leisure-time physical activity appears to have increased since 1981, a majority of Canadian adolescents do not meet current recommendations for physical activity.

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Suzy Lai Wong, Rachel Colley, Sarah Connor Gorber, and Mark Tremblay

Background:

Actical accelerometer thresholds have been derived to enable objective measurement of time spent performing sedentary activity in children and adolescents, but not adults. Thus, the purpose of this study was to determine Actical accelerometer sedentary activity thresholds for adults.

Methods:

Data were available from 3187 participants aged 6 to 79 years from a preliminary partial dataset of the Canadian Health Measures Survey, who wore an Actical for 7 days. Step count data were used to evaluate the use of 50, 100, and 800 counts per min (cpm) as sedentary activity thresholds. Minutes when no steps were recorded were considered minutes of sedentary activity.

Results:

The use of higher cpm thresholds resulted in a greater percentage of sedentary minutes being correctly classified as sedentary. The percentage of minutes that were incorrectly classified as sedentary was substantially higher when using a threshold of 800 cpm compared with 50 or 100 cpm. Results were similar for children, adolescents, and adults.

Conclusions:

These findings suggest that a threshold of 100 cpm is appropriate for classifying sedentary activity of adults when using the Actical. As such, wear periods with minutes registering less than 100 cpm would be classified as time spent performing sedentary activity.

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Mark S. Tremblay, J. Wyatt Inman, and J. Douglas Willms

This study examined the relationships between children’s reported levels of physical activity, body-mass index, self-esteem, and reading and mathematics scores, while controlling for sex, family structure, and socioeconomic status. The data were collected from the full population of Grade 6 students (N = 6,923) in New Brunswick (NB), Canada in 1996, as part of the Elementary School Climate Study, and the NB Department of Education’s Grade 6 Assessment. Physical activity had a negative relationship with body-mass index. Physical activity had a positive relationship with self-esteem, and a trivial negative relationship with academic achievement. The analysis revealed that both females and males who were more physically active had considerably higher levels of self-esteem. The study suggests that the relationship between physical activity and academic achievement is weak. For some children, physical activity may be indirectly related to enhanced academic performance by improving physical health and self-esteem.

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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.