Changes in training activity post COVID-19 infection in recreational runners and cyclists

Background

Anecdotal evidence suggests that athletes struggle to return to exercise post COVID-19 infection. However, studies evaluating the effect of COVID-19 on athletes' exercise activity are limited.

Objectives

The objectives of this study were: (i) to describe the perceptions of recreational runners and cyclists recovering from COVID-19 on their training activity and general well-being, (ii) to compare device-measured training data in runners and cyclists pre- and post COVID-19, with non-infected controls that had a training interruption.

Methods

Participants who were recruited via social media completed an online questionnaire (n=61), including demographic, health and COVID-19 descriptive data. In a sub-sample, device-measured training data (heart rate, time, distance and speed, n=27) were obtained from GPS devices for four weeks before infection and on resumption of training. Similar data were collected for the control group (n=9) whose training had been interrupted but by factors excluding COVID-19.

Results

Most participants experienced a mild to moderate illness (91%) that was associated with a training interruption time of two-four weeks. Decreases in heart rate, relative exercise intensity, speed, time and distance were observed during the first week of returning to training for both groups, followed by an increase from Week two onwards.

Discussion

Results failed to support a 'COVID-19 effect' on exercise activity as reductions in training variables occurred in both the COVID-19 and control groups. A possible explanation for the reductions observed is a deliberate gradual return to training by athletes post-COVID-19.

Conclusion

More research is needed using device-measured training data prior to and post COVID-19 infection to better understand the impact of the SARS-CoV-2 virus on the exercise activity of athletes.

Inequality in physical activity, global trends by income inequality and gender in adults

Background

Physical inactivity is a global pandemic associated with a high burden of disease and premature mortality. There is also a trend in growing economic inequalities which impacts population health. There is no global analysis of the relationship between income inequality and population levels of physical inactivity.

Methods

Two thousand sixteen World Health Organisation’s country level data about compliance with the 2010 global physical activity guidelines were analysed against country level income interquantile ratio data obtained from the World Bank, OECD and World Income Inequality Database. The analysis was stratified by country income (Low, Middle and High) according to the World Bank classification and gender. Multiple regression was used to quantify the association between physical activity and income inequality. Models were adjusted for GDP and percentage of GDP spent on health care for each country and out of pocket health care spent.

Results

Significantly higher levels of inactivity and a wider gap between the percentage of women and men meeting global physical activity guidelines were found in countries with higher income inequality in high and middle income countries irrespective of a country wealth and spend on health care. For example, in higher income countries, for each point increase in the interquantile ratio data, levels of inactivity in women were 3.73% (CI 0.89 6.57) higher, levels of inactivity in men were 2.04% (CI 0.08 4.15) higher and the gap in inactivity levels between women and men was 1.50% larger (CI 0.16 2.83). Similar relationships were found in middle income countries with lower effect sizes. These relationships were, however, not demonstrated in the low-income countries.

Conclusions

Economic inequalities, particularly in high- and middle- income countries might contribute to physical inactivity and might be an important factor to consider and address in order to combat the global inactivity pandemic and to achieve the World Health Organisation target for inactivity reduction.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12966-020-01039-x.

Thresholds of physical activity associated with obesity by level of sedentary behaviour in children

BACKGROUND

It is unknown whether moderate-to-vigorous physical activity (MVPA) thresholds for obesity should be adapted depending on level of sedentary behaviour in children.

OBJECTIVE

The objective of the study is to determine the MVPA thresholds that best discriminate between obese and non-obese children, by level of screen time and total sedentary time in 12 countries.

METHODS

This multinational, cross-sectional study included 6522 children 9-11 years of age. MVPA and sedentary time were assessed using waist-worn accelerometry, while screen time was self-reported. Obesity was defined according to the World Health Organization reference data.

RESULTS

Receiver operating characteristic curve analyses showed that the best thresholds of MVPA to predict obesity ranged from 53.8 to 73.9 min d^-1 in boys and from 41.7 to 58.7 min d^-1 in girls, depending on the level of screen time. The MVPA cut-offs to predict obesity ranged from 37.9 to 75.9 min d^-1 in boys and from 32.5 to 62.7 min d^-1 in girls, depending on the level of sedentary behaviour. The areas under the curve ranged from 0.57 to 0.73 ('fail' to 'fair' accuracy), and most sensitivity and specificity values were below 85%, similar to MVPA alone. Country-specific analyses provided similar findings.

CONCLUSIONS

The addition of sedentary behaviour levels to MVPA did not result in a better predictive ability to classify children as obese/non-obese compared with MVPA alone.

Inequality in physical activity, sedentary behaviour, sleep duration and risk of obesity in children: a 12-country study

OBJECTIVE

Studies examining associations between movement behaviours (i.e. physical activity, sedentary behaviour and sleep duration) and obesity focus on average values of these movement behaviours, despite important within-country and between-country variability. A better understanding of movement behaviour inequalities is important for developing public health policies and behaviour-change interventions. The objective of this ecologic analysis at the country level was to determine if inequality in movement behaviours is a better correlate of obesity than average movement behaviour volume in children from all inhabited continents of the world.

METHODS

This multinational, cross-sectional study included 6,128 children 9-11 years of age. Moderate-to-vigorous physical activity (MVPA), total sedentary time (SED) and sleep period time were monitored over 7 consecutive days using waist-worn accelerometry. Screen time was self-reported. Inequality in movement behaviours was determined using Gini coefficients (ranging from 0 [complete equality] to 1 [complete inequality]).

RESULTS

The largest inequality in movement behaviours was observed for screen time (Gini of 0.32; medium inequality), followed by MVPA (Gini of 0.21; low inequality), SED (Gini of 0.07; low inequality) and sleep period time (Gini of 0.05; low inequality). Average MVPA (h d-1) was a better correlate of obesity than MVPA inequality (r = -0.77 vs. r = 0.00, p = 0.03). Average SED (h d-1) was also a better correlate of obesity than SED inequality (r = 0.52 vs. r = -0.32, p = 0.05). Differences in associations for screen time and sleep period time were not statistically significant. MVPA in girls was found to be disproportionally lower in countries with more MVPA inequality.

CONCLUSIONS

Findings from this study show that average MVPA and SED should continue to be used in population health studies of children as they are better correlates of obesity than inequality in these behaviours. Moreover, the findings suggest that MVPA inequality could be greatly reduced through increases in girls' MVPA alone.

The relationship between functional status, physical fitness and cognitive performance in physically active older adults: A pilot study

OBJECTIVE

Ageing is associated with a progressive decline in physical function and cognitive performance which could result in a shift from an independent to a more dependent lifestyle. The aim of this research study was to assess the fitness, functional performance and cognitive ability in independently living older South Africans and to determine which fitness parameters and functional performance tests best explain the variance in cognitive function.

DESIGN

Descriptive observational study.

PARTICIPANTS

Older adults with a mean age 71±4.7 years (n = 70; 28 men and 42 women) were recruited. Sixty percent of the sample completed at least secondary schooling and more than two-thirds were taking medication for a chronic medical condition.

MEASUREMENTS

Self-reported physical activity was assessed using the Yale Physical Activity Survey. Fitness tests included the 6-minute walk test and Bicep Curls. The functional performance tests were; Static and Dynamic balance, Timed Up and Go, Sit to Stand, Grip strength and Functional Reach. The Stroop Task and 6-Item cognitive impairment test were used to measure cognitive performance. Bivariate and multivariate analyses were conducted between performance on the novel cognitive Stroop Task and functional and cognitive tests.

RESULTS

We found significant relationships between the number of correct responses on the Stroop Task and scores on the 6-Item Cognitive Impairment test (-0.520, p < 0.01) and grip strength (r = 0.42, p< 0.01). The number of incorrect responses was inversely associated with functional reach (r = -0.445, p< 0.01). The final regression model included: age, dynamic balance, right arm grip strength and the score on the 6-item cognitive impairment test, and explained 44% of the variance in performance of the Stroop Task.

CONCLUSIONS

The results of this study showed that measures of physical function were associated with cognitive performance even in highly functioning older South African adults. Further research is needed to determine the extent to which exercise training can improve functional capacity and the effect on cognitive performance.

The adiposity of children is associated with their lifestyle behaviours: a cluster analysis of school-aged children from 12 nations

BACKGROUND

The relationship between children's adiposity and lifestyle behaviour patterns is an area of growing interest.

OBJECTIVES

The objectives of this study are to identify clusters of children based on lifestyle behaviours and compare children's adiposity among clusters.

METHODS

Cross-sectional data from the International Study of Childhood Obesity, Lifestyle and the Environment were used.

PARTICIPANTS

the participants were children (9-11 years) from 12 nations (n = 5710).

MEASURES

24-h accelerometry and self-reported diet and screen time were clustering input variables. Objectively measured adiposity indicators were waist-to-height ratio, percent body fat and body mass index z-scores.

ANALYSIS

sex-stratified analyses were performed on the global sample and repeated on a site-wise basis. Cluster analysis (using isometric log ratios for compositional data) was used to identify common lifestyle behaviour patterns. Site representation and adiposity were compared across clusters using linear models.

RESULTS

Four clusters emerged: (1) Junk Food Screenies, (2) Actives, (3) Sitters and (4) All-Rounders. Countries were represented differently among clusters. Chinese children were over-represented in Sitters and Colombian children in Actives. Adiposity varied across clusters, being highest in Sitters and lowest in Actives.

CONCLUSIONS

Children from different sites clustered into groups of similar lifestyle behaviours. Cluster membership was linked with differing adiposity. Findings support the implementation of activity interventions in all countries, targeting both physical activity and sedentary time.

Mid-upper arm circumference as a screening tool for identifying children with obesity: a 12-country study

BACKGROUND

No studies have examined if mid-upper arm circumference (MUAC) can be an alternative screening tool for obesity in an international sample of children differing widely in levels of human development.

OBJECTIVE

Our aim is to determine whether MUAC could be used to identify obesity in children from 12 countries in five major geographic regions of the world.

METHODS

This observational, multinational cross-sectional study included 7337 children aged 9-11 years. Anthropometric measurements were objectively assessed, and obesity was defined according to the World Health Organization reference data.

RESULTS

In the total sample, MUAC was strongly correlated with adiposity indicators in both boys and girls (r > 0.86, p < 0.001). The accuracy level of MUAC for identifying obesity was high in both sexes and across study sites (overall area under the curve of 0.97, sensitivity of 95% and specificity of 90%). The MUAC cut-off value to identify obesity was ~25 cm for both boys and girls. In country-specific analyses, the cut-off value to identify obesity ranged from 23.2 cm (boys in South Africa) to 26.2 cm (girls in the UK).

CONCLUSIONS

Results from this 12-country study suggest that MUAC is a simple and accurate measurement that may be used to identify obesity in children aged 9-11 years. MUAC may be a promising screening tool for obesity in resource-limited settings.

Sources of variability in childhood obesity indicators and related behaviors

The purpose of this study was to describe sources of variability in obesity-related variables in 6,022 children aged 9–11 y from 12 countries. The study design involved recruitment of students, nested within schools, which were nested within study sites. Height, weight and waist circumference (WC) were measured and BMI was calculated; sleep duration and total and in-school moderate-to-vigorous physical activity (MVPA) and sedentary time were measured by accelerometry; and diet scores were obtained by questionnaire. Variance in most variables was largely explained at the student level: BMI (91.9%), WC (93.5%), sleep (75.3%), MVPA (72.5%), sedentary time (76.9%), healthy diet score (88.3%), unhealthy diet score (66.2%), with the exception of in-school MVPA (53.8%) and in-school sedentary time (25.1%). Variance explained at the school level ranged from 3.3% for BMI to 29.8% for in-school MVPA, and variance explained at the site level ranged from 3.2% for WC to 54.2% for in-school sedentary time. In general, more variance was explained at the school and site levels for behaviors than for anthropometric traits. Given the variance in obesity-related behaviors in primary school children explained at school and site levels, interventions that target policy and environmental changes may enhance obesity intervention efforts.

Enhanced insulin sensitivity in successful, long-term weight loss maintainers compared with matched controls with no weight loss history

Background:

Weight gain is associated with deterioration in metabolic health, whereas weight loss improves insulin sensitivity. This study assesses the impact of long-term, successfully maintained weight loss and weight-loss relapse on measures of insulin sensitivity and identifies factors that explain variability in insulin sensitivity.

Methods:

Women (20–45 years) were recruited into four groups: reduced-overweight/obese (RED, n=15); body mass index (BMI)-matched controls (stable low-weight, n=19), BMI⩽27 kg m⁻²; relapsed-overweight/obese subjects (REL, n=11); and BMI-matched controls (obese stable weight, n=11), BMI⩾27 kg m⁻². A 75 g oral glucose tolerance test determined fasting and 2 h plasma glucose and insulin. Homeostatic Model Assessment (HOMA-IR) and insulin sensitivity index (ISI_(0,120)) assessed insulin sensitivity. Anthropometric measurements, fasting resting metabolic rate (RMR) and respiratory quotient (RQ) were measured. Questionnaires and dietary intake were recorded, and physical activity was measured using accelerometers.

Results:

RED were more insulin sensitive, characterised by lower fasting (P=0.001) and 2 h insulin (P=0.003) levels compared with all other groups. There were no significant differences in dietary intake, sedentary, light and moderate activity, RMR or RQ in the RED compared with the other three groups. % Body weight (BW) lost (P<0.001), % BW regained (P<0.05), body fat %, light activity (P<0.05, only log HOMA), vigorous activity (P<0.05) and RQ (P<0.01) predicted 61.4% and 59.7% of variability in log HOMA and log ISI_(0,120), respectively, in multiple linear regression models.

Conclusion:

This study showed sustained enhanced insulin sensitivity in successful weight loss maintainers compared with BMI-matched controls with no weight loss history. Weight-loss-relapsed individuals were indistinguishable from controls. Weight loss itself was the strongest predictor of improved insulin sensitivity, whereas weight regain significantly predicted reduced insulin sensitivity. Weight-loss maintenance programs are essential to retaining metabolic benefits acquired through weight loss. Being physically active, reducing sedentary behaviour and, in particular, including small amounts of vigorous physical activity significantly predicted improved insulin sensitivity.

Relationships between different nutritional anthropometric statuses and health-related fitness of South African primary school children

BACKGROUND

A double burden of both under- and over-nutrition exists among South African children.

AIM

To describe associations between nutritional statuses and health-related fitness test performances.

SUBJECTS AND METHODS

Height and weight of 10 285 children (6-13 years; n = 5604 boys and 4681 girls) were measured and used to calculate body mass index (BMI) and prevalence of overweight and obesity, stunting, wasting and underweight. Physical fitness scores for standing long jump, shuttle run, sit-and-reach, sit-up (EUROFIT) and cricket ball throw were assessed. Age- and gender-specific z-scores were calculated for these variables. Physical fitness for each nutritional status group was compared to children of normal weight.

RESULTS

Compared to normal weight children, overweight and obese children scored lower on all fitness tests (p < .001), except cricket ball throw (p = .235) and sit-and-reach (p = .015). Stunted and underweight children performed poorer than normal weight children on most fitness tests (p < .001), except sit-and-reach (stunted: p = .829; underweight: p = .538) and shuttle run (underweight: p = .017). Performance of wasted children was not as highly compromised as other under-nourished groups, but they performed poorer on the cricket ball throw (p < .001).

CONCLUSIONS

When compared to normal weight children, both under- and over-nourished children performed poorer on some, but not all, health-related fitness tests.

Maternal and early life nutrition and physical activity: setting the research and intervention agenda for addressing the double burden of malnutrition in South African children

Early life is important for later health outcomes, yet there are few studies which adequately address all of the potential early life insults that may affect later life health and growth trajectories. This is particularly evident in low- to middle-income countries such as South Africa, where women of childbearing age are particularly vulnerable to high levels of physical inactivity, malnutrition, and obesity. Pregnancy may therefore be an opportune time to change behaviours and improve maternal and offspring health outcomes, and decrease the inter-generational transfer of risk. We show clear evidence that physical activity and nutrition are important target areas for intervention during pregnancy and in the early years of life, yet that current literature in Africa, and specifically South Africa, is limited. We have outlined the available literature concerning the impact of maternal and early life nutrition and physical activity on the health status of South African children, and have provided some recommendations for future research and policy.

Visual Stimulus Deprivation and Manipulation of Auditory Timing Signals on Pacing Strategy

In this study the effect of complete visual stimulus deprivation and manipulation of auditory timing signals during this deprivation on pacing strategy during an exercise bout were examined. 7 moderately trained men completed four 40-km cycling time trials under laboratory conditions in either normal light or absolute darkness, with either correct or manipulated auditory timing signals and without any other timing cues. The subjects were told to perform the time trial in the fastest time possible. There was no significant difference among trials for time to perform the trial, power output, heart rate, or ratings of perceived exertion, indicating that brain-control mechanisms responsible for pacing are not affected by manipulation of light or auditory signals.

Physical activity as a global risk factor for non-communicable diseases: time for action, what, why, when, who and how?

Chronic, non-communicable diseases (NCDs) account for more than two-thirds of global mortality, at least 50% of which is preventable on the basis of modifiable lifestyle behaviours. In the wake of the UN Global Summit on NCDs, the World Health Organization produced a discussion paper that emphasised the need for a global monitoring framework and voluntary global targets for the prevention and control of NCDs.1 The WHO discussion paper presents 10 suggested voluntary targets including the reduction in deaths due to NCDs, cardiovascular disease and diabetes, an overall reduction in blood pressure and obesity, as well as reduced smoking, alcohol and dietary salt intake, increased screening for cervical cancer and the elimination of trans-fats from the food supply. Physical activity is notable by its absence from this critical list of voluntary global targets for preventing and controlling NCDs

Association between body mass index and body fat in 9-11-year-old children from countries spanning a range of human development

The purpose was to assess associations between body mass index (BMI) and body fat in a multinational sample of 9-11-year-old children. The sample included 7265 children from countries ranging in human development. Total body fat (TBF) and percentage body fat (PBF) were measured with a Tanita SC-240 scale and BMI z-scores (BMIz) and percentiles were computed using reference data from the World Health Organization and the U.S. Centers for Disease Control and Prevention, respectively. Mean PBF at BMIz values of -1, 0 and +1 were estimated using multilevel models. Correlations between BMI and TBF were >0.90 in all countries, and correlations between BMI and PBF ranged from 0.76 to 0.96. Boys from India had higher PBF than boys from several other countries at all levels of BMIz. Kenyan girls had lower levels of PBF than girls from several other countries at all levels of BMIz. Boys and girls from Colombia had higher values of PBF at BMIz=-1, whereas Colombian boys at BMIz 0 and +1 also had higher values of PBF than boys in other countries. Our results show a consistently high correlation between BMI and adiposity in children from countries representing a wide range of human development.

Associations between sleep patterns and lifestyle behaviors in children: an international comparison

OBJECTIVES

Although evidence is accumulating on the importance of a good night's sleep for healthy eating and activity behaviors, existing research has mainly been conducted in high-income, developed countries with limited sociocultural variability. This study is the first to examine the associations between sleep patterns and lifestyle behaviors in children from 12 countries in five major geographic regions of the world.

METHODS

This observational, multinational cross-sectional study included 5777 children aged 9-11 years from sites in Australia, Brazil, Canada, China, Colombia, Finland, India, Kenya, Portugal, South Africa, the United Kingdom and the United States. Nocturnal sleep duration (hours per night), sleep efficiency (%) and bedtime (h:min) were monitored over 7 consecutive days using an accelerometer. Lifestyle behaviors included moderate-to-vigorous physical activity (MVPA), total sedentary time (SED), self-reported screen time (ST) and healthy/unhealthy diet patterns (HDP/UDP). Multilevel modeling analyses were used to account for the hierarchical nature of the data.

RESULTS

Overall, participants averaged 8.8 (s.d. 0.9) hours of sleep with 96.2% (s.d. 1.4) sleep efficiency and a mean bedtime of 2218 hours. After adjustment for age, sex, highest parental education and BMI z-score, results showed that (i) sleep duration was negatively associated with MVPA, SED and UDP score; (ii) sleep efficiency was negatively associated with MVPA and UDP score, and positively associated with SED; and (iii) later bedtime was positively associated with SED, ST and UDP score, and negatively associated with MVPA and HDP score. Results using categories of sleep patterns were consistent with the linear associations. Results also revealed that associations between sleep patterns and MVPA, SED and ST were significantly different between study sites, with stronger associations in high-income countries compared with low/middle-income countries.

CONCLUSIONS

Sleep characteristics are important correlates of lifestyle behaviors in children. Differences between countries suggest that interventions aimed at improving sleep and lifestyle behaviors should be culturally adapted.

Nocturnal sleep-related variables from 24-h free-living waist-worn accelerometry: International Study of Childhood Obesity, Lifestyle and the Environment

OBJECTIVES

We describe the process of identifying and defining nocturnal sleep-related variables (for example, movement/non-movement indicators of sleep efficiency, waking episodes, midpoint and so on) using the unique 24-h waist-worn free-living accelerometer data collected in the International Study of Childhood Obesity, Lifestyle and the Environment (ISCOLE).

METHODS

Seven consecutive days of 24-h waist-worn accelerometer (GT3X+, ActiGraph LLC) data were collected from over 500 children at each site. An expert subgroup of the research team with accelerometry expertize, frontline data collectors and data managers met on several occasions to categorize and operationally define nocturnal accelerometer signal data patterns. The iterative process was informed by the raw data drawn from a sub set of the US data, and culminated in a refined and replicable delineated definition for each identified nocturnal sleep-related variable. Ultimately based on 6318 participants from all 12 ISCOLE sites with valid total sleep episode time (TSET), we report average clock times for nocturnal sleep onset, offset and midpoint in addition to sleep period time, TSET and restful sleep efficiency (among other derived variables).

RESULTS

Nocturnal sleep onset occurred at 2218 hours and nocturnal sleep offset at 0707 hours. The mean midpoint was 0243 hours. The sleep period time of 529.6 min (8.8 h) was typically accumulated in a single episode, making the average TSET very similar in duration (529.0 min). The mean restful sleep efficiency ranged from 86.8% (based on absolute non-movement of 0 counts per minute) to 96.0% (based on relative non-movement of <100 counts per minute).

CONCLUSIONS

These variables extend the potential of field-based 24-h waist-worn accelerometry to distinguish and categorize the underlying robust patterns of movement/non-movement signals conveying magnitude, duration, frequency and periodicity during the nocturnal sleep period.

Associations between breakfast frequency and adiposity indicators in children from 12 countries

OBJECTIVES

Reports of inverse associations between breakfast frequency and indices of obesity are predominantly based on samples of children from high-income countries with limited socioeconomic diversity. Using data from the International Study of Childhood Obesity, Lifestyle and the Environment (ISCOLE), the present study examined associations between breakfast frequency and adiposity in a sample of 9-11-year-old children from 12 countries representing a wide range of geographic and socio-cultural variability.

METHODS

Multilevel statistical models were used to examine associations between breakfast frequency (independent variable) and adiposity indicators (dependent variables: body mass index (BMI) z-score and body fat percentage (BF%)), adjusting for age, sex, and parental education in 6941 children from 12 ISCOLE study sites. Associations were also adjusted for moderate-to-vigorous physical activity, healthy and unhealthy dietary patterns and sleep time in a sub-sample (n=5710). Where interactions with site were significant, results were stratified by site.

RESULTS

Adjusted mean BMI z-score and BF% for frequent breakfast consumers were 0.45 and 20.5%, respectively. Frequent breakfast consumption was associated with lower BMI z-scores compared with occasional (P<0.0001, 95% confidence intervals (CI): 0.10-0.29) and rare (P<0.0001, 95% CI: 0.18-0.46) consumption, as well as lower BF% compared with occasional (P<0.0001, 95% CI: 0.86-1.99) and rare (P<0.0001, 95% CI: 1.07-2.76). Associations with BMI z-score varied by site (breakfast by site interaction; P=0.033): associations were non-significant in three sites (Australia, Finland and Kenya), and occasional (not rare) consumption was associated with higher BMI z-scores compared with frequent consumption in three sites (Canada, Portugal and South Africa). Sub-sample analyses adjusting for additional covariates showed similar associations between breakfast and adiposity indicators, but lacked site interactions.

CONCLUSIONS

In a multinational sample of children, more frequent breakfast consumption was associated with lower BMI z-scores and BF% compared with occasional and rare consumption. Associations were not consistent across all 12 countries. Further research is required to understand global differences in the observed associations.

Active school transport and weekday physical activity in 9-11-year-old children from 12 countries

OBJECTIVES

Active school transport (AST) may increase the time that children spend in physical activity (PA). This study examined relationships between AST and weekday moderate-to-vigorous physical activity (MVPA), light physical activity (LPA), sedentary time (SED) and total activity during naturally organized time periods (daily, before school, during school and after school) in a sample of children from 12 countries.

METHODS

The sample included 6224 children aged 9-11 years. PA and sedentary time were objectively measured using Actigraph accelerometers. AST was self-reported by participants. Multilevel generalized linear and logistic regression statistical models were used to determine associations between PA, SED and AST across and within study sites.

RESULTS

After adjustment for age, highest parental educational attainment, BMI z-score and accelerometer wear time, children who engaged in AST accumulated significantly more weekday MVPA during all studied time periods and significantly less time in LPA before school compared with children who used motorized transport to school. AST was unrelated to time spent in sedentary behaviors. Across all study sites, AST was associated with 6.0 min (95% confidence interval (CI): 4.7-7.3; P<0.0001) more of weekday MVPA; however, there was some evidence that this differed across study sites (P for interaction=0.06). Significant positive associations were identified within 7 of 12 study sites, with differences ranging from 4.6 min (95% CI: 0.3-8.9; P=0.04, in Canada) to 10.2 min (95% CI: 5.9-14.4; P<0.0001, in Brazil) more of daily MVPA among children who engaged in AST compared with motorized transport.

CONCLUSIONS

The present study demonstrated that AST was associated with children spending more time engaged in MVPA throughout the day and less time in LPA before school. AST represents a good behavioral target to increase levels of PA in children.

Relationships between active school transport and adiposity indicators in school-age children from low-, middle- and high-income countries

OBJECTIVES

Within the global context of the nutrition and physical activity transition it is important to determine the relationship between adiposity and active school transport (AST) across different environmental and socio-cultural settings. The present study assessed the association between adiposity (that is, body mass index z-score (BMIz), obesity, percentage body fat (PBF), waist circumference) and AST in 12 country sites, in the International Study of Childhood Obesity, Lifestyle and the Environment (ISCOLE).

METHODS

The analytical sample included 6797 children aged 9-11 years. Adiposity indicators included, BMIz calculated using reference data from the World Health Organization, obesity (BMIz ⩾+2 s.d.), PBF measured using bioelectrical impedance and waist circumference. School travel mode was assessed by questionnaire and categorized as active travel versus motorized travel. Multilevel linear and non-linear models were used to estimate the magnitude of the associations between adiposity indicators and AST by country site and sex.

RESULTS

After adjusting for age, sex, parental education and motorized vehicle availability, children who reported AST were less likely to be obese (odds ratio=0.72, 95% confidence interval (0.60-0.87), P<0.001) and had a lower BMIz (-0.09, s.e.m.=0.04, P=0.013), PBF (least square means (LSM) 20.57 versus 21.23% difference -0.66, s.e.m.=0.22, P=0.002) and waist circumference (LSM 63.73 cm versus 64.63 cm difference -0.90, s.e.m.=0.26, P=0.001) compared with those who reported motorized travel. Overall, associations between obesity and AST did not differ by country (P=0.279) or by sex (P=0.571).

CONCLUSIONS

AST was associated with lower measures of adiposity in this multinational sample of children. Such findings could inform global efforts to prevent obesity among school-age children.

Birth weight and childhood obesity: a 12-country study

OBJECTIVES

Few studies have investigated the association between the full range of birth weight and the risk of childhood obesity in high-, middle- and low-income countries. The aim of the present study is to assess the association between different levels of birth weight and the risk of obesity among children aged 9-11 years in 12 countries.

METHODS

A multinational, cross-sectional study of 5141 children aged 9-11 years was conducted in 12 countries. Height and weight were obtained using standardized methods. Time spent in moderate-to-vigorous physical activity (MVPA), sedentary and sleeping were objectively measured using 24-h, waist-worn accelerometer (Actigraph GT3X+) monitored for 7 days. Birth weight and other factors (regions, parental education, maternal history of gestational diabetes, children age, gender, breast feeding, gestational age, unhealthy diet scores and healthy diet scores) were collected by parental and children's questionnaires. Multilevel modeling was used to account for the nested nature of the data.

RESULTS

The overall prevalence of obesity (BMI z-score>+2 s.d.) was 15.4% for boys and 10.0% for girls. There was a positive association between birth weight and BMI z-scores. The multivariable-adjusted odds ratios (ORs) of childhood obesity were significantly higher among children whose birth weights were 3500-3999 g (OR 1.45; 95% confidence interval (CI): 1.10-1.92), and >4000 g (OR 2.08; 95% CI: 1.47-2.93), compared with the reference group (2500-2999 g). The positive association between birth weight and the odds of childhood obesity was seen in girls, whereas a U-shaped association appeared in boys.

CONCLUSIONS

High levels of birth weight, defined as birth weight ⩾3500 g, were associated with increased odds of obesity among 9-11-year-old children in 12 countries. However, sex differences in the association between birth weight and the risk of obesity need to be considered when planning interventions to reduce childhood obesity.

Are participant characteristics from ISCOLE study sites comparable to the rest of their country?

OBJECTIVES

The International Study of Childhood Obesity, Lifestyle and the Environment (ISCOLE) provides robust, multi-national information on physical activity, diet and weight status in 9-11-year-old children around the world. The purpose of this analysis was to examine the similarities and differences between participant characteristics from ISCOLE sites and data from nationally representative surveys from ISCOLE countries (Australia, Brazil, Canada, China, Colombia, Finland, Kenya, India, Portugal, South Africa, the United Kingdom and the United States).

METHODS

Distributions of characteristics were assessed within each ISCOLE country-level database, and compared with published data from national or regional surveys, where available. Variables of comparison were identified a priori and included body mass index (BMI), physical activity (accelerometer-determined steps per day) and screen time (child-report).

RESULTS

Of 12 countries, data on weight status (BMI) were available in 8 countries, data on measured physical activity (steps per day) were available in 5 countries and data on self-reported screen time were available in 9 countries. The five ISCOLE countries that were part of the Health Behaviour in School-aged Children Survey (that is, Canada, Finland, Portugal, the United Kingdom (England) and the United States) also provided comparable data on self-reported physical activity. Available country-specific data often used different measurement tools or cut-points, making direct comparisons difficult. Where possible, ISCOLE data were re-analyzed to match country-level data, but this step limited between-country comparisons.

CONCLUSIONS

From the analyses performed, the ISCOLE data do not seem to be systematically biased; however, owing to limitations in data availability, data from ISCOLE should be used with appropriate caution when planning country-level population health interventions. This work highlights the need for harmonized measurement tools around the world while accounting for culturally specific characteristics, and the need for collaboration across study centers and research groups.

Cardiovascular fitness is associated with bias between self-reported and objectively measured physical activity

The aim of this research study was to determine whether the level of agreement between self-reported and objective measures of physical activity (PA) is influenced by cardiovascular fitness. Participants (n = 113) completed the Global Physical Activity Questionnaire (GPAQ), a health risk assessment and a sub-maximal 12-minute step test. Age-predicted VO2max was used to classify participants as lower fit and higher fit (HF). ActiGraph (GT3X) accelerometers were worn for 7 consecutive days. Matthews cut points were used to calculate minutes of moderate and vigorous PA (MVPA) per week. Bland-Altman plots were used to measure limits of agreement between GPAQ and ActiGraph MVPA. The participants' mean age was 37.9 ± 12.7 years and more than 60% were categorised as HF (n = 71). Moderate PA was over-reported in 39% of all participants. Most of the over-reporters for moderate PA were in the HF group (64.1%). Vigorous PA was over-reported by 72.6% of all participants. The discrepancy between self-reported and objective measures of vigorous PA increased with increasing self-reported time spent in vigorous PA. Fitter individuals appear to over-report PA more than lesser fit participants, suggesting that fitness could influence the level of agreement between self-reported and objective measures of PA.

Innovative strategies targeting obesity and non-communicable diseases in South Africa: what can we learn from the private healthcare sector?

Over 50% of South African adult women and 30% of adult men are either overweight or obese, and nearly half of all adults are insufficiently active, with major increases in obesity-associated healthcare expenditures since 1980, a high proportion of which are paid by private health insurance. In this paper, we describe the Vitality programme, an incentivized health promotion programme from South Africa's largest private health insurer, Discovery Health, with over 2.5 million beneficiaries. Wellness activities of the programme include health risk assessments, subsidized gym memberships and smoking cessation or weight loss programmes with many incentives, including cash back on purchases of healthy foods. This incentive-based programme has shown a significant relationship between levels of engagement in wellness activities, in particular increasing participation in fitness-related activities, with lower healthcare expenditure and an increase in the overall ratio of healthy foods to total food purchases. This programme demonstrates that incentives may reduce the barriers for entry into care, increase preventive screening and increase engagement in healthy behaviours for prevention and management of obesity. This 'carrots versus sticks' approach may have implications for public health policy even in lower- and middle-income settings and underserved communities.

Prediction of fat-free mass using bioelectrical impedance analysis in young adults from five populations of African origin

BACKGROUND/OBJECTIVES

Bioelectrical impedance analysis (BIA) is used in population and clinical studies as a technique for estimating body composition. Because of significant under-representation in existing literature, we sought to develop and validate predictive equation(s) for BIA for studies in populations of African origin.

SUBJECTS/METHODS

Among five cohorts of the Modeling the Epidemiologic Transition Study, height, weight, waist circumference and body composition, using isotope dilution, were measured in 362 adults, ages 25-45 with mean body mass indexes ranging from 24 to 32. BIA measures of resistance and reactance were measured using tetrapolar placement of electrodes and the same model of analyzer across sites (BIA 101Q, RJL Systems). Multiple linear regression analysis was used to develop equations for predicting fat-free mass (FFM), as measured by isotope dilution; covariates included sex, age, waist, reactance and height(2)/resistance, along with dummy variables for each site. Developed equations were then tested in a validation sample; FFM predicted by previously published equations were tested in the total sample.

RESULTS

A site-combined equation and site-specific equations were developed. The mean differences between FFM (reference) and FFM predicted by the study-derived equations were between 0.4 and 0.6 kg (that is, 1% difference between the actual and predicted FFM), and the measured and predicted values were highly correlated. The site-combined equation performed slightly better than the site-specific equations and the previously published equations.

CONCLUSIONS

Relatively small differences exist between BIA equations to estimate FFM, whether study-derived or published equations, although the site-combined equation performed slightly better than others. The study-derived equations provide an important tool for research in these understudied populations.

Near infrared reactance for the estimation of body fatness in regularly exercising individuals

Near infrared reactance (NIR) is used to measure body fat percentage (BF%), but there is little data on its use in non-obese, regularly exercising individuals. Therefore, this study aimed to examine the limits of agreement between NIR compared to dual x-ray absorptiometry (DXA) for the measurement of BF% in 2 cohorts of regularly exercising individuals. BF% was measured using DXA and NIR in a regular exercising (≥3 sessions/week), healthy active cohort (HA; n=57), and in a regularly exercising and resistance trained (≥2 sessions/week) cohort (RT; n=59). The RT cohort had lower BF% than the HA cohort (15.3±5.5% and 25.8±7.1%, P<0.001). In the HA and RT cohorts, NIR BF% was associated with DXA BF% (R2=0.72, SEE=3.7, p<0.001 and R2=0.50, SEE=4.1 p<0.001, respectively). In the HA cohort, NIR tended to under-predict BF% (mean difference: - 1.3%; 95% limits of agreement (LOA); - 8.8 to 6.2%) whereas in the RT cohort, NIR tended to over-predict BF% compared to DXA (mean difference: 1.1; 95% LOA; - 8.1 to 10.3%). In conclusion, NIR and DXA yield similar average BF% measurements in 2 cohorts of non-obese regularly exercising individuals. However, the rather broad LOA of NIR need to be considered when using NIR to screen for overweight and obesity, or measure and track changes in body composition.

Physical activity as a global risk factor for non-communicable diseases: time for action, what, why, when, who and how?

Chronic, non-communicable diseases (NCDs) account for more than two-thirds of global mortality, at least 50% of which is preventable on the basis of modifiable lifestyle behaviours. In the wake of the UN Global Summit on NCDs, the World Health Organization produced a discussion paper that emphasised the need for a global monitoring framework and voluntary global targets for the prevention and control of NCDs.1 The WHO discussion paper presents 10 suggested voluntary targets including the reduction in deaths due to NCDs, cardiovascular disease and diabetes, an overall reduction in blood pressure and obesity, as well as reduced smoking, alcohol and dietary salt intake, increased screening for cervical cancer and the elimination of trans-fats from the food supply. Physical activity is notable by its absence from this critical list of voluntary global targets for preventing and controlling NCDs

Site-specific differences in bone mineral density in black and white premenopausal South African women

SUMMARY

We examined ethnic differences in bone mineral density (BMD) and the contribution of body composition, lifestyle and socioeconomic factors in South African women. Femoral neck and total hip BMD were higher, but lumbar spine BMD was lower in black women, with body composition, lifestyle and socioeconomic status (SES) factors contributing differently in ethnic groups.

INTRODUCTION

There is a paucity of data on the relative contribution of body composition, lifestyle factors and SES, unique to different ethnic groups in South Africa, to BMD. We examined differences in femoral neck (FN), total hip (TH) and lumbar spine (LS) BMD between black and white premenopausal South African women and the associations between BMD and body composition, lifestyle factors and SES in these two ethnic groups.

METHODS

BMD and body composition were measured in 240 black (27 ± 7; 18-45 years) and 187 white (31 ± 8; 18-45 years) women using dual-energy X-ray absorptiometry. Questionnaires were administered to examine SES, physical activity and dietary intake.

RESULTS

After co-varying for age, FN and TH were higher in black than white women (FN 0.882 ± 0.128 vs. 0.827 ± 0.116 g/cm(2), P < 0.001; TH 0.970 ± 0.130 vs. 0.943 ± 0.124 g/cm(2), P = 0.018). When adjusting for ethnic differences in body composition, LS was higher in white than black women. In black women, fat-free soft tissue mass, SES and injectable contraceptive use explained 33-42% of the variance in BMD at the hip sites and 22% at the LS. In white women, fat-free soft tissue mass and leisure activity explained 24-30% of the variance in BMD at the hip sites, whereas fat mass, leisure activity and oral contraceptive use explained 11% of the variance at the LS.

CONCLUSION

FN and TH BMD were higher, but LS BMD was lower in black than white South African women with body composition, lifestyle and SES factors contributing differently to BMD in these women.

Secular trends in the prevalence of stunting, overweight and obesity among South African children (1994-2004)

BACKGROUND/OBJECTIVES

Various nutrition programs and free health care for children less than 6 years old were introduced in South Africa in the mid-1990s. We aim to describe secular trends for nutritional status of South African (SA) children in the 10-year period following these reforms.

SUBJECTS/METHODS

The SA National Primary Schools' Anthropometric Survey (n=105 000) is a cross-sectional survey of children from all SA Education Departments sampled during 1994. The Health of the Nation Study (n=10 295) is a cross-sectional study, including children from primary schools in five SA Provinces sampled from 2001 to 2004. Height and weight of SA children were measured during both surveys. In 8-11 year olds, the National Centre for Health Statistics reference was used to calculate the prevalence of mild and moderate stunting, and overweight and obesity were calculated according to the International Obesity Task Force reference. Coexistence of stunting, overweight and obesity among these two age- and sex-matched cohorts were also calculated.

RESULTS

When compared with previous SA data, moderate stunting (24.6-4.9%, P<0.001) decreased over the 7-10 years considered, whereas overweight (1.2-13.0%, P<0.001) and obesity (0.2-3.3%, P<0.001) prevalence increased. There were lower levels of mild stunting and similar levels of moderate stunting among overweight/obese children when compared with non-overweight/non-obese children.

CONCLUSIONS

Our findings suggest that feeding policies may have been effective in reducing the prevalence of under-nutrition. However, inter-sectoral policies should recognize the apparent secular trend for an increased prevalence in overweight/obesity among young South Africans.

Evaluation of a school-based physical activity intervention in Alexandra Township

Objectives. Non-communicable diseases and limited participation in school physical education have become increasing concerns in South Africa. In response to these concerns, a schoolbased physical activity intervention, Healthnutz, was implemented in three primary schools in Alexandra Township, Johannesburg. Evaluation of Healthnutz included assessing its feasibility and acceptability, and short-term changes in learners’ physical fitness, knowledge and attitudes. Methods. To assess feasibility and acceptability, a situational analysis and focus groups with teachers and programme monitors were conducted. Pre-post fitness testing (3-month interval) was conducted with learners, and a questionnaire assessed changes in learners’ knowledge, attitudes, self-efficacy, and perceived barriers to physical activity, in control and intervention schools. Results. At implementation, teachers identified the need for more physical activity in the school environment and were positive about Healthnutz. Follow-up focus group discussions suggested that it was positively impacting teachers, learners and the school in general. Scores for sit and reach (p<0.001), sit ups (p<0.02) and shuttle run (p<0.0001) improved significantly in intervention but not control schools. A significant decrease was observed in learners’ perceived external barriers to physical activity (p<0.0001) along with a positive change in learners’ self-efficacy for physical activity (p<0.05). Conclusions. Healthnutz raised awareness of the importance of physical activity in intervention schools. Findings indicate that even limited exposure to a physical activity intervention can lead to a significant improvement in aspects of learners’ fitness, knowledge, attitudes and perceptions regarding physical activity. Furthermore, training and support of teachers needs to be nonjudgemental and empowering.

Effect of body mass and physical activity volume and intensity on pedometry-measured activity energy expenditure in rural black South Africans in the Limpopo Province

Objectives. We developed a novel approach to investigate patterns of pedometry-measured total weekly activity energy expenditure (EEAct) in rural black South Africans in the Limpopo Province. Design. We analysed 7-day pedometry data in 775 subjects (female: N=508; male: N=267). Variance components models for EEAct were used to estimate the variance explained by body mass (BM), total weekly steps (volume) and estimated intensity (kcal. kg-1.step-1). Univariate General Linear Models, adjusting for age, BM and physical activity (PA) volume, were used to determine if EEAct was primarily affected by volume or intensity. Results. BM (13.1%), PA intensity (24.4%) and PA volume (56.9%) explained 94.4% of the variance in EEAct. Adjusted EEAct did not differ between sexes (78 kcal.week-1, p =0.2552). There were no significant differences across activity categories (sedentary to very active) for adjusted EEAct (62 - 287 kcal.week-1, p>0.1). Adjusted EEAct for 6 - 7 days of compliance (≥10 000 steps.day-1) differed significantly from 1 - 2 days of compliance (266 - 419 kcal.week-1, p<0.04). Obese (body mass index ≥30 kg.m-2) and normal weight (body mass index 18.5 - 24.9 kg.m-2) women did not differ significantly across activity categories for EEAct (200 - 592 kcal.week-1, p>0.30). Conclusions. We have highlighted an intensity effect for days of compliance and at very active ambulatory levels (≥12 500 steps. day-1). A volume effect appeared to dominate between sexes, across activity categories and weight-by-activity categories. It is important that post hoc statistical adjustments be made for body mass and PA volume when comparing EEAct across groups.

Comparison of site-specific bone mass indices in South African children of different ethnic groups

This study reports on ethnic differences in bone mass before and after adjusting for differences in body size and bone area (BA). Lumbar spine (LSBMC), proximal femur (PFBMC) and femoral neck (FNBMC) bone mineral contents were measured in black ('black'; n = 263) and white ('white'; n = 73) children from Johannesburg and children of mixed ancestral origin ('mixed'; n = 64) from Cape Town, South Africa. Geometric estimates and the power coefficient from the regression analyses of BMC on BA were calculated. After adjusting for age, weight, and height, LSBMC in girls and FNBMC in girls and boys were greatest in mixed, followed by black and then white, groups. Mixed boys and girls also had greater PFBMC than their black and white peers, but only in the boys was PFBMC greater in the black than the white groups. When including BA in the adjustment, differences remained at the FN in boys and girls, and the LS and PF in girls, but disappeared at the PF in mixed and black boys. The difference in LSBMC between mixed and black boys became significant after adjustment for age, weight, height, and BA. Geometric estimates at the femoral neck were greater in the mixed group. Power coefficients were greater in the white group, suggesting differences in shape or bone distribution. In conclusion, this study suggests that, in addition to differences in BMC, differences in bone strength and geometry are present which might confer advantages to the bone of mixed-ancestry children.

Impact of a primary school-based nutrition and physical activity intervention on learners in KwaZulu-Natal, South Africa: A pilot study

No Abstract.

Monitor placement, sources of variance and reliability of free-living physical activity: a pilot investigation

No Abstract.

Exercising with reserve: exercise regulation by perceived exertion in relation to duration of exercise and knowledge of endpoint

OBJECTIVE

The purpose of this study was to examine ratings of perceived exertion (RPE) and performance during repetitive maximal effort 40 km time trials as well as after an intervention that aimed to decrease certainty about the remaining distance of the exercise bout. In addition, we examined the RPE during exercise bouts of markedly different duration.

METHODS

Part 1: 12 well-trained, competitive-level cyclists completed five 40 km time trials. During the final time trial all feedback was withheld until the final kilometre. In addition, to cause confusion about the remaining distance, they were asked to report their RPE at random intervals from 18 km to 38 km. Part 2: 6 well-trained, recreation-level cyclists randomly completed a 5 km, 10 km, 40 km and 100 km time trial.

RESULTS

Part 1: Mean RPE increased during the first four trials and decreased during the final trial. The rate of RPE progression increased in linearity during the first four trials and became more conservative in the final trial. These changes were directly related to performance. Part 2: Mean RPE for longer duration trials (40 km, 100 km) were lower during the first half of trial duration but matched those of shorter trials in the final 20%.

CONCLUSIONS

Increased familiarity of the exercise bout and certainty about its endpoint are associated with a more aggressive RPE strategy that produces a superior exercise performance. Certainty about the endpoint and the duration of exercise affect both the RPE strategy and performance.

Sources of variance and reliability of objectively monitored physical activity in rural and urban Northern Sotho-speaking blacks

Objectives. We investigated the sources of variance and reliability in an objective measure of physical activity for a 14- hour and 4-day monitoring period. Design. A convenience sample of rural (N=31) and urban (N=30) adult, Northern Sotho-speaking blacks was recruited. Physical activity was assessed for 8 consecutive days using a uni-axial accelerometer. Physical activity indices were total counts, average counts, inactivity (

Validity and reliability of a physical activity/inactivity questionnaire in South African primary schoolgirls

Objective. We sought to determine the validity and reliability of a self-report physical activity questionnaire (PAQ) measuring physical activity/inactivity in South African schoolgirls of different ethnic origins. Methods. Construct validity of the PAQ was tested against physical activity energy expenditure estimated from an ACTIVITYGRAM and inactivity from reported television programme viewing in 332 girls (ages 9 - 12 yrs, grades 4 - 5). Body composition (WHO BMI percentiles and percentage body fat) was used as an indirect measure of validity for the PAQ. Test-retest reliability of the PAQ was assessed in a convenience sample of 14 girls. Results. Weak but significant associations were found between the body composition and PAQ-derived total energy expenditure (r=-0.18; p

Early life and current determinants of bone in South African children of mixed ancestral origin

BACKGROUND

The influence of early life factors on the bone mineral density of children has been identified, however the contribution of these determinants may vary.

AIM

The study investigated determinants of bone mineral content (BMC) in South African children of mixed ancestral origin.

SUBJECTS AND METHODS

Early life data including birth weight, maternal alcohol consumption and smoking during pregnancy were collected on 9-year-old children of mixed ancestral origin (n = 64). Grip strength was measured, and physical activity, housing density and dietary data were collected. Whole body BMC (WB BMC), fat-free soft tissue and fat tissue were measured using dual energy X-ray absorptiometry.

RESULTS

Maternal alcohol consumption during pregnancy was associated with WB BMC, however after adjusting for possible confounders, this was no longer significant. When combined with gender, gestational age and maternal BMC in a multiple regression, maternal alcohol consumption during pregnancy could explain 20% of the variance in the WB BMC, however when current height was included in the model, the contribution of the other factors was insignificant. There was however a significant correlation between current height and birth weight (r = 0.34; p < 0.01) and alcohol consumption during pregnancy (r = 0.34; p < 0.05). A model consisting of current factors such as age, weight, gender, grip strength and calcium intake was able to explain 81.5% of the variance. Housing density was negatively correlated with WB BMC (r =-0.11; p = 0.05).

CONCLUSION

These data suggest that although early life factors may contribute indirectly to the bone mass of children of mixed ancestral origin, the contribution of current factors is greater. In addition, environmental factors such as housing density have a direct effect on bone mass, independent of body size.

Sources of variance and reliability of objectively monitored physical activity in rural and urban Northern Sotho-speaking blacks

Objectives. We investigated the sources of variance and reliability in an objective measure of physical activity for a 14- hour and 4-day monitoring period. Design. A convenience sample of rural (N=31) and urban (N=30) adult, Northern Sotho-speaking blacks was recruited. Physical activity was assessed for 8 consecutive days using a uni-axial accelerometer. Physical activity indices were total counts, average counts, inactivity (

Validity and reliability of a physical activity/inactivity questionnaire in South African primary schoolgirls

Objective. We sought to determine the validity and reliability of a self-report physical activity questionnaire (PAQ) measuring physical activity/inactivity in South African schoolgirls of different ethnic origins. Methods. Construct validity of the PAQ was tested against physical activity energy expenditure estimated from an ACTIVITYGRAM and inactivity from reported television programme viewing in 332 girls (ages 9 - 12 yrs, grades 4 - 5). Body composition (WHO BMI percentiles and percentage body fat) was used as an indirect measure of validity for the PAQ. Test-retest reliability of the PAQ was assessed in a convenience sample of 14 girls. Results. Weak but significant associations were found between the body composition and PAQ-derived total energy expenditure (r=-0.18; p

Factors associated with menstrual dysfunction and self-reported bone stress injuries in female runners in the ultra- and half-marathons of the Two Oceans

OBJECTIVE

To investigate factors associated with menstrual dysfunction, self-reported bone stress injuries and energy balance in women runners.

METHODS

613 runners were randomly sampled during the registration period for an endurance event. Demographic information, including self-reported height and weight, training and injury history and menstrual history, was collected by questionnaire.

RESULTS

Ultra-marathon (ULTRA) participants (n = 276) were significantly older (mean (SD) 39 (8.2) vs 34 (10.5) years; p<0.001), lighter (58.2 (6.6) vs 59.6 (8.3) kg; p<0.05) and reported a higher training volume (p<0.001) than half-marathon (HALF) participants (n = 337). Significantly more ULTRA subjects than HALF subjects reported a previous bone stress injury (21% vs 14%; p<0.05). There was no difference between the groups for menstrual status, but age at menarche was later (p<0.01) in the ULTRA group. Data were combined according to the absence (REG; n = 368/602 (61%)) or presence (IRREG; n = 234/602 (39%)) of a history of menstrual irregularity. Subject morphology was similar between groups, but the IRREG group had a higher self-reported measure on the self-loathing subscale (SLSS; p<0.01). The whole group was then classified according to current menstrual status, with 165 women being classified as currently irregular. (OLIGO/AMEN; 11.6%) and 445 women as currently regular (EUMEN; 88.4%). There were no morphological differences between the groups, however the OLIGO/AMEN group had a later age of menarche (p<0.01) than the EUMEN group. Further, women who reported a previous bone stress injury had higher SLSS scores than those who did not (2.91 (0.98) vs 2.68 (0.84); p<0.05).

CONCLUSIONS

There may be two independent mechanisms associated with energy balance, which are related to bone stress injuries, but may not necessarily be related to menstrual dysfunction.

BMI, fat and muscle differences in urban women of five ethnicities from two countries

OBJECTIVE

To investigate body composition differences, especially the relationship between body mass index (BMI) and percent body fat (%BF), among five ethnic groups.

DESIGN

Cross-sectional.

SUBJECTS

Seven hundred and twenty-one apparently healthy women aged 18-60 years (BMI: 17.4-54.0 kg/m(2)) from South Africa (SA, 201 black, 94 European) and New Zealand (NZ, 173 European, 76 Maori, 84 Pacific, 93 Asian Indian).

MEASUREMENTS

Anthropometry, including waist circumference, and total, central and peripheral body fat, bone mineral content and total appendicular skeletal muscle mass (ASMM) derived from dual X-ray absorptiometry.

RESULTS

Regression analysis determined that at a BMI of 30 kg/m(2), SA European women had a %BF of 39%, which corresponded to a BMI of 29 for SA black women. For a BMI of 30 kg/m(2) in NZ Europeans, equivalent to 43% body fat, the corresponding BMIs for NZ Maori, Pacific and Asian Indian women were 34, 36 and 26 kg/m(2), respectively. Central fat mass was lower in black SA than in European SA women (P<0.001). In NZ, Pacific women had the lowest central fat mass and highest ASMM, whereas Asian Indian women had the highest central fat mass, but lowest ASMM and bone mineral content.

CONCLUSIONS

The relationship between %BF and BMI varies with ethnicity and may be due, in part, to differences in central fatness and muscularity. Use of universal BMI or waist cut-points may not be appropriate for comparison of obesity prevalence among differing ethnic groups, as they do not provide a consistent reflection of adiposity and fat distribution across ethnic groups.

Prediction of energy expenditure from heart rate monitoring during submaximal exercise

The aims of this study were to quantify the effects of factors such as mode of exercise, body composition and training on the relationship between heart rate and physical activity energy expenditure (measured in kJ x min(-1)) and to develop prediction equations for energy expenditure from heart rate. Regularly exercising individuals (n = 115; age 18-45 years, body mass 47-120 kg) underwent a test for maximal oxygen uptake (VO2max test), using incremental protocols on either a cycle ergometer or treadmill; VO2max ranged from 27 to 81 ml x kg(-1) x min(-1). The participants then completed three steady-state exercise stages on either the treadmill (10 min) or the cycle ergometer (15 min) at 35%, 62% and 80% of VO2max, corresponding to 57%, 77% and 90% of maximal heart rate. Heart rate and respiratory exchange ratio data were collected during each stage. A mixed-model analysis identified gender, heart rate, weight, V2max and age as factors that best predicted the relationship between heart rate and energy expenditure. The model (with the highest likelihood ratio) was used to estimate energy expenditure. The correlation coefficient (r) between the measured and estimated energy expenditure was 0.913. The model therefore accounted for 83.3% (R2) of the variance in energy expenditure in this sample. Because a measure of fitness, such as VO2max, is not always available, a model without VO2max included was also fitted. The correlation coefficient between the measured energy expenditure and estimates from the mixed model without VO2max was 0.857. It follows that the model without a fitness measure accounted for 73.4% of the variance in energy expenditure in this sample. Based on these results, we conclude that it is possible to estimate physical activity energy expenditure from heart rate in a group of individuals with a great deal of accuracy, after adjusting for age, gender, body mass and fitness.