1. Introduction

Adults of South Asian background have a unique obesity phenotype of high abdominal fat and low lean body mass at a given body size ^[1], which lends itself to greater disease risk at a younger age ^[2]. This is also evident in South Asian children who tend to have an elevated body fat despite a lower body mass index (BMI) ^[3] with greater body fat in the trunk region. It is unclear what may account for this difference in body composition, but low physical activity and physical fitness levels are associated with greater fat mass and lower lean mass ^[4].

There is a large public health concern over the upwards trend in childhood overweight and obesity ^[5]. Childhood obesity is associated with many medical complications such as hypertension, dyslipidemia, insulin resistance and non-alcoholic fatty liver disease ^[6]. Participating in regular physical activity and having a high cardiorespiratory (physical) fitness level are associated with improved health, greater well-being, less obesity and less chronic disease ^[7]. As a result, the Canadian Physical Activity Guidelines recommend that children get 60 minutes of daily moderate to vigorous physical activity ^[8]. Children who participate in a greater amount of vigorous physical activity score better on measures of physical fitness than children who are more sedentary ^[9].

South Asian children in the United Kingdom have been reported to have lower levels of objective physical activity compared to Europeans with greater amounts of time spent in sedentary pursuits than their European peers ^[10]. Most recently, this lower level of objective physical activity is associated with a lower aerobic fitness level in South Asian children compared to their European counterparts ^[11]. In addition, physical fitness levels are also correlated with resting metabolic rate ^[12], therefore, putatively low levels of physical activity and physical fitness may be a possible determinant of the thin-fat body type in South Asians and this association may be established in childhood.

The associations between physical fitness and levels of obesity related measures have been well documented in a number of ethnic groups ^{[13, 14, 15]} but there is a paucity of data regarding South Asian children. Therefore, the purpose of this study was to provide a descriptive analysis of the associations between measures of physical fitness and obesity related measures in South Asian children aged 7 to 10 years. It is hypothesized that there will be significant associations between obesity related measures and physical fitness in South Asian children.

2. Methods

This was a sub-study of a child health study entitled Research in International Cardiovascular Health – Lifestyles, Environments and Genetic Attributes in Children and Youth (RICH LEGACY). Participants who were recruited for the RICH LEGACY project who chose to return for a follow-up visit were asked if they were interested in participating in the current sub-study. From March 2013 to December 2015, 45 children were recruited at local elementary schools and community events through the RICH LEGACY project in the Surrey community. Children were eligible to participate if they were of South Asian origin, were between 7 to 10 years of age and were comfortable performing three physical fitness tests. The study was approved by the Simon Fraser University Research Ethics Board. Parental consent and child verbal assent were obtained from all participants.

All measurements took place at Simon Fraser University and parents were given the option of remaining with their child during all measurements.

Aerobic capacity was assessed through the completion of a 20 metre shuttle test which has shown a correlation of 0.71 with direct maximal aerobic capacity testing ^[16]. This test involved having children run between two lines spaced 2 metres apart at a pace set by signals on a pre-recorded audio file. The starting speed was 8.5 km/hour and the frequency of the signals increased 0.5 km/hour each minute ^[16]. The child was encouraged to run back and forth until they could not longer maintain the desired pace. The last completed stage was used to predict maximal aerobic capacity based on the multiple regression prediction equation developed for children aged 8-19 years of age ^[16].

Handgrip dynamometry and standing long jump have been shown to be valid field tests for assessing upper and lower body strength respectively in youth ^[17]. For the handgrip dynamometry test children were told to grip the handgrip dynamometer, hold it parallel to the body at a 45 degree angle and to squeeze as hard as possible for 2 seconds. This was repeated twice on each side and the highest score was counted. For the standing long jump test children were asked to jump as far as possible horizontally from a marked starting line. The average of two scores was used for statistical analyses.

Mass in kilograms and height in metres were assessed with participants in light clothing, footwear removed and pockets emptied. Body mass index (BMI) was assessed as mass in kilograms over height in metres squared. Waist circumference (WC) was measured as the midway point between the lower anterior ribs and the top of the iliac crest and recorded in centimetres as the average of two measures taken against the skin at the point of maximal narrowing from the anterior view following a normal expiration. A sub set of children (n=22) completed whole body scans using a dual energy x-ray absorptiometry (DXA) scanner (Hologic Discovery QDR 4500w, Bedford, Massachusetts) to determine lean mass (kg), fat mass and percent body fat. The percentage of total body fat was calculated by dividing fat mass by total body mass.

The following data were non-normally distributed and natural log transformed: resting heart rate, body mass index, waist circumference (WC), lean mass, fat mass and body fat percentage. Data were natural log transformed are presented as geometric means with 95% confidence intervals while all remaining data are presented as means and standard deviations.

An independent t-test was used to compare cardiovascular, obesity related measures and physical fitness data between boys and girls. Given that there were no significant differences between sexes, data were combined for all additional analyses. Pearson correlations were used to assess the linear associations between physical fitness measures (grip strength, long jump and aerobic capacity) and obesity related measures (WC, BMI, body fat, lean mass, body fat percentage). Linear regression analyses were used to model the association between physical fitness measures and obesity related measures. Separate multiple linear regression models were constructed with, physical fitness measures as the predictor variables of interest and obesity related measures as the outcome variable. For each predictor, models were additionally adjusted for age and sex. Statistical analysis was completed using SPSS v. 23.0 and significance was set at p<0.05.

3. Results

There were 17 boys and 28 girls between the ages of 7 and 10 with a mean age of 8 who participated in this study (Table 1). There were no significant differences in cardiovascular, obesity related measures or physical fitness characteristics between South Asian boys and girls. Of those, 11 boys and 11 girls completed a body scan for further assessment of body composition (Table 2). There were no significant differences in obesity related measures or physical fitness measures among children who completed the body scan and those who opted not to (Appendix – Table 1a).

There were significant linear associations between a number of obesity related measures and physical fitness measures (Table 3 and Table 4). In the larger sample of 45 South Asian children, upper body strength as assessed by grip strength was positively associated with BMI and WC in unadjusted analyses. Analyses remained significant after further adjustment for age, sexand household income with BMI (Table 3-Model 1c). Lower body strength as assessed by horizontal jump was not significantly associated with BMI or WC (Table 3). Completion of shuttle run stage was used to predict VO₂max and there were significant negative associations between VO₂max and obesity related measures (Figure 1). These associations remained significant after further adjustment for age, sex and household income (Table 3).

In the smaller sample of 22 South Asian children which completed body scans, upper body strength as assessed by grip strength was positively associated with lean massand remained significant after further adjustment for age, sex and household income (Table 4 - Model 2c). Lower body strength as assessed by horizontal jump was negatively associated with fat mass and body fat percentage in unadjusted analyses (Table 4 – Model 1a and Model 3a) and remained significant after further adjustment for age and sex (Table 4- Model 1b and 3b) but not household income (Table 4- Model 1c and 3c). Shuttle run stage and VO₂max were negatively associated with fat mass, lean mass and body fat percentage after adjustment for age, sex and household income (Table 4).

Table 1. Comparison of cardiovascular, anthropometric and fitness characteristics between South Asian boys and girls

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Table 2. Comparison of body composition characteristics between South Asian boys and girls

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Table 3. Regression models showing associations between physical fitness measures and anthropometric data (n=45)

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Table 4. Regression models showing associations between physical fitness measures and obesity related measures (n=22)

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Figure 1. Pearson correlations between obesity related measures and maximal oxygen consumption

4. Discussion

South Asian boys and girls showed significant associations between obesity related measures and physical fitness variables after adjustment for age and sex thus supporting our hypothesis. Given the paucity of data regarding South Asian children and the association between obesity related measures and physical fitness measures this study is of importance as it provides further context for the impact of physical activity and fitness on the health of South Asian children. Specifically, upper body strength as measured by maximal grip strength was positively associated with BMI, WC and lean body mass while lower body strength as measured by horizontal long jump was negatively associated with fat mass and body fat percentage. Aerobic fitness was negatively associated with all obesity related measures.

We found upper body strength as measured by maximal grip strength was positively associated with BMI which suggests that larger children score better on upper body strength. This was also found when physical fitness was assessed among children 7 to 11 years of age in Europe ^[14] and Mexican and Canadian children 9 to 13 years of age ^[15]. In addition, in a subset of our population that completed body scans and we found lean body mass to also be positively associated with maximal grip strength. This suggests that it is muscle mass rather than body fat that is resulting in the positive association with BMI. This is logical given than muscle mass tends to increase with body mass ^[18]. This was also suggested by Heroux et al., to explain the positive associations between BMI and grip strength in Mexican and Canadian children ^[15]. Comparatively, measures of lower body strength as measured by horizontal long jump were negatively associated with fat mass and body fat percentage. Thus children with greater leg strength tended to have a lower amount of body fat.

We found significant negative associations between aerobic capacity and obesity related measures in our population of South Asian children. This finding parallels results seen in Iranian children 11 to 13 years of age ^[13], European children 7 to 11 years of age ^[14] as well as Kenyan, Mexican and Canadian children 9 to 13 years of age ^[15]. We have also previously shown significant negative associations between aerobic capacity (using direct metabolic assessment) and abdominal fat in older South Asian women ^[19]. Given the known association between physical activity levels and physical fitness in children ^[20], one could conclude that low levels of physical activity in South Asian children ^[10] may be associated with the unique obesity phenotypeof high abdominal fat and low lean body mass at a given body size in South Asian adults ^[6]. Further research is necessary to directly measure this association in South Asian children.

Limitations of this study include the small and non random sample which may not be representative of South Asian children in Canada, however, this was a community based sample in a Canadian city with a large South Asian population. In addition, in order to improve the feasibility of the study, we used a number of field tests to assess measures of physical fitness. The field tests were chosen due to their reported validity in school aged children. Specifically, the 20 meter shuttle run test has a moderate validity (r=0.71) in school aged children with indirect calorimetry and is consistently used to measure physical fitness in this population ^[16]. Furthermore, we were able to have a sub set of children complete body scans for direct assessment of body composition and were therefore able to add to the body of literature with a strong measure of body composition.

In conclusion, we found significant associations between measures of physical fitness and obesity related measures in South Asian children 7 to 10 years of age. This is especially relevant as South Asian children report objectively lower levels of physical activity than Europeans in the United Kingdom with greater amounts of time spent in sedentary pursuits than their European peers ^[10]. Given the unique obesity phenotype in the South Asian population ^[1] and its association with greater disease risk at a younger age ^[2] improving physical fitness and specifically aerobic fitness may be a useful and inexpensive modality for reducing disease risk in South Asian children. Further research is necessary to assess whether low levels of physical activity and fitness in South Asian children explains the unique obesity phenotype seen in the South Asian population.

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Appendix

Table 1a. Comparison of participants who opted to complete the body scan vs. those who opted not to

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