Relationship between resting metabolic rate and physical activity in adolescents : the PAHL study

Abstract

Obesity is affecting an increasingly larger proportion of adolescents in the world, and this can be attributed to low resting metabolic rate (RMR) as well as reduced physical activity (PA) levels. Little is known about objectively determined habitual PA and RMR in 16 year old African adolescents. The purpose of this study is twofold. Firstly, to determine the objectively measured PA status of adolescents and secondly, to determine the relationship that exists between RMR and PA in 16 year old adolescents. Two hundred and twenty six (226) adolescents aged sixteen (16) wore the Actiheart® monitor, combined accelerometry and heart rate for seven (7) consecutive days. Six high schools were recruited to take part in the study: two from town (high socio-economic status) and four from the township (low socio-economic status) of the Potchefstroom area of the North West Province of South Africa. Times spent in moderate to vigorous physical activity, physical activity counts per minute (CPM), total energy expenditure (TEE), active energy expenditure (AEE) and physical activity levels (PAL) were assessed using the Actiheart®. The participants’ RMR was measured by indirect calorimetry using the Fitmate Pro (Cosmed, Italy). All data analyses were performed with the SPSS Version 20 software (IBM SPSS, II). The descriptive statistics (mean and standard deviations) as well as independent t-tests and Mann-Whitney U test were performed to determine differences between ethnicity and genders and to calculate practical significance. A Type I error rate of p ≤ 0.05 was used for statistical significance. To investigate the relationship between RMR and physical activity regression analysis was performed with adjustment for gender, race and fat free mass. Results: Significantly higher PAL (1.57 ± 0.15) were determined in girls compared to boys (PAL = 1.41 ± 0.10). Black adolescents indicated significant higher PAL (1.53 ± 0.14) compared to white adolescents (1.45 ± 0.16). On average, regardless of race or gender, the participants were more active on weekdays than weekends. The current study shows that girls spent more minutes/day in moderate to vigorous physical activity (MVPA) than the boys. The results show that 16.4% of the study sample was either overweight or obese. After adjustment for gender, ethnicity and FFM, linear regression between RMR and moderate-to-vigorous PA yielded an r2 = 0.46 (p ˂ 0.05.) Conclusion: Objectively determined PA of adolescents in South Africa indicates that only one third of adolescents are meeting the recommended 60 minutes of daily MVPA. Gender and race specific interventions are needed to increase habitual physical activity levels in adolescents. Given the fact that the studied sample did not meet recommended daily physical activity and the adverse effect of inactivity and chronic diseases of life style, urgent strategies to inculcate the culture of regular physical activity as a preventative measure of chronic diseases of life style are needed. Behaviour that is carried on into adulthood is established during adolescence. Civic health efforts should focus on encouraging adolescent involvement in regular moderate-to-vigorous PA, which will subsequently increase RMR and lower the risk of the development of non-communicable chronic diseases such as obesity. Further local research is needed to confirm the association between RMR and PA in the local population.