Identifying new associations between physical activity and cardiometabolic risk, aerobic fitness, and adiposity and exploring correlates of physical activity in high-risk youth.
Abstract: In recent
decades, research and policies related to nutrition and physical activity (PA) have
increasingly converged, particularly amid concerns around energy imbalance and obesity.
Low-income and racial/ethnic minority youth are disproportionately exposed to obesogenic
environments and at risk of obesity and related disorders. This dissertation addresses
questions around how youth ... read morePA relates to cardiometabolic health and what factors predict
PA in a population of overweight/obese, low-income, Hispanic youth. While research and
recommendations tend to emphasize moderate-to-vigorous PA (MVPA), there are open
questions on whether benefits of PA accrue specifically above the moderate-intensity
threshold or through total movement at any intensity. Our first aim used NHANES data to
compare the strength of associations between minutes of MVPA and total PA volume
(accelerometer-derived total activity counts) and cardiometabolic risk factors,
controlling for BMI z-score, dietary factors, and other covariates. Both MVPA minutes
and total PA volume were associated with clustered cardiometabolic risk scores, systolic
and diastolic blood pressure, insulin, and HDL (p<0.05), but not with waist
circumference or triglycerides; associations were stronger for total PA volume than for
MVPA minutes for all outcomes except insulin, where associations were similar. Future
research that explores the broader relationships among PA volume, intensity, and health
may have important implications for research, policy, and practice. Our second and third
aims used original data collected in partnership with Let's Get Movin' (LGM), a
community-based, twice-weekly after-school PA program for low-income, overweight/obese,
mostly Hispanic youth aged 8-14. For Aim 2, linear mixed models tested associations
between number of program sessions attended and changes in cardiorespiratory fitness
(CRF) and BMI. Attendance was associated with increases in CRF (p=0.01) but not with
change in BMI (p=0.97). There were significant interactions between attendance and
pedometer-measured in-program activity: attendance was associated with more favorable
changes in CRF (p<0.0001) and BMI (p=0.03) as in-program activity levels increased.
Prior studies in controlled settings have shown efficacy of PA programs for improving
CRF and adiposity in overweight youth; our analysis provides novel evidence that such
programs may also confer benefits in community settings, particularly when youth
regularly attend and participate actively. Using this same LGM dataset, Aim 3 used
multivariable regression models to test potential demographic, physiologic, and
psychosocial correlates of PA, including self-reported PA in general living (PA
Questionnaire) and pedometer-measured PA in structured exercise and sports sessions.
General-living PA was significantly associated with age (−) and perceived
athletic competence (+). Pedometer steps/minute in structured exercise was significantly
associated only with age (−). Steps/minute in structured sports was associated
with age (−), CRF (+), and male sex (+). These results suggest that correlates of
PA in overweight/obese, low-income, Hispanic youth may vary depending on the context
where that PA occurs. Together, these analyses reinforce the benefits of PA for child
and adolescent health but also suggest that conceptualizing PA in narrowly-defined terms
(e.g., "60 minutes of MVPA" or "PA program enrollment") may not fully account for
important nuances. Future research, policies, and programs may benefit from more broadly
accounting for the complexity in how youth move and how that complexity relates to
children and adolescents' health and
Thesis (Ph.D.)--Tufts University, 2015.
Submitted to the Dept. of Food Policy & Applied Nutrition.
Advisor: Christina Economos.
Committee: Virginia Chomitz, Kenneth Chui, and Jennifer Sacheck.
Keywords: Nutrition, and Public health.read less