The overall goal of this project is to examine the physiological and metabolic effects of a
16-week circuit-training (strength training + aerobic activities) program, with and without a
behavioral component utilizing motivational interviewing, in 45 overweight Latina adolescent
girls (14-18 years of age). This 16-week randomized control study will examine the
incremental effects of the following 3 intervention groups on insulin sensitivity, insulin
secretion, adiposity, and habitual and ad libitum physical activity:
- Control group (delayed circuit training intervention; n=15)
- Circuit training group (strength + aerobic training; 2 times per week; n=15)
- Circuit training (same as above) + weekly motivational interviewing sessions (n=15)
Specific Aim 1: To examine the effects of a 16-week circuit training program on adiposity,
insulin dynamics, other associated hormones and adipocytokines, cardiorespiratory fitness,
and muscular strength in overweight Latina adolescent girls. Hypothesis 1: Participation in
the circuit-training program will result in significant improvements in both physiological
and metabolic outcomes, including: a) body composition as measured by DEXA, b) fat
distribution as measured by MRI, c) adipose tissue hormones (e.g. leptin, adiponectin, TNF-α)
as measured by fasting blood samples, d) insulin sensitivity and secretion as measured by
frequently sampled intravenous tolerance test, e) aerobic fitness as measured by the single
stage submaximal treadmill test, and f) increase muscular strength as measured by repetition
Specific Aim 2: To examine the incremental effects of adding the motivational interviewing
sessions to the circuit training on self-selected ad libitum physical activity during a
5-hour observational period, habitual physical activity levels using 7 day accelerometry, and
the meanings and motivation to exercise using questionnaires before and after the
intervention. Hypothesis 2: The addition of motivational interviewing will encourage and
empower participants to be more active outside of the intervention and foster healthy
physical activity behaviors in daily life. Improvements in physical activity behaviors will
lead to greater improvements in all other health outcomes listed in specific aim 1 compared
to circuit training alone and control group.
- At Risk of Overweight and Overweight (age- & sex-specific body mass index ≥ 85th
percentile based on CDC BMI growth charts [US Department of Health and Human Services,
2000]. There will not be an upper BMI limit. In our experience, we have had numerous
children above the 99th percentile for BMI complete the outcome measures, and this
group could benefit greatly from participation.
- Gender & Age: Females from grades 9th to 12th (approximately 14-18 years of age). We
chose to study adolescents because pubertal youth will likely possess the requisite
hormonal milieu needed to elicit physiologically and metabolic changes in response to
resistance and aerobic training. In addition physical activity declines are more
pronounced in minority females. By limiting the study to just females, we will retain
a more homogenous group. This will eliminate sensitive gender issues related to
exercise such as body image concerns, goal setting, and motivations for behavioral
changes. To reduce effects of the menstrual cycle, all females will be tested during
the follicular phase, while those with irregular/unpredictable menses will be studied
at random times.
- Latino origin all four grandparents must be of Hispanic heritage (reported on
screening forms). This approach is consistent with all of our previous and ongoing
- Presently taking medication(s) or diagnosed with any syndrome or disease that could
influence physical activity, body composition and fat distribution, or insulin action.
- Previously diagnosed with any major illness since birth (e.g. chronic birth asphyxia,
- Children with type 1 and/or type 2 diabetes will be excluded and referred to a
physician. Children with impaired glucose tolerance (fasting glucose >100 mg/dL during
a fasting blood draw) and/or conditions associated with insulin resistance (e.g.
acanthosis nigricans, hypertension, dyslipidemia) will be eligible, as long as they
are not receiving treatment and meet other eligibility criteria.
- Children who have any physical, cognitive, or psychological disabilities that would
prevent them from participating in an exercise program.
- Currently, or in the past 6 months, involved with any dietary, physical activity or
weight loss program.
- Children who live farther than 20 miles away from the GCRC.