We have previously shown that a CT intervention with integrated nutrition and MI sessions significantly decreased overall adiposity levels and improved fasting glucose in Latina adolescent girls who were overweight (8
). However, for this study, we wanted to know how much the CT, without nutrition and MI sessions, contributed to these effects. The current study shows that the CT only group reduced waist circumference, VAT, SAT, fasting insulin, and insulin resistance in Latina adolescent girls. These results suggest that the CT exercise approach, without additional nutritional or behavioral therapy sessions, may be an excellent starter program for Latino youth who are overweight or obese to reduce adiposity and improve metabolic parameters.
To date, few studies have examined the combined effect of aerobic exercise and strength training on body composition and insulin resistance. In an intense 10-month after-school exercise program (80 min of a combination of sport skill development, aerobic exercise, and strength training × 5 d·wk−1
) conducted in 200 black girls (8–12 yr old), participants in the exercise program decreased body fat percent, BMI, and VAT compared with C group (P
= 0.003) (2
). Bell et al. (3
) showed that an 8-wk combined aerobic and strength training program (60 min × 3 d·wk−1
), without weight loss, resulted in decreased insulin resistance in Caucasian children and adolescents (age 9–16 yr) who were sedentary and obese. Our previous 16-wk CT pilot intervention, which included nutrition (60 min × 1 d·wk−1
), CT (60–90 min × 2 d·wk−1
), and MI sessions (8 × 20-min sessions throughout) with 41 Latina adolescent girls who were overweight, significantly improved fasting glucose levels and decreased overall adiposity levels compared with a nutrition-plus-strength-training program (9
). The current study was the first to show the positive effects of CT alone on reducing specific fat depots and insulin resistance in Latino youth who are overweight or obese.
Some pediatric exercise intervention studies have examined the effects on reducing specific fat depots, like visceral adiposity. Owens et al. (31
) showed that an intense 4-month aerobic exercise intervention (40 min × 5 d·wk−1
) with 74 children (age 7–11 yr) who were obese significantly decreased SAT and attenuated increases in VAT compared with a nonexercising control group. Similarly, Gutin et al. (17
) showed that an intensive 8-month aerobic physical activity intervention (30 min × 5 d·wk−1
) resulted in significant improvements in cardiovascular fitness and reductions in total body composition and VAT compared with a lifestyle education intervention group (20
). A recent study by van der Heijden et al. (38
) conducted with 15 Hispanic adolescents who were obese showed that a 12-wk aerobic exercise intervention (30 min × 4 d·wk−1
) resulted in significant improvements in cardiovascular fitness and reductions in VAT and hepatic fat, fasting insulin, and HOMA-IR, without weight loss or change in BMI; however, there was no control group in this study. Yet, the above studies included relatively high frequency of exercise sessions (4 or 5 d·wk−1
) and the current study showed that 2 d·wk−1
of CT could result in significant reductions in both VAT and SAT. Starting a 2-d·wk−1
CT program might be easier and more feasible for adolescents who are overweight or obese and seems to be just as effective at reducing metabolic risk.
The CT approach may a good starter program for children population who are overweight or obese because it includes only short bouts of cardiovascular components (2 min in length) coupled with strength training. The intense aerobic intervention may not be initially feasible, or as easily attainable, for children who are overweight or obese. CT allows children who are overweight/obese to accumulate 30–45 min of cardiovascular exercise and 30–45 min of strength training in an achievable fashion. This approach allows participants to maintain their HR between 70% and 85% of their max for every exercise session (~60–90 min). Thus, the CT approach may allow individuals who are overweight or obese to enhance fitness and strength while promoting initial fat loss and improvements in metabolic profiles, thereby serving as a good “jump start” to an exercise program.
To our knowledge, the current study was the first to show that MI sessions did not significantly improve health outcomes, and CT alone showed more promising results. During the past 10 yr, MI has been incorporated into pediatric obesity prevention and treatment efforts to improve diet and physical activity behaviors (33
). In a 6-month, church-based, nutrition and physical activity program called “Go Girls” with 123 African American adolescent girls, a high-intensity intervention (30 min × 20–26 sessions) with four to six telephone MI calls (20–30 min) compared with moderate-intensity groups (6 sessions) did not result in reductions in obesity (34
). In another nonrandomized clinical trial of 91 children (3–7 yr), children who received a total of four MI sessions from their physician and a registered dietitian did not have significant reductions in BMI percentiles compared with those receiving control and minimal intervention (36
). However, most of the studies utilizing MI use it in combination with other exercise or diet programs, and the separate or additive effects of using MI techniques in obesity prevention/treatment programs have not been thoroughly evaluated.
The CT group reduced VAT and insulin resistance, whereas the CT +MI group did not, despite similar increases in strength and fitness in both groups. Although there were no significant differences in habitual intake and physical activity (as measured by diet records and accelerometer before and after intervention), there may have been acute changes in these variables throughout the intervention. It is possible that the CT group compared with the CT + MI group increased habitual physical activity outside of the exercise sessions and/or decreased energy intake or consumed healthier foods/beverages (i.e., lower in fat and sugar) throughout the intervention, and these changes were simply not captured by the postintervention measures. Interestingly, MI sessions in this intervention were designed to specifically target improved dietary and physical activity behaviors outside the exercise sessions. Some possible explanations for the null MI effects might be that the MI sessions were too frequent (eight sessions for 4 months) and were held before or immediately after the exercise sessions (for logistical and transportation issues). It is possible that the MI sessions will lead to more long-term changes in behaviors and subsequent improvements in health. However, these results suggest that MI in a startup program may not be necessary for initial metabolic improvements.
One possible mechanism to explain why the CT intervention reduced VAT, without reductions in weight and BMI, is that visceral fat is more metabolically active and responsive to catecholamines than other fat depots (19
) and catecholamines are known to increase with exercise (35
). More is known about the mechanism on how exercise affects insulin sensitivity. Strength training has also been shown to increase insulin-mediated glucose uptake and enhance insulin sensitivity (18
). Strength training improves up-regulation of components of the insulin-signalizing cascade, such as protein concentrations of the insulin receptor, protein kinase B, glycogen synthase, and GLUT-4 (22
). These mechanisms support our findings that the combination of aerobic and strength training can reduce adiposity, specifically VAT, and reduce insulin resistance.
There are limitations of this study that should be considered. The first limitation is that this study was conducted in Latina adolescent girls who are overweight or obese and cannot be generalized to other pediatric populations or males. However, the homogeneity of this population allows us to test the efficacy of an exercise intervention in a high-risk sample. Another limitation is the relatively small sample size (n = 38). Additional studies in larger samples that include males, subjects who are lean, and/or other ethnicities are warranted to further understand the effects of CT on reducing specific fat depots and improving metabolic parameters. The current CT intervention was also conducted in a fully equipped and well-supervised exercise gym, and future research examining the effects of CT interventions conducted in home, school, or community settings is warranted.
In conclusion, these findings suggest that a 16-wk starter CT program can reduce adiposity depots, specifically VAT, and insulin resistance, thus decreasing metabolic disease risk in Latino adolescents who are overweight or obese. The MI sessions had no additive beneficial effect on improving health outcomes in the short term. Given that CT approach included a fairly modest dosage of two times a week for 60–90 min, and only required short bouts of cardiovascular and strength training, this may be an excellent starter exercise program for adolescents who are overweight or obese and has the potential to have far reaching improvements on metabolic parameters. Interventions examining the effects of the CT approach, on improving metabolic profiles with larger samples, mixed ethnicities, genders, comparing it with other established exercise approaches, and expanding the duration are warranted.