According to the U.S. Department of Health and Human Services (HHS), children and teens should be physically active for at least 60 minutes on most, if not all, days of the week. This recommendation states that the 60 minutes may be accrued in “smaller chunks” of time throughout the day (HHS 2010). However, Troiano et al. (2008) report that only 8% of youth aged 12–19 years are active for a full 60 minutes per day.
Alas, a sedentary lifestyle as a youth can lead to a similar lifestyle as an adult. In an attempt to get more children exercising, a number of personal trainers are now designing resistance training programs for preadolescent youth and teenagers, to give them another option besides sports, games and cardiovascular activities. Despite the contention that youth strength training is risky, its safety and effectiveness is now well documented (Washington et al. 2001). Nevertheless, the research on the metabolic effects of resistance training versus aerobic exercise in obese youth is very limited. Two recent studies led by van der Heijden (2009, 2010) present new data in this area.
Twelve sedentary, obese teenagers (body mass index > 35 kg/m2; % body fat > 40%; aged 15.5 years) volunteered for this study. The subjects (six male, six female) had been obese for more than 5 years and self-reported engaging in less than 45 minutes of light to moderate activity per week. The youth were not on medication and had no first-degree relatives (i.e., parents or siblings) with diabetes.
Resistance Training Program
Subjects completed resistance training 2 days per week (with 1 day of rest between workouts) for 12 weeks. Sessions lasted about 1 hour. They included a 10-minute warm-up, 40 minutes of weight training and a 10-minute cool-down. The program followed a periodized training design, with the youth starting at ~50% of their 3-repetition maximum (3-RM) and completing 2–3 sets of 8–12 repetitions for most exercises (see Table 1 for the list of exercises). The program gradually increased in intensity, with the youth progressing to ~80%–85% of their 3-RM and completing 15–20 repetitions per set during weeks 9–12. A trained exercise physiologist supervised all workouts, and subjects did not complete any other physical activity during the week.
Variables Measured and Results
The young subjects completed 96% of their 24 workouts during this 12-week training program. All subjects showed a significant increase in upper-body strength (biceps, triceps and pectorals) as well as lower-body strength (quadriceps and hamstrings). There was a slight increase in body weight due to the increase in muscle mass, but no change in percent body fat or in visceral fat was observed.
Insulin concentrations (a marker for prediabetes) were slightly lower (a positive adaptation, yet not a significant decrease). There was no change in fasting glucose, but the youth were producing less glucose, which is a beneficial adaptation for prediabetes risk reduction. There was no significant change in LDL cholesterol (the unhealthy type), HDL cholesterol (the good type) or triglycerides (blood fats). No significant changes were seen in leptin (hormone regulating energy intake and energy expenditure), adiponectin (hormone regulating glucose and fatty-acid breakdown) and hs-CRP (inflammatory protein marker for cardiovascular disease) levels. In summary, the major findings of this study were that resistance training increased strength and lean body mass and improved insulin sensitivity (which is a preventive adaptation for the development of prediabetes).
Twenty-nine postpuberty youth—17 male (10 lean, 7 obese) and 12 female (4 lean, 8 obese), with leanness and obesity determined by percent body fat—volunteered for this study. They had been lean or obese for the previous 5 years. As with the resistance training study, subjects reported engaging in less than 45 minutes of light to moderate activity per week. The youth were not on any medication and had no first-degree relatives with diabetes.
Cardiovascular Training Program
The subjects completed 12 weeks of cardiovascular exercise. Each subject self-selected a treadmill, an elliptical trainer or a cycle ergometer for his or her mode of exercise. All subjects completed four 30-minute cardiovascular workouts per week (two supervised and two on their own) at 70% of their aerobic capacity. A VO2peak was determined at the beginning of the study to establish proper workout intensity for each subject. The youth wore heart rate monitors in an attempt to ensure they were exercising at an intensity that would raise their heart rates above 140 beats per minute during every 30-minute workout, which included warm-up and cool-down periods.
Variables Measured and Results
Several of the main variables measured and the results detected are presented in Table 2.
The major findings of this study were the significant improvements in cardiovascular fitness and insulin sensitivity. As with the resistance training study, no significant changes occurred in adiponectin, leptin and hs-CRP levels.
In a position statement, the American Academy of Pediatrics asserts that resistance training programs for preadolescents and adolescents (see Figure 1) do not adversely affect linear growth patterns or have any long-term detrimental effect on cardiovascular health (Washington et al. 2001). Combined with this assertion, the two studies reviewed in this column suggest that for overall health, cardiovascular fitness, muscular strength and prevention of obesity, diabetes and cardiovascular disease, personal trainers can best serve youth populations by incorporating both cardiovascular exercise and resistance training interventions into exercise program designs.
Exercise professionals are the finest “agents of change” for promoting physical activity. It’s time to get our youth “moving and lifting” for life!
- Always include warm-up and cool-down components with workouts.
- Initially, teach exercises without any load. Incrementally add resistance as proper exercise skill is mastered.
- Train in 8- to 15-repetition zones, completing 1–3 sets, with 2–3 sessions per week.
- For general strength, train all major muscle groups (with various exercises) through a complete range of motion.
- Match the program to the needs, abilities and interest of the youth.
- Carefully design, competently teach and properly supervise all workouts.
Avoid competitive weightlifting, power lifting, bodybuilding and maximal lifts until the youth reaches physical and skeletal maturity.
Sources: Washington et al. 2001; Faigenbaum 2010.
Note: The American Academy of Pediatrics (Washington 2001) states that a medical evaluation may be needed for some youth prior to initiating a resistance training program, to identify any possible risk factors for injury and/or to provide guidance on weight training goals.
Troiano, R.P., et al. 2008. Physical activity in the United States measured by accelerometer. Medicine & Science in Sports & Exercise, 40 (1), 181-88.
U.S. Department of Health & Human Services (HHS). 2008. How much physical activity should your family get? www.nhlbi.nih.gov/health/public/heart/obesity/wecan/get-active/physical-activity-guidelines.htm; retrieved Nov. 15, 2010.
van der Heijden, G–J., et al. 2009. Aerobic exercise increases peripheral and hepatic insulin sensitivity in sedentary adolescents. The Journal of Endocrinology & Metabolism, 94, 4292–99.
van der Heijden, G–J., et al. 2010. Strength exercise improves muscle mass and hepatic insulin sensitivity in obese youth. Medicine & Science in Sports & Exercise, 42 (11), 1973–80.
Washington, R.L., et al. 2001. Strength training by children and adolescents. Pediatrics, 107 (6), 1470–72.