Intense Exercise an Efficient Way to Improve Cardiovascular Risk

Jim Kling

April 08, 2011

April 8, 2011 — Brief, intensive exercise is an effective way to lower cardiovascular disease (CVD) risk factors in adolescents, according to a study published online April 6 in the American Journal of Human Biology.

CVD events usually occur during adulthood, but it is generally accepted that CVD risk factors begin developing in childhood and carry over into adult years, and that an ongoing unhealthy CVD profile may increase the risk for early mortality. Preventive health strategies therefore include identifying youth with abnormal or just below the maximum level of accepted CVD risk and intervening with appropriate measures.

Modifiable risk factors associated with CVD (eg, poor diet, physical inactivity, low aerobic fitness, obesity and overweight, hypertension, and abnormal lipid profiles) are interwoven and nearly all tied to obesity; therefore, prevention of weight gain is a vital strategy. Poor diet and physical inactivity are the 2 most important factors in weight gain in youth.

Studies that have looked at the effectiveness of programs to increase activity levels in youth have been inconclusive. There are few such programs available, and existing studies have tended to look at nonrepresentative samples of obese and overweight youth.

In obese and overweight youths with poor cardiometabolic profiles, brief interval training has been shown to improve health. Studies in adults have shown that low-volume sprint interval and traditional endurance training are associated with similar metabolic changes during a period of 6 weeks.

To compare 2 exercise protocols of different intensities in adolescents, the researchers divided 47 boys and 10 girls (16.4 ± 0.7 years old) into 3 groups: moderate intensity (MOD, 12 boys, 4 girls), high intensity (HIT, 15 boys and 2 girls), and a control group (20 boys, 4 girls). Overall, 25% of the participants were overweight, and 2% were underweight.

The MOD group ran for 20 minutes at an intensity of 70% maximal oxygen uptake. The HIT group did a maximum-effort sprint for 30 seconds in a course separated by cones. They repeated the exercise 4 to 6 times after 30-second recovery intervals. Both groups exercised 3 times a week for 7 weeks. No injuries were reported during exercise.

The MOD group exercised a total of 420 minutes (total energy expenditure, 4410 kcal) during the 7-week period compared with 63 minutes (total energy expenditure, 907.2 kcal) for the HIT group, the members of which also had an 85% lower training volume.

Metabolic measurements were taken before and after exercise. In the HIT group, the researchers noted significant improvements in systolic blood pressure (112 ± 10 mm Hg preintervention vs 106 ± 11 mm Hg postintervention; P ≤ .05), aerobic fitness (82.00 ± 25.8 shuttles preintervention vs 88.78 ± 26.4 shuttles postintervention; P ≤ .01), and body mass index (21.61 ± 2.2 kg/m2 preintervention vs 21.31 ± 2.1 kg/m2 postintervention; P ≤ .05). The MOD group showed significant improvements in aerobic fitness (73.56 ± 21.8 shuttles preintervention vs 93.25 ± 23.2 shuttles postintervention; P ≤ .01), percentage body fat (19.73% ± 8.6% preintervention vs 17.64% ± 6.5% postintervention; P ≤ .05), body mass index (22.4 ± 3.3 kg/m2 preintervention vs 22.10 ± 3.3 kg/m2 postintervention; P ≤ .01), fibrinogen levels (170.5 ± 65.8 mg/dL preintervention vs 106.2 ± 79.3 mg/dL postintervention; P ≤ .05), plasminogen activator inhibitor 1 levels (23.4 ± 11.3 ng/mL preintervention vs 11.7 ± 9.8 ng/mL postintervention; P ≤ .05), and insulin concentrations (6.04 ± 5.30 μIU/mL preintervention vs 2.02 ± 3.13 μIU/mL postintervention; P ≤ .05).

Study limitations include the small sample size.

"To our knowledge, this is the first study to demonstrate the effects of a novel interval training program on both traditional and novel CVD risk factors in adolescents," the authors write. "The findings demonstrate significant improvements in cardiorespiratory fitness, blood pressure, body composition, insulin resistance, [fibrinogen]...and [plasminogen activator inhibitor]-1 levels in healthy adolescent youth after a 7 week intervention of different exercise intensities. Different exercise intensities and durations may have different cardioprotective effects on youth," they conclude. The authors suggest that "further research is needed to evaluate the use of intermittent activity protocols," particularly "larger scale and extended interventions."

The authors have disclosed no relevant financial relationships.

Am J Hum Biol. Published online April 6, 2011.