The Feasibility of High Intensity Interval Exercise in Obese Adolescents

Introduction

Exercise is a critical component in the management of pediatric obesity. Currently, continuous aerobic exercise (AE) is the standard of care for pediatric weight management programs. The 2008 Physical Activity Guidelines for Americans primarily promote aerobic activity for children, and aerobic-based exercise at a steady intensity (AE) is typically prescribed in pediatric weight management programs¹. Several studies in adults, however, show advantages of high-intensity interval exercise (HIIE) over continuous A Eat improving fitness and health in both healthy and obese people^2–4.

These benefits of HIIE compared to AE have also been demonstrated in some limited studies in children. In a sample of healthy prepubescent children, Borel et al showed the immediate effects on oxygen uptake (VO2) of HIIE to be comparable to continuous AE by continuously monitoring gas exchange of subjects at various points in an exercise protocol Farpour et al showed improved health and fitness measures in healthy children as a result of HIIE^5,6.

Some of this work in children extends into the obese population. Ingul et al showed that impaired cardiac function in obese adolescents can be improved by 3 months of HIIE training on a treadmill twice a week for 13 weeks⁷. Tjonna et al studied obese adolescents in twice weekly HIIE intervention for 12 weeks compared to subjects receiving bimonthly education from multidisciplinary health professionals⁸. HIIE was superior to educational classes at improving subject BMI, body fat, blood pressure, blood glucose, and endothelial function. A study from the Sao Paulo School of Medicine compared HIIE and AE in obese 8–12 year old children with treadmill training protocols twice a week for 12 weeks. Both were found to be equally effective in improving aerobic fitness, insulin sensitivity, and BMI in obese children but the study may have had too few enrolled to show a difference between modes of exercise⁹.

While these few studies of HIIE in obese children have shown benefits on fitness and cardiovascular risk factors, the acceptability and enjoyment of this protocol in children is not clear. Enjoyment of the exercise is a crucial component if our goal is long-term adherence. Another limitation of many HIIE studies in children is restriction of the interval training to treadmill protocols; a more varied exercise protocol would be more comparable to the current standard of care, which includes group games and more variable equipment choices. The purpose of this HIIE study was to measure the enjoyment and acceptability of HIIE as well as the feasibility of a multimodal protocol in obese teenagers enrolled in a multi-disciplinary pediatric weight management program as a precursor for a larger, definitive study.

Methods

Adolescents with BMI at or above the 95^th percentile for age and sex were recruited from a multi-disciplinary pediatric weight management program at a large academic medical center. All subjects were between 12 and 18 years of age. Exclusion criteria included the following: taking medication that may affect the heart rate and/or blood pressure, inability to exercise for any reason, pregnancy within 6 months, stage 2 hypertension, and history of significant cardiac disease leading to cardiovascular instability.

The intervention group and control groups were enrolled and completed sequentially; ten obese adolescents were recruited for the HIIE group and then 8 were recruited for the AE group. The intervention group received four weeks of HIIE training and the control group received the standard pediatric exercise classes, consisting of traditional aerobic exercise. All participants were required to attend at least 3 of 4 structured 50-minute exercise sessions each week for 4 weeks. Subjects present for at least 3 exercise sessions per week received a ten dollar gift card at the end of each week.

The control exercise protocol included: 50 minutes of supervised aerobic exercise (AE) with a regimen consisting of a 10-minute warm-up, 30 minutes of relatively continuous aerobic exercise at 65% of estimated exercise capacity, and a 10 minute cool down period. Participants wore a portable heart rate monitor and were observed by the study exercise physiologists to ensure that effort was maintained at 65%.

The following protocol was used for HIIE group sessions: a 10 minute warm-up, 30 minutes of HIIE with 10 cycles of I minute vigorous exercise at 80 to 90% maximum heart rate followed by 2 minutes of active recovery at 60% maximum heart rate, and 10 minutes of cool-down. Participants wore a portable heart rate monitor and were observed by the study exercise physiologists to ensure that effort was maintained at target heart rate goals throughout the session. The protocols were designed to be consistent with published exercise intensity definitions, consistent with previously studied protocols, and comparable to each other in terms of energy expenditure.^6–8

Physiologic and anthropometric data of subjects in both groups was obtained at entry and after completing the 4-week intervention. Evaluation of fitness included VO_2max test and VO_2sub-max (at 6 and 9 minutes) testing on the treadmill using Cosmed k4B2 Mobile Cardiopulmonary Exercise Test equipment (Cosmed USA Inc., Chicago Ill) following a modified Bruce Protocol. To assess body composition, weight and height were used to calculate BMI and body fat was determined via bioelectrical impedance using a HBF-306C Body Fat Analyzer (Omron Healthcare, Inc. Lake Forest Illinois).

At the end of the intervention, participants in the HIIE group completed a satisfaction survey to compare their experience with their previous experience with the traditional exercise program.

All analyses were done using SAS (ver. 9.3, SAS Institute, Inc., Cary, North Carolina). Descriptive statistics were summarized as frequency for categorical variables; mean, standard deviation for continuous variables by groups. Paired T-test was performed to compare changes pre- and post-intervention of each group. T-test was performed to compare values between intervention groups. A p-value less than 0.05 was considered significant.

The study was approved by the Cincinnati Children’s Hospital Institutional Review Board.

Results

In the intervention group, 9 teens consented to participate, 2 attended no exercise sessions and 7 completed the study; the mean age of those in the HIIE group was 13.7 years (Table 1). Five of the 7 were female and 4 were African American. Six out of 7 subjects attended every required session of exercise; the mean attendance rate was 95%. In the control group, 8 teens consented to participate and 6 completed the study with a mean age of 14.4 years. Five of the 7 were female and 6 were African American. The average attendance was 11.3 of 16 sessions for both groups.

Table 1.

Clinical Characteristics of Study Population and Pre/Post variables (values are ± one standard deviation).

Variable	HIIE (N=7)	Standard AE (N=6)	P Value
Age	13.7 ± 2.0	14.3 ± 1.2	0.52
Gender, n (%)
.     Male	2 (29%)	1 (17%)	NA
.     Female	5 (71%)	5 (83%)	NA
Race, n (%)
.     Black or African American	4 (57%)	5 (83%)	NA
.     White	3 (43%)	1 (17%)	NA
Average Exercise Visits	11.4	11.2	NA
SBP (mmHg)	117.4 ± 3.4	123.3 ± 6.8	0.07
DBP (mmHg)	64.6 ± 5.0	66.7 ± 4.1	0.43
Height (cm)	165.3 ± 8.6	170.4 ± 11.4	0.37
Weight (kg)	89.6 ± 25.5	106.3 ± 20.1	0.22
Body Mass Index (kg/m2)
Baseline	32.5 ± 7.6	36.4 ± 4.7	0.29
End	32.6 ± 7.1	36.4 ± 4.5	0.28
Change	0.119 ± 0.887	−0.048 ± 0.615	0.71
% Body Fat
Baseline	37.9 ± 3.6	39.7 ± 1.6	0.3
End	38.3 ± 3.7	41.5 ± 2.3	0.1
Change	0.327 ± 1.06	1.750 ± 2.66	0.22
VO2max (ml/kg/min)
Baseline	29.1 ± 3.5	26.8 ± 4.9	0.34
End	32.7 ± 4.0	30.2 ± 2.6	0.31
Change	2.70 ± 2.97	2.99±1.72*	0.87
VO2max indexed to lean mass (ml/kg/min) 10
Baseline	46.9 ± 4.7	44.5 ± 8.2	0.52
End	51.8 ± 5.5	50.9 ± 3.7	0.78
Change	4.43 ± 4.19*	5.27 ± 3.42	0.75
9 minute submaxVO2 (ml/kg/min)
Baseline	21.6 ± 3.2	21.4 ± 2.0	0.92
End	21.1 ± 3.0	22.3 ± 4.8	0.63
Change	−0.450 ± 4.48	0.537 ± 4.10	0.73
9 minute submaxVO2(ml/kg/min, indexed to lean mass)
Baseline	34.7 ± 4.1	35.7 ± 3.0	0.66
End	34.4 ± 5.1	37.5 ± 7.9	0.43
Change	−0.375 ± 7.06	1.15 ± 6.52	0.73

NA =Not applicable

^*p<0.05 for changes from baseline.

Both the HIIE and AE group showed improvement in VO_2max with the AE significant for VO2 max per kg, and the HIIE significant when indexed to fat free mass¹⁰. Neither group demonstrated a significant change in BMI or in percent body fat.

Seven of 8 HIIE participants completed the satisfaction survey. All 7 reported they would “recommend this type of exercise program to a friend.” Six out of 7 participants responded they desired “to continue with the same type of exercise program.” When asked “overall, how would you rate” the four-week exercise program on a scale from 0–100, the average response was 85. All 7 responded they were able to hit their “heart rate goals most of the time.” The AE group was not surveyed.

Discussion

With our feasibility study we demonstrate that obese teens can be successfully recruited and complete a pilot study of HIIE. Retention of subjects was satisfactory and participants reported satisfaction with HIIE. The use of HIIE exercise classes in obese teens was shown to be structured, realistic, and highly desired. Using small incentives for attendance was an effective method of subject participation in both groups.

As this was a feasibility study, there were many limitations which include small sample size, lack of randomization, and short duration of intervention. Only the HIIE was surveyed for acceptability. Still, our study demonstrates that teens find HIIE acceptable and that such a study comparing the two modes is feasibility. Both AE and HIIE led to an improvement in fitness as in previous studies.

Future research is warranted to determine the relative effect of HIIE versus standard exercise in obese children. In this study the intervention period of 4 weeks was not expected to lead to significant physiologic change in subjects. A study with more subjects and more substantial intervention periods, such as 12 or more weeks of exercise, is necessary to demonstrate significant physiologic change in submaximal and maximal VO₂, BMI, and body fat.