Changes in physical fitness of a home-based physical exercise program in childhood obesity: A quasi-experimental uncontrolled study

Abstract

Few studies have evaluated the changes in physical fitness (PF) of obese children and adolescents of a physical activity program for the treatment of obesity, and even fewer have explored the modality of home-based physical exercise. The objective of this study is to evaluate the changes in PF and body composition (BC) of a home-based physical exercise for treating childhood obesity. Thirty-three overweight/obese children and adolescents participated for six months in a home-based intervention that combined aerobics and muscular strength exercises. The results were compared, before and after the intervention, for the different PF components (VO2_max, abdominal muscle resistance strength, and lower body explosive strength) and BC (body mass index Z-score (BMI-Z), percentage of body fat, and fat-free mass) variables. A significant reduction was observed in the percentage of body fat (4.7%) and the BMI-Z score (.23), and there was an increase in the fat-free mass of 2.9 kg (p < .001). In addition, the VO2_max showed a significant increase (p < .05). The results of the different strength tests also showed significant improvements (p < .05). Our findings support the effectiveness of this program improving not only BC but also PF. However, our results should be interpreted with caution due to lack of control group.

Keywords

Adolescents cardiorespiratory fitness children exercise program home-based treatment muscular strength obesity physical fitness

Introduction

Although the rise in obesity prevalence in several high-income countries might be reaching a plateau, prevalence of childhood overweight and obesity has reached alarming rates worldwide and remains high. One of the main factors contributing to this pandemic is a considerable decline in the levels of physical activity (PA) during the past decades (Atkin et al., 2008; Du Bose et al., 2008). The World Health Organization (WHO) currently considers insufficient PA, the fourth leading risk factor for mortality, ahead of obesity, which is the fifth (WHO, 2009). Physical inactivity, in addition to having a negative effect on body composition (BC), reduces physical fitness (PF) (Mesa et al., 2006), a physiological state of well-being that provides the basis for daily life tasks and an important level of protection against chronic diseases (Eisenmann, 2007). PF components related to health are cardiorespiratory fitness (CRF), muscular strength (MuS), BC, and flexibility (Ruiz et al., 2009).

Many studies support the importance of PF (Blair and Jackson, 2001; Bovet et al., 2007). Ortega et al. (2013) concluded in a recent review—which summarizes the most relevant information from cross-sectional and longitudinal studies on the relationships between PA, PF, and overweight in early life—that high fitness levels may counteract the negative consequences attributed to body fat and that increasing PF in overweight children and adolescents may have many positive effects on health, including lower body fat levels.

Adequate CRF in childhood improves and prevents metabolic and cardiovascular diseases in adulthood (Carnethon et al., 2003; Kvaavik et al., 2009). In obese children, low CRF has shown to be an independent predictive factor of morbidity–mortality (Ekelund et al., 2007). MuS has also been related to lower cardiovascular risk (Jackson et al., 2010). The Alimentación y Valoración del Estado Nutricional de los Adolescentes (AVENA) study showed that adolescents with greater MuS presented better metabolic profile. Moreover, for a certain level of CRF, those with higher MuS had a better metabolic risk profile (García-Artero et al., 2007).

In a recent randomized controlled trial (RCT), our group evaluated the effects of a combined (CRF and MuS) home-based physical exercise program on the BC of overweight/obese (OW/O) children and adolescents, obtaining positive results (Lisón et al., 2012). Our home-based exercise program (HEP) was primarily designed to maximize health benefits without increasing the demand on resources or personnel. The scientific literature contains few studies that have evaluated the effects of a combination of exercises to improve both, CRF and MuS, and even fewer that have also measured their effects on PF (Watts et al., 2005). Moreover, the large majority of physical exercise interventions have been conducted in groups in controlled settings (hospitals, schools, and universities) (Atlantis et al., 2006), without having fully explored the easy to apply and cost-saving modality of home-based physical exercise. In order to make our HEP feasible for an outpatient clinic, we have reduced the intervention to an initial contact with the patient and parents, where the intervention is explained, and a trimestral follow-up, reviewing the adherence and the evolution of BC.

We hypothesized that a simplified version of this HEP, focused on PA intervention, produces a positive effect on PF. The purpose of the present study was to analyze the effects of the program on BC, PF, and MuS, three of the components of PF related to health.

Material and methods

This is a prospective pre-post test design study. Subjects were recruited at random from the outpatient clinic for obesity and cardiometabolic risk assessment at the Cardiovascular Risk Unit of the Hospital General of the University of Valencia. Patients from 8 years to 16 years of both sexes were sent by primary care pediatricians to participate in the study during the three months of the recruitment period.

The criteria used to diagnose OW/O were, respectively, a body mass index (BMI) in the 85–95 percentiles and a BMI above 95 percentile (values adjusted for age and sex). The extent of OW/O was quantified with the use of a Cole’s lambda–mu–sigma method (Cole et al., 2000). After pediatric evaluation, subjects were excluded if they suffered from (1) severe obesity (Z-score > 2.5)—individuals in this category require specific individualized programs to avoid potential orthopedic problems—and (2) an acute disease, secondary obesity syndromes or any other disease, handicap, or lesion that would impede or contraindicate the performance of physical tests and/or the intervention program exercises. Moreover, none of the subjects participated simultaneously in other interventions designed to improve their PF. Informed consent was signed by participating subjects and their parents. The study was conducted in accordance with the Second Helsinki Declaration and approved by the ethics committee of the hospital.

General description of the intervention

This simplified version of the HEP exactly reproduces the exercise program reported by Lisón et al., but in order to simplify the intervention and limit the influence of diet on the results, we decided not to add special dietetic counseling only the general recommendations promoted by the Strategy for Nutrition, Physical Activity and Obesity Prevention (NAOS), summarized in the NAOS pyramid (AESAN, 2010). Thus, it has been reduced to four of the number of contacts during the six-month study period: two intervention visits (weeks 0 and 12) and two evaluation contacts (weeks 1 and 24). Subjects who failed to attend any of these contacts were excluded from the final analysis.

Home-based physical exercise intervention (intervention visits)

The study volunteers and their parents attended one educational session (week 0) that lasted one and a half hour, led by two pediatricians and a fitness specialist in the hospital. The topics addressed included the decisive role of PA in PF and the importance of losing and maintaining weight. All exercises were explained and detailed written instructions were given to each participant. Parents were told that their children had to engage in a minimum of three exercise sessions per week to achieve the desired results and not to start with the program before the first evaluation contact.

This exercise program, which replicates the one designed by Lisón et al., includes a total of 120 sessions distributed over six months, with five 60-minute exercise session per week. Each session was composed of two activities to improve CRF (brisk walking and scissor jumps) and a total of 10 MuS exercises. The MuS exercises involved the main muscle groups and were performed under low load and high repetition. The intensity of the exercises increased along the program. Special attention was paid to the walking speed, as it had to be done at a fast pace. Emphasis was also placed on the importance of reducing the rest periods between the CRF and MuS exercises as much as possible. All participants were provided with a daily exercise log book for six months and were instructed to complete it for each exercise session, including date and duration. A detailed explanation of how to perform the exercises is summarized in Figure 1 (see Online supplementary Material).

At third month, all participants were invited to a following consultation at the outpatient clinic. At this contact, the pediatrician reviewed the adherence to the program and encouraged the participants to continue.

Evaluation of BC and PF (evaluation contacts)

Evaluations and physical examinations were performed before and after the intervention by the same researchers and following a standardized protocol (weeks 1 and 24). All of the physical tests were carried out on the same afternoon, with a rest period of five minutes after each test. Moreover, and to avoid undesired interactions produced by the physical requirements of each test, they were always performed in the same order—described below—and after the anthropometry tests.

The participants were measured and weighed without shoes and wearing only underwear. Height was recorded with a precision of .5 cm using a wall stadiometer (model 216, SECA, Germany). Body weight, measured with a precision of .1 kg, fat-free mass, and percentage of body fat were determined by means of a body fat analyzer (TBF-410 M, TANITA, Japan), following the standard procedure.To evaluate CRF, participants performed the UKK (Urho Kaleva Kekkonen) test, following the published standardized conditions (Oja et al., 2001). This test, validated in an overweight population (Laukkanen et al., 1992), consists of walking a distance of 2 km in as little time as possible. For each participant, the time spent walking the 2 km, the mean heart rate (MHR) during the test, and the HR during the recovery phase at one-minute post-effort were continuously monitored using sport testers (model 610si, Polar, Finland). Participant’s VO2_max, the main indicator of CRF, was calculated using the specific formulas for each sex (Laukkanen et al., 1992).

To evaluate the explosive strength of the extensor muscles of the lower body, a battery of jumps was performed, composed of (1) squat jump, (2) counter movement jump, and (3) Abalakov—a variation of the counter movement jump test where arm swinging is allowed to assist in generating maximum height (Ortega et al., 2008). Each participant performed three consecutive trials for each jump modality, with one minute of rest between each jump. To determine the height of the jump (in cm), the contact platform Ergo Jump Plus Bosco System was used. To evaluate abdominal muscle resistance strength, participants had to perform the greatest number of “sit-ups” (cycles of bending–extending the spine) for 30 seconds (Adam et al., 1988).

Statistical analysis

After testing the normality of the data (Kolmogorov–Smirnov test), the following statistical tests were carried out as follows: (1) t-tests of related samples to compare the pre- and post-intervention values of the anthropometric variables, abdominal muscle resistance strength, and CRF and (2) Wilcoxon test to compare the pre- and post-intervention values of the lower body explosive strength variables. The data are presented as mean ± standard deviation. The data analysis was performed with the statistical program SPSS version 18.0 for Windows (SPSS, Chicago, Illinois, USA). For all of the statistical tests, a significance level of p < .05 was established.

Results

From a total of 40 subjects recruited, seven were excluded (two subjects did not attend follow-up visits and five missed the final evaluation), which implied an 82.5% retention. None of the subjects were excluded for meeting exclusion criteria. The analysis was made of 33 OW/O children and adolescents of both sexes (18 males and 15 females), between 8 years and 16 years of age (11.6 ± 2.5).

The results of the study showed significant improvements in almost all of the anthropometric variables (BMI (1.2 kg/m²), BMI Z-score (BMI-Z; .23), percentage of body fat (4.7%), and fat-free mass (2.9 kg); p < .001), with the exception of weight, which only showed a slight decline (Table 1).

Table 1.

Results of the comparison of the pre- and post-intervention values for the different body composition variables.

	Baseline	Six months	p Value
Height (m)	1.52 ± .13	1.55 ± .12	.000
Weight (kg)	67.2 ± 17.3	66.9 ± 16.8	.561
BMI (kg/m²)	28.4 ± 3.8	27.2 ± 4	.000
BMI-Z	2.09 ± .32	1.86 ± .39	.000
Percentage of fat	38.5 ± 4.4	33.8 ± 6.08	.000
Fat-free mass (kg)	41.5 ± 10.7	44.4 ± 11.8	.000

Note: BMI: body mass index; BMI-Z: body mass index Z-score. The values are expressed as mean ± standard deviation.

Likewise, the results showed improvements in the participants’ PF (Table 2). Regarding CRF, VO2_max showed a significant improvement after the intervention (2.4 ml/kg/min; p < .05). Moreover, although the participants did not improve the time it took them to walk 2 km, the mean HR during the test declined significantly (7 bpm, p = .019), and the HR after one minute of recovery was lower.

Table 2.

Results of the comparison of the pre- and post-intervention values of the different physical fitness variables.

	Baseline	Six months	p Value
Cardiorespiratory fitness
UKK test duration (s)	1174 ± 102	1177 ± 110	.807
MHR (b/min)	156 ± 17	149 ± 19	.019
RHR1 (b/min)	132 ± 22	127 ± 18	.139
VO2_max (ml/kg/min)	26.8 ± 5.1	29.2 ± 5.5	.028
Lower body explosive strength
Squat jump (cm)	12.1 ± 3.6	13 ± 3.4	.008
Counter movement jump (cm)	13.0 ± 3.7	13.4 ± 3.3	.001
Abalakov (cm)	15.5 ± 4.4	16.1 ± 3.6	.020
Abdomen muscle resistance strength
Sit-ups, number of repetitions	23.4 ± 5.6	28.4 ± 4.6	.001

Note: MHR: mean heart rate during the UKK-test; RHR1: heart rate one-minute post-test. The values are expressed as the mean ± standard deviation.

The results of the different lower body and abdominal muscle strength tests also showed significant improvements after the six-month intervention (Table 2).

Discussion

To the best of our knowledge, this is the first study to simultaneously evaluate the effects of a combined (CRF + MuS) home-based physical exercise program on the BC and PF in childhood obesity. This study is especially relevant due to the important role of both, BC and PF, in the cardiovascular health of children and adolescents (Ortega et al., 2008). Our results support that a physical exercise program of these characteristics (home-based exercise circuit) is valid for improving both the CRF and MuS components of PF. Furthermore, the results in terms of BC improvement of this simplified version of HEP are on the line of those obtained in an RCT conducted by the same researchers.

Regarding CRF, the physical quality most closely related to cardiovascular health, there was a significant improvement, as demonstrated by increases in VO2_max (2.4 ml/kg/min; p < .05). Moreover, although the children did not walk the 2 km in less time, there was a reduction in their MHR (156 vs. 149 b/min, p = .019). This result could be explained due to the different temperatures when the test was held (December at 13°C vs. June at 29°C). It has been shown that in warm humid environments, the higher body and skin temperatures increase the sensation of perceived effort and reduce cardiorespiratory performance (Asplund et al., 2011; Cheuvront et al., 2010). On the other hand, our results are consistent with others reported in previous combined (CRF + MuS) exercise programs but implemented in controlled settings. Park et al. (2012) in an RCT with a sample of 29 OW/O children reported significant improvements in BMI (1.2 kg/m²) and VO2_max (3.7 ml/kg/min). Another RCT (Davis et al., 2011) with 38 OW/O adolescents informed significant improvements in VO2_max (3.1 ml/kg/min) and subcutaneous and visceral adipose tissues (10%). Similarly, Tan et al. (2010) showed significant improvements on BC and functional capacity compared with control groups.

Based on recent scientific evidence, our program included a combination of physical exercises to improve CRF and MuS. Both modalities can contribute to maintaining the fat-free mass metabolically active when combined with a low calorie diet, especially the modality of MuS exercises, thus avoiding the reduction in the basal metabolic rate induced by diet (Dulloo and Jacquet, 1998). Some authors have pointed out that MuS exercises specifically contribute to increasing fat-free mass (Sothern et al., 2000) and that they play a fundamental role in preventing post-intervention weight gain (Schwingshandl et al., 1999). In this sense, although the total weight of the subjects in our study did not decline significantly, there was a remodeling of the fat-free and fat masses, which increased and diminished, respectively. These results agree with those obtained by other authors (García-Artero et al., 2007; Sothern et al., 2000; Woo et al., 2004). Likewise, the results obtained on the strength tests show significant improvements in all the pre- and post-intervention comparisons. These improvements could be mainly due to the MuS exercises (Treuth et al., 1998).

In another vein, the home-based modality offers important advantages for families limited by economic, time, or location problems (Lisón et al., 2012). Interventions held in controlled settings, unlike home-based ones, cannot be implemented on a large scale, and their economic/human cost is considerable. In contrast, the home-based modality offers patients flexibility and privacy, and it can be particularly beneficial for socially and economically disadvantaged families who do not have a safe place to do physical exercise. In addition, this reduced version of the program, consisting of an initial meeting and a quarterly contact with the patient, could be perfectly adaptable to most pediatric consults, even in primary care.

As in any experimental study, the present investigation has limitations that should be taken into account. A major limitation of this study is the lack of a concurrent control group. Although the positive body composition results are supported by those obtained in our previous RCT (Lisón et al., 2012), the absence of a control group has to be considered when interpreting the presented PF results. Effectively, controls eliminate the alternate explanations of experimental results, especially confounding variables and experimenter bias, enabling the investigator to control for threats to validity. In this study, changes in CRF, MuS, and body composition may have occurred for reasons unrelated to treatment, such as age, developmental stage, or gender. Therefore, the positive results may require discounting due to the absence of a control group.

The study design did not allow us to independently evaluate the impact of exercise and diet on the different variables analyzed, thus an additional alternative component of diet adherence could not be excluded. The intensity of the exercise was not individually monitored, and there were no daily dietary records kept of the participants’ food consumption. Furthermore, treatment individualization is not compatible with large-scale implementation. However, the improvements in BC and PF suggest that the program was followed satisfactorily. Although our study has shown efficacy in improving PF and BC in the short-term, long-term outcome data for successful treatment approaches is required. Finally, the sample size was small (n = 33), so we are not allowed to detect differences in response between sexes. Consequently, taking into account these limitations, caution is warranted when interpreting or generalizing the results of the present study.

In summary, the results of the present study suggest that an ambulatory self-administer physical exercise program could be effective for improving BC and PF of obese children and adolescents and might be a useful tool to be implemented on a large scale without considerable economic cost and time and personnel. Future research should investigate the long-term effectiveness of such program through an RCT.

Footnotes

Acknowledgments

The authors would like to acknowledge the Comunidad Valenciana Government and the Centros de Investigación Biomédica en Red Fisiopatología Obesidad y Nutrición, Instituto de Salud Carlos III, Spain, for funding support.

Declaration of conflicting interests

The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Funding

The author(s) disclosed receipt of the following financial support for the research, authorship, and/or publication of this article: This work was supported by the Comunidad Valenciana Government (grant GV06/227) and the Centros de Investigación Biomédica en Red Fisiopatología Obesidad y Nutrición (CB06/03), Instituto de Salud Carlos III, Spain.

Supplemental material

The online data supplements are available at .

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