The Role of Physical Activity in the Management of Childhood Obesity

| May 1, 2007

by Harry Pino, PhD and Alexis Smith, MS

From the Obesity Consult Center, Tufts-New England Medical Center, Boston, Massachusetts

“To understand the obese child, one needs to remember that he accumulated his extra weight while living in a family that, wittingly or unwittingly, encouraged overeating and inactivity.”[1]

INTRODUCTION

By simply taking a look at children playing in a schoolyard, it can be clearly seen that the obesity epidemic has now reached our most vulnerable population, our children, who are our future. There is much debate as to the most contributable cause of this epidemic, but researchers are now coming to some sort of consensus by slowly accepting the idea that obesity is a multifactorial problem.

First, obesity is a battle between genetics, hormones, and parental influences.[2] It is a known fact that some children and adults are more susceptible to certain conditions, such as obesity. When environmental factors (high fat foods, lack of physical activity) interact with the genes (ob-gene, B3 adrenoreceptors, and D2 dopamine receptors) and hormones (leptin, ghrelin, uncoupling protein-2) found to be linked with obesity, the genetic predisposition has a much higher likelihood of revealing itself.[2] Combine bad genes with parents who are uneducated about nutrition and activity, and the result is an uneducated child heading down the long and painful path of overweight and obesity. In another situation, combine the bad genes with overbearing parents who utilize food restriction secondary to their fear of childhood obesity, and the end result could also be an obese child who is headed for a sometimes even more painful path of overweight and obesity.

For all children and adults who are trying to fend off obesity, the major battle lies within keeping a zero (maintenance of weight) or negative (loss of weight) energy balance. This consists of maintaining a balance between energy intake (low-calorie, nutrient-dense foods) and energy output (physical activity and exercise). It is important to place an emphasis on energy output in the obese child so that a negative energy balance exists, which will ultimately promote weight loss.

It is often difficult to distinguish what factors occur first in the development of a child’s obese condition. Was the child depressed, causing him or her to find comfort in food, resulting in an overweight/obese condition? Or was the child overweight to begin with, and subsequently encountered teasing at school or by family, became depressed, sought comfort in food, and consequently has become obese? The debate can go on for eternity, but what is important in this day and age is what can be done to decrease the prevalence, morbidities, and mortalities of this condition. The scope of this article is to investigate the role of physical activity in the management of childhood obesity, particularly in promoting a negative energy balance to induce weight loss, as well as instilling lifelong lifestyle changes that will improve the child’s sense of accomplishment and overall health.

Table 1

DEFINITIONS

Sedentary activity is defined as any activity that is less than or equal to 1.5 metabolic equivalents (MET). It closely resembles energy expenditure while the body is “at rest.”[3] Several studies have targeted sedentary behavior as a way of decreasing childhood obesity rather than taking the traditional approach of increasing daily physical activity.[4-6] All have found varying levels of success in keeping a focus on decreasing sedentary behavior, partly because children are not as responsive when they are told to increase physical activity. When children are asked to decrease sedentary activities, they may substitute that time with more active behaviors or may substitute one sedentary behavior (watching television) with another (reading a book, playing a board game).[4-6]

Sedentary behavior is linked with several comorbidities and complications, particularly those associated with the development of overweight/obesity. Cardiovascular health is compromised by the negative effects of physical inactivity on lipid profiles, along with a significant rise in blood pressure toward a hypertensive state.[7] An increase in serum insulin—insulin resistance—leading to impaired glucose tolerance and, ultimately, type 2 diabetes mellitus is just the tip of the endocrinological “iceberg.” Several other hormones are altered in response to extra adipose tissue, leading to further complications, such as menstrual irregularity and liver disease.[7] The fragile skeletal system of a child is altered by massive amounts of extra weight in the form of slipped capital femoral epiphyses, hip/knee pain, limited hip ROM, and Blount’s disease (tibia vara).[8] Mentally, sedentary activity that promotes obesity can be linked with the development of depression and low self esteem. Finally, sleep apnea or obesity hypoventilation syndrome may be present, particularly in those children who are extremely sedentary and thus quite obese.[7,8] A study done over a period of nine years explored habitual activity in girls beginning at ages 9 to 10 and then at years 3, 5, 7, 8, 9, and 10, and skinfold thickness was measured annually. It was found that each 10 MET/week-decrease in physical activity correlated with a 0.14Kg/m2 and 0.09Kg/m2 in black and white girls, respectively.[9] This further supports the idea that physical inactivity is strongly linked with overweight and obesity in children and adolescents.

Physical activity is defined as any bodily movements produced by skeletal muscles that result in energy expenditure.[10] It can be classified in several different categories and can be based on varying intensities. Physical activity can either be structured or unstructured, with each having its own advantages and disadvantages. Each type of activity works differently in various populations.

Structured physical activity is simply regular exercise. It is routinely performed with the intention to improve overall physical health and wellbeing. Structured physical activity offers the most benefits multisystematically due to its routine aspect. Once in a regular exercise routine, benefits in all body systems will be seen in as little as four but as many as 12 weeks. Adults and older children usually respond best to this type of activity secondary to their busy schedules.

On the other hand, unstructured physical activity is activity that is either done unintentionally, intentionally, or spontaneously, and is usually sporadic in nature. For instance, walking up a flight of stairs, incorporating extra steps into the child’s day, and encouraging free play (games like tag, red rover, etc.) are all examples of unstructured physical activity. Children from ages 3 and 4 to adolescents 13 and 14 years of age respond best to this type of activity, as it gives them autonomy in deciding what type of activity they want to do. Typically, children will feel that a regular exercise routine may be punishment for being obese. However, if children are let loose in a giant safe area, they are more inclined to run around at higher intensities because they are “playing,” not “exercising,” thus optimizing energy expenditure.[8] Physical activity, when incorporated in the correct amounts and at the optimal intensities, is found to provide significant health benefits. Ribeiro, et al., explored vasodilatory responses via forearm vascular conductance (FVC) in obese children and lean sedentary controls. It was found that obesity did indeed exacerbate blood pressure responses and blunts FVC during the Stroop color word test and a hand dynamometer exercise, but that after a four-month diet and exercise intervention consisting of three days/week for 60 minutes, with half dedicated to structured activity and the other half devoted to recreational activity, FVC and BP returned to nearnormal or normal levels.[11]

Another four-month study, with an exercise intervention consisting of five days a week with a $1 incentive for 40-minute sessions, with half devoted to structured activity and half devoted to unstructured activity, resulted in children ages 7 to 11 experiencing positive improvements in triglycerides, blood serum insulin levels, and percent body fat.[12] Figure 1 and Figure 2 show the results of this study. As suspected, when training was ceased for four months, gains in all decreased parameters occurred. This further merits the idea of substituting physical activity for sedentary activities.

FACTORS INFLUENCING CHILDHOOD PHYSICAL ACTIVITY/INACTIVITY

Parents have a major influence on their children regarding their activity/inactivity levels. Wardle, et al., found that children from overweight/obese families had higher preferences for a sedentary lifestyle when compared to children from normal weight families.[13] Another study looked at parental activity patterns and compared them to a child’s likelihood to participate in extracurricular sporting activities. It was found that if both parents were identified to be active, their children would participate in more (0.6) sports and have slightly better cardiovascular fitness than the children who had only one parent active or both parents inactive.[14]

In addition to parental activity status, the home environment, which is created by the parents, is also thought to influence physical activity. Strauss and Knight found that children with low cognitive stimulation were found to be at an increased risk for the development of obesity.[15] Therefore, a home that offers cognitive stimulation (which normally does not occur through television, but rather stems from interaction between family members) will likely result in children who are less sedentary and thus at less risk for obesity.[15]

Yet another disturbing trend is the overindulgence in various forms of media by the youth of today. With every hour increase spent in front of the television or other forms of media, a 10- to 12-percent increase in the risk of obesity has been seen,[16] and in another study there was a 2- to 3-fold increase in the risk of obesity.[17] Proctor, et al., found that by age 11, those children who watched an average of 3+ hours a day of television had a mean skinfold thickness sum of 106.2mm, while those children who watched less than 1.75 hours of television/day had a skinfold thickness sum of 76.5mm.[18]

ASSESSMENT OF PHYSICAL ACTIVITY

There are few validated methods to assess physical activity in children. The methods most often utilized are questionnaires, heart rate monitoring, accelerometry, and pedometry. There are several questionnaires that exist, but only a few that are normally used repetitively. It must be kept in mind that when a questionnaire is being administered, all information is being collected in a self-report, recall basis manner. Therefore, if a 5- or 6-year old child is being questioned, the likelihood of the child giving accurate information is slim. In this case, a parent should be asked to describe the child’s activity patterns and answer questions related to an activity history. As children get older, their ability to recall may get better, but it may also be influenced by testers in that the adolescent may report activities that are suspected to be expected of them (i.e., participation in gym class even though they may sit out more than 50% of the time). While questionnaires may offer a significant amount of information, it is very difficult to translate the qualitative information to quantitative information in a manner that allows validity and accuracy to remain.[19] Heart rate monitoring allows for a cardiovascular view of physical activity in that elevated heart rates indicate activity that is not sedentary, and greatly elevated heart rates imply moderate-tovigorous activity.

However, some limitations of this method include that it is time-consuming and requires cooperation from the subject, which in and of itself can be difficult to obtain in a 7- or 8-year old child (who must be sitting still), not to mention in one that is attempting to be active. As already stated, heart rate monitoring is based on intensity of the activity at hand, and thus for children who are constantly on the move, it may not be the best way to assess physical activity. However, it may be more applicable in those older adolescents who are beginning a regular exercise routine.

Pedometers and accelerometers offer a physical assessment of activity. Pedometers are not as accurate or as useful as accelerometers. They can only count steps at a fixed stride length; therefore, they do not take into account changes in speeds, direction, or activities that do not require walking (i.e., cycling, rowing, etc.). On the other hand, accelerometers are based on the relationship between muscular force and body acceleration that occurs during movement patterns.[19] Unlike pedometers, accelerometers measure activity in all three planes and can distinguish between a multitude of speeds. This means their use in children is practical considering the sporadic nature of children’s activity patterns.[19]

ASSESSMENT OF PHYSICAL INACTIVITY

Assessment of sedentary behaviors is usually done on a selfreport basis using questionnaires or simple intake forms. Again, the recall error is present and parents and children are usually both asked the questions, which will offer some form of comparison, as was the case in a study done by Robinson.[4] Accelerometers can also be a way of measuring inactivity, as all movement is measured. If Child A has much less movement recorded than Child B, Child A could be deemed less active than Child B if an error did not occur.

TRENDS OF PHYSICAL ACTIVITY

Childhood physical activity is on the decline in part because of the societal changes that have occurred over the past few decades.[20] Typically, there are now two working parents in the home, leaving the parents to rely on media as a distraction so they can tend to their errands without worrying about their child’s safety. As a result, children’s leisure activity is no longer mostly active, but increasingly sedentary. In addition, as more families hire outside help (i.e., housekeepers and nannies), the children’s physical activities of daily living, such as walking to and from school and doing chores, are decreasing.[20] Children now play less outside and focus more on the internet, computers, and television.[21] As a result, approximately 25 percent of children are now classified as overweight (BMI>85th percentile) and 11 percent are classified as obese (BMI>95th percentile).[22] Even more compelling is that 70 percent of these obese adolescents will likely grow up to be obese adults.[22] Burke, et al., completed surveys covering dietary intake and lifestyle measures (alcohol intake and physical activity) at 9, 12, 15, and 18 years of age. Figure 3 shows the results of the all surveys looked at retrospectively, and it was found that those adolescents who were obese at the last resurvey (age 18) were either overweight or obese at age 15, and 90 percent and 91 percent of those obese at 18 were also overweight/obese at ages 9 and 12, respectively.[23] It is evident that something must be done to prevent these trends from tracking into adulthood.

In general, physical activity in children is on the decline secondary to several different factors: Lack of interest in activity, greater interest in sedentary activities, lack of encouragement to walk to school when possible, and decline in quality and quantity of physical education offered to children and adolescents.[24,25]

What’s interesting is that there is a general trend between genders that finds boys are generally more active than girls, and that younger boys are more active than younger girls and their older counterparts.[26, 27]

There has also been a trend for more and more children failing to meet minimum physical activity guidelines. Table 2 shows that the percentage of young boys who met the physical activity guidelines of greater than 60 minutes at a moderate intensity decreased by 15.5 percent, and an amazing 35.6 percent decreased over the course of six years in girls.[27] Rasmussen, et al., found similar results in a study of the population of 15-year-old boys and girls.[28]

Table 3

In addition, this trend tracks children and adolescents through grades 1 to 12, finding that compliance with recommended physical activity guidelines is typically 100 percent in the first grade, much thanks to free play (which, although sporadic, contributes to the equation); whereas, on the other hand, compliance was found to be only a mere 29 percent in grades 10 to 12.[29]

The presence of new technologies may be beneficial to some, but in our children they appear to be one of the reasons kids are not meeting physical activity guidelines and, consequently, new technologies are at the root of the obesity epidemic. Children are more apt to watch television, play video games, or surf the internet than they are to go out for a walk or to play a game of basketball. As a result, what activity children do get is not in the ideal intensity range, nor does it typically meet duration recommendations. Results from the Youth Risk Behavioral Surveillance System showed that a good percentage of students are not meeting guidelines for physical activity (at least 60 minutes of moderate to vigorous activity with at least half of it focusing on vigorous activity).[30] Figures 4 and 5 exhibit percentages of students not meeting minimum requirements for vigorous physical activity.

SCHOOL PHYSICAL EDUCATION PROGRAMS

As childhood activity declines, one would think that the schools and communities would work hand-inhand to keep physical education and after-school programs in the school. It is thought that at least 97 percent of children can be exposed to physical activity guidelines and lifestyle changes through physical education.[25] However, because of budget cuts and staffing issues, physical education enrollment has decreased from 42 percent in 1991 to 25 percent in 1995; physical education enrollment declined slightly from 32 percent in 2001 to 28 percent in 2003.[32]

While allowing our children to have access to physical education on a daily basis is a start, the types of physical education classes included is of particular interest. To optimize physical activity and its potential benefits in an allotted slot of time, the class size should be decreased to half (~15 students) of what it normally is (35–40 students).

Skipping the change of clothes and instructions means less time for idling and allows for more time to be spent on activity.[33] Incorporating a lifestyle focus in the physical education class will allow students to carry over what they learn in class to everyday life. Developing an individualized curriculum for each grade will allow age-appropriate skill activities to be taught and thus be at the point where an optimal amount of participation can occur. While the emphasis is on skill, there should be a de-emphasis on competitive sport so as to get more students involved during class time and increase the effectiveness of the physical education program. These slight changes in a physical education program have resulted in a decrease in body fat percentage and improvements in cardiovascular fitness and fasting insulin levels.[33]

EXERCISE PRESCRIPTION GUIDELINES FOR THE OBESE CHILD

Obese children have to work harder than normal-weight children to accomplish the same task and thus need adjusted workloads. Workloads should be based on time rather than distance. All children do not and should not have to do the same workload. It is unreasonable to expect obese children to be capable of workloads similar to those of lean youngsters. An exercise program for obese children should be designed to increase caloric expenditure rather than to improve cardiovascular fitness. The intensity of the activity should be secondary to the amount of time the child is involved in some type of moderate activity.

TYPE OF ACTIVITY

One of the most important considerations when developing a physical activity program for an obese or overweight child is the type (mode) of activity prescribed. The type of activity is critical, particularly with respect to minimizing the risks of injury and maximizing energy expenditure, but it can also serve as the cornerstone of a potentially successful program.

The type of activity with which an overweight or obese child should initiate a physical activity program is dependent on several factors, including his or her medical history (as co-existing medical conditions can affect the physical activity prescription), level of fitness, past experiences with activity, and the child’s interests and needs.

Walking, although challenging for the morbidly obese child, can be implemented into virtually every child’s daily routine. It is weightbearing, which maximizes energy expenditure; and it is a familiar form of activity, thereby minimizing the chances of injury. Initially, the emphasis should simply be placed on incorporating walking into a child’s daily activities, whether it be a prescribed amount of time daily or simply increasing the amount of walking each day at home. As the child becomes stronger and more confident and capable in his or her abilities, a specific walking or activity program can be prescribed. Once this point has been reached, additional considerations must be made when developing the program, including the frequency, intensity, and duration of the activity to be prescribed.

ACTIVITY FREQUENCY

The overall objective when developing an activity program for an overweight or obese child is to set the individual up for success rather than failure. Prescribing too much activity too soon will surely lead the child to experience frustration and failure. Again, the objective is to incorporate regular, daily activity into their lives to increase their daily energy expenditure. In developing such a program, the frequency of activity must carefully be considered. The Surgeon General recommends that children engage in regular activity on most, if not every, day of the week.[25]

However, for the obese and overweight child, this is very likely to be an unrealistic starting point. Again, the objective is to instill positive activity habits through positive reinforcement. Hence, one must be realistic when prescribing the frequency of activity, starting more slowly with 3 to 5 times per week and building from there. Adopting and reiterating the philosophy that some (activity) is better than none will help to instill positive activity behaviors and associations. Once the frequency of activity can realistically be established, the intensity of the activity should then be considered.

ACTIVITY INTENSITY

The intensity of the activity performed must also be carefully considered and prescribed. An obese or overweight child will reach his or her prescribed level of intensity much more quickly than a normal weight person simply because of the burden of the extra weight they carry. Once again, prescribing too much too soon will likely set the child up for failure, while also placing them at greater risk for injury. More importantly, it is the total energy expenditure (calories burned), rather than the specific intensity of the activity, that should be emphasized. For example, walking one mile will expend the same number of calories as will running one mile, although one takes longer than the other. For this reason, the intensity of the activity should be low and gradually increased as the program progresses.[34]

There are several methods to consider when recommending and monitoring the intensity of an activity, but the most practical approach to prescribing intensity is via use of perceived exertion. The rating of perceived exertion (RPE)—the intensity of the activity prescribed based on a child’s “perceived” level of exertion—is an easier way for children to monitor their intensity of activity. Not only is the use of RPE easier to incorporate and monitor, but research has found that RPE is correlated to physiological parameters, such as heart rate and oxygen uptake.[35] The recommended RPE zone in which children should be encouraged to be active is between 11 and 13.

Although using the RPE scale can be effective in prescribing intensity of activity, when working with the obese and overweight children, particularly at the beginning phases of the activity program, it is important to begin the exercise program slowly so as to avoid injury. Having this in mind, the focus should be placed on low-to-moderate intensity-type activities. There are a number of obese children in whom the intensity will not be significant enough to improve their cardiovascular fitness level. Yet weight loss and caloric expenditure should be the initial focus, and for that reason, the duration rather than the intensity of the activity should be the starting point of any and all activities. Higher intensity activities should be promoted as the patient improves and progresses through exercise on a regular basis. (Donnelly JE, in press)

ACTIVITY DURATION

The duration of activity, or amount of time per activity session prescribed, is the second most critical component for the obese and overweight child’s activity program. As mentioned previously, the Surgeon General recommends that children should attain at least 30 to 60 minutes of daily activity on all or most days of the week.[25]

The objective is to instill positive activity behaviors with positive reinforcement. Asking a child who carries an extra 80 to 100 pounds to walk for 30 minutes nearly every day is simply unrealistic.

The old school of thought used to be that the activity needed to be continuous (i.e., one 30–45 minute session) to reap the benefits of the exercise. However, research has shown that shorter, more frequent bouts of activity are just as effective.[36] For the obese or overweight child, this is ideal, as one can prescribe a program with a goal of 20 minutes per day and slowly increase the duration of exercise until 60 minutes has been reached. Notably, this activity can be broken up into several 10-minute bouts with the same activity benefits gained. Furthermore, not only are these shorter bouts more attainable, but they can also be broken down into shorter increments as needed (and increased as the patient becomes stronger, more fit, and more confident and capable in abilities). These shorter bouts can also be incorporated into their daily lives with minimal inconvenience. The key is to prescribe a duration that is realistic and attainable for the overweight or obese child.

MEDICAL CONCERNS DURING EXERCISE FOR THE OBESE CHILD

Special considerations to be made for the obese child/adolescent include maintaining a balance between intensity and duration to promote higher total caloric expenditure. There is also the chance of an increased risk in orthopedic injury secondary to the child/adolescent carrying extra weight. Consequently, initial intensity may need to be kept at a lower level than what is ideal to promote cardiorespiratory fitness. Non-weightbearing activities would be ideal for the obese patient, particularly for those with Blount’s disease and those with a history of slipped capital epiphyses. Secondary to pre-existing respiratory problems, obese subjects may experience more severe dyspnea upon exertion. Balance and anxiety problems may also exist and, consequently, it is of the utmost importance to initially supervise obese patients and offer them encouragement to increase compliance as they begin to implement physical activity into their daily routine. Obese subjects tend to have difficulty in regulating temperature, which raises the concern for hyperthermia during exercise. Adequate hydration is also necessary to ensure proper electrolyte balance is maintained.[38] Due to the potential for subjects to be largely overweight or obese, some modifications to equipment may be necessary. Larger seats for bikes, rowers, and treadmills built for heavier people are an absolute necessity for fitness centers that will be working with overweight children/adolescents.[39] Obese subjects are likely to present with severe motivational problems, which means the fitness staff should be prepared to deal with these appropriately and be ready to offer suggestions to overcome the many excuses/obstacles that may come up.[2] Activities should be consistent with the patient’s interests so that adherence is strengthened, further increasing the chances of success.

SUMMARY

Physical inactivity is one of the leading contributing factors toward the development of childhood obesity. The answer to this problem of physical inactivity is to decrease sedentary behaviors and increase physical activity. Because it would be unreasonable to expect obese children to work at the same workload as lean children, obese children require an exercise program specifically designed for them. An exercise program for obese children should be designed to increase caloric expenditure rather than to improve cardiovascular fitness. The intensity of the activity should be secondary to the amount of time the child is involved in some type of moderate activity. Therefore, the workloads should be based on time rather than distance. The benefits of regular physical activity remain only as long as the child continues to exercise; therefore, lifetime physical activity is the ultimate goal.

ACKNOWLEDGMENTS

Special thanks to Tracey Fegan, a graduate assistant, for her contributions to this paper.

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