Sports Medicine

, Volume 37, Issue 6, pp 533–545

The Contribution of Physical Activity and Sedentary Behaviours to the Growth and Development of Children and Adolescents

Implications for Overweight and Obesity

Authors

  • Andrew P. Hills
    • School of Human Movement Studies, Institute of Health & Biomedical InnovationQueensland University of Technology
    • School of Human Movement Studies, Institute of Health & Biomedical InnovationQueensland University of Technology
    • Biopsychology Group, Institute of Psychological SciencesUniversity of Leeds
  • Timothy P. Armstrong
    • Department of Chronic Diseases & Health Promotion, Surveillance and Population-Based Primary Prevention of Chronic DiseasesWorld Health Organization
Review Article

DOI: 10.2165/00007256-200737060-00006

Cite this article as:
Hills, A.P., King, N.A. & Armstrong, T.P. Sports Med (2007) 37: 533. doi:10.2165/00007256-200737060-00006

Abstract

The obesity epidemic is a global trend and is of particular concern in children. Recent reports have highlighted the severity of obesity in children by suggesting: “today’s generation of children will be the first for over a century for whom life expectancy falls.” This review assesses the evidence that identifies the important role of physical activity in the growth, development and physical health of young people, owing to its numerous physical and psychological health benefits. Key issues, such as “does a sedentary lifestyle automatically lead to obesity” and “are levels of physical activity in today’s children less than physical activity levels in children from previous generations?”, are also discussed.

Today’s environment enforces an inactive lifestyle that is likely to contribute to a positive energy balance and childhood obesity. Whether a child or adolescent, the evidence is conclusive that physical activity is conducive to a healthy lifestyle and prevention of disease. Habitual physical activity established during the early years may provide the greatest likelihood of impact on mortality and longevity. It is evident that environmental factors need to change if physical activity strategies are to have a significant impact on increasing habitual physical activity levels in children and adolescents. There is also a need for more evidence-based physical activity guidelines for children of all ages. Efforts should be concentrated on facilitating an active lifestyle for children in an attempt to put a stop to the increasing prevalence of obese children.

The value of physical activity to normal growth and development, including the health and well-being of children and adolescents is undisputed.[14] This includes the concept that humans have an evolutionary-derived and genetically-primed need for regular physical activity to maintain optimal metabolic function[3,5,6] and to prevent chronic disease and death.[7]

It is logical that at the extremes, under- (hypo) and over- (hyper) activity could be harmful to the growing child. Physical activity is one of a number of factors that influence the growth and development of children and adolescents. During the formative years, changes in health and motor-related fitness are influenced by growth and maturation. It is difficult to isolate the specific effects of regular physical activity on health and fitness status from the inherent adjustments in growth and development during childhood and adolescence.[8] When assessing habitual physical activity and associated activity interventions in children, caution is required; the normal development of height and weight of children should not be jeopardised.[9] During childhood and adolescence, nutrition and physical activity influence the growth and development of numerous body tissues, including body fat, skeletal muscle tissue and bone.[10] It is important to bear in mind that growth and maturation will continue even when physical activity is limited,[11] whereas appropriate nutrition (ideally in combination with physical activity) is essential for optimal growth and development. Children who experience appropriate nutrition and regular physical activity during the growing years may be expected to display healthy patterns of physical maturation consistent with their genetic potential. Unfortunately, the opportunity for many youngsters to be physically active has reduced over time - probably due to a series of changing environmental factors. The environment exerts a strong influence on physical activity.[12]

Physical activity and food are basic needs for survival; however, cultural changes in many parts of the world have ‘engineered’ spontaneous physical activity out of the daily lives of many.[3] Reduced activity and concomitant poor food choice contribute to an increase in overweight and obesity, particularly in the developed world. A recent phenomenon in developing countries is the combination of underweight children and overweight adults, frequently coexisting in the same family.[13]

Despite gaps in the knowledge and understanding of the specific effect of regular physical activity in children and the longer term impact on adult chronic disease, there is a general consensus that long term benefits to health, in respect to desirable body composition, require the incorporation of habitual physical activity from an early age.[14] The progressive introduction of habitual physical inactivity into daily living has been a major contributor to chronic health conditions.[3,15] Potential benefits of physical activity must be considered on the basis of the age at which regular activity commences and the nature of the physical activity experience. Desirable patterns of habitual physical activity, if established during the early years of life and sustained across the lifespan, may provide the greatest likelihood of impact on mortality and longevity.[16] Chakravarthy and Booth[3,17] have hypothesised that there is a threshold of physical activity (for optimal expression of inherited genes and genotypes) and falling below this threshold has been defined as ‘physical activity deficiency’. The manifestation of this concept, ‘sedentary death syndrome’, contributes to a significant public health burden associated with chronic disease and premature death.[18] Olshansky et al.[19] have recently provided a profound summary of the consequences of obesity by suggesting that “unless effective population-level interventions to reduce obesity are developed, the steady rise in life expectancy observed in the modern era may soon come to an end and the youth of today may, on average, live less healthy and possibly even shorter lives than their parents.” In addition, one of the key conclusions from the recent UK Health Committee on Obesity Report[20] was that “...today’s generation of children will be the first for over a century for whom life expectancy falls.” Therefore, it is of little surprise that the combined benefits of adequate physical activity and sound nutritional practices have been regularly cited as public health’s “best buy.”[21]

The main aim of this article is to highlight the important role of physical activity in the growth, development and physical health of young people. In addition, it aims to provide a balanced review of the evidence assessing physical activity levels in children and whether this contributes to the increasing prevalence of obesity.

1. Measurement of Physical Activity

The measurement of physical activity in children and adults inherently involves methodological and validity problems. However, measurement problems are augmented in paediatric research. A range of subjective (e.g. activity diaries) and objective (e.g. doubly-labelled water) techniques are available – each with their relative strengths and limitations (detailed reviews are available in the literature[2224]). Inconsistencies in the relationship between habitual physical activity and cardiovascular disease risk factors in younger children[25] can be attributed to the variation in methods used to measure physical activity.[26] In young children, direct observation is the primary form of assessment of physical activity. McKenzie et al.[27] and Elder et al.[28] utilised the Behaviours of Eating and Activity for Children Health Evaluation System, which characterises the child’s physical activity level, physical environment and social environment (presence of others and prompts or consequences for physical activity). DuRant et al.[25] utilised the Children’s Activity Rating Scale, which identifies types of activities and intensities of those activities. The work of Pellegrini and Smith[29] also relied heavily on observational periods that allow classification of the types of activities that young children engage in.

The gold standard for measuring total energy expenditure is doubly-labelled water.[30] This technique provides an accurate measure of daily energy expenditure in the free-living environment and allows the energy cost of activity to be calculated if resting metabolic rate is known. The introduction of motion sensors (e.g. pedometers and accelerometers) provides a relatively inexpensive alternative to objectively measure physical activity levels of children. In most cases, motion sensors provide frequency, duration and intensity of physical activity. Heart rate monitors provide a continuous physiological response to physical activity; however, the validity of this technique is reduced at lower levels of physical activity.[25] New variations on existing techniques are continuously being developed in an attempt to improve the range of techniques available.[31,32] For a more extensive review of measurement and validity issues related to physical activity in children, see Livingstone et al.[22]

2. Physical Activity During the Growing Years

Physical activity is particularly important for the physical health of young people and should be a normal part of growth and development.[33,34] Regular weight-bearing activity: (i) contributes to the growth and maintenance of a healthy musculoskeletal system; (ii) helps maintain a desirable body composition by controlling weight and minimising body fat; and (iii) helps to prevent and reduce high blood pressure.[35] In addition to the physical benefits, participation in physical activity plays a key part in the social and mental development of young children.[34] In recent years, the psychosocial benefits of physical activity have been highlighted, including a reduction in the symptoms of depression and possibly stress and anxiety,[36] and improvements in self-confidence, self-esteem, energy levels, sleep quality and the ability to concentrate.[37]

There are a number of key periods and points of transition during childhood and adolescence where additional emphasis on the role of physical activity may be important.[8] These include the early childhood years, the commencement of formal schooling, the transition from primary or elementary school to high school[38] and, finally, between high school and higher education or the workforce.[39,40] These critical points may be times when the physical activity patterns of some young people change considerably and when they may not be sufficiently physically active to gain a health benefit.[41] Insufficient levels of physical activity at any stage during the growing years, but particularly during these key periods of transition, are major contributing factors to overweight and obesity.

Although few would contest the position that physical activity is a healthy behaviour, very little direct evidence exists that demonstrate the health benefits of physical activity in children. It is logical that an association is more difficult to demonstrate in children because the negative health outcomes (with the exception of obesity and possibly type 2 diabetes mellitus) are less prevalent during childhood compared with adulthood – hence, there are fewer detectable markers of disease.[42] Therefore, due to the lack of direct, convincing evidence, qualitative recommendations, such as ‘desirable’, have been used for the promotion of physical activity in children.[43]

Participation in sport is a positive way to encourage children to be physically active. However, for some, the cost of equipment and uniforms can be an impediment. Additionally, if children are already overweight, they may feel uncomfortable or incapable of participating in sport if the focus is more on achievement rather than participation and having fun.[44] Finally, as is the case for nutrition and appropriate eating behaviour, children may not be inclined to participate in physical activity if their parents are not modelling active lifestyle behaviours themselves.[45] Again, parents may find it difficult to engage in active play with their children due to increased demands on their time, or because of poor health or disability.

3. Physical Activity During the Early Childhood Years

Despite the well documented benefits of physical activity to health, fitness, and normal growth and development in adults,[35] there is a paucity of information regarding the interrelationship between habitual physical activity, physical fitness and health status in children of preschool age. A combination of sound nutritional practices and adequate physical activity for all young people represents a cost-effective option to reduce the risk or prevent obesity and other chronic diseases.[10] Regular physical activity and appropriate eating behaviours should be employed from birth. This requires a consolidated approach from all sectors, but particularly health professionals, teachers and parents, to influence the knowledge, attitudes and behaviours of young people. Part of this process is for all concerned to have an appreciation of the normal individual variability in physical growth during infancy, childhood and adolescence, particularly in relation to body size, shape and composition.[46] Very young children are dependent on responsible adults to provide guidance, to act as role models for acceptable behaviour and to be conscious of special needs. Therefore, adults need to be made aware of the importance of enjoyment and safety in physical activity and appreciate the central place that activity should take in the growth and development of a child. Shared environmental factors have been shown to have a powerful influence on children’s physical activity.[45,47] There is also evidence to support a genetic or familial aggregation of physical activity.[48] Therefore, parents’ attitudes, encouraging family-based activity and providing opportunities in the environment to facilitate activity should be targeted when considering interventions in children.[49]

The first years of life represent an intense period of motor learning that provides the foundation for later, more complex and skilled performance. In later years (5–8 years of age), an active lifestyle is associated with improved motor skills and development.[50] The development of the fundamental movement patterns of crawling, standing, walking, running and jumping in younger children is fostered by the opportunity to play. However, without this opportunity, habitual physical activity could be jeopardised and, as a result, a lowering of energy expenditure (and potentially weight gain) could occur.[51] Young children need to explore their environment through movement and experiment with the movement capabilities of their bodies. They have both a desire and need to engage in progressively more vigorous and physically challenging activities. Whether this behaviour is biologically programmed[52] or random is unknown.

Pellegrini and Smith[29] identified three different types of physical activity play that occur during early childhood and ascribed general age trends to these behaviours. During infancy, ‘rhythmic stereotypes’ is the term assigned to activities that involve gross motor movements that are difficult to ascribe a goal or purpose to, for example, foot kicking or body rocking. These behaviours peak during the mid-point of the first year of life. At 6 months of age, some infants spent ≈40% of the observational period of the study in stereotypic behaviour. At the start of the second year of life, children become involved in ‘exercise play’, defined as gross motor movements in the context of play. The characteristic feature of this play is physical vigour. This type of play may or may not occur in a social context and increases from toddler age onwards and peaks during the preschool period (4–5 years of age) and then declines during the primary school years. At ≊4 years of age, 20% of children’s activity is characterised as physically vigorous.

Early childhood is also a time when socialisation becomes important and behavioural norms are established with a strong dependence on responsible adults. Particularly in relation to movement and physical activity, there is an increasing reliance on parents as the child moves from a self-centred focus to actively seeking assistance then approval from others in relation to physical performance. ‘Rough and tumble play’ is the third type of physical activity play identified by Pellegrini and Smith.[29] Rough and tumble play refers to vigorous behaviours such as wrestling, kicking and tumbling. This type of play is essentially a social behaviour, with the earliest cases often supported by a parent. At 4 years of age, this type of play accounts for ≈8% of observed child-parent behaviour and ≈3–5% of play behaviour in preschool children. This type of play peaks at around 8–10 years of age.

Individual differences in growth and development contribute to variability in the attainment of motor milestones, physical maturational status and the appearance of specific characteristics in young children such as an awareness of the rewards of physical activity, experiencing self-esteem and self-confidence, and feelings of mastery and competence. Through movement, a child receives and acts upon sensory information from external stimuli through visual, tactile and auditory mechanisms, and internally from vestibular and kinesthetic receptors. Gallahue[53] has suggested that young children engage in movement activities that may be categorised as tasks of ‘learning to move’ and ‘learning through movement’. Both of these activities play important roles in the overall growth and development of children.

McKenzie et al.[27] found that 4-year-old children were sedentary (lying down, sitting and standing) during 58.9% of the observed 26-minute recess period, whilst 41.1% of the time was classified as moderate to vigorous physical activity. Elder et al.[28] found that over a 2-year period, parental and peer prompts (measured over a 1-hour period) to be physically active decreased by more than one and a half times, especially for children who were already sedentary. Compliance with physical activity prompts increased over the 2-year period.

The early establishment of appropriate lifestyle practices is critical for young children. Sedentary behaviours in children can be reinforcing, which are more likely to facilitate a habitually sedentary lifestyle in later years.[54] Encouragement for physical activity, however, must be paralleled with opportunity. It is not sufficient to suggest that physical activity is desirable if changes are not made to one’s environment in order to support the incorporation of activity. The opposing forces of the changing environment are continually reducing such opportunities, thus making encouragement more of a futile challenge. Unless interventions are introduced that eradicate the environmental barriers to facilitate and promote an active lifestyle, the problem is going to get worse.[55] However, there is some evidence to suggest that even when opportunity and choice (sedentary vs active) are provided, children elect to be sedentary.[56] Physical activity experiences need to be positive and conducted in a manner that fosters fun and enjoyment, capitalising on the spontaneity and pleasure in movement that are hallmarks of most young children.[57] To establish habitual physical activity for the longer term, each child must experience a measure of success in the activity setting, as poor experiences may be associated with diminished levels of participation and perpetuate any weight problem that might exist.[58] Many children are not given the opportunity to be sufficiently active to establish a sound motor-skill base. A good level of motor skill is necessary to broaden activity opportunities, although this should not be confused with a high level of proficiency. Competency in the activity domain is one of the factors likely to have a bearing upon participation levels in later years.[59] Improving self-efficacy, enjoyment and all-round competence related to physical activity and knowledge of healthy eating habits are associated with beneficial effects of exercise and diet interventions in children.[60,61] A reasonable standard of competency, along with knowledge and understanding of the health benefits of physical activity should assist informed decision making.[44]

To achieve the goals mentioned in this section and prevent obesity in young people requires far more than the current ad hoc approach. Numerous multi-level strategies are required to maximise the impact of intervention work to address the level of inactivity and prevent or reduce undesirable weight gain in young people.[20,62] All young children should be provided with a wide range of movement experiences from birth to harness their natural enjoyment and spontaneity. Quality activity programmes and physical education curriculum are necessary to encourage the development of health and motor-related fitness in all young children.[34]

4. Physical Activity During Childhood and Adolescence

The gradual decline in physical activity between childhood and adolescence is a robust epidemiological phenomenon.[38] Social, environmental and biological factors are likely to contribute to such a marked trend. Participation in school-based activities, sport clubs and general ‘play’ will be most prevalent during childhood. As a child enters adolescence, physical activity and exercise become less of a priority and is displaced by other behaviours and interests. Participation in physical activity during childhood could have important implications for adulthood. Although the evidence is limited, it has been shown that physical activity in childhood can predict participation in activity during adulthood.[6365] In contrast, there is also evidence to suggest weak associations.[66,67]

Children spend a majority of their waking day at school, hence, it is during this window of opportunity that physical activity could be influenced the most. The combination of breaktimes and physical education classes should provide the opportunity to significantly contribute to overall daily activity and energy expenditure. However, children will also spend a large amount of time seated during study and education classes at school. With a trend towards less time for physical education and sport participation in the schools,[68] the amount of time spent sedentary at school will gradually increase. The net impact of physical education classes on total daily energy expenditure has been questioned.[69] Indeed, one study demonstrated that physical activity was independent of the amount of curriculum-based physical education.[70] That is, children who attended schools with more time allocated to curriculum-based physical education classes had similar levels of total net daily physical activity compared with children who spent less time doing physical education classes. These results need to be considered in the context of the quality of the physical education experience. More specifically, time in physical education classes does not necessarily equate with time spent in activity per se. Greater attention needs to be given to ‘active’ physical education where time on the physical activity task is maximised.

5. Physical Activity and Musculoskeletal Health

The foundation for longer term skeletal health is established during childhood and adolescence. Physical activity represents a major mechanical loading factor for bone through a combination of growth (determining bone size), modelling (determining the shape of bone) and remodelling (maintaining the functional competence of bone).[71] Peak bone mass and density is achieved in early adulthood [72] and this serves as a ‘bone-bank’ for the remainder of adult life.[73]

Childhood and adolescence are commonly dynamic periods for skeletal growth and development, including deposition of bone mineral. In healthy children and adolescents, the tempo of bone mineral acquisition largely parallels the pattern of linear growth, increasing rapidly during infancy, more gradually throughout childhood and accelerating again at puberty. Gains in bone mineral and the ability of bone to adapt to mechanical loading are much greater at or before puberty than after physical maturation.[74,75] Under normal conditions of growth and development approximately half of the peak bone mass is gained during the adolescent period.

The amount of bone deposited by early adulthood is largely determined by genetic factors, but environmental factors, such as diet and physical activity, account for 20–40% of the variability in peak bone mass.[76] The achievement of one’s genetic potential for peak bone mass is only possible when environmental factors are favourable; however, there is a poor understanding of the type, intensity, duration and frequency of exercise that will optimise bone mineral accumulation. Similarly, both the chronological age at which exercise would be most crucial and the extent to which physical activity can modify the development of bone is unclear.[77,78] Children and adolescents who are overweight or obese may be vulnerable with respect to skeletal health as they commonly have marginal nutrition and are sedentary, which are the most common risk factors for low bone mineral.

The importance of physical activity to skeletal health must also be considered in concert with the ingestion of calcium. Interestingly, the beneficial effects of physical activity are only noted when calcium[79] or circulating sex steroids[80] are adequate. Exercise has been described as a double-edged sword in relation to skeletal health. Immobility results in bone loss while moderate weight-bearing activity has been correlated with increased bone mineral in children and young adults.[75] Moderate levels of activity do not usually cause problems; however, at the other end of the physical activity/exercise continuum, high levels of more intense training may create conditions in which the susceptibility of injury increases,[4] along with the risk of osteopaenia and bone fracture.[81,82]

6. Sedentary Behaviours and Obesity

When considering the relationship between habitually activity, sedentary behaviours and obesity in children, the following two issues need to be addressed: (i) does a sedentary lifestyle automatically lead to weight gain and obesity? and (ii) how do current levels of physical activity compare with physical activity recommendations, and are current levels of physical activity low compared with previous generations?

6.1 Does a Sedentary Lifestyle Automatically Lead to Weight Gain?

The principle of energy balance is simple; if energy intake (EI) exceeds energy expenditure (EE), a positive energy balance occurs, which if it persists will automatically lead to weight gain. However, understanding the underlying factors and mechanisms that contribute to a low EE and high EI is more complex. A combination of environmental pressures, technological factors and societal transitions from childhood to adolescence are likely to promote sedentary behaviour, which could potentially lead to weight gain.[83] As a result of the cause-effect problem and methodological flaws in measuring physical activity per se, proving a direct link between a sedentary lifestyle and weight gain is difficult. In adults, there is convincing evidence to show that a sedentary lifestyle is associated with debilitative lipoprotein regulation,[84] and a greater risk of cardiovascular disease and mortality in adults.[85] The evidence for a causal link between sedentariness and obesity in adults is weaker.[86,87] However, there is some evidence to demonstrate that sedentary behaviours are associated with overweight and obesity in children.[22,88] For example, television viewing is associated with lower habitual physical activity and cardiorespiratory fitness,[89,90] and increased obesity.[91,92] In contrast, it has been proposed that sedentary and active behaviours can co-exist,[43] and that one type of behaviour does not automatically displace the other. For example, it is possible for children to combine physically active behaviours (e.g. participate in sport and exercise) with sedentary behaviours (e.g. computer games, watching television) within the same day. In essence, the most important issue is that EE is equal to EI. Despite this, there is some controversy over the true, direct effect of sedentary behaviours on weight gain and obesity in children.[43] It is intuitive that sedentary behaviours should be limited because of their contribution to a reduction in EE and promotion of a positive energy balance. One of the key features of sedentary behaviours is that they typically co-exist with eating, which, in turn, could augment the obesity epidemic.[93] Recent evidence supports this phenomenon by demonstrating that sedentary behaviours are associated with a higher snack intake in children and adolescents.[94]

6.2 Current Physical Activity Levels

There is a trend for sedentary lifestyles across most of the developed world.[95] Children are at risk as a result of their susceptibility to a technologically changing environment and issues concerning their perceived safety. A possible implication of a more safety-conscious culture is that parents are increasingly protective of their children during transport to school and playing outdoors compared with previous generations of parents. However, suggestions of an increased danger to children are not evidence-based and could be as a result of parents’ misperceptions. Despite this, Harten and Olds[96] have reported that active transport levels of Australian children are very low. In addition, children are gaining little benefit from incidental exercise with the widespread use of labour-saving devices. Changes in children’s entertainment choices have also contributed to an increase in sedentary behaviour. Playing console and computer games and watching television and DVDs/videos are very popular leisure pursuits among children.[97] Coupled with unprecedented access to the internet and mobile phones, children need not even leave home to maintain contact with their friends outside school hours. As a result, there is speculation that activities undertaken by children are predominantly sedentary in nature and involve minimal EE.

Due to a lack of comparable data, it is difficult to demonstrate that the level of physical activity (and EE) in today’s children is low compared with their counterparts several decades ago. However, this is an area that has attracted some controversy because of the lack of a ‘benchmark’ of physical activity with which to compare current levels.[98,99] Most of the evidence comes from indirect, surrogate measures,[100] for example, walking and cycling to school being replaced by the car.[96,101] However, there is some evidence that, similar to adults, many children do not participate in appropriate levels of physical activity[62,102105] and that activity levels are lower than recommended.[106] Indeed, Salbe et al.[106] demonstrated that 5-year-old white and Pima Indian children had a physical activity level (PAL) [PAL = EE/basal metabolic rate] of 1.35, which is significantly lower than the WHO recommendations of 1.7–2.0 for children aged 4–6 years. The indications are that for today’s children, physical activity levels are low and, more importantly, progressively decreasing. If this behavioural trend occurs in synergy with an increase in EI, levels of overweight and obesity will escalate.[58,107,108]

7. Implications for Physical Activity Recommendations and Guidelines for Children and Adolescents. Recommendations for Children: What is the Evidence?

Recommendations about physical activity and healthy lifestyle are continually being made, for example, “…when daily physical activity of 1 hour is performed in combination with a natural food diet, high in fibre-containing fruits, vegetables and whole grains, and naturally low in fat, containing abundant amounts of vitamins and minerals, and phytochemicals, the vast majority of chronic diseases may be prevented.”[109] Despite the well established and uncontested health benefits associated with physical activity,[110] and the increasing epidemic of obesity, relatively less attention is paid to generating evidence-based knowledge to formulate physical activity recommendations and guidelines for children.[111] However, a recent review contributed significantly to the understanding of the effects of regular physical activity on health in children.[88] In addition to providing support for the beneficial effects of physical activity on a wide range of health outcomes in children, Strong et al.[88] recommended a minimum of 1 hour/day of moderate to vigorous activity. This is similar to other recommendations concerning physical activity in children.[112115] Making recommendations is relatively easy – achieving the recommendations is the most challenging task. To make the situation more complicated, there is also the issue of differentiating between the health benefits of activity when making physical activity recommendations. For example, should the recommendations be the same for cardiovascular-related and bodyweight (prevention or treatment of weight gain) benefits?[116] It is only recently that recommendations for adults have differentiated between these two activity-related health benefits.[117] Most physical activity recommendations are too general and do not take into consideration factors such as body mass index.[118,119] For children, it is not necessary or pragmatic to complicate the situation further by differentiating between the different health benefits. Any significant increase in physical activity would be a positive outcome. In very young children, the promotion of physical activity could be more successful by encouraging play rather than focusing on the physical health benefits.[120] Recommendations should target parents and schools by encouraging physical activity and incorporating activity into the habitual lifestyle.[37] Such approaches should be widespread and form the foundation upon which more definitive guidelines are based as evidence becomes available.

8. Preventing a Worsening of the Situation

The most important and immediate action required is to prevent the obesity problem getting worse. A wholesale reduction in obesity (i.e. via treatment) is an almost impossible task. Therefore, efforts should be concentrated on facilitating an active lifestyle for children in an attempt to put a stop to the increasing prevalence of obese children.[50] Although it can be considered as simplistic and vague, one approach is to recommend reducing the proportion of sedentary to active behaviours,[62] rather than quantifying specific amounts of physical activity (periodicity, intensity, duration). In theory, by limiting sedentary behaviour, physical activity should automatically increase; the activity does not necessarily have to be structured or prescribed sessions of exercise.[121,122] Therefore, it may be more useful to make recommendations about limiting sedentary behaviours rather than targeting a threshold of physical activity (e.g. 1 hour/day). Of course, this is not simple to achieve given the continuing environmental pressures that promote and facilitate a sedentary lifestyle. Therefore, environmental factors need to change if physical activity strategies and interventions are going to be successful.[123] Targeting transport policies[37,124,125] and replacing car travel to and from school with walking and cycling[126] are a few examples of suggestions for interventions that could significantly contribute to increasing physical activity.

If incidental activity of children is decreasing, the participation in structured physical activity becomes even more important in the maintenance of a healthy weight and body composition. In turn, a major determinant of participation in structured physical activity is the availability of public facilities, such as playgrounds, bike paths, parks and so on, and whether this physical environment is conducive to exercise by children.[43] The lack of suitable physical infrastructure or the perception that a physical space is unsafe, actively discourages parents and children alike. Evidence suggests that physical activity interventions in children, which incorporate whole-school approaches (e.g. curriculum, policy and environmental strategies), prove to be more effective.[127] In their excellent overview of the evidence, Smith and Bird[125] make the following conclusions about the current situation regarding the effectiveness of evidence-based physical activity recommendations:
  • Evidence-based practice needs to progress to evidence-based policy.

  • It is a political issue at national and local level.

  • Transport rather than health policy should be the focus.

  • Young people deserve our attention.

9. Conclusions

Although there is not a plethora of empirical evidence on which to base physical activity guidelines for children and adolescents, a physically active lifestyle, whether as a child or adolescent, is conducive to a healthy lifestyle and preventing disease. A sedentary lifestyle is associated with chronic disease and ill health. The message is clear and simple – reduce sedentary behaviours. In reality, the situation is more complex. Physical activity is influenced by a range of factors, the environment being the most potent and influential. The focus should be to prevent the obesity epidemic getting worse. Targeting children is a starting point. The treatment of obesity in children using dietary and physical activity intervention is not efficient.[128] Preventing more children becoming obese, which, in turn, will prevent them becoming obese adults, should be the focus of future interventions. To maximise impact, physical activity interventions should focus on environmental and policy changes in children and adolescents.[129]

Acknowledgements

No sources of funding were used to assist in the preparation of this review. The authors have no conflicts of interest that are directly relevant to the content of this review.

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© Adis Data Information BV 2007