Behavior change stages related to physical activity in adolescents

Abstracts

Estudos relacionados ao comportamento quanto à prática de atividades físicas vêm despertando interesse cada vez maior nos pesquisadores. Porém, especialmente em adolescentes ainda percebe-se grande carência de investigações com esse enfoque. O objetivo desta pesquisa do tipo descritivo analítico foi classificar a prática de atividade física segundo a teoria dos estágios de mudança de comportamento (EMC) de acordo com o sexo, série e nível socioeconômico. Os sujeitos foram adolescentes do ensino médio, da cidade do Recife-PE, com média de idade de 16,2 ± 1,1 (14 a 19 anos), selecionados por amostragem por conglomerados, totalizando 2.271 estudantes (1.022 rapazes e 1.249 moças), de 29 escolas de ensino privado. Características sociodemográficas e EMC foram levantados mediante aplicação de um questionário de auto-relato. As análises dos dados foram feitas usando a estatística descritiva, o teste do qui-quadrado, a correlação de Spearman e o teste U de Mann-Whitney (p < 0,05). Os estudantes apresentaram as seguintes características: 66,3% pertenciam à classe econômica A1 e A2, o que evidenciou o alto poder aquisitivo da amostra. No grupo estudado, 61,6% dos adolescentes foram classificados como inativos ou irregularmente ativos, e 26,2%, como sedentários (pré-contemplativos e contemplativos); na análise por sexo, os rapazes eram mais ativos fisicamente que as moças segundo os EMC agrupados. Verificou-se ainda declínio na prática de atividades físicas com o avanço na série escolar. Sugere-se a criação de intervenções nas escolas da região, com o intuito de incentivar a prática de atividades físicas, principalmente nas moças, que contemplem opções escolhidas pelos jovens, reformas estruturais para adequar horários/atividades, como formas eficazes de mudança de comportamento em relação às atividades físicas.

Escolares; Estágios de mudança; Comportamento

ORIGINAL ARTICLE

Behavior change stages related to physical activity in adolescents

Estadios de cambio de comportamiento relacionados a la actividad física en adolescentes

Gustavo de Sá e Souza^I; Maria de Fátima da Silva Duarte^II

^ISanta Catarina University - Unisul - Palhoça, SC. Physical Effort Laboratory - Unisul

^IISanta Catarina Federal University - UFSC/CDS - Florianópolis, SC. Health and Physical Activity Research Center - NuPAF

^{Correspondence}

ABSTRACT

Studies related to behavior in relation to the practice of physical exercises have attracted the attention of many researchers. However, there is still a lack of investigations on this topic especially among adolescents. The objective of this descriptive-analytical type research was to classify the practice of physical exercise according to the Behavior Change Stages (BCS) theory, according to gender, grade and socioeconomic level. The subjects were high-school adolescents from the city of Recife-PE with average age of 16.2 ± 1.1 (14 to 19 years of age) selected by conglomerate sampling totalizing 2,271 students (1,022 boys and 1,249 girls) from 29 private schools. Social-demographic and BCS characteristics were surveyed by means of the application of a self-report questionnaire. The analysis of data were conducted using the descriptive statistics, the chi-squared test, the Spearman correlation and the Mann-Whitney U test (p < 0.05). The students presented the following characteristics: 66.3% belonged to economical classes A1 and A2, what evidenced the high purchasing power of the sample. In the group studied, 61.6% of the adolescents were classified as inactive or irregularly active and 26.2% were classified as inactive (precontemplative and contemplative), and in the analysis by gender, boys were physically more active than girls according to grouped BCS. A decline on the practice of physical activities with the grade advance was also verified. The creation of interventions in schools of the region with the objective of encouraging the practice of physical activities is suggested, especially among girls, that contemplate the option selected by the students, and structural reformulations to suit schedule/activity as effective ways to change the behavior in relation to physical activities.

Key words: Schoolgirls. Schoolboys. Change stages. Behavior.

RESUMEN

Estudios relacionados al comportamiento en relación a la práctica de actividades físicas vienen despertando un interés cada vez mayor en los investigadores. Por ello, especialmente en adolescentes aún se percibe una gran carencia de investigaciones con ese enfoque. El objetivo de esta investigación, de tipo descriptivo analítico fue el de clasificar la práctica de actividad física según los Estadios de Cambios de Comportamiento (EMC) de acuerdo con el sexo, años de estudio y nivel socioeconomico. Los sujetos fueron adolescentes de enseñanza media de la ciudad de Recife-PE, con una media de edad de 16,2 ± 1,1 (14 a 19 años), seleccionados por amuestras en conglomerados, totalizando 2.271 estudiantes (1.022 jóvenes y 1.249 chicas), de 29 escuelas de enseñanza privada. Características socio-demográficas y los EMC fueron levantados mediante la aplicación de un cuestionario de auto relato. Los análisis de los datos fueron hechas usando la estadística descriptiva, el test de Qui-cuadrado, la correlación de Spearman y el test U de Mann-Whitney (p < 0,05). Los estudiantes presentaron las siguientes características: 66,3% pertenecían a la clase económica A1 y A2, lo que evidenció un alto poder adquisitivo de la muestra. En el grupo estudiado, 61,6% de los adolescentes fueron clasificados como inactivos o irregularmente activos, y 26,2% fueron clasificados como sedentarios (pre-contemplativos y contemplativos), siendo que en el análisis por sexo, los varones fueron más activos físicamente que las chicas según los EMC agrupados. Se verificó aún un descenso de actividades físicas con el avance de la serie escolar. Se sugiere la creación de intervenciones en las escuelas de la región, con el intento de incentivar la práctica de las actividades físicas principalmente en las chicas, que contemplen opciones escogidas por los jóvenes, reformas estructurales para adecuar horarios/actividades, como formas eficaces de cambio de comportamiento en relación a las actividades físicas.

Palabras-clave: Escolares. Estadios de cambio. Comportamiento.

INTRODUCTION

In the last years, studies on the physical activity area related to health have indicated life-style as one of the most important health indicatives of the population. Nahas⁽¹⁾ defines life-style as "the set of habitual actions that reflect attitudes, values and opportunities in the lives of individuals", emphasizing the wideness of the term.

Specifically among young individuals, this definition receives a particular feature, considering the complexity and variability of behaviors observed in adolescents worldwide, considering, for example, cultural, social and political differences.

A study performed in France showed that, among 15-25 year old young individuals, accidents and suicide respond for 71% of deaths causes, and in many cases, followed by psychological disturbances⁽²⁾. In Spain, one observes reduction on the number of infections and nutritional diseases and increase on the number of adolescents exposed to drugs, violence, accidents, sexually transmissible diseases, undesired pregnancy, alimentary disorders among others factors potentially preventable⁽³⁾.

In the United States, available data indicate situation similar to Spain's, with the use of drugs and alcohol and improper sexual behavior leading the causes of morbidity, mortality and social problems among young individuals⁽⁴⁾.

A healthy life-style including the regular practice of physical activities is vital, both in the prevention and in the control of some non-transmissible chronic diseases, such as the cardiovascular diseases, obesity and dyslipidemia, and in the reduction of morbidity and mortality caused by many other diseases^(5-9).

In this context, physical activity is presented as one of the main components of a healthy life-style but, unfortunately, has undergone reduction on its regular practice. The numbers relative to inactiveness obtained in a national survey in the USA in the years of 1997 and 1998 showed that approximately four out of ten American adults (38.3%) do not participate in any type of physical activity in leisure⁽⁸⁾. These data currently indicate physical inactiveness as one of the most important public health problems in that country⁽¹⁰⁾.

In countries from the European Union, a large variability on the prevalence of physical activities practiced in leisure was found, where countries such as Finland and Sweden showed prevalence slightly above 90%; on the other hand, Portugal presented the worst situation, with 40.7% of prevalence⁽¹¹⁾.

In Brazil, studies are indicating values of 60% and 67% of sedentary behavior in the Northeastern, Southern and Southeastern regions and specific populations^(12-16). In study involving adolescents from the Southern region of Brazil, Silva and Malina⁽¹⁷⁾ found results even more disappointing, once 94% of girls and 85% of boys, according to the criteria adopted, were classified as inactive.

There are evidences in literature demonstrating that habits and behaviors related to health adopted in childhood and adolescence tend to stabilize in the adult life⁽¹⁸⁾; in the adult phase, the interventions undergo more resistance and behaviors are less passible of alteration. An intense decrease on the practice of physical exercises during adolescence especially among 15-year old girls on has been observed⁽¹⁹⁾.

The increase on the number of studies on the effects of physical activity regularly practiced is not only justified by benefits scientifically verified of a healthy lifestyle, but also by inferring definitely on the quality of life of these individuals.

Despite researches involving physical activity are countless in the world literature, there is a lack of studies that identify the practice of physical activity, especially in Brazilian adolescents within the age range with several possibilities of behavior change and by representing, at least theoretically, the school age.

In the theory elaborated by Prochaska and Marcus⁽²⁰⁾, the expected behavior change follows a sequence of stages in which the individual reaches the next stage, in case the characteristics of the stage he is found are already incorporated. Chart 1 shows the behavior change stages and their respective characteristics.

The change stages model, also known as transtheoretical model, although primarily psychological, recognizes that change process specific factors, such as the perception of benefits (pro) and the barriers (against), include social and environmental factors.

Maybe considering the cognitive and behavioral processes, besides the internal and environmental factors involved in the adoption of a new behavior related to health, is the reason attributed for this model to be emphasized in the area related to health and particularly in the area involving physical activity.

Other advantage of this model lies in the fact that when an individual is classified, there are evidences of what could be the most suitable intervention for each type of behavior identified⁽²⁰⁾.

In this context, the present study searched to perform the physical activity classification according to the Behavior Change Stages theory (BCS) proposed by Prochaska and Marcus⁽²⁰⁾ in a sample of high-school adolescents from private schools of Recife, PE.

METHODS

According to Thomas and Nelson⁽²¹⁾, this is an descriptive, analytical type study. The orientations of the Ethics Committee of Researches involving Human Beings of the Santa Catarina Federal University were followed. Thus, the Consent Form was sent to all schools selected for this study and received properly signed by the data collection.

According to the last School Census, the city of Recife currently has 192 high-schools (three federal public schools, two municipal public schools, 87 state public schools and 100 private schools) (State of Pernambuco, 2002). To develop studies involving schools not always is an easy task, and one still observes that the large majority of studies involve adolescents from public schools, due to the most different and not less important reasons. These characteristics justify the selection of the private school segment, besides the fact that it represents 52.1% of the total number of schools.

A total of 93,577 registrations were performed in high-schools of the city of Recife. From this total, 28,688 registrations (approximately 33%) were performed in the 100 private schools selected. As the schools are not uniformly distributed in the two Teaching Executive Management (DEE) actuation regions (North and South), 29 schools were randomly and proportionally selected as follows: 12 schools (41%) DEE North and 17 schools (59%) DEE South using a nominal relation provided by the Department of Information and Statistics (DIE) of the Education State Ministry in order to perform the allotment⁽²²⁾. In order to estimate the size of the sample, the Barbetta⁽²³⁾ proposition was used, adopting a sampling error of 2%. Thus, 2,299 students were randomly selected and, after applying the exclusion criteria (refusal to participate and filling errors), 2,271 young individuals were totalized (1,022 boys and 1,249 girls) with age average of 16.2 ± 1.1 years.

For selection purposes, the sampling was randomly performed by conglomerate with groups as sampling units. Thus, with the objective of obtaining a sample representative of the DEE actuation region and the school grade, a sequence in two stages was determined:

1^st stage: the representativeness of the number of students of each DEE actuation region in relation to the total population was determined;

2^nd stage: the representativeness of the number of students considering the region and the high-school grade was determined.

A questionnaire composed of the identification items (age, gender and school grade), the socioeconomic level classification proposed by the National Association of Research Companies ANEP⁽²⁴⁾, and the questions with regard to the BCS, was used in the data collection. According to the literature, the BCS were grouped into three categories, where the precontemplation and contemplation stages called as inactive, the preparation stage called as irregularly active and the action and maintenance stages called as active. This instrument was constructed based on a pilot study and applied in a self-administrated way. Its quality was verified through face validity and classification concordance procedures, according to the Kappa index classification table, obtaining score of k = 0.88.

The data collecting occurred in August 2002 and the questionnaire was applied in classroom. Initially, the research objectives were presented and later the students read the instrument. A period of 45 minutes was given to students to respond the questionnaire and the researcher was always present for any explanation.

For the analysis of data, the Mann-Whitney U tests and the Spearman rank order correlation were used in the inductive and descriptive non-parametric statistical analyses, respectively. The two-way contingency tables of BCS in relation to gender and age range were also used. The statistical package SPSS version 10.0 for Windows was used for all procedures and the significance level adopted was of 5%.

RESULTS

According to the ANEP socioeconomic classification, 66.3% of adolescents were classified in categories A1 and A2. Bungum and Vincent⁽²⁵⁾ assured that the NSE may influence the number of opportunities offered to adolescents, once the wealthiest may be involved both in structured activities such as academies and clubs and in free activities in parks, neighborhood or playgrounds, while the poorest would theoretically only have the second choice.

In the BCS analysis, one observes that 38.3% of the adolescents practice regular physical activity (action and maintenance), while 35.4% practice physical activities irregularly (preparation). In this context, these findings show a value of 26.2% for inactiveness (precontemplation and contemplation). The relative numbers of inactive and irregularly active altogether reached 61.6%, too high considering the favorable climatic conditions and environment the city of Recife offers during the entire year.

Analyzing by gender, it was verified that, according to literature, boys are more active than girls, once values found in action and maintenance stages were higher (figure 1). Based on the Mann-Whitney U test, statistically significant result between the BCS classification of boys and girls was found, and the boys were in more active stages than girls (p = 0.000).

Analyzing BCS by school grade (figure 2) it was verified that in the 5^th grade, the prevalent stage was maintenance (32.8%), while in 6^th and 7^th grades, the preparation stage was the most prevalent, with 35.2% and 39.7%, respectively.

In this context, it is verified that, while in the 5^th grade, 54.3% of the adolescents are concentrated in preparation, precontemplation and contemplation stages, this percentile is of 55.8% in the 6^th grade and 76.1% in the 7^th grade, emphasizing the decline observed in the practice of physical exercises with the school grade advance, possibly due to factors such the ingress in the labor market or the study for the college entrance examinations.

Figure 3 shows the BCS prevalence grouped by chronological age. It is observed that at ages from 17 to 19 years, the highest frequency of inactive and irregularly active was found, equal to or greater than the actives.

Two distinct pictures were observed when information relative to BCS grouped by gender were analyzed, once the number of active (48.6%) exceeded the number of irregularly active (33.7%) and inactive (17.7%) among boys, while, among girls, the number of active (29.9%) was overcome both by the number of irregularly active (36.9%) and inactive (33.1%). These information are corroborated by literature, where boys are more active than girls, and that there is a general decline, regardless the gender, in the physical activity levels with the advance in age^(26,27).

From information collected, one could verify that BCS are negative and significantly correlated with chronological age (r_s = -0.129; p = 0.000), with school grade (r_s = -0.187; p = 0.000) and positively with NSE (r_s = 0.053; p = 0.012).

It is worth mentioning that the division of groups into active, irregularly active and inactive was not the same for all works found in literature, and some studies divided samples only into active and inactive, where the preparation stage is included in the first group. It must be warned that this is a discussible analysis option, once subjects found in the preparation stage, according to Prochaska and Marcus⁽²⁰⁾, still intend to change behavior in the near future or present irregular behavior and, hence, it would be more acceptable to include them in the inactive group and not otherwise.

Anyway, after the general analysis of the sample, one concludes that some information deserve emphasis, for example, the behavior of boys being differentiated from that reported by girls.

These results are in agreement with results found in literature, which indicate positive association between NSE and the increase on the physical activity level, besides the reduction on the physical activity levels with age advance^(28-31). However, the values found in the present study are too low, thus hindering any inference.

Sallis et al.⁽³²⁾ analyzed differences in the physical activity practice levels by NSE, emphasizing that the regularity of Physical Education classes in wealthier schools is higher than in schools with less financial resources, where absences of both students and teachers are frequent.

For the performance of the Mann-Whitney U test, two age range groups were formed: one group with adolescents from 14 to 16 years old and another group with adolescents from 17 to 19 years old, this way attending to the test conditions.

There is certain scientific consistence, showing that boys are more active than girls, once the difference in the physical activity practice levels between genders is the most studied socio-demographic factor⁽³²⁾.

Based on the Mann-Whitney U test, a statistically significant result between the BCS classification of boys and girls was found in the present study, and boys were found in more active stages than girls (p = 0.000) (table 1).

Table 2 shows the decline on the physical activity levels between age groups. Similar result was found in 1999 by the Risky Behavior Supervising System in Youths - US Department of Health Prevention and Control⁽⁸⁾.

Studies have pointed to a decline on the physical activity levels at the end of the adolescence⁽³³⁾. This fact may be observed, once the younger group is more active than the older one.

DISCUSSION

Despite governmental, medical and scientific community recommendations that, in order to maintain oneself healthy, the adolescents need to practice physical activities regularly, there is still a lack of epidemiological studies that investigate the middle and long-term effects of physical activity on health⁽³²⁾.

The decline observed on the number of active with ages between 15 and 16 years and the maintenance of the increasing curve of inactive and irregularly active perhaps may be explained by the great percentile of youths getting prepared for the college entrance examinations, and therefore they dedicate more hours to study in this age range. Furthermore, the Brazilian adolescent is more and more searching for work and, according to the DIEESE, Brazil figures among the countries with more working adolescents⁽³⁴⁾.

The numbers relative to BCS are corroborated with indexes found in other countries, such as the United States, that currently strongly invest in campaigns that encourage the practice of physical activities in all ages, fact not observed in our country with the same intensity.

Despite the decline on the physical activity levels along the years is a well accepted and studied phenomenon, Sallis⁽²⁶⁾ reports that this phenomenon is not yet fully understood; in other words, it is not known yet whether this decline is due to a biological or environmental phenomenon.

In longitudinal research performed in American adolescents, an intense decline on the physical activity practice levels was found, especially at the end of the adolescence, what led authors to see schools as the perfect target for the implantation of public policies in adolescents health⁽³⁵⁾.

To promote researches on the prevalence of physical inactiveness among Brazilian adolescents is a latent need for the development of physical activities increment interventions. This recommendation is corroborated with authors from other parts of the world, emphasizing that this is not a lack only among Brazilian adolescents^(2,3,36).

To perform researches without, however, pointing the evidences found for further interventions in order to make them more susceptible to success seems less and less acceptable.

It is known that almost all studies are limited. From the countless aspects presented by the human behavior in relation to physical activities, we would like to emphasize the fact that the application of the results of this study in other regions of Brazil may be defective, once there are reports in literature about seasonal influences in the physical activity levels and selection⁽²⁵⁾.

This alert suggests that intervention strategies should be carefully selected in order to assure affinity between the cultural/demographic characteristics and the peoples' wishfulness.

To observe the role each health professional plays and to encourage his leader position based on specialized improvement and actualization programs seem a reasonable way to narrow relations between researchers and health professionals in the labor market, who, many times, keep a quite unfavorable distance to dialogue.

According to Possebon and Cauduro⁽³⁷⁾, the veracity of medical certificates the students exhibit in order to be exempted of attending physical activity classes is discussible and yet, some of the reasons reported do not belong to the list of dispensations authorized by law. In addition, the authors report that these dispensations make the subject Physical Education discredited in school.

This complex situation must be discussed in a multidisciplinary way, once there are two problems: on one hand, the quality of the Physical Education class offered in school that leads to the students' refusal, and on the other, medical professionals who "cover" the situation with the issue of false certificates. The effect? A vicious circle that maintains the refusal and the low participation of youths in physical activities in the school environment.

The knowledge of the students' wishfulness in relation to physical activities may lead to a radical change in curriculums offered in schools, once students are tired of activities (repetitive) and the way they are offered (not much stimulating), and the physical activities remain unchanged.

To create spaces in schools, public parks and squares for the practice of physical activities with skates and roller skates with bicycle parking does not seem to be relevant reforms in such structure in order to offer environmental facilitators for the practice of physical activities in schools and to stimulate the use of more active transportation.

Santos⁽³⁸⁾ emphasizes that the lack of spaces and security, besides extinguishing street children's play, especially in large cities, has more and more led young individuals to select television and computer, resulting in youth with higher levels of relative body fat.

On the other hand, governmental institutions may contribute with structural changes in cities, such as streets specially built for bicycle traffic and to remove obstructions from sidewalks, without, however, leaving public security as the users guarantee behind.

CONCLUSION

One may conclude that 62.1% of adolescents are inactive or insufficiently active according to BCS and that boys are more physically active than girls. Youth tend to reduce the practice of physical activities with the advance in the school grade and this decline is also evidenced when the data are analyzed by chronological age.

Carrying out further studies on the physical activity level in young individuals from other Brazilian regions is suggested for explanations with regard to behavioral differences in function of the geographic positioning, urbanization, climate, among others.

REFERENCES

Received in 30/8/04. 2^nd version received in 7/12/04. Approved in 11/2/05.

All the authors declared there is not any potential conflict of interests regarding this article.

• 1. Nahas MV. Atividade física, saúde e qualidade de vida: conceitos e sugestões para um estilo de vida ativo. Londrina: Midiograf, 2001.
• 2. Simeoni MC, Sapin C, Antoniotti S, Auquier P. Health-related quality of life reported by French adolescents: a predictive approach of health status. J Adolesc Health 2001;28:288-94.
• 3. Hidalgo I, Garrido G, Hernandez M. Health status and risk behavior of adolescents in the north of Madrid, Spain. J Adolesc Health 2000;27:351-60.
• 4. Topolski TD, Patrick DL, Edwards TC, Huebner CE, Connell FA, Mount KK. Quality of life and health-risk behavior among adolescents. J Adolesc Health 2001; 29:426-35.
• 5. Kujala UM, Kaprio J, Seppo S, Koskenvuo M. Relationship of leisure-time physical activity and mortality: the finish twin cohort. JAMA 1998;279:440-4.
• 6. Pols MA, Peeters PHM, Twisk JWR, Kemper HCG, Grobbee DE. Physical activity and cardiovascular disease risk profile in women. Am J Epidemiol 1997;146: 322-8.
• 7. Stofan JR, DiPietro L, Davis D, Kohl HW, Blair SN. Physical activity patterns associated with cardiorespiratory fitness and reduced mortality: the Aerobics Center longitudinal study. Am J Publ Health 1998;88:1807-13.
• 8. US Department of Health and Human Services - USDHHS. Physical activity fundamental to preventing disease. Office of the Assistant Secretary for Planning and Evaluation, 2002;1-19.
• 9. Wannamethee FG, Shaper AG, Walker M. Changes in physical activity, mortality and incidence of coronary heart diseases in older man. Lancet 1998;351:1603-8.
• 10. Sallis JF, Bauman A, Pratt M. Environmental and policy intervention to promote physical activity. Am J Prev Med 1998;15:379-97.
• 11. Martinez-Gonzalez MA, Varo JJ, Santos JL, Irala J, Gibney M, Kearney J, et al. Prevalence of physical activity during leisure time in the European Union. Med Sci Sports Exerc 2001;33:1142-6.
• 12. Farias Jr JC. Estilo de vida de escolares do ensino médio no município de Florianópolis, Santa Catarina, Brasil [Dissertação], Centro de Desportos: UFSC, 2002.
• 13. Martins MO. Estudo dos fatores determinantes da prática de atividade física de professores universitários [Dissertação], Centro de Desportos: UFSC, 2000.
• 14. Miranda VM. Estilo de vida e estágios de mudança de comportamento para atividade física em mulheres de diferentes etnias em Santa Catarina. [Dissertação], Centro de Desportos: UFSC, 1999.
• 15. Matsudo SM, Matsudo VR, Araújo T, Andrade D, Andrade E, Oliveira L, et al. Nível de atividade física da população do Estado de São Paulo: análise de acordo com o gênero, idade, nível socioeconômico, distribuição geográfica e de conhecimento. Revista Brasileira de Ciência e Movimento 2002;10:41-50.
• 16. Souza GS, Silva DK, Anegues ALA, Barros MVG. Estilo de vida e aptidão física relacionada à saúde de servidores da Universidade de Pernambuco. Revista Baiana de Educação Física 2000;1:6-14.
• 17. Silva RCR, Malina RM. Nível de atividade física em adolescentes do município de Niterói, Rio de Janeiro, Brasil. Cadernos de Saúde Pública 2000;16:1091-7.
• 18. Kimm SYS, Kwiterovich PO. Childhood prevention of adult chronic diseases: rationale and strategies. In: Cheung LWY, Richmond JB, editors. Child health, nutrition, and physical activity. Champaign, IL: Human Kinetics, 1995;249-73.
• 19. Mechelen WV, Twisk JWR, Post GB, Snel J, Kemper HCG. Physical activity of young people: the Amsterdam Longitudinal Growth and Health Study. Med Sci Sports Exerc 2000;32:1610-6.
• 20. Prochaska JO, Marcus BH. The transtheoretical model: applications to exercise. In: Dishman RK, editor. Advances in exercise adherence. Champaign, IL: Human Kinetics, 1994;181-90.
• 21. Thomas JR, Nelson JK. Métodos de pesquisa em atividade física. 3Ş ed. Porto Alegre: Artmed Editora, 2002.
• 22. Crespo AA. Estatística fácil. 16Ş ed. São Paulo: Saraiva, 1998.
• 23. Barbetta PA. Estatística aplicada às ciências sociais. 4Ş ed. Florianópolis: EDUFSC, 2001.
• ²⁴
  ANEP Associação Nacional das Empresas de Pesquisa. Critério de Classificação Econômica Brasil [acessado em 21 de outubro de 2002]. Disponível em: http://www.anep.org.br/mural/anep/04-12-97-cceb.html
• 25. Bungum TJ, Vincent ML. Determinants of physical activity among female adolescents. Am J Prev Med 1997;13:115-22.
• 26. Sallis JF. Age-related decline in physical activity: a synthesis of human and animal studies. Med Sci Sports Exerc 2000;32:1598-600.
• 27. Ingram DK. Age-related decline in physical activity: generalization to nonhumans. Med Sci Sports Exerc 2000;32:1623-9.
• 28. Dishman RK. Advances in exercise adherence. Champaign, IL: Human Kinetics, 1994.
• 29. Leslie E, Fotheringham MJ, Owen N, Bauman A. Age-related differences in physical activity levels of young adults. Med Sci Sports Exerc 2001;33:255-8.
• 30. Reis RS. Determinantes ambientais para a realização de atividades físicas nos parques urbanos de Curitiba: uma abordagem sócio-ecológica da percepção dos usuários [Dissertação], Centro de Desportos: UFSC, 2001.
• 31. Telama R, Yang X. Decline of physical activity from youth to young adulthood in Finland. Med Sci Sports Exerc 2000;32:1617-22.
• 32. Sallis JF, Zakarian JM, Hovell MF, Hofstetter R. Ethnic, socioeconomic, and sex differences in physical activity among adolescents. J Clin Epidemiol 1996;49:125-34.
• 33. Garcia AW, Broda MAN, Frenn M, Coviak C, Pender NJ, Ronis DL. Gender and developmental differences in exercise beliefs among youth and prediction of their exercise behavior. J Sch Health 1995;65:213-9.
• ³⁴
  DIEESE. O trabalho tolerado de crianças até catorze anos. [acessado em 15 de dezembro de 2001]. Disponível em: http://www.dieese.org.be/esp/especial.html
• 35. Kimm SYS, Glynn NW, Similo SL, Cable DM, Barton BA, Kriska AM. Determinants of the decrease in physical activity during adolescence (resumo). Anais da 38Ş Conferência Anual sobre Epidemiologia e Prevenção da Doença Cardiovascular, 1998.
• 36. Motl RW, Dishman RK, Ward DS, Saunders RP, Dowda M, Felton G, et al. Examining social-cognitive determinants of intention and physical activity among black and white adolescent girls using structural equation modeling. Health Psychol 2002;21:459-67.
• 37. Possebon M, Cauduro MT. Educação física no ensino médio: o lado oculto das dispensas. Kinesis 2001;25:129-47.
• 38. Santos VC. Sedentarismo: invalidez voluntária. Âmbito Farmacêutico 1997;9:55-8.

Publication Dates

• Publication in this collection
  30 July 2005
• Date of issue
  Apr 2005

History

• Reviewed
  07 Dec 2004
• Received
  30 Aug 2004
• Accepted
  11 Feb 2005