Introduction
Psychological positive health is a multifactor construct that describes a state beyond the mere absence of disease. It is considered an index of subjective health status (3) and refers to an individual's subjective evaluation of his or her physical and mental health and social functioning (36). Several studies have suggested that psychological positive health alleviates depression (37), promotes better relationships (14), acts as a preventive against the common influenza (12), protects against cardiovascular events (21), and predicts lower mortality (20).
Health complaints and health risk behaviors have well-known deleterious consequences on health. Health complaints refer to somatic and psychological symptoms experienced by the individual with or without a defined diagnosis such as abdominal pain, headache, backache, nervousness, and sleeping difficulties. Such symptoms constitute both everyday experiences and health problems and are common causes of disability and sickness certificates in adults (38). Several studies showed that weekly health complaints negatively influence an adolescent's well-being and functional ability (16).
Health risk behaviors, especially smoking and drinking, are one the major health concerns among adolescents in western countries. Both are associated with the leading causes of mortality and morbidity, posing immediate risks to health during adolescence and increasing the likelihood of excess preventable morbidity and death in adulthood (5,30).
Muscular fitness is emerging as an important marker of health throughout life (26,32,34,35). Muscular fitness is associated with a healthier cardiovascular profile already in childhood and adolescence (26), and longitudinal studies have shown that changes from childhood to adolescence are associated with changes in overall and central adiposity, systolic blood pressure, blood lipids, and lipoproteins (32). Less is known however on the association of muscular fitness with psychological positive health, health complaints, and health risk factors in children and adolescents. Therefore, the question “Is muscular fitness a marker of psychological positive health, health complaints and health risk behaviors in youth?” remains to be answered.
The aim of this study was to examine the association of muscular fitness with psychosocial positive health, health complaints, and health risk behaviors in Spanish children and adolescents.
Methods
Experimental Approach to the Problem
It is well known that muscular fitness is emerging as an important marker of physical health throughout life (26,32,35). However, to our knowledge, there are no studies investigating the association of muscular fitness with psychological positive health, health complaints, and health risk factors in children and adolescents. To clarify whether having higher levels of muscular fitness could exert a positive effect on psychological positive health indicators health complaints and health risk factors in youth, we conducted a cross-sectional study examining the association of muscular fitness with psychological positive health, health complaints, and health risk behaviors in children and adolescents aged 6–17 years.
Subjects
A total of 690 (368 boys and 322 girls) healthy Caucasian children and adolescents (6–17.9 years of age) participated in the study. The sample was randomly selected by means of a 2-phase, proportional cluster sampling using as a reference the database of the census of the province of Cádiz (Spain). In the first phase, the school was selected from the stratum. The different strata were selected according to the geographical localization, by age and sex. A total of 18 governmental schools agreed to participate in the study. In the second phase, classes from schools were randomly selected and used as the smallest sampling units. All the children of the selected classroom were invited to participate in the study. The participation was >95%.
A comprehensive verbal description of the nature and purpose of the study was given to the children, adolescents, their parents, and their teachers. This information was also sent to the parents or the children's supervisors by regular email. An informed consent form from the parents or the children's supervisors, children, and adolescents was requested before the study. The Institutional Review Board for use for humans at the University of Cádiz (Spain) approved the study.
Procedures
Psychological positive health (perceived health status, life satisfaction, quality of family relationships, quality of peer relationships, academic performance), health complaints, and health risk behaviors (tobacco and alcohol use, and drunk) were assessed by the Health Behavior in School-aged Children (HBSC) questionnaire (2,40). The participants completed the questionnaire in the school classroom in the presence of trained investigators. All the questions used in the HBSC questionnaire have a good validity and reliability for schoolchildren (4,31).
Psychological Positive Health
(a) Perceived health status: The participants reported how they perceived their health status at present (3-point scale: excellent, good, and fair). (b) Life satisfaction: The participants indicated how they felt about their life at present (4-point scale response options: very happy, happy, not very happy, and not happy at all). (c) Quality of family relationships: The participants indicated how easy it was to talk to their family members about things that were bothering them (5-point scale response options: very easy, easy, difficult, very difficult, and I don't have). The internal consistency of the items of quality of family relationships (father, mother, other adults, brother, sister) was acceptable (Cronbach's alpha = 0.734). (d) Quality of peer relationships: The participants indicated how easy it was to talk with friends about things that were bothering them (5-point scale response options: very easy, easy, difficult, very difficult, and not relationship). The internal consistency of the items of quality of peer relationships (to talk with friends, to go out with friends, to have good friends, to find new friends) was acceptable (Cronbach's alpha = 0.684). (e) Academic performance: The participants indicated what they think about their academic performance compared with those of their classmates (4-point scale response options: very good, good, average, and under average).
Health Complaints
The participants indicated how frequently they had each of the following symptoms: headache, stomach ache, backache, feeling low, irritability or bad temper, feeling nervous, difficulties getting to sleep, feeling dizzy (5-point scale response options: rarely or never, almost every month, almost every week, more than once a week, and almost every day, coded as 1, 2, 3, 4, 5, respectively). The mean of the responses represented subjective health complaint index (17). The internal consistency of the items of health complaint index was acceptable (Cronbach's alpha = 0.714).
Health Risk Behaviors
Tobacco use: A single item was used to assess cigarette smoking: “How often do you smoke tobacco at present?” (4-point scale: I do not smoke, <once a week, at least once a week but not every day, and every day).
Alcohol use: The participants indicated how frequently they drunk each of 3 beverages (beer, wine, combined liquors). The answers were recoded to days per week: never (0), rarely (0.1), every month (0.25), every week (1), and every day (7) The mean of the responses represented alcohol use (17). The internal consistency of the items of alcohol use was high (Cronbach's alpha = 0.937).
Drunk: A single item asking “Have you ever got drunk any time?” (5-point scale: never [0], once [1], 2–3 times [2], 4–10 times [3], and >10 times [4]) indicated get drunk.
Muscular Fitness
Lower body muscular fitness was assessed by means of the standing long jump test. The participant stood behind the starting line, with feet together, and pushed off vigorously and jumped forward as far as possible. The distance was measured from the take-off line to the point where the back of the heel nearest to the take-off line lands on the mat or nonslippery floor. The test was repeated twice, and the best score was retained (in centimeters) (8,9).
Upper-body explosive strength was assessed by means of the throw basketball test. The participant stood at a line with the feet slightly apart, holding the ball with the hands and facing the direction in which the ball was going to be thrown. The ball was brought back behind the head and then thrown vigorously forward as far as possible. The throwing action was similar to that used for a football sideline throw-in. The subject was encouraged to use the legs, back, and arms to assist in maximizing the distance thrown. The subject was not allowed to fall forward over the line or detach the feet from the floor, before, during, or after the throw. Two attempts were allowed, and the best mark was retained. The distance from the starting position to where the ball landed was recorded. The measurement was recorded to the nearest 10 cm (8,9).
A muscular fitness index was computed by means of standardized measures of the standing long jump (in centimeters) and the throw basketball (score in centimeters divided by body weight in kilograms). The participants were classified into low and high muscular fitness level categories, according to the median value. All the participants received a comprehensive instruction of these tests after which they also practiced the tests. They were instructed to abstain from strenuous exercises 48 hours before the test. Before testing, the participants were asked to perform 15 minutes of warm-up consisting of running, callisthenics, and 6 submaximal jumps and throw basketball tests. These tests have shown to be valid and reliable (1,7,9).
Statistical Analyses
Data are presented as mean and SD, unless otherwise indicated. Analyses were performed using the PASW (v. 18.0 for Windows, Chicago, IL, USA), and the level of significance was set to 0.05.
The association of muscular fitness with psychological positive health, health complaints, and health risk behavior indicators was examined using multiple regression analysis. Further, we performed binary logistic regression analysis to examine the association of low muscular fitness (below vs. above the mean) with psychological positive health (perceived health status: excellent [referent] vs. good and fair; life satisfaction: very happy [referent] vs. lower; quality of family relationships: very easy [referent] vs. lower; quality of peer relationships: very easy [referent] vs. lower; academic performance: very good [referent] vs. lower), health complaint index (never vs. sometime), and health risk behaviors (tobacco use, alcohol use, and getting drunk: never [referent] vs. sometime). Because there were no sex × muscular fitness interactions with any of the study outcomes, all the analyses conducted were performed jointly for boys and girls, and all the models were adjusted for sex.
Results
Means and SDs for measures on muscular fitness, psychological positive health, health complaints, and health risk behaviors by sex are presented in Table 1.
The association of muscular fitness with psychosocial positive health, health complaints, and health risk behavior measures is presented in Table 2. Muscular fitness was positively associated with all the studied psychological positive health indicators (all p < 0.03), except quality of peer relationships (p = 0.941) in both children and adolescents. Muscular fitness was inversely associated with both, tobacco (p = 0.014) and alcohol use (p = 0.049).
Children and adolescents having low muscular fitness had a significantly higher odds ratio (OR) of reporting fair (vs. excellent) perceived health status, low life satisfaction (vs. very happy), low quality of family relationships (vs. very good), and low academic performance (vs. very good) (Table 3). Likewise, children and adolescents having low muscular fitness had a significantly higher OR of reporting smoking tobacco sometimes (vs. never), drinking alcohol sometimes (vs. never), and getting drunk sometimes (vs. never). We repeated the analysis further adjusting for height, or BMI, or age, and the findings did not materially change (data not shown).
Discussion
The results of this study showed that muscular fitness is positively associated with psychological positive health in children and adolescents. Furthermore, muscular fitness is negatively associated with tobacco and alcohol use in children and adolescents. Although no conclusion can be drawn from the present cross-sectional study as to whether improvements in muscular strength leads to improvements in psychological positive health in children and adolescents, these findings are of public health and clinical interest and extend previous results that suggested the potential benefit of cardiorespiratory fitness on psychological positive health already in youth (27). Controlled experimental designs are desirable for establishing causal relations, that is, to show whether improvements in muscular strength lead to improvements in psychological positive health in youth. Observational studies, however, can provide data that are consistent or inconsistent with causal hypotheses. To our knowledge, there are no studies investigating the association of muscular fitness with measures of psychological positive health, health complaints, and risk behaviors, which hamper further comparisons.
This study showed that muscular fitness is positively associated with perceived health status and life satisfaction in children and adolescents. A number of studies revealed that perceived health is a widely used health status measure in clinical medicine, epidemiological studies, and health promotion (29). The perceived health status seems to be an effective summary of health and seems to be a strong predictor of future functional limitations, cognitive impairment, and mortality (19). Additionally, life satisfaction is an essential criterion of psychological health (14), and it is likely a goal rated at the top of the importance scale of people's well-being (13). Taken together, these results indicate the importance of improving muscular fitness levels in children and adolescents.
Educational and health professionals have intuitively believed that individuals who are physically active and fit perform better in school. However, the relationship between physical fitness and academic performance still remains unclear (22,33,39). This study showed a positive association between muscular fitness and academic performance in children and adolescents. These results are consistent with those reported in a previous study in children and adolescents (11). In contrast, 3 studies showed a weak association or no association, between academic performance and muscular fitness in children and adolescents (6,15,33).
Health complaints and health risk behaviors (such us smoking and drinking) are frequently used as a frame of reference to health perceptions in children and adolescents (18,28). It has been suggested that cardiorespiratory fitness attenuates the deleterious consequences of health complaints, smoking, and drinking (10). However, less is known about the association between these negative health indicators and muscular fitness. In this study, there was no association between health complaints and muscular fitness in children and adolescents.
We also observed that smoking and drinking were inversely associated with muscular fitness in children and adolescents. These findings are particularly important from a public health perspective given the well-known negative consequences of smoking and drinking and the fact that these behaviors start already at these ages. Further studies are needed to clarify the association between health complaints and health risk behaviors and muscular fitness.
The limitation of this study includes its cross-sectional nature, which does not permit inferences about causality to any of the associated factors in the study. In addition, it has been suggested that children and adolescents might be less accurate than adults when reporting the psychological indicators and health risk behaviors. However, intentional misreporting was probably minimized by the fact that the study participants completed the questionnaires anonymously, and the questions used in this study, belonging to the HBSC questionnaire, are valid and reliable (4,31). It should also be recognized that although sampling of this study was not meant to be representative of the Spanish children and adolescent population, the levels of physical fitness, body composition, and subjective indicators (HBSC items) observed in our sample were similar to Spanish nationally representative data obtained from the AVENA study (24,25) and the HBSC 2005/2006 survey (23). In addition, muscular fitness and fatness were assessed by objective measures.
In summary, the findings of this study indicate that muscular fitness is positively associated with psychological positive health in children and adolescents. Both, smoking and drinking are inversely associated with muscular fitness in children and adolescents. The results of this study suggest that increasing muscular fitness could exert a positive effect on psychological health indicators in children and adolescents. As psychological positive health, health complaints, and risk behaviors are potentially modifiable during the first decades of life, it would be of interest to investigate whether targeted muscular-strength enhancing interventions specially on individuals at risk might influence psychological positive health, health complaints, and risk behaviors during adolescence and in later life.
Practical Applications
The findings from this study suggest that there is a link between muscular fitness and psychological positive health and health risk behavior indicators in children and adolescents. Based on these results, increasing muscular fitness could influence positively on psychosocial positive health and decreasing health risk behavior indicators in children and adolescents. Intervention studies are needed to confirm or refute the present findings.
Acknowledgments
The study was funded by Centro Andaluz de Medicina del Deporte, Junta de Andalucía, Orden 4/02/05, BOJA no. 37 (Ref. JA-CTD2005-01), the Spanish Ministry of Education (EX-2008-0641), and the Spanish Ministry of Science and Innovation (RYC-2010-05957).
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