Physical Activity And Health Research Paper

1. The Effects Of Physical Activity On Physical Health

1.1 Overall Mortality

Epidemiological studies suggest that persons with moderate to high levels of regular physical activity or cardiorespiratory fitness have lower mortality rates than persons who are inactive or have low fitness levels (e.g., Sherman et al. 1999). This is supported by longitudinal research examining how changes in the level of cardiorespiratory fitness may affect subsequent mortality risks. For example, in a study by Blair et al. (1995), healthy men with an initially low level of cardiorespiratory fitness participated in two exercise tests about five years apart. Five years after the second exercise test, men in the bottom fifth of the initial fitness distribution who improved their fitness to at least a moderate level had a 44 percent lower mortality rate than men who remained in the bottom fifth. Similar results had already been found by Paffenbarger et al. (1993) in a cohort of initially sedentary Harvard alumni. Those men who started and maintained moderately intense activities extended their longevity on average by 0.72 years.

1.2 Cardiovascular Diseases (CVD)

Cardiovascular diseases, in particular coronary heart disease and stroke, are major causes of death, disability, and health care expenditures in Western societies. There is clear evidence that, within populations, the incidence of CVD is inversely related to habitual physical activity levels (Bauman and Owen 1999). Some of the studies in this field demonstrated a dose–response gradient between level of physical activity and risk of CVD outcome. Dose–response relationships were also found in those investigations in which measures of cardiovascular fitness, instead of physical activity estimates, were related to CVD mortality.

1.2.1 Coronary Heart Disease (CHD). Since 1953, about 40 studies analyzing the association between physical activity and risk of (CHD) have been published. The first study in this field was conducted by Morris et al. (1953), who examined 31,000 employees of the London Transport Executive. A comparison between bus drivers and bus conductors revealed that physically active conductors clearly had a lower risk of a ‘first coronary episode’ than sedentary drivers. Classifying physically active and inactive people according to job title or occupational activity is typical for studies published before 1978. In the following years, level of physical activity was defined mostly by self-report measures of leisure-time activity or by indices that combined levels of occupational and leisure-time activities. More recent investigations have also emphasized the necessity to control for potentially confounding variables (e.g., age, sex, functional status) and to adjust for factors that are considered causal links between physical activity and CHD, such as serum cholesterol, blood pressure, diabetes, or body mass index.

Reviews of relevant literature have concluded consistently that physical activity is strongly related to a reduced risk of CHD. Furthermore, there is evidence in recent studies that this relationship holds true for both men and women. For example, findings from a prospective study among 72,488 female nurses who were 40–65 years old at the onset of the study suggest that sedentary women who became active in middle adulthood or later had a lower risk of coronary diseases than their counterparts who remained sedentary. Relative to women who walked infrequently, those who walked at a brisk pace three or more hours per week had a multivariate relative risk of 0.65 for coronary events (Manson et al. 1999). Physical exertion may temporarily increase the likelihood of an acute coronary event among persons with advanced coronary atherosclerosis who are not used to regular exercise. Although this risk needs to be taken seriously, it does not affect the general fact that physical activity is associated with a substantially lower overall risk for CHD.

1.2.2 Stroke. Contrary to the results for CHD, epidemiological data do not unequivocally confirm a relationship between stroke and level of physical activity. Most investigations in this field were planned as population-based cohort studies with follow-up ranges of 5–26 years. Among those studies that were designed to detect possible dose–response effects, many did not find a clear linear association. Some studies even suggested a U-shaped relationship between physical activity level and risk of stroke. By trying to explain these contradictory findings, it was assumed that the two different types of stroke, namely ischemic stroke and hemorrhagic stroke, need to be regarded separately. Since both types have specific pathophysiologies, it may be possible that physical activity affects them in different ways. In a study by Abbott et al. (1994), inactive men had a higher risk of hemorrhagic stroke than active men, but there was no main effect on ischemic stroke. More research is needed to further clarify whether physical activity plays a protective role against stroke.

1.2.3 Biological mechanisms. Several biological mechanisms may be responsible for the beneficial effects of physical activity on cardiovascular risks. These mechanisms involve the impact on blood pressure, atherosclerosis, plasma lipid lipoprotein profile, availability of oxygenated blood for heart muscle needs (ischemia), thrombosis, heart rhythm disturbances, overweight, and healthier distribution of body fat.

1.3 Cancer

Cancer is one of the leading causes of death in industrialized countries. It is predicted that this proportion will increase in the next few years. Numerous studies have examined the role of physical activity in the prevention of cancer.

1.3.1 Colon Cancer. Systematic literature analyses reveal that colon cancer is probably the most often studied cancer in the field of physical exercise epidemiology. In 1996, a total of 29 studies on colon cancer were published (DHHS 1996). Of these, 18 studies considered only occupational physical activity, and 11 examined leisure-time or total physical activity. The results of the 18 studies using a measure of occupational physical activity draw a rather consistent picture: 14 studies found a significant inverse relationship between level of activity and risk of colon cancer; in four studies no such associations were observed. The 11 studies that referred to measures of leisure-time or total physical activity provided a similar pattern: eight reported an inverse association between level of physical activity and risk of colon cancer, while in three studies this was not the case.

In these studies, the level of physical activity during early adulthood was used as an effector variable. It is possible that this life period is too early to find an effect on colon cancer incidence in late adulthood. In most studies that controlled for potentially confounding dietary factors, the relationship between physical activity and risk of colon cancer remained significant. Taken together, the findings strongly suggest a significant association between level of physical activity and the occurrence of colon cancer.

1.3.2 Breast Cancer. The report of the Surgeon General of 1996 reviews the results of 13 studies that examined the effects of habitual physical activity on risk of breast cancer (DHHS 1996). Of the 13 studies, four referred only to occupational physical activity; the remaining nine studies used a leisure-time or total physical activity estimate. Of the four studies that focused on occupational physical activity, two found a significant inverse relationship between physical activity and breast cancer, but the other two did not. The nine studies considering leisure-time or total activity provide a contradictory picture: two studies found a significant inverse association, two reported a nonsignificant inverse association, three others could not observe any relationship, and the remaining two identified direct associations (i.e., the more active the person was, the higher the risk of cancer). Thus, there is only limited evidence for a protective effect of physical activity against the risk of breast cancer.

1.3.3 Conclusion. Epidemiological studies have also examined the relationship between physical activity and other cancers, such as prostate, testicular, ovarian, and endometrial cancer. Firm conclusions regarding these diseases cannot be drawn because data are often very limited or are inconsistent. The only clear association in this area seems to be the one between level of physical activity and the likelihood of developing colon cancer. To explain this finding, it has been assumed that physical activity reduces gastrointestinal transit time and thus diminishes the contact duration between the colon mucosa and potential carcinogens in the fecal stream.

1.4 Further Chronic Diseases

Level of physical activity has been related to further chronic diseases and conditions, in particular to diabetes, arthritis, osteoporosis, and obesity. Several prospective cohort studies lend strong support to the hypothesis that regular physical activity offers protection against the risk of noninsulin-dependent diabetes mellitus. Whether or not physical activity may prevent the development of osteoarthritis is still unknown. In postmenopausal women, physical exercise may impede the rapid decline in bone mass, thus protecting against osteoporosis, but this effect has not yet been unequivocally established. Reducing obesity by increased physical activity alone is a relatively slow process. Physical activity programs in combination with strategies of dietary management seem to be more effective in this regard.

2. The Effects Of Physical Activity On Mental Health

There is a large amount of literature dealing with the psychological effects of physical activity. Numerous reviews and meta-analyses have dealt with this literature (Fox 1999, Morgan 1997). In studies examining the effects of physical activity on mental health, the most frequently observed outcomes include depression, anxiety, mood, self-esteem, self-efficacy, perceived stress, and cognitive functioning. On the other hand, the role of physical activity in the development and treatment of psychiatric disorders such as schizophrenia, dementia, personality disorders, or eating disorders has only seldom been investigated. The following section focuses on the association of physical activity with depression and anxiety.

2.1 Depression

Research using correlational designs suggests a substantial relationship between physical activity and reduced symptoms of depression in men and women (Morgan 1997). In summarizing the existing literature, it was concluded that physically inactive persons are twice as likely to have symptoms of depression than their physically active counterparts. The association between level of physical activity and depression has been found in the general population as well as in clinical subpopulations (Fox 1999).

Correlational studies are often based on cross-sectional data, leaving the question unanswered whether physical activity has an effect on depression, or whether persons with good mental health are simply more likely to be active. In an attempt to resolve this problem of causality, cohort studies have been conducted in which the relationship between physical activity and depressive symptoms were examined in a longitudinal perspective. One of these cohort studies was conducted by Paffenbarger et al. (1994), who revealed that level of physical exercise reported at an initial interview was predictive of physician-diagnosed depression about 25 years later. In this investigation with 10,201 participants, the relative risk of depressive symptoms was 27 percent lower for men who had reported spending more than 3 hours of sports activities each week than for men who had reported no such activities. However, in other population studies, the level of physical exercise at baseline was not a risk factor for incidence of depressive symptoms years later (Weyerer 1992). Thus, the empirical evidence from cohort studies is still limited and inconsistent.

Another approach to resolve the problem of causality is intervention studies conducted in community or laboratory settings (Morgan 1997). A classical and often-cited work in this field is the experimental study by McCann and Holmes (1984). Altogether, 43 women students who scored higher than the cut-off point on the Beck Depression Inventory were randomly allocated to one of three groups: (a) aerobic exercise group, (b) placebo group, and (c) no treatment group. After five weeks, the aerobic exercise group showed a significant reduction in depressive symptoms compared with the two other groups, supporting the hypothesis that increased physical activity resulted in a reduction in depression. A more recent experimental study by King et al. (1993) demonstrated that greater exercise participation was significantly related to fewer depressive symptoms, independent of changes in physical fitness or body weight. Other intervention studies have shown that the antidepressant effect of physical activity may be greatest in those with higher levels of initial depressive symptoms (Brown et al. 1995), suggesting that the psychological benefits of exercise are likely to be different for different people. Several biological and psychosocial mechanisms have been proposed in order to explain the antidepressant effects of physical activity. In particular, it has been hypothesized that physical activity may induce changes in brain neuroreceptor concentrations of monoamines (norepinephrine, dopamine, or serotonin) or endogenous opiates (endorphins and enkephalins), which in turn are responsible for changes in the affective level (Morgan 1997). However, the observed depression-reducing effects of physical exercise may also be mediated by psychological factors such as exercise-induced feelings of mastery and self-efficacy, or by positive social and emotional experiences in the sport context.

2.2 Anxiety

Research has also suggested that physical activity may be linked to a reduction in anxiety. The psychological assessment of anxiety usually includes state and trait measures. State measures refer to the actual feeling of anxiety, whereas trait measures evaluate the stable personality characteristic of anxiety. In physical exercise research, state measures have been used mainly in pre-post-designs of intervention studies to explore whether a specific activity episode may have triggered changes in currently experienced anxiety. Results are relatively unequivocal in this respect. Immediately after a session of physical activity, most people report an improvement in mood, including a reduction in level of state anxiety (Berger and Owen 1998). However, this decrease in anxiety may persist for only 2–6 hours following the activity episode (Morgan 1997). In order to continuously profit from the anxiety-reducing effects of physical activity, it is obviously necessary to engage in physical activity on a daily basis. There is no clear evidence that regular physical exercise may have a general impact on trait anxiety (Schlicht 1994).

2.3 Further Psychological Effects

Physical activity has been considered to be a stress buffer in critical life situations (Fuchs and Hahn 1992). This has been explained by two different processes: physical exercise may affect the transactional stress coping process, either by influencing an individual’s appraisal of the potentially stressful situation, or acting as an emotion-focused coping strategy. However, empirical evidence supporting the stressbuffering role of physical activity is still very limited. Another psychological construct often linked to physical exercise is self-esteem. In his review, McAuley (1994) concluded that the positive association between physical activity and self-esteem is observed both as an enduring consequence of habitual exercise training and as an immediate, short-term effect of single exercise episodes. Finally, several studies suggest that there is a direct relationship between level of physical activity and measures of cognitive performance, such as reaction time, nonverbal reasoning, and memory.

3. Conclusions

There is clear evidence that physical activity is significantly associated with reduced risk of allcause mortality, all cardiovascular diseases combined, CHD, hypertension, colon cancer, and non-insulin dependent diabetes mellitus. Findings also strongly suggest that regular physical activity may reduce the risk of developing obesity, osteoporosis, depression, and state anxiety. However, effects on psychological factors such as cognitive functioning, self-esteem, body image, self-efficacy, control beliefs, or optimism are less clearly documented. Future research should focus on these emotional and cognitive factors that may be mediators in the relationship between physical activity and mental health. Based on data from epidemiological studies, it has been concluded that physical activity that increases the weekly energy expenditure by about 1,000 kcal (equivalent to about 90 minutes of running or 120 minutes of jogging) may be associated with substantial physical health benefits (DHHS 1996). But how much physical activity is needed to improve or maintain psychological wellbeing? Probably the mental health benefits of physical exercise are not only a matter of expended kilocalories (if at all), but also of exercise-related social interactions and emotional experiences. Clarifying the mechanisms by which physical activity may affect mental health dimensions is a challenge to sport and health psychology in the coming years.

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