HEALTH-EFFECTS OF RECREATIONAL RUNNING IN WOMEN - SOME EPIDEMIOLOGIC AND PREVENTIVE ASPECTS

Estimated maximum oxygen uptake of middle-aged nonelite road race entrants is around 45 to 50 ml/kg/min, which is 40 to 100% higher than values from the female general population. Endurance training, low bodyweight, and nonsmoking of runners explain part of, but not the whole, difference in aerobic capacity observed between athletes and the general population. Sedentary women can improve cardiorespiratory fitness through aerobic exercise programmes, and the women with the lowest level of initial fitness have the highest proportional improvement following training. Regularly exercising women have a significantly reduced risk of fatal and nonfatal coronary events, and low cardiorespiratory fitness is associated with an increased risk of death and nonfatal stroke. The influence of habitual running on the female blood lipid profile is not clear. Cross-sectional studies have found elevated HDL cholesterol concentrations in distance runners, but intervention studies on the effect of jogging on lipid and lipoprotein levels have provided equivocal results. A higher level of physical fitness is associated with a lower risk to subsequently develop hypertension. Experimental studies have shown that moderate intensity aerobic exercise (40 to 60% VO2max) is able to reduce blood pressure significantly in hypertensive subjects. An athletic lifestyle may be associated with a reduced risk of adult-onset diabetes mellitus (via an exercise-induced increase in insulin sensitivity), and with a reduced risk of cancers of the reproductive system, breast, and colon. Recreational running is also correlated with better weight control. Surveys of recreational and elite distance runners show a great variability in the prevalence of secondary amenorrhoea, between 1 and 44%. Environmental factors determining the risk of amenorrhoea in runners are low body fat content, mileage, and nutritional inadequacy, with low intakes of calories, protein, and fat. Amenorrhoeic athletes in their third and fourth decade have lower vertebral bone density, which is improved after resumption of menses but does not completely reach age-specific average values. Regardless of menstrual status, the effectiveness of exercise to maintain bone mass throughout life is an important issue. Habitual exercise is associated with increased bone density of the spine both in premenopausal and postmenopausal women. Several controlled training studies suggest that postmenopausal women may at least retard their bone loss with regular aerobic exercise. Running-related injuries and complaints are common in recreational joggers, even though the reported 1-year incidence, varying between 14 and approximately 50%, depends on injury definition. Mileage and a history of previous running injury are known risk factors. Overweight, irregular menses, and absence of oral contraceptive use have been identified as risk factors in single studies. Female gender itself does not seem to be a major risk factor of running injuries among habitually active subjects, but it may be a relevant factor for sedentary subjects taking up jogging. Regarding the effect of habitual running on the development of osteoarthritis in weight-bearing joints, available data suggest that reasonable recreational exercise, carried out within limits of comfort, putting joints through normal motions, without underlying joint abnormality, even over many years, is unlikely to lead to significant joint injury. Habitual exercise is associated with reductions in anxiety and depression as well as increased self-esteem. The latter is an empirically supported outcome of exercise, and programmes of aerobic exercise seem also to be effective in reducing state anxiety and symptoms of mild depression. The prevalence of anorexia nervosa among competitive distance runners is not higher than among the general population, but it is the best runners who are most likely to be anorectic. Nonsmoking is highly prevalent among runners, and habitual runners who smoke have a quit rate of roughly 75%, with the rate of smoking cessation being related to mileage. Compared with the general population, age-matched runners have significantly fewer medical consultations, and probably less missed work days. Little data on the health effects of recreational, in contrast to competitive, running is available, and most epidemiological studies on prevention through exercise suffer from methodological shortcomings that hamper the ability to evaluate the health potential of aerobic exercise in an unbiased way. Nevertheless, there is a broad consensus that an energy expenditure of at least 150 to 400 kcal/day (corresponding to jogging 2.5 to 6 km/day) at a moderate intensity, should be the goal for health-oriented exercise.