ABSTRACT
Physical activity can be hazardous as well as beneficial to health. Jogging, walking and cycling inevitably increase exposure to the risk of injury through collisions with vehicles and falls. Cycling is particularly hazardous. In the United Kingdom, more than 1,300 cyclists were killed or seriously injured on the roads in 2005, which was 4% of all road accident fatalities. Around 540,000 injuries incurred during cycling are treated every year in US departments of emergency medicine, and nearly 800 people die; about one-third of these injuries are to the head and two-thirds of deaths are attributable to traumatic brain injury. Rather fewer injuries are incurred during swimming, but deaths do occur from drowning in swimming pools, mainly among young children. A number of other negative outcomes from exercise have been documented. Prolonged exercise in the heat can lead to hyperthermia, particularly if fluid intake is insufficient, and even to electrolyte imbalance. Hypothermia can be experienced by
Introduction 249 ❚
Female athlete triad 255 ❚
Prevention 263 ❚
Summary 265 ❚
Study tasks 265 ❚
Further reading 266 ❚
those engaging in water sports, hill-walking and even marathon running (deep body temperature can fall in individuals who cannot maintain a speed of walking or running sufficient to match heat production to heat loss). Rhabdomyolisis (sporadic appearance in blood of abnormal levels of myoglobin) has been reported among endurance runners engaged in high volume training. There may be an increased likelihood of osteoarthritis in individuals who engage over many years in sports involving a lot of high impacts and/or torsional loading of joints. There are also reports of exercise ‘dependence’ – a craving for leisure-time activity that results in uncontrollable excessive exercise behaviour that manifests in psychological and/or physiological symptoms. Criteria to define ‘how much is too much’ and the development of more objective measures are needed, however, before this area of research yields secure findings. Specific hazards are, of course, associated with physical activity for people with existing disease. Exercise can lead to hypoglycaemia in diabetics who take insulin or hypoglycaemic agents because it increases the rate of glucose uptake into muscle. Asthma may be precipitated by exercise – running in cold weather is a particularly potent trigger. In urban environments, air contains small amounts of gases and particulates other than its normal constituents. The increased ventilation of the lungs during exercise increases exposure to this pollution and may exacerbate respiratory problems in asthmatics. Even in healthy people, ozone and sulphur dioxide impair lung function. Thus, while the incidence of serious health problems among people who engage in physical activity at a moderate intensity in moderate amounts is very low, participation in vigorous exercise or sports can be hazardous. The best-documented hazards are: musculoskeletal injuries; triggering of heart attack or sudden cardiac death; the socalled ‘Female athlete triad’ and the impairment of aspects of immune function.
