book about swimming, Colymbetes, sive de arte natandi dialogus et festivus et iucundus lectu (The Swimmer, or A Dialogue on the Art of Swimming and Joyful and Pleasant to Read). Purpose There are many reasons why people swim, from swimming as a recreational pursuit to swimming as a necessary part of a job or other activity. Swimming may also be used to rehabilitate injuries, especially various cardiovascular and muscle injuries. People may also pursue swimming as a career or field of interest. Some may be gifted and choose to compete professionally and go onto claim fame. Recreation Many swimmers swim for recreation, with swimming consistently ranking as one of the physical activities people are most likely to take part in. Recreational swimming can also be used for exercise, relaxation or rehabilitation. The support of the water, and the reduction in impact, makes swimming accessible for people who are unable to undertake activities such as running. Swimming is one of the most relaxing activities, water is known to calm us and can help reduce stress. Health Swimming is primarily a cardiovascular/aerobic exercise due to the long exercise time, requiring a constant oxygen supply to the muscles, except for short sprints where the muscles work anaerobically. Furthermore, swimming can help tone and strengthen muscles. Swimming allows sufferers of arthritis to exercise affected joints without worsening their symptoms. However, swimmers with arthritis may wish to avoid swimming breaststroke, as improper technique can exacerbate arthritic knee pain. As with most aerobic exercise, swimming reduces the harmful effects of stress. Swimming is also effective in improving health for people with cardiovascular problems and chronic illnesses. It is proven to positively impact the mental health of pregnant women and mothers. Swimming can even improve mood. Although many forms of physical activity have been shown to improve bone density and health, this is where swimming has its downfalls. Due to the low-impact nature of the sport, studies have demonstrated that bone mass acquisition will be negatively impacted, which could be an issue for adolescent athletes in particular. Disabled swimmers Since 2010, the Americans with Disabilities Act has required that swimming pools in the United States be accessible to disabled swimmers. Elderly swimmers "Water-based exercise can benefit older adults by improving quality of life and decreasing disability. It also improves or maintains the bone health of post-menopausal women." Swimming is an ideal workout for the elderly, as it