单项选择题

Physical Exercise
Declaring that physical exercise is one of the most powerful medicines to help improve our quality of life is not an exaggeration. The World Health Organization expressed the same view in its 2002 World Health Report, emphasizing that the damage produced by lack of physical activity was equal to the strong probability of serious illness such as heart disease and even some kinds of cancer.
Those who have embraced an active lifestyle for years are familiar with the sort of physical and psychological benefits that come from exercise. Nevertheless a lot of people would never think of physical activity as a way of feeling better, simply because they don’t think they are in need of it, or because they are lazy or maintain that they haven’t got enough time.
There are many positive effects that result from physical exercise and they are not only concerned with the physical aspects but also psychological and social ones.
Beginning with the physical benefits, physical activity improves the life of the heart, burns off fat, lowers high blood pressure, makes tissues more resistant, and increases muscle flexibility and joint mobility.
On a psychological level, physical activity helps reduce anxiety and stress by causing tension to disappear and by encouraging us to have a better sense of ourselves through listening to our bodies during movement.
Lastly, seeing ourselves in better health is advantageous socially. The sense of satisfaction thus obtained will result in an increase of self-respect and self-confidence in terms of our ability to interact with others.
The benefits linked to exercise have also not gone unnoticed in the business world, with more and more companies setting up gyms on-site. Employees’ improved health translates into better performance and reduced costs as well as an increase in people’s satisfaction in the work place. Physical activity is recommended for all age groups, including children. It is an important growth factor in a child’s education.
And for the elderly There is no doubt that regular physical activity allows greater efficiency in daily life as well as creating more basic independence day by day, including the possibility of keeping in touch with others and not feeling isolated. Many people do not engage in physical exercise mainly because ______.