|A chart that illustrates the finding of the survey, by the NewYork Times.|
So what is causing this gap of 10%? I believe that a contributing factor is the increased amount of leisure time that the more wealthy have. This extra time can then be used to exercise, instead of working or being consumes with other responsibilities. Another connection this this distinction could be a result of different types of jobs.
Lower class jobs, which provide less income, are sometimes more physically demanding, and could be physical labor. Therefore, after work, these people would be too tired to exercise additionally, or they may feel as though they have already exercised enough for the day, although it is a different type of physical activity that they are preforming then say jogging or biking or weightlifting. On the other hand, more upper class jobs are less physically demanding, such as jobs in an office that leading to a somewhat sedentary day, which then require additional exercise after work.
This is just a rough idea as to why there is a difference in exercise between people of higher and lower income. What do you think can explain this gap?