[?] is very important. The [?] is a muscle and like any [?] the more it is used,the [?] it becomes. Some types of exercise make the heart [?] than others. Exercises include activities such as [?], [?], and [?]. They all use the large [?] of the body,making big movements, and this increases the amont of [?] the body needs. To get extra [?] to the muscles, the heart has to pump [?] arould the body more quickly. This makes it [?] and [?] the amont of [?] that it can pump. These [?] can also help lower blood pressure and keep body [?] down. Over a period of [?], they can also increase the mass of the [?], making it stronger. Most [?] recommend three to twenty-minute [?] sessons a week. This should keep the [?] and circulatory system at [?] fitness.