Chinese martial arts, also referred to by the Mandarin Chinese term wushu (simplified Chinese: 武术; traditional Chinese: 武術; pinyin: wǔshù) and popularly as kung fu or gung fu (Chinese: 功夫; pinyin: gōngfu), are a number of fighting styles that have developed over the centuries in China. These fighting styles are often classified according to common traits, identified as "families" (家, jiā), "sects" (派, pài) or "schools" (門, mén) of martial arts. Examples of such traits include physical exercises involving animal mimicry, or training methods inspired by Chinese philosophies, religions and legends. Styles which focus on qi manipulation are labeled as internal (内家拳, nèijiāquán), while others concentrate on improving muscle and cardiovascular fitness and are labeled external (外家拳, wàijiāquán). Geographical association, as in northern (北拳, běiquán) and southern (南拳, nánquán), is another popular method of categorization.