Contortion (sometimes contortionism) is an unusual form of physical display which involves the dramatic bending and flexing of the human body. Contortion is often part of acrobatics and circus acts. In general, "contortionists" have unusual natural flexibility, which is then enhanced through acrobatic training, or they put themselves through intense, repetitive and consistent training to gain this flexibility. However, even those with genetic, sex, or age disadvantages can attain the same level of flexibility albeit with slower progress.In some countries like Mongolia and Russia many people (mainly girls) learn contortion and it is considered a nationally respected art form that holds cultural importance. For hundreds of years contortionists have entertained crowds all over Mongolia. Contortionists usually start practicing from a very early age. In Mongolia the minimum acceptable age is 5, as they believe contortion can cause bone deformities in younger children.[citation needed] Some sports, rhythmic gymnastics for example, demand extreme flexibility but not the hand balancing skills or performance skills of a contortionist.