Ten healthy males and females performed coitus in the following pre-selected positions and variations : QUADRUPED ( fQUAD1 and fQUAD2 where the female is supporting her upper body with her elbows and hands , respectively ) , MISSIONARY ( fMISS1 and fMISS2 where the female is minimally and more flexed at the hips and knees , respectively ) , and SIDELYING .