BioProp 100 is a testosterone propionate injection that is used to build muscle mass. It is a basic steroid that is anabolic and androgenic in nature. Bodybuilders often use it as the base steroid in cycles because it clears the body quickly after use is discontinued. It aromatizes easily, so bodybuilders often use anti-estrogens to help keep estrogen related side effects to a minimum. The male bodybuilder's dosage would typically be in the 400-1200 mg per week range.