1. Pectoralis major - these are large chest muscles found to either side of breastbone. Its main job is to bring upper arm inwards across body, a movement that is known as horizontal adduction.

2. Latissimus dorsi - this is largest back muscle that runs from lower back to upper arm bone. It pulls upper arm towards body and acts as an internal rotator of upper arm.

3. Trapezius - this muscle runs from mid spine to shoulder and then to neck. Its main role is to faciltiate movement of shoulder blades.

Safety concerns are similar to those that relate to steroids. Some studies report that side effects can include acne, production of estrogen, development of breast tissue in males and development of masculine features in females.

At time of writing some doubts surround future of prohormones as health authorities may consider selective banning of some products.