Myofibrillar vs. Sarcoplasmic hypertrophy. Simply put, myofibrillar hypertrophy is achieved through damage to the contractile components of muscle fibers. These are the myofilaments that are composed of two proteins, myosin and actin. These protein strands bond to one another in a “cross bridge” and pull against each other to shorten a muscle fiber in an act known as a “power stroke”. When these components get damaged through resistance training, they heal and remodel, thicker, and more numerous