Skeletal muscle hypertrophy is an increase in a muscle’s cross-sectional area
(CSA). Skeletal muscle hypertrophy is governed by a host of hormones and growth
factors, including satellite cells, testosterone, IGF-I, IL-1 & IL-6, to name just a few. An
increase in muscle CSA is accomplished by:
• Increase in the size of myofibrils
o Incorporation of new contractile proteins into the Actin and Myosin filaments
o Incorporation of new proteins to the structural filaments
• Increase in Sarcoplasm
• Increase in the connective tissues surrounding the muscle, myofibrils, and muscle fibers.
An increase in CSA can be accomplished by two forms of hypertrophy: sarcomere
and sarcoplasmic.
Sarcomere Hypertrophy—Incorporate of New Proteins in Actin and Myosin
Sarcomere hypertrophy is an enlargement of a muscle fiber as a result of anincrease in sarcomere number and size. Sarcomeres, which contain the contractile
proteins actin and myosin are the “functional units” of myofibrils. The incorporation of
new contractile proteins into Actin and Myosin filaments increases a muscle fiber’s size
and ability to produce force, commonly referred to as strength. These new proteins must
be created through the process of protein synthesis.
Sarcoplasmic Hypertrophy—Increase in Sarcoplasm and Connective Tissue
Sarcoplasmic hypertrophy is an increase of the sarcoplasm (muscle fibersemifluid cytoplasm) and noncontractile proteins. The fiber’s ability to produce force
does not increase from sarcoplasmic hypertrophy.
The emerging theory behind skeletal muscle hypertrophy is that a bout of exercise
causes protein degradation or damage (myotrauma), which leads to a period of enhanced
protein synthesis or supercompensation when the bout ceases (Zatsiorsky, 1995). This
increase in protein synthesis not only repairs the damage from the bout of exercise, but
also makes the muscle stronger and therefore more resistant to future damage.
We are not doing to discuss the steps involved in skeletal muscle hypertrophy,
just how to stimulate it with weight training workouts. This book will first outline a 9-
week workout program designed to add overall mass and then go into muscle specific
hypertrophy workouts.