Consistent exercise brings about many adaptations in muscle cells. Some of the most obvious adaptations include increased strength, endurance, and size.
<Muscular Hypertrophy An increase in muscle size is known as muscular hypertrophy. Hypertrophy can be classified into two different types:
Myofibrillar Hypertrophy Occurs as a result of an increase in cell contractile tissue. The increased contractile tissue leads to an increase in force production. This type of adaptation is typical of high intensity (heavy weight), low repetition training.
Sarcoplasmic Hypertrophy Occurs as a result of an increase in metabolic fuel (glycogen) and fluids stored in the cell. Muscle size increase is also more dramatic than in myofibrillar hypertrophy. This type of adaptation is typical of high volume, low intensity training.
<Regional Hypertrophy Originally thought not to occur, studies from the past two decades indicate that regional hypertrophy--or non uniform development of a muscle fiber-- does occur. Although not fully understood, it is thought that such development may be caused by uneven distribution of skeletal muscle type throughout muscle fiber. Another theorized cause is muscle fiber being innervated by separate branches of nerves at different points, with partial activation of the fiber at different ranges of motion.
It is possible that regional hypertrophy contributes to why strength gains are joint angle specific (strength gains don't transfer well outside of the range of motion you train), although this may be due to neurological factors. Regardless, it might hold some bearing on exercise selection when considering movements with exaggerated auxotonic contractions.
