Types of hypertrophy
There are two different types of muscular hypertrophy: sarcoplasmic and myofibrillar. During sarcoplasmic hypertrophy, the volume of sarcoplasmic fluid in the muscle cell increases with no accompanying increase in muscular strength. During myofibrillar hypertrophy, actin and myosin contractile proteins increase in number and add to muscular strength as well as a small increase in the size of the muscle. Sarcoplasmic hypertrophy is characteristic of the muscles of certain bodybuilders while myofibrillar hypertrophy is characteristic of Olympic weightlifters. These two forms of adaptations rarely occur completely independently of one another, one can experience a large increase in fluid with a slight increase in proteins, a large increase in proteins with a small increase in fluid, or a relatively balanced combination of the two.
Main article: Strength training
Strength training typically produces a combination of the two different types of hypertrophy: contraction against 80 to 90% of the one repetition maximum for 2-6 repetitions (reps) causes myofibrillatedhypertrophy to dominate (as in powerlifters, olympic lifters and strength athletes), while several repetitions (generally 12 or more) against a sub-maximal load facilitates mainly sarcoplasmic hypertrophy (professional bodybuilders and endurance athletes). The first measurable effect is an increase in the neural drive stimulating muscle contraction. Within just a few days, an untrained individual can achieve measurable strength gains resulting from "learning" to use the muscle. As the muscle continues to receive increased demands, the synthetic machinery is upregulated. Although all the steps are not yet clear, this upregulation appears to begin with the ubiquitous second messenger system (including phospholipases, protein kinase C, tyrosine kinase, and others). These, in turn, activate the family of immediate-early genes, including c-fos, c-jun and myc. These genes appear to dictate the contractile protein gene response.[citatio