Hipertrofia Muscular

by

Aaron

Bubbico

and

Len

Kravitz,

PhD
QUIZ 2: PAGE 85

Muscle Hypertrophy
New insights and training recommendations.
Muscle hypertrophy, or muscle cell enlargement, is a topic of great debate and interest in all fields of health, fitness and sports. How the body responds to muscular overload to elicit muscle growth is still under much scientific investigation. Many types oftraining educe muscle hypertrophy. This is evidenced by the fact that athletes in numerous sports exhibit wonderful muscular development even though they follow different training protocols. With this in mind, it makes sense to examine contemporary understandings of muscle hypertrophy and highlight some effective training approaches. With muscle hypertrophy at the cellular level in humans, theactin and myosin contractile proteins increase in size and number (Schoenfeld 2010). In addition, as Schoenfeld explains, there is an increase in thefluid(sarcoplasm) and noncontractile connective tissues interspersed within muscle, a concept collectively referred to
as sarcoplasmic hypertrophy. In eccentric

Satellite Cells, Cytokines and Hornnones: Exploring New Insights Into Muscle HypertrophyMechanisms
Satellite cells are the "stem" cells of skeletal muscle (Schoenfeld 2010). Like stem cells, satellite cells have unique physiological characteristics and functions. They can be characterized as small, mononuclear cells located between the basement membrane of a muscle fiber (called the basal lamina) and the sarcolemma (the polarized plasma membrane). They function to repair damagedmuscle tissue and trigger skeletal muscle growth after any type of overload. Once satellite cells are stimulated by muscular overload, they fuse to the muscle fiber and facilitate muscle hypertrophy by forming a new nucleus. Uniquely to human physiology, muscle fibers have numerous nuclei. Each nucleus is responsible for afinitearea of volume and tissue within the musclefiber,a concept calledmyonuclear domain (Schoenfeld 2010). The exercise-induced stimulus from resistance exercise activates a complex response of cellular messaging pathways, cytokines and hormones that set muscle
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Muscle Hypertrophy
Muscle hypertrophy is an increase in muscle fiber size, observed when the muscle achieves a larger diameter or thickness. New muscle fibers are not created during hypertrophy in humans,although Paul and Rosenthal (2002) note new-fiber creation has been observed in some animal studies, owing to unique structural differences in muscle anatomy between species.

training, which overloads the muscle during lengthening, muscle cells also add sarcomeres (the smallest functional unit of musclefibers)longitudinally, thus adding length to the musclefiberas well (Proske & Allen 2005). Itis important to note that strength gains made in the first couple of months of training are primarily neural adaptations (Schoenfeld 2010). Gabriel, Kamen and Frost (2006) explain that in early training phases, the muscle is acquiring greater neural input, referred to as neural drive. Underlying this greater neural input are the motor unit recruitment patterns of muscle fiber types (see Figure 1for an explanation of motor unit recruitment). Each motor unit represents a single nerve and the many musclefibersit innervates.
November-December 2011 IDEA Fitness Journal

hypertrophy in motion (see Figure 2). Three distinct messaging pathways (calcium-dependent pathway, mitogen-activated protein-kinase pathway and rapamycin pathway) shift the cell into a protein synthesis condition whilealso inhibiting protein breakdown (Schoenfeld 2010). Cytokines are messaging proteins from the immune system that interact with specialized receptors on muscle to promote tissue growth. Significantly, some anabolic (muscle growth-promoting) hormones—including insulin-lßce growth factor, testosterone and growth hormone—play a primary role in promoting hypertrophy (Schoenfeld 2010).

promote muscle...