Atrophy and hypertrophy of skeletal muscles: structural and functional aspects

Abstract

This review summarizes current information on structural and functional changes that occur during muscle atrophy and hypertrophy. Most published studies consider an increase in total mass of a muscle as hypertrophy, whereas a decrease in total mass of a muscle is referred to as atrophy. In hypertrophy, the rate of synthesis is much higher than the rate of degradation of muscle contractile proteins, leading to an increase in the size or volume of an organ due to enlargement of existing cells. When a muscle remains in disuse for a long period, the rate of degradation of contractile proteins becomes greater than the rate of replacement, resulting in muscle atrophy. This defect may occur as a result of lack of nutrition, loss of nerve supply, micro-gravity, ageing, systemic disease, prolonged immobilization or disuse. An understanding of the specific modifications that occur during muscle atrophy and hypertrophy may facilitate the development of novel techniques, as well as new therapies for affected muscles.

Ultrasound biomicroscopy for biomechanical characterization of healthy and injured triceps surae of rats

“…Studies with humans that investigated the changes in muscle architecture caused by strength training showed that muscle fibers hypertrophy in response to the training and, consequently, increase in size (Blazevich, 2006;Blazevich et al, 2007;Boonyarom and Inui, 2006;Kawakami, 2005). These studies measured muscle size using indirect estimates of MT.…”

“…These studies have demonstrated changes of the muscle architecture due to joint angle and contraction condition (passive or active). Additionally, muscle plasticity, when submitted to different experimental models of increased use or disuse, is also reported in studies with humans (Blazevich, 2006;Blazevich et al, 2007;Boonyarom and Inui, 2006;Kawakami, 2005). However, the tracking of the muscle degeneration-regeneration process in humans with reliable methodologies and quantification of architectural parameters has not yet been carried out because of inherent ethical difficulties.…”

Skeletal muscle mass and composition during mammalian hibernation

“…Commonalities amongst these models are a decrease in muscle mass (Musacchia et al, 1983;Thomason et al, 1987), protein concentration (Bajotto and Shimomura, 2006;Larsson et al, 1996) and fiber size (Pellegrino and Franzini, 1963;Rittweger et al, 2005;Wagatsuma et al, 2011). Most studies also show a conversion from slow to fast fiber types (Boonyarom and Inui, 2006) and a decline in muscle strength (Adams et al, 2003;Larsson et al, 1996;Thomason and Booth, 1990). Different training regimes can also lead to substantial changes in muscle morphology.…”

Nuclear factor-kappa B signaling in skeletal muscle atrophy

“…Resistance exercise and nutritional uptake leads to skeletal muscle hypertrophy which is characterized by increased muscle size, protein content, and strength [1,2]. Conversely, prolonged inactivity that occurs during unloading, immobilization, microgravity, bed rest, or nerve injury results in the loss of skeletal muscle mass commonly known as skeletal muscle atrophy or wasting [3]. Skeletal muscle atrophy is also a devastating complication of several disease states such as cancer, AIDS, inflammatory bowel disease, sepsis, diabetes, chronic obstructive pulmonary disease (COPD), chronic heart failure (CHF), high dose glucocorticoid therapy, renal failure, burn injury, and cystic fibrosis [4,5].…”