Muscle Hypertrophy Models: Applications for Research on Aging

Abstract

Muscle hypertrophy is an adaptive response to overload that requires increasing gene transcription and synthesis of muscle-specific proteins resulting in increased protein accumulation. Progressive resistance training (P(RT)) is thought to be among the best means for achieving hypertrophy in humans. However, hypertrophy and functional adaptations to P(RT) in the muscles of humans are often difficult to evaluate because adaptations can take weeks, months, or even years before they become evident, and there is a large variability in response to P(RT) among humans. In contrast, various animal models have been developed which quickly result in extensive muscle hypertrophy. Several such models allow precise control of the loading parameters and records of muscle activation and performance throughout overload. Scientists using animal models of muscle hypertrophy should be familiar with the advantages and disadvantages of each and thereby choose the model that best addresses their research question. The purposes of this paper are to review animal models currently being used in basic research laboratories, discuss the hypertrophic and functional outcomes as well as applications of these models to aging, and highlight a few mechanisms involved in regulating hypertrophy as a result of applying these animal models to questions in research on aging.

Anaerobic performance in masters athletes

“…A similar observation has also been made by Alway and others [3] who observed a loss of muscle strength in older endurance-trained athletes relative to untrained younger men. Results from our laboratory also suggest a decrease in knee extensor isokinetic strength in aged sprint and endurance runners (>60 year) compared to younger (20-25 years) runners matched for body mass, training status, and training volume [126].…”

Nuclear Apoptosis Contributes to Sarcopenia

“…For example, 30 d of overload results in increases in muscle mass of 44% and 25% in adult and aged quails, respectively (6). Fourteen days of functional overload in the rat plantaris muscle increases muscle weight by 25% in young adult animals but only by 9% in old rats (2,3).…”

“…Taken together, these findings suggest that exercise and muscle overload even at old age is able to at least partially offset muscle loss via an attenuation of the proapoptotic signaling potential. This provides the possibility that exercise may delay the onset and/or attenuate the rate of progression of sarcopenia by reducing the proapoptotic environment of old muscles (3,19,22,24,25,29).…”

“…Partial restoration of muscle mass and function can be achieved through increased loading and high resistance exercise programs by activating satellite cells (2,3). Satellite cells proliferate to increase the total number of myonuclei, and this in turn leads to increases in muscle fiber size (3,6); however, activated satellite cells are also vulnerable targets for apoptosis (11,27).…”

“…Satellite cells proliferate to increase the total number of myonuclei, and this in turn leads to increases in muscle fiber size (3,6); however, activated satellite cells are also vulnerable targets for apoptosis (11,27).…”