Muscle hypertrophy models: applications for research on aging.

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.