Key result
Overload in the stretched position induced the adult rabbit tibialis anterior muscle to grow by up to 30% and increase RNA content by up to 250% within 4 days, activating slow-type genes.
Mechanical activity (stretch and overload) rapidly induces skeletal muscle hypertrophy and switches gene expression from fast-type to slow-type myosin heavy chains.
May inform mechanisms of muscle adaptation; leaves open translation to human cardiac or skeletal remodeling and requires clinical validation.
Using electrical stimulation to control force generation and limb immobilization to alter the degree of stretch, we have studied the role of mechanical activity in inducing hypertrophy and in determining fast and slow muscle fibre phenotype. Changes in gene expression were detected by analysing the RNA in hybridization studies employing cDNA probes specific for fast and slow myosin heavy chains and other genes. As a result of overload in the stretched position, the fast contracting tibialis anterior muscle in an adult rabbit is induced to synthesize much new protein and to grow by as much as 30% within a period as short as 4 days. This very rapid hypertrophy was found to be associated with an increase of up to 250% in the RNA content of the muscles and an abrupt change in the species of RNA produced. Both stretch alone and electrical stimulation alone caused repression of the fast-type genes and activation of the slow-type genes. it appears that the fast-type IIB genes are the default genes, but that the skeletal slow genes are expressed as a response to overload and stretch. These findings have implications as far as athletic training and rehabilitation are concerned.
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Goldspink et al. (1991) studied Muscle hypertrophy. Electrical stimulation and limb immobilization (stretch) was evaluated on Muscle growth and RNA content. Overload in the stretched position induced the adult rabbit tibialis anterior muscle to grow by up to 30% and increase RNA content by up to 250% within 4 days, activating slow-type genes.