[Molecular mechanisms in muscle adaptation]

Skeletal muscle shows a unique ability to adapt its structure and function to various stimuli. The recent use of molecular-biological technology indicates that in human skeletal muscle exercise stimuli cause a rapid increase in the transcription of DNA sequences for metabolic and regulatory genes into messenger RNA. Additionally, repetitive and systematic exercise stimuli cause a change in the concentration of certain mitochondrial and contractile RNAs. These distinct changes in gene expression reflect the specific adaptations of the mitochondrial and myofibrillar structure of skeletal muscle to different stimuli as endurance exercise, strength training, and immobilization, respectively. Multiple molecular sensors have been identified which are involved in the sensation, transmission and integration of mechanical, metabolic, hormonal and neuronal signals of the more complex stimuli of exercise training into the observed adaptations of gene expression. The data support the fundamental concept, that by instructing the synthesis of encoded protein(s) changes in gene expression are responsible for the microadaptations of regularly exercised human skeletal muscles leading towards a new training steady-state.