Skeletal muscles are used for a wide variety of motor tasks ranging from maintaining posture to whistling, from jumping to breathing, from running at ∼40Km/h for 10s (100 meters) to running at half the speed for ∼2h (i.e., the marathon, 42,195Km). The capacity to accomplish such variable motor tasks relies on the very fine motor control performed by the nervous system and on the very large functional heterogeneity and plasticity of skeletal muscles. The nervous system can finely tune the performance of a given muscle adapting its power output to the motor task on a very short time base, milliseconds/seconds (phasic control). Skeletal muscles can adapt their contractile properties to the requirements of their predominant motor tasks by changing their structure on a long time base, weeks-months (tonic control). Skeletal muscles are known to differ regarding a variety of aspects, among which the most relevant are their power output and their energy metabolism. Several reviews have recently dealt in detail with most aspects of skeletal muscle plasticity [1 3]. This chapter will consider the variability in the parameters at the basis of power generation (force, velocity, ATP consumption). It is not meant to be a review on such a wide topic, but it will tell the story of how the understanding of the mechanisms underlying the heterogeneity and plasticity of skeletal muscle power output has been developing in our laboratory and of how our experimental approach has been updated to further our knowledge of the mechanisms from the cellular level to the molecular level.
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