ENERGY CONVERSION IN SKELETAL MUSCLES: OLD AND RECENT VIEWS

Abstract

The conservation of mass was the basic principle of the approach of Santorio Santorini to human physiology: perspiratio insensibilis allowed a perfect balance between input and output: si cibus et potus unius diei sit ponderis octo librarum, transpiratio insensibilis ascendere solet ad quinque libras circiter. Muscle contractile activity (corporis motus violentus), however, disturbs the balance between visible and invisible evacuations. At the time of Santorio, the pneuma hypothesis of muscle contraction was still generally accepted and a long series of studies were necessary before the energy conservation principle could be applied to muscle contraction. The idea that, in accordance with the energy conservation principle, chemical energy is transformed into work (mechanical energy) and heat (thermal energy) during muscle contraction was accepted only in the first half of the nineteenth century. It took, however, approximately one hundred year before ATP was identified as the unique source of chemical energy for muscle contraction and the different ATP regeneration pathways could be discovered. Today, a wealth of tools are available to study the energy conversion in muscle contraction in single muscle fibers in vitro as well as in muscle in situ or in the whole organism during exercise. Myosin has been identified as the molecular motor performing the chemo-mechanical energy conversion and a number of specialized variants of myosin, employed for postural tasks or for power generation, have been discovered and analysed in detail.