Regulation of human muscle contraction at the cellular and molecular levels

The rat is the most extensively characterized species with regard to regula tion of muscle contraction and myofibrillar protein isoform expression, but there is reason to question whether results from small mammals, such as th e rat, can be extrapolated directly to larger mammals, such as man. Studies of human muscle contraction have primarily used different in vivo muscle f unction measurements, i.e. measurements of force at different speeds of mov ement during electrical stimulation or voluntary activation. These measurem ents give important information on overall muscle function, but they are of limited value for our understanding of regulation of muscle contraction. I n basic science, cellular- and molecular-physiological methods have been us ed for many years, but these techniques have so far only rarely been used i n studies of human muscle contraction. Detailed studies of human muscle con traction can be performed in the short muscle fibre segments obtained by th e percutaneous muscle biopsy technique both at the cellular and molecular l evel. The skinned fibre preparation in combination with a novel in vitro mo tility assay offers a unique possibility to investigate regulation of human muscle contraction at the cellular and molecular levels in the same muscle cell segment in both health and disease, i.e. in muscle cells characterize d according to the type and amount of expressed myofibrillar protein isofor ms.