The sarcoplasmic reticulum (SR) regulates intracellular calcium and therefore largely determines the rates of contraction and relaxation in skeletal muscle. However, little is known about SR function in human skeletal muscle. This thesis therefore investigated several factors that could potentially influence SR function in human skeletal muscle, including the effects of acute exercise, training status, chronic inactivity and the influence
of muscle fibre type. A final study investigated the effects of an immunosuppressive drug on SR function in rat skeletal muscle.