Comparing fatigue induced by isometric and shortening contractions in skeletal muscle

The intramuscular mechanisms causing greater fatigue-induced reduction in force during shortening compared with isometric contractions is not completely understood. The focus of this thesis was to compare fatigue in repeated shortening contractions and isometric contractions and investigate if greater force loss during repeated shortening contractions is attributed to more severe reductions in sarcoplasmic reticulum Ca2+ release. Single intact flexor digitorum brevis muscle fibres from C57Bl/6 mice were mechanically dissected and loaded with indo-1 AM fluorescent dye to assess myoplasmic free [Ca2+]. Fibres were either placed in an isometric or shortening protocol which were both stimulated at 70Hz of 600ms duration and 4 seconds rest for 50 tetani. The results of this thesis did not show that repeated shortening contractions cause greater fatigue-induced reductions in force compared with repeated isometric contractions, and there were no differences in the fatigue-induced reductions in SR Ca2+ release during the repeated contractions.