Lengthening contractions differentially affect p70s6k phosphorylation compared to isometric contractions in rat skeletal muscle.

The purpose of this investigation was to determine if p70(s6k) phosphorylation is dependent on the mode of resistance exercise (e.g. isometric vs. lengthening). Two groups (n = 5 each) of Female Sprague Dawley rats, approximately 12 weeks old, were tested. Rats were anesthetized and indwelling electrodes used to stimulate the right hind limb muscles via the sciatic nerve. The tibialis anterior (TA) muscle of Group 1 rats were exposed to three sets of ten isometric resistance contractions while the TA of Group 2 rats were exposed to three sets of ten resistance contractions that involved lengthening. Contralateral TA muscles served as non-exercised controls. The TA muscle was harvested 6 h post exercise and then the rat was euthanized. Muscle samples were processed to compare p70(s6k) phosphorylation between groups. A single bout of TA contractions that involved muscle lengthening resulted in significantly (p < 0.05) higher levels of phospho-p70(s6k) six hours post exercise compared to controls and isometric contractions. The differences in total p70(s6k) six hours post exercise were not significantly different between groups. Results suggest that signal transduction pathways activated by isometric exercise may differ (i.e., a non-p70(s6k) activation pathway) from that activated by lengthening exercise.