High-frequency initial pulses do not affect efficiency in rat fast skeletal muscle

This study investigated the effects of high-frequency initial pulses on the efficiency (=total work output/high-energy phosphate consumption) of rat f ast skeletal muscle. In situ rat medial gastrocnemius muscles performed 15 repeated shortening contractions (2 s(-1); velocity 50 mm s(-1)) with occlu ded blood how while activated with triplets of 400 Ha followed by 60 Hz tra ins (T400;60) or with constant-frequency trains of either 60 or 91 Hz. All stimulation patterns consisted of sis pulses. After the last contraction, t he muscles were quickly freeze-clamped and analysed for metabolite levels. The calculated efficiencies were 20.4 +/-3.0 mJ mu mol(-1) P (N=7), 19.4 +/ -1.8 mJ mu mol(-1) P (N=8) and 19.6 +/-2.5 mJ mu mol(-1) P (N=7; means +/- S.D.) for T400;60, 60 and 91 Hz stimulation respectively (P >0.05). It is c oncluded that, although high-frequency initial pulses can enhance muscle pe rformance, the efficiency of rat fast skeletal muscle did not differ from t hat for submaximal constant-frequency stimulation patterns.