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 fast skeletal muscle. In situ rat medial gastrocnemius muscles performed 15 repeated shortening contractions (2 s(-1); velocity 50 mm s(-1)) with occluded blood flow while activated with triplets of 400 Hz followed by 60 Hz trains (T400;60) or with constant-frequency trains of either 60 or 91 Hz. All stimulation patterns consisted of six pulses. After the last contraction, the muscles were quickly freeze-clamped and analysed for metabolite levels. The calculated efficiencies were 20.4+/-3.0 mJ micromol(-1 )P (N=7), 19.4+/-1.8 mJ micromol(-1 )P (N=8) and 19.6+/-2.5 mJ micromol(-1 )P (N=7; means +/- s.d.) for T400;60, 60 and 91 Hz stimulation respectively (P>0.05). It is concluded that, although high-frequency initial pulses can enhance muscle performance, the efficiency of rat fast skeletal muscle did not differ from that for submaximal constant-frequency stimulation patterns.