Energetic patterns of normally circulated mammalian muscle in situ.

To determine if the energetic patterns of in situ normally circulated mammalian skeletal muscle are similar to those obtained using myothermic and chemical methods, oxygen uptake by gastrocnemius-plantaris and semitendinosus muscles was measured during contractions. The relationships between oxygen uptake and load in twitch and tetanic contractions are similar to those obtained by other methods, provided comparable initial lengths were used. The relations observed among oxygen uptake and load, tension, work, and shortening were observed under a wide range of mechanical conditions. Two factors were found to be related to oxygen uptake: 1) non-cross-bridge energy use and 2) cross-bridge cycling.