Variation in the isometric maintenance heat rate with muscle length near that of maximum tension in frog striated muscle.

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Abstract
Tension and heat rate were measured as a function of muscle length in the range 0.75-1.25 l0 in 10 s isometric tetani in frog striated muscle at 0.degree. C in 7 experiments. l0 was defined as the length at which maximal tension was developed. The length at which the stable maintenance heat rate (.ovrhdot.hB) was maximal was 7-16% l0 shorter than the length at which tension was maximal (Pmax). The range of .ovrhdot.hB at the length at which tension was maximal was 0.82-0.97 times the maximum value of .ovrhdot.hB. For equal values of tension of 0.9 Pmax on each side of l0, .ovrhdot.hB was almost 40% greater at the shorter muscle length. .ovrhdot.hB varies considerably with muscle length near l0, where tension varies little. Tension is probably not the sole determinant of energy liberation in this length region.