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

1. Tension and heat rate were measured as a function of muscle length in the range 0.75--1.25 lO in 10-sec isometric tetani in frog striated muscle at 0 degrees C in seven experiments. lO was defined as the length at which maximal tension was developed. 2. The length at which the stable maintenance heat rate (hB) was maximal was 7--16% lO shorter than the length at which tension was maximal (Pmax). 3. The range of hB at the length at which tension was maximal was 0.82-0.97 times the maximum value of hB. 4. For equal values of tension of 0.9 Pmax on each side of lO, hB was almost 40% greater at the shorter muscle length. 5. The results show that h(B) varies considerably with muscle length near lO, where tension varies little, and imply that tension is not the sole determinant of energy liberation in this little region.