Infrared thermography of bullfrog skeletal muscle at rest and during an isometric tetanus

Abstract

Heat production in skeletal muscle has been studied with a thermopile consisting of several thermocouples in contact with muscle surface, and the experimental results have been interpreted on the assumption that heat is produced in a uniform manner. In the present study we have examined the temperature distribution of bullfrog sartorius muscle by the technique of infrared thermography, in which muscle temperatures at various regions can be measured and displayed as a thermogram on the monitor screen without thermal contact. It was found that in the muscle at rest and during an isometric tetanus, the temperature was not uniform, but differed from region to region. The amount of heat production during an isometric tetanus also differed from region to region, but the time course of heat production was nearly uniform in every region. By putting position markers on the muscle surface, it was possible to record muscle segment length changes together with temperature changes. It was found that during an isometric tetanus, the tibial region was stretched by the other regions, and the amount of heat produced was significantly greater in the other regions than in the tibial region. The application of infrared thermography in muscle energetics studies seems promising if the sensitivity of infrared detectors is improved.