Effects of Temperature on Low‐Frequency Fatigue in Isolated Skeletal Muscle

Abstract

Muscles exposed to sustained, low‐frequency stimulation experience a reduction in force production known as low‐frequency fatigue. Also, many aspects of the contractile process in skeletal muscle are influenced by ambient temperature. The purpose of this study was to investigate what interactions might exist between variations in temperature and this form of muscle impairment. Paired sartorii muscles (60–70 mg) from male R. pipiens (N=10) were dissected‐free and vertically‐mounted in water‐jacketed chambers containing oxygenated (100%), Ringer solution (pH 7.2). Both muscles from a single animal were stimulated identically for 20s (supramaximal square wave pulses; 0.2 ms; 25 Hz) albeit at two different temperatures (15°C and 25°C). Peak tensions (PT, g; means ± SEM) were 35.0 ± 2.4 (15°C) v. 23.2 ± 1.8 (25°C). Average tensions (AT, g) were 12.9 ± 2.1 (15°C) and 8.0 ± 0.7 (25°C). Tension‐time integrals (TTI, g·s) were 234.6 ± 30.5(15°C) and 145.8 ± 14.8 (25°C). In each instance, differences between 15°C and 25°C were highly significant (p<.01). Nevertheless, the total percent decline in force over the stimulation period did not appear to be greatly influenced by ambient temperature (−86.4 ± 0.9% (15°C) v. −89.3 ± 0.7% (25°C; p>.01). Results suggest that variations in the thermal environment may have a somewhat lesser effect on relative fatigue in skeletal muscle when compared to other indices of muscle function.