Slow- and fast-contracting skeletal muscle fibers have more similar cellular and molecular contractile function at 37°C than at 25°C in older adults.

As human skeletal muscle cellular and molecular contractile properties are temperature-sensitive, the ability to perform experiments at body temperature (∼37°C) may lead to a better understanding of their Abstract Figure: KEY POINTS SUMMARY: Although skeletal muscle function is highly sensitive to temperature, human single fiber studies have only been conducted at ≤30°C.Small-amplitude sinusoidal perturbations were utilized to elucidate mechanisms of single fiber force production at human physiological temperature (37°C).We found that functional differences in slow-contracting myosin heavy chain (MHC I) and fast-contracting MHC IIA fibers observed at 25°C were less apparent at 37°C, as force, crossbridge kinetics, and strongly-bound crossbridges increased more in MHC I fibers than MHC IIA fibers at 37 vs. 25°C. These results indicate that, given the different sensitivity of each fiber type to changes in temperature, functional assessments of muscle should be conducted at 37°C to better translate to