The interaction between peripheral and central fatigue at different muscle temperatures during sustained isometric contractions

Changes in central fatigue have been linked to active and passive changes in core temperature, as well as integration of sensory feedback from thermoreceptors in the skin. However, the effects of muscle temperature (Tm), and thereby metaboreceptor and local afferent nerve temperature, on central fatigue (measured using voluntary activation percentage) during sustained, high muscle fatigue exercise remain unexamined. In this study, we investigated Tm across the range of cold to hot, and its effect on voluntary activation percentage during sustained isometric contractions of the knee extensors. The results suggest that contrary to brief contractions, during a sustained fatiguing contraction Tm significantly ( P < 0.001) influences force output (−0.7%/°C increase) and central fatigue (−0.5%/°C increase), showing a negative relationship across the Tm continuum in moderately trained individuals. The negative relationship between voluntary activation percentage and Tm indicates muscle temperature may influence central fatigue during sustained and high muscle fatigue exercise. On the basis of on an integrative analysis between the present data and previous literature, the impact of core and muscle temperature on voluntary muscle activation is estimated to show a ratio of 5.5 to 1, respectively. Accordingly, Tm could assume a secondary or tertiary role in the reduction of voluntary muscle activation when body temperature leaves a thermoneutral range.

Measurements of Drill-Induced Temperature Change in the Facial Nerve during Mastoid Surgery: A Cadaveric Model Using Diamond Burs

The purpose of this study was to investigate the changes in temperature in the facial nerve that occur during mastoid drilling by the facial recess approach and to confirm the beneficial effects of constant irrigation while drilling. Mastoid drilling was performed on human cadaveric temporal bones by means of 4-mm diamond burs with and without irrigation. There were 6 subjects in each group. Changes in facial nerve temperature were recorded on a continuous-output monitor. Significant changes were found in temperature for both the irrigation and non-irrigation groups (p < .0001). Constant irrigation minimized the rise in temperature. Facial recess drilling poses a potential threat to cranial nerve VII via thermal injury. The temperature elevation in the non-irrigation group was significantly greater than that in the irrigation group and was greater than the tolerable limits of peripheral nervous tissue. This finding supports the need for constant irrigation during the approach to the facial recess in mastoid surgery.