Abstract
We examined the effect of mental stress on hemoglobin concentrations in the trapezius muscles of 20 healthy, non-smoking women. The participants held their arms out horizontally (physical stimulus) while standing upright for 1 min with 5 min intervals of seated rest, or performed Stroop's Color Word Test (mental stimulus), or both simultaneously. We measured heart rate, muscle tissue hemoglobin (oxy-hemoglobin, OxyHb; deoxy-hemoglobin, DeoHb; total hemoglobin, TotHb) concentrations in, and obtained surface electromyograms from the right upper trapezius muscle. Changes in the hemoglobin concentration (DeltaOxyHb, DeltaDeoHb, DeltaTotHb) induced by physical and/or mental stimuli were calculated. Changes with physical stimulus alone were compared with those induced by physical plus mental stimuli using repeated measures ANOVA. The DeltaDeoHb with physical and mental stimuli was significantly lower (p=0.013) than that with the physical stimulus alone, whereas the DeltaOxyHb and the DeltaTotHb values did not significantly differ (p=0.281, p=0.230). This finding indicates that mental load affects DeltaDeoHb in the trapezius muscle. We think that mental stimulus might provoke a reduction in oxygen consumption by the trapezius muscle. Further investigations using a longer duration of physical and mental stimuli are required.
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