Se. Larsson et al., EFFECTS OF PSYCHOPHYSIOLOGICAL STRESS ON TRAPEZIUS MUSCLES BLOOD-FLOWAND ELECTROMYOGRAPHY DURING STATIC LOAD, European journal of applied physiology and occupational physiology, 71(6), 1995, pp. 493-498
Mental stress was induced by the Stroop colour word task (CW task) and
the effects on the microcirculation and electromyography (EMG) in the
upper portion of the trapezius muscle were studied during a series of
fatiguing, standardized static contractions. A lowered blood flow of
the skin recorded continuously by laser-Doppler flowmetry (LDF) was us
ed as a stress indicator in addition to an elevated heart rate. Muscle
blood flow was recorded continuously by LDF using a single optical fi
bre placed inside the muscle, and related to surface EMG. A group of 2
0 healthy women of different ages was examined. Recordings were made d
uring a 50-min period in the following sequence: a 10-min series of al
ternating 1-min periods of rest and stepwise increased contraction ind
uced by keeping the arms straight and elevated at 30, 60, 90 and 135 d
egrees with a 1-kg load carried in each hand; a 10-min recovery period
without load; a repeated contraction series with simultaneous perform
ance of the CW task; a second 10-min recovery period, and a second con
traction series without CW task. Signal processing was done on line by
computer. The LDF and root mean square (rms)-EMG values were calculat
ed, as well as the EMG mean power frequency (MPF) for fatigue. The CW-
task added to the contraction series caused an increase in the heart r
ate accompanied by a decrease in the blood flow to the skin and a 30%
increase in the blood flow in the exercising muscle. Both returned to
normal during the subsequent recovery period and showed normal levels
during the final contraction series without CW. The rms EMG showed a 2
0% increase that persisted during the final contraction series perform
ed without CW. There was no influence on MPF. This CW has previously b
een shown to evoke an increased secretion of adrenaline from the adren
al medullae to the blood. The increased blood flow in the exercising m
uscle would therefore appear to have been caused by beta-adrenoceptor
vasodilatation, and the fall ill the blood flow in the skin by cu-adre
noceptor vasoconstriction. The findings may have implications for work
situations characterized by repetitive static loads to the shoulder m
uscles and psychological stress.