MICROCIRCULATION IN THE UPPER TRAPEZIUS MUSCLE DURING VARYING LEVELS OF STATIC CONTRACTION, FATIGUE AND RECOVERY IN HEALTHY WOMEN - A STUDYUSING PERCUTANEOUS LASER-DOPPLER FLOWMETRY AND SURFACE ELECTROMYOGRAPHY

Microcirculation in the upper portion of the trapezius muscle was meas ured percutaneously by continuous laser-Doppler flowmetry (LDF) during two 10-min series of alternating 1-min periods of static contraction and rest determined electromyographically (EMG). Stepwise increased co ntraction was induced by keeping the arms straight and elevated at 30, 60, 90 and 135-degrees, which was repeated with a 1-kg load carried i n each hand. Thereafter, fatigue and recovery were recorded while the subject kept her arms straight and elevated at 45-degrees carrying the 1-kg hand load as long as possible, followed by rest with arms hangin g and no load. A group of 16 healthy women of different ages was studi ed. Signal processing was done on line using a 386 SX computer. The LD F- and root-mean-square (rms) EMG signals were normalized. Spectrum an alyses of EMG mean power frequency (MPF) and median spectrum frequency were performed. The rms-EMG increased significantly with an increase in the calculated shoulder torque (r = 0.75). Accumulated local fatigu e was indicated by a decrease in MPF with increased shoulder angle and added load (r = -0.54). Blood flow increased with increased shoulder angle (r = 0.82, with hand load r = 0.62) and with increased shoulder torque (r = 0.72), and also showed a significant increase with increas ed EMG activity (r = 0.74). The LDF showed a negative correlation to M PF (r = -0.67), with increased values when MPF was lowered. During the endurance test, a moderate increase of LDF occurred which reached its maximum during the 1st min of recovery. Then, a slow return to the ba se level was recorded. The ability to increase the flow in the microci rculation with increasing muscle load was not diminished with age.