The aim of this study was to assess the blood flux responses to isometric contractions and recovery. We also wanted to assess the variations in Laser Doppler blood fluxes (LDF) within the upper trapezius muscles, the concordance between the left and right sides and the reliability of blood-flux measurements between contractions and over measurement days. Ten subjects, mean age 25 years (21–35 years), performed two isometric shoulder abduction contractions at 10% of maximal voluntary contraction torque (MVC), repeated on two separate days. LDF were measured in three sites in the upper trapezius muscles bilaterally. Mean arterial pressure, heart rate and electromyography from the upper trapezius muscles was also recorded. The reliability of blood flux measurements during rest and contractions are good; however, considerable variations between positions and between measurements in different muscles were observed. Laser-Doppler measurement of microcirculation is a promising method. Considerable variations between measurement sites, muscles, and variations over measurement days indicate caution with interpretation of blood flux responses between conditions and individuals.