Microcirculation in the upper trapezius muscle during sustained shoulder load in healthy women an endurance study using percutaneous laser-Doppler flowmetry and surface electromyography

Abstract

Microcirculation in the upper portion of the trapezius muscle was measured percutaneously in a group of 16 healthy women of different ages by continuous laser-Doppler flowmetry (LDF) in relation to electromyography (EMG) during an endurance test. During the measurements the subject kept her arms straight and elevated at 45 degrees in the scapular plane and held a 1-kg load in each hand as long as possible. This was followed by rest with the arms hanging and carrying no load. The 10-min recording period comprised 1-min initial rest followed by the endurance test and then recovery. Signal processing was done by computer on line. The LDF and root-mean-square (rms) EMG signals were normalized. Spectrum analyses of EMG mean power frequency (MPF) were performed. The amount of load produced was on average 2,267 (SD 939) N.m.s, i.e. shoulder torque x time expressed as Newton meter seconds, and the endurance time was 4.3 (SD 1.20) min. The rms-EMG as well as the LDF increased significantly during endurance, both when related to endurance time and to amount of load. The MPF showed no significant changes. The mean total increase in muscle blood flow was 175% of that recorded in the initial rest period. The average increase per each 10 s of contraction was 2.9%. Maximum was reached during the 1st min of recovery followed by a fall to the base level that was reached within 77 s on average. The amount of load produced and the blood flow increase was smaller than that found in a separate study of men, indicating a lower functional capacity.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of mechanical compression due to load carrying on shoulder muscle fatigue during sustained isometric arm abduction: an electromyographic study

“…Results concerning UT fatigue parameters were in agreement with previous studies (Larsson et al 1993b(Larsson et al , 1995Farina et al 2003). In the study of Farina et al (2003), the mean value of UT fatigability (also estimated from the normalised MPF slope) was of about ¡0.05%MPF i /s, which was close to that obtained during the reference condition, i.e.…”

Influence of electrode position on changes in electromyograph parameters of the upper trapezius muscle during submaximal sustained contractions

“…Takala et al 1993;Nieminen et al 1993;Ö berg et al 1994;Larsson et al 1995), it has been found that the recording of a signal 2-cm lateral of the midpoint not only gave a higher signal, but also showed a higher repeat consistency or lower variation (Veiersted 1991;Jensen et al 1993). The larger variation in EMG amplitude at the midpoint has been explained by the location of the bipolar electrodes symmetrically around the innervation zone and therefore the more lateral position has been considered as the most suitable location for representing the upper trapezius and for measurement of shoulder muscle activity in laboratory or occupational settings.…”

Mathematical and empirical proof of principle for an on-body personal lift augmentation device (PLAD)

“…Unlike a backpack, the PLAD would normally load and unload the shoulders during lifting tasks and hence workers should be able to tolerate the PLAD forces for extended periods of time. However, higher shoulder contact forces may be problematic for static holding tasks, such as needed by mechanics, dentists and carpet layers, since blood would be occluded to the shoulder muscles (Larsson et al, 1995).…”