Differences in the mitochondrial and lipid droplet morphology in female office workers with trapezius myalgia, compared to healthy controls. A muscle biopsy study Objective Trapezius myalgia, or more specific, myofascial dysfunction of the upper trapezius mainly affects women performing jobs requiring prolonged low level activation of the muscle. This continuous low muscle load can be accompanied by a shift to a more anaerobic energy metabolism, causing pain. To investigate whether morphological signs of an impaired aerobic metabolism are present in female office workers with trapezius myalgia. Design Muscle biopsy analysis, using electron and light microscopy, was performed to compare mitochondrial and fat droplet morphology, and irregular muscle fibers, between female office workers with (n=17) and without (n= 15) work-related trapezius myalgia. Results The patient group showed a significantly higher mean area (P=0.023) and proportion (P=0.029) for the subsarcolemmal and intermyofibrillar mitochondria respectively, compared to the control group. A significantly lower mean area of subsarcolemmal lipid droplets was found in the patient group (P=0.015), which also displayed a significantly higher proportion of lipid droplets touching the mitochondria (P=0.035). A significantly higher amount of muscle fibers with COX deficient areas were found in the patient group (P=0.030). Conclusion The results of the present study may be indicatve for an impaired oxidative metabolism in work-related trapezius myalgia. However, additional research is necessary to confirm this hypothesis. Corresponding author: Kayleigh De Meulemeester Corneel Heymanslaan 10, 9000 Ghent (Belgium) Kayleigh.demeulemeester@ugent.be No conflicts of interest were present in writing this article. Kayleigh De Meulemeester is funded by BOF- UGent 01N04215. Copyright © 2019 Wolters Kluwer Health, Inc. All rights reserved.