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BioMed Research International
Volume 2015, Article ID 265278, 11 pages
Research Article

Neuronal Nitric Oxide Synthase Is Dislocated in Type I Fibers of Myalgic Muscle but Can Recover with Physical Exercise Training

1Institute of Sports Science and Clinical Biomechanics, University of Southern Denmark, 5000 Odense C, Denmark
2Institute of Clinical Research, Pathology and SDU Muscle Research Cluster, University of Southern Denmark, 5230 Odense M, Denmark
3National Research Centre for the Working Environment, 2100 Copenhagen, Denmark

Received 15 December 2014; Revised 24 January 2015; Accepted 18 February 2015

Academic Editor: Leonardo F. Ferreira

Copyright © 2015 L. Jensen et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.


Trapezius myalgia is the most common type of chronic neck pain. While physical exercise reduces pain and improves muscle function, the underlying mechanisms remain unclear. Nitric oxide (NO) signaling is important in modulating cellular function, and a dysfunctional neuronal NO synthase (nNOS) may contribute to an ineffective muscle function. This study investigated nNOS expression and localization in chronically painful muscle. Forty-one women clinically diagnosed with trapezius myalgia (MYA) and 18 healthy controls (CON) were included in the case-control study. Subsequently, MYA were randomly assigned to either 10 weeks of specific strength training (SST, ), general fitness training (GFT, ), or health information (REF, ). Distribution of fiber type, cross-sectional area, and sarcolemmal nNOS expression did not differ between MYA and CON. However, MYA showed increased sarcoplasmic nNOS localization (18.8 ± 12 versus 12.8 ± 8%, ) compared with CON. SST resulted in a decrease of sarcoplasm-localized nNOS following training (before 18.1 ± 12 versus after 12.0 ± 12%; ,027). We demonstrate that myalgic muscle displays altered nNOS localization and that 10 weeks of strength training normalize these disruptions, which supports previous findings of impaired muscle oxygenation during work tasks and reduced pain following exercise.