Increase in muscle nociceptive substances and anaerobic metabolism in patients with trapezius myalgia: microdialysis in rest and during exercise

Abstract

Local metabolic changes are suggested to be involved in muscle pain development in humans. Nineteen women with chronic work-related trapezius myalgia (TM) and 20 healthy female controls (CON) were studied during baseline rest, 20 min repetitive low-force exercise, and 120 min recovery. Interstitial serotonin (5-HT), glutamate, lactate, pyruvate, and blood flow were determined by microdialysis in the trapezius muscle. Baseline pressure pain threshold (PPT) was lower (143±18 (TM) vs. 269±17 (CON) kPa) (mean±SEM), pain intensity (visual analogue scale, VAS) higher (33±5 vs. 2±1 mm), muscle 5-HT higher (22.9±6.7 vs. 3.8±1.3 nmol/l), and glutamate higher (47±3 vs. 36±4 μmol/l) in TM than in CON (all P<0.05), whereas muscle blood flow was similar in groups. Furthermore, muscle pyruvate was higher (180±15 vs. 135±12 μmol/l) and lactate higher (4.4±0.3 vs. 3.1±0.3 mmol/l) in TM than in CON ( P<0.001). In response to exercise, VAS and glutamate increased in both TM and CON (all P<0.05). In TM only, lactate and pyruvate increased significantly ( P<0.02), whereas blood flow increased to similar levels in both groups. During the initial 20 min recovery period, blood flow remained increased in TM ( P<0.005) whereas it decreased to baseline levels in CON. In conclusion, patients with chronic work-related TM have increased levels of muscle 5-HT and glutamate that were correlated to pain intensity ( r=0.55, P<0.001) and PPT ( r=−0.47, P<0.001), respectively. In addition, TM was associated with increased anaerobic metabolism, whereas a normal rise in blood flow was seen with exercise. These findings indicate that peripheral nociceptive processes are active in work-related TM.