Pain and tenderness of the upper trapezius muscle is frequent in several occupational groups. The objective of this study is to investigate the effect of three contrasting interventions on muscle function and pain in women with trapezius myalgia. A group of employed women (n = 42) with a clinical diagnosis of trapezius myalgia participated in a 10-wk randomized controlled intervention: specific strength training of the neck/shoulder muscles, general fitness training performed as leg bicycling, or a reference intervention without physical activity. Torque and electromyography (EMG) were recorded during maximal shoulder abductions in an isokinetic dynamometer at -60, 60, 0, and 180 degrees /s. Furthermore, a submaximal reference contraction with only the load of the arms was performed. Significant changes were observed only in the specific strength training group. Pain decreased by 42-49% (P < 0.01-0.05). Whereas the EMG activity of the unaffected deltoid remained unchanged during the maximal contractions, an increase in EMG amplitude (42-86%; P < 0.001-0.05) and median power frequency (19%; P < 0.001) were observed for the painful trapezius muscle. Correspondingly, torque increased by 18-53% (P < 0.001-0.05). EMG during the reference contraction decreased significantly for both the trapezius and deltoid muscles (P < 0.01). In conclusion, specific strength training relieves pain and increases maximal activity specifically of the painful trapezius muscle, leading to increased shoulder abduction strength in women with trapezius myalgia. Furthermore, decreased relative workload may indirectly augment pain reduction.