Increases in local pressure pain thresholds after muscle exertion in women with chronic shoulder pain.

Abstract

To examine the relation between muscular tenderness and local muscular fatigue. Before-after trial, measuring pressure pain thresholds and signs of local muscular fatigue by using surface electromyography before, after, 10 minutes after, and 20 minutes after intervention. University rehabilitation department in Sweden. Nineteen female hospital cleaners with unilateral chronic shoulder pain for 1 year. No previous trauma, surgery, or signs of systemic or neurologic disease. Static abduction endurance test with submaximal unilateral activation of the trapezius and deltoid muscles. Pressure pain thresholds and electromyographic fatigue parameters (root mean square [RMS]; mean power frequency [MPF]). Mean normalized pressure pain threshold values increased significantly (95% confidence interval [CI]) and lasted for 20 minutes: in the trapezius, threshold values increased to 115% to 120% (95% CI, 100%-140%; P=.04-.05); and in the deltoid, the threshold increased to 112% to 115% (95% CI, 100%-130%; P=.02-.05). Development of significant electromyographically defined fatigue was seen: in the trapezius, the RMS increased to 130% (95% CI, 119%-141%), and in the deltoid, the MPF decreased to 78% (95% CI, 74%-82%), but normalized within 15 seconds to 10 minutes. Lasting bilateral increases in pressure pain thresholds but transient local muscular fatigue were seen after a unilateral static endurance test. The sensitivity of the sensory nervous system may change during a static muscle contraction and sometimes contributes to a localized sensation of numbness.