Abstract
Objectives. To investigate associations between muscle strength and pain sensitivity among healthy volunteers and associations between different pain sensitivity measures. Methods. Twenty-eight healthy volunteers (21 females) participated. Pressure pain thresholds (PPTs) were obtained from 1) computer-controlled pressure algometry on the vastus lateralis and deltoid muscles and on the infrapatellar fat pad and 2) computerized cuff pressure algometry applied on the lower leg. Deep-tissue pain sensitivity (intensity and duration) was assessed by hypertonic saline injections into the vastus lateralis, deltoid, and infrapatellar fat pad. Quadriceps and hamstring muscle strength was assessed isometrically at 60-degree knee flexion using a dynamometer. Associations between pain sensitivity and muscle strength were investigated using multiple regressions including age, gender, and body mass index as covariates. Results. Knee extension strength was associated with computer-controlled PPT on the vastus lateralis muscle. Computer-controlled PPTs were significantly correlated between sites (r > 0.72) and with cuff PPT (r > 0.4). Saline induced pain intensity and duration were correlated between sites (r > 0.39) and with all PPTs (r < −0.41). Conclusions. Pressure pain thresholds at the vastus lateralis are positively associated with knee extensor muscle strength. Different pain sensitivity assessment methods are generally correlated. The cuff PPT and evoked infrapatellar pain seem to reflect the general pain sensitivity. This trial is registered with ClinicalTrials.gov: NCT01351558.
Highlights
Most pain sensitivity measures were not associated with muscle strength (Table 2), except for the PPTCCPA at the infrapatellar fat pad and vastus lateralis muscle that were significantly positively associated with isometric knee extension muscle strength
When adjusting for age, gender, and BMI, only the PPTCCPA at vastus lateralis remained positively associated with isometric knee extension muscle strength
The PPTCCPA at the vastus lateralis muscle was significantly associated with isometric knee flexion muscle strength in the univariate regression, but this association was not significant when adjusting for covariates (Table 2)
Summary
While pain is the cardinal symptom in many musculoskeletal diseases, impaired muscle function is a typical sign of musculoskeletal diseases, such as fibromyalgia and osteoarthritis [3, 4]. Many musculoskeletal diseases have been associated with increased pain sensitivity. The increased pain sensitivity has been reported [6], and widespread increased pain sensitivity have been demonstrated in subgroups of patients with osteoarthritis, lateral epicondylitis, and low back pain [7,8,9]. Jespersen et al showed recently that the pain sensitivity on the lower leg assessed using cuff pressure algometry was associated with quadriceps muscle strength in fibromyalgia patients; patients with lower thigh muscle strength had higher pain sensitivity at the lower leg [10]. As muscle strength is a general marker of physical function, this finding suggests an association between physical function and generalized
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