The Effect of Experimental Quadriceps Muscle Pain on Nociceptive and Non-nociceptive Somatosensation

Purpose: Both hyperalgesia and hypoesthesia have been reported in individuals with chronic pain. Although previous studies have investigated clinical characteristics of chronic pain, less is known on the effect of persistent pain on somatosensation. Specifically, while hypoesthesia in terms of proprioceptive deficits and vibration perception deficits have been reported in different chronic pain populations, a direct relationship between pain and hypoesthesia has not been demonstrated. The purpose of this study is to examine the effect of experimentally induced quadriceps muscle pain on nociceptive and non-nociceptive somatosensation and to investigate whether changes in measures of hypoesthesia correlate following induction of pain. Methods: In ten healthy individuals, quadriceps pain was induced via an eccentric exercise protocol. The dominant limb served as the experimental side and the non-dominant limb served as a control. Measurements which included pressure pain threshold (PPT), proprioception, measured via threshold to detect passive movement (TDPM), vibration perception threshold (VPT), subjective report of pain measured via visual analog scale (VAS) and Y-balance test were performed at baseline, immediately following the exercise and two days post-exercise. Results: Compared with baseline measures, a significant difference was found in all measures of hyperalgesia, as by PPT (P<0.05), and in measures of hypoesthesia including TDPM (P<0.05) and VPT (P<0.05) at the experimental knee post-exercise. PPT measures were also significantly reduced at the vastus medialis muscle (P<0.05), the tibialis anterior muscle (P<0.05) and the webspace between the 1st and 2nd metacarpals of the contralateral hand (P<0.05) at two days post-exercise. Measures of TDPM (P=0.19) and VPT (P=0.74) on the contralateral knee were not significantly different as compared to baseline. Change scores for measures of hypoesthesia, ie, proprioception and VPT, were moderately correlated (r=0.439), however this relationship was not significant (P=0.106). Conclusion: This study found that experimentally induced quadriceps pain resulted in widespread hyperalgesia and hypoesthesia locally at the painful limb, as measured by knee proprioception and VPT at the knee. Pain induced hypoesthesia may occur through central inhibitory mechanisms. A moderate but non-significant relationship was found between change scores of hypoesthesia, indicating that the two modalities, while distinct, may be affected via similar mechanisms.