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The nociceptive flexion reflex (NFR) is a polysynaptic withdrawal reflex that occurs in response to painful stimulation. In human studies, NFR responsiveness has been used as a direct measure of nociception as well as an indirect measure of supraspinal modulation of nociceptive transmission. Previous studies have suggested that anxiety may influence NFR responding, and therefore it has been recommended that anxiety be reduced by familiarizing participants with assessment methodology prior to formal NFR assessment. The present study was designed to assess the influence of anxiety on NFR threshold. Using a repeated measures design, 40 men and women completed an NFR threshold assessment twice within session one, and twice again during a second session conducted 24 h later. Within each assessment session, state anxiety was measured at the beginning of the session and immediately following each NFR threshold assessment. Results indicated that although anxiety increased in response to NFR threshold assessment and was positively related to subjective pain reports, anxiety was not related to observed NFR threshold levels. These findings suggest that individual differences in anxiety do not significantly affect NFR threshold level determinations under standard testing conditions.

Catastrophizing is reliably associated with increased reports of clinical and experimental pain. To test the hypothesis that catastrophizing may heighten pain experience by increasing nociceptive transmission through spinal gating mechanisms, the present study examined catastrophizing as a predictor of pain ratings and nociceptive flexion reflex (NFR) thresholds in 88 young adult men (n = 47) and women (n = 41). The NFR threshold was defined as the intensity of electrocutaneous sural nerve stimulation required to elicit a withdrawal response from the biceps femoris muscle of the ipsilateral leg. Participants completed an assessment of their NFR threshold and then provided pain ratings using both a numerical rating scale (NRS) and the short-form McGill pain questionnaire (SF-MPQ). Pain catastrophizing was assessed using the catastrophizing subscale of the coping strategies questionnaire (CSQ). Although catastrophizing was positively related to both NRS and SF-MPQ pain ratings, catastrophizing was not significantly related to NFR threshold. These findings suggest that differential modulation of spinal nociceptive input may not account for the relationship between catastrophizing and increased pain.