Pain in Subjects with High Capacity Cognitive Abilities

Perceived quality of life was measured with the 36Item Short Form Health Survey (SF-36) scale validated in Spanish. This self-administered scale consists of 36 items in eight domains: physical functioning, limitations due to physical problems, physical pain, social role or function, mental health, limitations due to emotional problems, vitality and general perception of health.

The Tampa Scale of Kinesiophobia (TSK-11) was used to assess patients' fear of moving or engaging in physical activity. We used the Spanish version of this self-administered instrument, which consists of 11 items rated on a 4-point Likert scale. The total score ranges from 11 to 44, with higher values corresponding to a greater fear of being injured again by the movement. Scores of more than 27 points are considered high. The minimum detectable change of this instrument is 5.6

Catastrophism was assessed with the Pain Catastrophizing Scale. This scale is composed of 13 items rated on a scale from 0 to 4 points (a lower score indicates lower catastrophism). The questionnaire used is validated in Spanish

Anxiety was evaluated with the validated Spanish version of the State-Trait Anxiety inventory (STAI) questionnaire. This measuring instrument has two self-assessment scales to measure two independent anxiety concepts: state and trait. Both scales have 20 items each, which are scored on a Likert scale having four possible replies (from 0 to 3). This questionnaire presents a good internal consistency in the Spanish version in anxiety/state (Cronbach's α = .90 - .93) and in anxiety/trait (Cronbach's α = .84 - .87)

The instrument used to determine participants' PA level was the IPAQ short form. Total weekly amount of PA was calculated according to the method for computation of metabolic equivalent of task (MET)minutes/week, previously established in the IPAQ instructions for analysis and data processing of the questionnaire. Then, PA level was classified as: low (<600 METmin/week), moderate ( 600 METmin/week) and high ( 3000 METmin/week), following the same guidelines. This questionnaire has acceptable validity ( = 0.30, 95% CI: 0.23-0.36) and reliability (Spearman's =0.81, 95%CI:0.79-0.82) [30]. It has also been validated in Spain (r = 0.277; p < 0.05; 75% of specificity and sensibility; k = 0.33).

The perceived pain intensity was evaluated using the visual analogue scale. This scale has shown good reliability and validity for the assessment of pain intensity.18 This measuring instrument evaluates the intensity of pain on a 10 cm line (0 being "no pain" and 10 being "the worst pain"). Participants were asked to make a mark on the line to represent the average intensity of the usual joint pain they endure in the last 30 days. Similarly, they were asked to mark the maximum degree of pain they report in the last month.