Tactile Acuity and Pain Modulation

The pressure pain threshold (PPTs) of the upper trapezius and dominant tibialis anterior muscles will be evaluated. For the upper trapezius muscle, assessment will be made approximately 5 to 8 cm superomedial to the superior angle of the scapula. For the tibialis anterior muscle, the assessment will be made muscle belly, which is approximately 2.5 cm lateral and 5 cm inferior to the tibial tubercle. Palpation during resisted active dorsiflexion ensured that the tibialis anterior muscle belly had been found. Pressure pain thresholds will assessed using a pressure algometer (Algometer) with a stimulation area of 1 cm2. The increment rate of pressure will be kept at approximately 1 kg/cm2/s. The first time the pressure perceived as pain will be recorded as a PPTs. Two PPT assessments with a 30 second will be completed, and the average was used for statistical analysis.

Temporal summation (TS) of pressure pain will be elicited at the upper trapezius muscle by administering 10 consecutive pressure pulses using the algometer. For each pulse of the TS procedure, the pressure will be increased at approximately 2 kg/s until the previously determined PPT will be reached and maintained for one second. Pressure pulses will be presented with an inter-stimulus interval of one second. Participants will be instructed to rate their perceived pain intensity during the first, fifth, and tenth pressure pulse using a verbal numeric rating scale (VNRS). The TS pain score will be obtained by subtracting the first VNRS score from the last VNRS, with increased number indicates higher pain facilitation

An inflated occlusion cuff placed on the contralateral arm will be used as a conditioned stimulus. The occlusion cuff will be inflated at a rate of 20 mm Hg/s until "the first sensation of pain". At that point, it will be maintained for 30 s. Pain intensity will then be rated on a VNRS. Next, cuff inflation will be increased or decreased until the VNRS will be rated as 3/10. PPTs assessment will be repeated during maintenance of the cuff inflation. CPM will be calculated as the first NRS score during cuff inflation minus the first VNRS score before cuff inflation, with more positive values indicating more pain inhibition and more negative values indicating more pain facilitation.

It will be assessed by using two-point discrimination threshold on both sides of the neck. A sliding two-point Vernier Calliper with digital measurement will be placed under its own weight on the participant's skin, to provide two simultaneous tactile stimuli. For the spinal measures, the caliper will be aligned vertically 15 mm lateral to the spinous processes of C7. Assessment will be commenced with the two-points at a 20 mm separation, and will be increased by 2 mm increments until the participant reported feeling two points of contact. If two distinct points perceived in three consecutive trials this value will be recorded. A series of three ascending and descending assessments will be performed, with the mean of the six values will be used for analyses.