Hypoalgesic Effect of Electrical Current and Cervical Manipulation

The subject's skin will be cleaned with mild soap and water. Two square self-adhesive electrodes (5x5cm) will be placed 1 cm below the olecranon of the ulna and 10 cm above the radiocarpal joint of the dominant hand, maintaining the PPT measurement region between two electrodes. Two identical TENS units will be used: an active and a placebo (Neurodyn Portable TENS, IBRAMED). The active unit will be applied with the patient in a supine position at a high frequency of 100 Hz, and pulse duration of 100 µs. Strong but comfortable intensity as dictated by each subject will be applied for 20 minutes. Participants will be asked about the intensity of TENS every 5 minutes, and if the intensity has faded, the intensity will be increased again to a strong but comfortable level.

The examiner 3, who is responsible for cervical joint manipulation, will enter the room and stand at the head of the patient. Using the middle phalanx of the second finger of one hand, the examiner will apply pressure laterally on the joint processes of C6 and C7 vertebrae; the examiner will cradle the patient's opposite side with the other hand and then perform an ipsilateral inclination towards the C6, C7 segments, followed by a contralateral rotation to the tissue barrier to perform a high-velocity low-amplitude manipulation (thrust). If the patient does not experience joint cavitation during the maneuver, two more attempts will be made. If no sound occurs on the third attempt, the joints will be considered manipulated.

The application of placebo TENS will be at a frequency of 100 Hz and pulse duration of 100 µs for 30 seconds. After the initial 30 seconds, the current amplitude will gradually decrease over 15 seconds until it reaches zero value. Participants will be informed that TENS can cause a slight tingling sensation or any sensation during the procedure. They will be asked every 5 minutes if they are comfortable, without increasing intensity as in the active TENS group

Placebo CJM will be performed using an identical position to the active manipulation, however, for only 15 seconds, as proposed by some authors that have used placebo group in their studies. The examiner shall not exert tension in the joint capsule of the segment to ensure the placebo effect. The maneuvers will be carried out by a physiotherapist with more than 5 years of experience in manual therapy. The active or placebo manipulation will be performed on the right or left side according to randomization.