Association between the analgesic effects of Conditioned Pain Modulation (CPM) and Manipulation induced Pain Modulation (MIPM)

Once eligibility criteria are confirmed, each participant will be asked to attend for preliminary assessment with CPM and MIPM assessment protocols in a single session. CPM and MIPM assessment protocols are described as follows: Conditioned Pain Modulation (CPM) Assessment Protocol Test stimulus: Pressure Pain Threshold (PPT) will be used as the test stimulus and measured by an electronic digital algometer (Somedic AB, Sweden). Participants will sit on a chair of adjustable height so the forearm is comfortably supported. PPT will be performed two marked locations of the affected arm, which will be positioned in pronation on a table. PPT will be tested at baseline prior to cold water immersion, after 1 min during immersion, and 1 min post immersion. At each time point, PPT will be measured three times with 10-15 s rest intervals in between. The mean value of the three measurements at each point will be used for analysis. Conditioning stimulus: The Cold Pressor Test (CPT) will be used as a conditioning stimulus to elicit the CPM response. The unaffected hand will be submerged 4 inches above the wrist crease in a cold water bath, with a temperature maintained at 7 degrees Celsius for a period of 2 min The water bath contains a mix of water and ice and it is supplied with a circulating pump to ensure uniformity of water temperature at the skin. The difference between PPT measurements taken before and after water immersion represents the CPM effect. This will be quantified as the percentage change in PPT relative to the baseline measure. Separate percentage change measures will be obtained for the wrist and elbow sites. Manipulation Induced Pain Modulation (MIPM) Assessment Protocol Test stimulus: PPT will be the test stimulus. The Pain Free Grip (PFG) test, Upper Limb Neurodynamic Test (ULNDT) with radial nerve bias and measures of PPT at both test sites will be carried out at baseline and then repeated immediately after the conditioning stimulus (C5/6 contralateral lateral glide mobilisation). Testing will be performed with the participants lying supine on a plinth. PFG and UNLDT will provide additional measures of the MIPM effect. Conditioning stimulus: a grade III passive oscillatory, contralateral lateral glide (CLG) mobilisation of the C5/6 motion segment of the cervical spine will be used to induce MIPM The participant will be comfortably lying supine with arms by their side and instructed to report if they feel any discomfort or pain during execution of the mobilisation. In contrast to CPM this conditioning stimulus should be painless. The therapist will depress the scapulae with one hand, while the other hand cradles the occiput and neck above the C5/6 segment. Using the cradling hand, the therapist will apply a grade III passive oscillatory CLG directed towards the unaffected upper limb. The CLG stimulus will be performed for 60 s, and will be repeated three times, with 60-s rest periods in between (5 min total). The difference between PTT measurements taken before and after CLG mobilisation represents the MIPM effect. This will be quantified as the percentage change in PPT relative to the baseline measure. Separate percentage change measures will be obtained for the wrist and elbow sites and the PFG and ULNDT measures. The CPM assessment protocol will be followed by the MIPM assessment protocol with a rest period of 15 min in between. All outcome measures will be performed by the same researcher applying the CPM and the manual therapy stimuli. All instructions will be standardized. Subjects will be asked to avoid physiotherapy and other forms of physical exercise on the day of assessment. A Physiotherapy PhD student, who has a masters degree in manual therapy and 8 years post masters experience in manual therapy, will conduct all assessment procedures previously described. Experimental procedures, including the eligibility testing, will be conducted at the Physiotherapy Clinic at the School of Physiotherapy and Exercise Science at the Bentley campus of Curtin University.