The Effects of Pain and the Memory of Pain on Autonomic and Neuromuscular Function

Study Design This study will utilize a repeated measures quasi-experimental case control design structure. Subjects will be placed into two groupings, those who have a history of prior lower extremity injury and those who have no history of lower extremity injury. The two groupings will be age and gender matched. Subjects who have no prior history of lower extremity injury will be matched to subjects with a prior history of injury. There will be an equivalent number of participants per group with similar demographic information in both groups in order to reduce the number of variables influencing the results of the experiment. Within each of these groupings, specific interventions will be clustered and performed as a set. These clusters of interventions will be randomized to minimize internal testing error. Both groups of participants will be exposed to the same interventions (baseline, pain pressure, visualization of pain pressure and prior injury, and mental challenge test). Investigators responsible for testing and outcome measurement will be blinded to the groupings of subjects (past history or no prior history of injury). It is anticipated that the testing, including initial set up, will take between 60 and 75 minutes. All testing will take place at the Mount St. Mary's College physical therapy exercise and research lab or in a private room at Knight Physical Therapy Inc.

Study Methods Initial Set Up (25 minutes) Upon commencement of the study, subjects will be asked to fill out the Tampa Kinesiophobia Questionnaire, Fear Avoidance Belief Questionnaire, Fear of Pain Scale, Pain Catastrophizing Scale, and the Vividness of Visual Imagery Questionnaire. This should take approximately 10 minutes. Following completion of these questionnaires, they will be introduced to the investigators and then asked to lie supine upon the treatment table. A pillow will be placed under their head for comfort. Surface EMG rRecording electrodes will be placed upon the belly of the tibialis anterior muscle. An electrode will be placed upon the medial tibia and will serve as a ground for the other two electrodes. Placement of electrodes will correspond to the side of injury (i.e. prior injury to the right ankle would result in electrode placement on the right tibialis anterior and right anterior deltoid muscles). In subjects without history of injury, side of electrode placement will be predetermined and randomized. Also at this time, subjects with a prior history of injury will be asked to identify the location of the injury. The tester will then palpate the area of previous injury and will locate the tender point in this area. This point will be marked with a pen for later use. In subjects with no prior injury, the anterior talofibular ligament, the lateral knee joint line, or the lateral belly of the gastrocnemius muscle will be located and marked on the side of testing. The site will be randomized so as to blind testers. Testers will be informed of the side to be tested through the sealed envelope that is opened prior to testing. They will be blinded as to prior injury grouping.

At this point, the subject will be walked through the procedure and an initial pain pressure threshold measurement will be taken and a simulated break test (see below for description of break test) will be performed at the foot / ankle in order to familiarize the subject with the test procedures and also to ensure that all equipment is functioning optimally. This process should take approximately 10 minutes.

Following this procedure, a timer will be set and the subject will rest in this position for five minutes to acclimate to the environment and to normalize their autonomic system.

Autonomic System Response (10 minutes) Following the five-minute acclimation period, heart rate variability (HRV) data will be recorded, marked, and used as a baseline measurement. The HRV data will be collected throughout each testing procedure. Initially, at the site of previous injury (or randomized pressure site for subjects with no prior history of injury), the tester will use their thumb to apply pressure to the site. The pressure will increase until the subject reports their maximal pain level. Prior to the application of pressure, the subject will be informed that they are to experience the maximum pain tolerable and to inform the tester when that level is reached. The subject will next be instructed to notify the testers when they have reached the maximum tolerable pain. Once achieve, the pressure will be maintained for 10 seconds in order to get a baseline HRV recording. After 10 seconds, the pressure will be released and the HRV recording will be marked. At this time, the subject will be asked to report their level of pain on a scale of 1 to 10. The subject will then rest for three minutes to return their HRV to baseline values. At this point, the subject will be instructed to close their eyes and imagine the pain pressure in their leg that was just applied. HRV and pain values will be marked and recorded. The subject will rest for another three minutes and then they will once again be asked to close their eyes. In this instance, they will be asked to visualize the details of their prior injury. In subjects with no prior injury, they will asked to visualize the muscles, bone, and blood flow of their tibia. Like before, HRV and pain values will be marked and recorded. Following another three minute rest period, the subject will be asked to complete a mental challenge test. This test will require subjects to count backwards as quickly as possible from 100 by 7. HRV and pain values will be marked and recorded. With this test, and with all testing, the subject will be allowed to withdrawal from the test for any reason and without repercussions.