Test-Retest Reliability of an Experimental Model of Shoulder Muscle Pain
Condition: Musculoskeletal Pain
MeSH terms: Musculoskeletal Pain; Myalgia
Study type: Interventional

Summary: 
      High frequency oscillations of non-ionizing electromagnetic fields range can heat deep
      tissues in a well-localized region. Recently, a new SWD-based model showed to be a promising
      tool for investigating muscle pain in humans. The main advantages of the model are its
      noninvasiveness, the ability to control stimulation parameters, and the convenience of the
      time frame in which pain and hyperalgesia are developed. This study assess the reliability of
      SWD pain model to induced transient and intensity-controlled muscle soreness on shoulder in
      healthy volunteers.
    

Detailed description: 
      This Test-Retest Reliability study comprises a sample of 31 healthy volunteers. Volunteers
      will be invited to participate in the study through social networks and e-mail.

      Experimental pain model assessment

      The radiofrequency electromagnetic fields can be produced in the range of 3 kHz to 300 GHz,
      but frequencies around 27 MHz (short-wave) are preferred to heat deep tissues. Deep tissue
      heating by means of RF is a safe and extensively used technique in palliative treatment of
      pain and as a healing agent in soft tissues. This study assess the reliability of SWD to
      induce soreness. The study will be conducted in two experimental sessions on different days,
      at least 48 to 72 hours apart each other in order to avoid carryover effects. In each
      experimental session, several measures will be performed to assess different physiological
      parameters, including: pressure pain thresholds (PPT), specific self-report questionnaire,
      isometric muscle strength, pain distribution and myoelectric activity.

      In the first session (Test), participants will be interviewed to collect anthropometric data
      and health history. Basic upper quadrant physical examination will be performed to check
      inclusion and exclusion criteria. Before and after the application of SWD, several
      assessments will be performed. Among the different assessment, myoelectric activity of
      infraspinatus and deltoid muscle will be recorded during isometric arm lifting task. The
      isometric task will consist in maintaining the arm in 90 degree elevation in the scapular
      plane (arm flexion) for 8 seconds. This task will be repeated 5 times with 15 seconds of rest
      between each trial. Finally, a fatiguing motor task will be performed, consisting of flexion
      and extension of the arm executed cyclically in a range of motion between 30 and 90 degree in
      the scapular plane. To ensure fatigue, volunteers will perform the task with an additional
      weight. The size of the weight will be calculated according to each volunteer body mass (1.25
      kg in participants under 68 kg and 2.5 kg in participants over 68 kg). The arm flexion and
      extension speed will be guided using a 60 beats/s metronome. Same process will be repeated in
      the second session (Retest).

      Sample size considerations:

      All the reliability assessment methods used in this study are related to the within-subject
      standard deviation (SD_w). For a test-retest experiment, the SD_w can be calculated as〖
      SD〗_w=(SD_diff)⁄√2, and the LoA can be reformulated as bias ± 1.96 〖SD〗_w √2. The precision
      to estimate SD_w depends on both the number of subjects, n, and the number of observations
      per subject. A sample size of 31 subjects is required considering a confidence interval of
      25% at either side of the estimation of SD_w, and for m=2 observations per subject.
    

Intervention name(s): Intervention: Short-wave diathermy
Intervention type(s): Other
Intervention description(s): The SWD will be applied using a CEC M-8 shortwave thermotherapy unit (CEC Electrónica S.R.L., Argentina) that emits RF at a frequency of 27.12 MHz. The device has two rectangular capacitive applicators (18 × 12 cm), which will be placed below and above the dominant shoulder. The coplanar application will be done using the continuous wave mode. The intensity of SWD will be gradually increased until the volunteer perceives a sensation of heat, and once familiar with this perception, the intensity will be increased until a sensation of constant but tolerable pain is evoked. This sensation will be maintained throughout the SWD application, and three repetitions will be performed. Healthy volunteers will be in a lateral supine position, and a cotton towel will be used to absorb perspiration and avoid unwanted heat effects.
Intervention model: Single Group Assignment
Intervention model description: The SWD will be applied using a CEC M-8 shortwave thermotherapy unit (CEC Electrónica S.R.L., Argentina) that emits RF at a frequency of 27.12 MHz. The device has two rectangular capacitive applicators (18 × 12 cm), which will be placed below and above the dominant shoulder. The coplanar application will be done using the continuous wave mode. The intensity of SWD will be gradually increased until the volunteer perceives a sensation of heat, and once familiar with this perception, the intensity will be increased until a sensation of constant but tolerable pain is evoked. This sensation will be maintained throughout the SWD application. Once the first application is completed, the volunteer will be allowed to rest for a period of 2-3 minutes and three repetitions will be performed. Healthy volunteers will be in a lateral supine position, and a cotton towel will be used to absorb perspiration and avoid unwanted heat effects.
Masking: None (Open Label)
Primary purpose: Basic Science
Keywords: Short-wave diathermy; Experimental pain model; Muscle pain; Generalized hypersensitivity; Shoulder pain