A COMPARISON OF HIP ROTATOR MUSCLE FORCE IN SITTING AND PRONE POSITIONS. Denise M. Cameron*; Lindsay Phillips; John Miller Physical Therapy Dept., Quinnipiac University, Hamden, CT PURPOSE: The primary purpose of this study was to examine hip medial and lateral rotator muscle force in the sitting and prone positions in individuals with no musculoskeletal injuries. A second purpose was to compare left to right symmetry of hip rotator muscle force measurements. BACKGROUNDS/SIGNIFICANCE: Clinical measurements of hip rotator muscle strength are taken in both the sitting and prone positions. Research has suggested that the function of the hip rotator muscles changes with the position of hip flexion/extension. SUBJECTS: Forty individuals (14 males, 26 females), age 23.2±2.77 years; weight 67.53±13.01 kg, without hip pathology, hip pain, or leg length discrepancy participated in this study. METHODS AND MATERIALS: A MicroFet2 (Hoggan Health Industries) hand held dynamometer was used to test force production of the hip rotators. For prone testing, participants were positioned in prone with the knee flexed to 90°. Stabilization belts were placed around the buttocks and thigh of the test leg. Dynamometer placement was on the distal lower medial and lateral sides for lateral and medial rotator muscles, respectively. To test participants in sitting a stabilization belt was placed around the mid thigh region of the test leg and a towel roll under the distal thigh of the same leg. Participants were instructed to cross their arms in front and dynamometer placement was on the distal lower leg medial and lateral sides for lateral and medial rotator muscles, respectively. One tester performed the test while a second examiner read and recorded the measurements. Two trials of each measurement were performed unless the two trials differed by more than 10% of the higher value, in which case a third trial was performed. ANALYSES: Hip medial and lateral force measures for both trials and sides were recorded in pounds, converted to kilograms and normalized to body weight. For the remainder of the analyses the two trials were averaged together. For the first purpose (prone versus sitting positions) left and right side normalized measures were averaged and paired t-tests comparing prone and sitting test measurements for the medial and lateral rotators were performed. To compare symmetry of measurements (i.e., left to right), four paired t-tests (i.e., medial and lateral rotators in sitting and prone) were performed. Intraclass correlation coefficients (ICC 2,1) were calculated to assess the reliability of the two trials for each of the eight measures (i.e., left and right medial and lateral rotation in prone and sitting). RESULTS: Normalized force measures for the medial rotators in sitting and prone were 0.190 (0.049) and 0.150 (0.037), respectively. Lateral rotator force measures 0.178 (0.178) and 0.158 (0.159) for sitting and prone, respectively. Force measures of both the medial and lateral rotators were greater in sitting than in prone (p<.0001). Force measures for lateral rotators were symmetrical left to right in both sitting and prone (p>.05). Force measures for left and right medial rotators were symmetrical in sitting (p>.05) but the medial rotators produced more force on the left in prone (p=.008). Intraclass correlation coefficients were 0.97 or higher for each of the eight measurements. CONCLUSIONS: Force measures of both hip medial and lateral rotators were greater in sitting than in prone. Symmetry between sides was found in both positions for the lateral rotators but only in sitting for the medial rotators. Clinicians should be aware of the differences in hip rotator muscle force between sitting and prone positions. FUNDING SOURCE: Quinnipiac University Interdisciplinary Research Committee KEYWORDS: hip rotator muscle force Copyright 2009 by the American Physical Therapy Association. Requests for reprints should be directed to the corresponding author of the article. Educators, students, and other academic customers may receive permission to reprint copyrighted material from Physical Therapy (ISSN 1538-6724) by contacting the Copyright Clearance Center Inc, 222 Rosewood Dr, Danvers, MA 01923. Other types of customers who want permission to reprint should contact the APTA Editorial Office, Attn: Physical Therapy.