Stretchability of the rectus femoris muscle: investigation of validity and intratester reliability of two methods including X-ray analysis of pelvic tilt

Validity and intratester reliability of two test methods designed to identify stretchability of the rectus femoris muscle (RFM) was investigated, combined with x-ray analysis of pelvic tilt in the sagittal plane. The first method is commonly used in clinical practice. The second is a new technique supposed to tilt the pelvis posteriorly and thus further separate the origin and insertion of the muscle. Investigation of validity and intratester reliability of the two methods was made by testing and retesting a random sample of 71 persons. The tests were performed with an equipment that automatically recorded the angle of knee flexion from a previously determined applied torque, indicating the end point of motion for that particular subject. Angle of knee flexion and subjective estimation of pain sensation due to stretch were recorded at each measurement. The pelvic tilt-analysis consisted of test-retest reliability of x-ray measurements, comparison between the methods in both starting and final position, and x-ray and electronic goniometer measurements. All applied torques were measured with a strain gauge. Two out of three criteria of validity favored the new method and the third pointed out the two methods as equal. The two methods as well as the x-ray measurements showed high reliability, and the hypothesis of a more posterior tilted pelvis in the new method was confirmed. The electronic goniometer was less sensitive than x-ray, but proposed to analyse pelvic tilt clinically. Methodology procedures for joint angle measurements are discussed.