The Impact of Skeletal Muscle Disuse on Distinct Echo Intensity Bands: A Retrospective Analysis

Echo intensity (EI) is a novel tool for assessing muscle quality. EI has traditionally been reported as the mean of the pixel histogram, with 0 and 255 arbitrary units (A.U.) representing exceptional and poor muscle quality, respectively. Analyzing specific EI bands, rather than the mean, may provide novel insight into changes in muscle quality. PURPOSE: As our previous work showed deterioration of muscle quality after knee immobilization, we sought to retrospectively explore whether the increase in EI following disuse was limited to specific bands of the EI histogram. METHODS: Thirteen females (age = 21 yrs) underwent two weeks of knee immobilization. Ultrasonography was utilized to obtain images of the immobilized vastus lateralis. The percentage of the total number of pixels in bands of 0-50, 51-100, 101-150, 151-200, 201-255 A.U. and 0-25, 26-50, 51-75, 76-100, 101-125, 126-150, 151-175, 176-200, 201-225, 226-255 A.U. was examined at pretest and after immobilization. RESULTS: A large decrease was found from 0-50 A.U. (p = .030, d = -1.011), with an increase of similar magnitude for 101-150 A.U. (p = .055, d = 0.954). Subdividing the 50 A.U. bands into 25 A.U. bands provided no additional information pertaining to changes in muscle quality. DISCUSSION: Knee immobilization affects distinct regions of the EI histogram. Analysis of EI bands may provide novel insights into changes in muscle quality during disuse and rehabilitation. We encourage investigators to think critically about the robustness of data obtained from EI histograms, rather than simply reporting the mean value, in muscle quality research