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Biomechanics/Neuromuscular

(12) ANALYSIS OF ULTRASOUND SIGNAL BANDS AND THE EFFECT OF SEX

Friday, July 14, 2023
10:30 AM – 12:00 PM East Coast USA Time
Location: Milano III-IV
Abstract Details: Ultrasound echo intensity (EI) is a method of quantifying muscle quality using non-invasive imaging. EI is often assessed as the mean pixel brightness within an area of interest. Recently, there has been interest in assessing individual sections of the EI signal (i.e., bands of signal). Analyzing bands may increase the sensitivity of EI and provide insight into functional outcomes. The effect of sex on EI band analysis has not been explored.

Purpose: The purpose of this study was to compare the effect of sex on the relationships between mean echo intensity and bands of echo intensity signal of the vastus lateralis with metrics of whole muscle performance in adults.

Methods: Twelve males (Mean±SD; 23.4±5.1 yrs) and twelve females (20.6±1.6 yrs) completed two visits to the laboratory, each separated by 2-7 days. During the first visit, participants completed Brightness mode ultrasound imaging and familiarization of an isokinetic fatigue assessment. Cross sectional images were taken of the vastus lateralis (VL) at 50% of the muscle length. VL cross-sectional area was traced using the polygon tool in an open-source image analysis software. As much of the muscle was selected without selecting any of the surrounding fascia. Each pixel is assigned a value from 0-255 based on gray scale analysis, with 0 as true black and 255 is as pure white. Mean EI was determined from the selected portion of the image. EI bands were calculated in pixel value intervals as follows: 0-50, 51-100, 101-150, 151-200, 201-255. The value utilized for the EI bands was assessed by: (number of pixels in each band / total number of pixels in the selected portion of the image)*100. During the fatigue assessment, participants completed 100 repeated, maximal, isokinetic muscle actions (120°/sec). Isokinetic peak torque (PT) was analyzed offline using custom written software. Initial and final PT were calculated by averaging the highest 3 of the first and last 5 repetitions respectively. PT percent decline (%Dec) was calculated by: %Dec = (initial PT–final PT)/initial PT and was used as a metric of fatigue. Pearson’s correlation coefficient (r) was used to assess the relationship between each EI band and %Dec as well as mean EI and %Dec. The Stieger’s Z procedure was used to compare correlation coefficients between mean EI, EI bands, and sex.

Results: There were no statistically significant relationships between any of the EI bands and %Dec (r=-0.05-0.47, p=0.13-0.87) or between mean EI and %Dec for females (r=0.28, p=0.38). There was statistical significance between all the EI bands and %Dec for males (r=-0.69-0.67, p=0.01-0.03) and the mean EI and %Dec (r=0.61, p=0.04). For females, there was no difference between analyzing mean EI and any EI bands (z=0.17-0.89, p=0.37-0.87). Males had a significant difference between mean EI and EI band 0-50 (z=3.27, p< 0.01). Sex had a significant effect on the 0-50 and 51-100 bands (z=2.3, p=0.02 and z=2.76, p=0.01).

Conclusions: The findings suggest the use of EI bands is beneficial for providing insight into fatigue within the 0-50 and 51-100 bands in males. This data suggests the use of EI bands may be sex dependent. Further investigation is needed to determine if the relationship is muscle dependent. PRACTICAL APPLICATIONS: When assessing fatigue, ultrasound measurements were unable to predict fatigue in females. However, researchers should consider investigating the use of unique EI bands when assessing fatigue in males.

Acknowledgements: None