Exercise induced changes in echo intensity within the muscle: a brief review

Abstract

Echo intensity is the mean pixel intensity of a specific region of interest from an ultrasound image. This variable has been increasingly used in the literature as a physiological marker. Although there has been an increased interest in reporting changes in echo intensity in response to exercise, little consensus exists as to what a change in echo intensity represents physiologically. The purpose of this paper is to review some of the earliest, as well as the most up to date literature regarding the changes in echo intensity in response to exercise. Echo intensity has been used to measure muscle quality, muscle damage, acute swelling, and intramuscular glycogen. The changes in echo intensity, however, are not consistent throughout the literature and often times lead to conclusions that seem contrary to the physiologic effects of exercise. For example, echo intensity increases in conjunction with increases in strength, contrary to what would be expected if echo intensity was a marker of muscle quality/muscle damage. It is conceivable that a change in echo intensity represents a range of physiologic effects at different time points. We recommend that these effects should be determined experimentally in order to rule out what echo intensity might and might not represent. Until this is done, caution should be employed when interpreting changes in echo intensity with acute and chronic exercise.

Muscle swelling following blood flow‐restricted exercise does not differ between cuff widths in the proximal or distal portions of the upper leg

“…It has been postulated by some that the acute changes in echo intensity are representing fluid movement into nearby muscle cells (Wong et al., 2019, 2020). This coincides with the finding that acute increases in muscle thickness are accompanied by decreases in plasma volume (Kim et al., 2017; Wong et al., 2020). However, findings from Wong et al.…”

“…This finding should be interpreted with caution, as it was only observed at one site. Future work could investigate this further to determine what, if anything, this represents physiologically (Wong et al., 2020).…”

Examination of the confounding effect of subcutaneous fat on muscle echo intensity utilizing exogenous fat

“…Acute and chronic changes in EI have been observed with exercise. However, further experimental work is needed to provide appropriate interpretations of these changes in physiological and clinical contexts (Routledge et al 2019;Rowe et al 2019;Wong et al 2020). The omission and/or inappropriate accounting of the effects of subcutaneous fat on EI might partly explain inconsistent results in skeletal muscle tissue quality following resistance training reported in a recent review (Wong et al 2020).…”

“…The confounding effect of subcutaneous fat thickness on EI estimates of muscle quality leads to an underestimation of the negative impact of obesity/overweight on muscle health (Oranchuk et al 2020;Ryan et al 2016) and may lead to erroneous conclusions regarding chronic exercise induced changes in muscle quality (Wong et al 2020) and differences in muscle quality between men and women or between muscles and muscle regions (Oranchuk et al 2020;Stock et al 2020). Until now, most studies that correct ultrasound-based estimates of muscle quality for the confounding effect of subcutaneous fat have counted on the equations developed by Young et al (2015).…”

Ultrasound Imaging Evaluation of Textural Features in Athletes with Soleus Pathology—A Novel Case-Control Study

“…Echogenicity, based on the pixel intensity quantification of an ultrasound image, could express different physiological views according to the literature and their study and utilization has increased in the last few years in order to provide a better understanding of ultrasound imaging analysis. Echointensity (EI) has been applied to the analysis of muscle strength in middle-aged and older adult populations [ 12 ], evaluating the muscle response to some types of exercise [ 13 , 14 ] or quantifying muscle size [ 15 , 16 ]. Moreover, EI has been considered a power biomarker for identifying the disruption of muscle structure in some degenerative muscle pathologies, for example lateral amyotrophic sclerosis [ 17 , 18 ] or muscle sarcopenia [ 19 ].…”