Corrected Echo Intensity Is Not Related to Fatigability or Indices of Aerobic Fitness in Healthy Young Adults: A Pilot Study

Authors

Kase J. Pennartz, University of North TexasFollow
Michael R. Perlet, University of North TexasFollow
Marek Kerr, University of North TexasFollow
Joshua L. Keller, University of North TexasFollow

Abstract

Muscle quality (MQ), measured via echo intensity, is regularly used to characterize muscle function and disease. Although it has been related to measures of cardiovascular performance, muscle strength, power, and function in elderly populations, these relations are not consistently observed in younger adult populations. Specifically, the relations of MQ and various functional outcomes (e.g., muscle strength, fatigability, and aerobic fitness) remain unclear, particularly given the interplay between age-related changes in fatiguability and performance. PURPOSE: Therefore, the purpose of this study was to examine the relation of MQ among muscle strength, fatigability, and indices of aerobic fitness in young healthy adults, as well as the contributions of these variables to peak power (PP) and fatigability. METHODS: Fourteen healthy adult men (n=11) and women (n=3) (age: 24 ± 5yrs, height: 175.0 ± 10.8cm, weight: 79.8 ± 18.0kg, body fat: 21.2 ±5.4%) participated. These participants completed body composition analysis, ultrasonography, Thorstensson fatigue, and aerobic fitness tests. Ultrasonography was used to calculate echo intensity, which was subsequently corrected for adipose tissue thickness. Peak torque (PT) (i.e., the highest torque achieved) and fatigability (i.e., the difference between the mean torque decline of the first three and the last 3 repetitions) were derived following the Thorstensson fatigue test. PP was recorded as the highest watt value observed during the maximal cardiorespiratory (VO_2max) fitness cycle test. Maximal effort during the VO_2max test was confirmed by meeting at least two of the following criteria: a rate of perceived exertion >17, heart rate exceeding 95% of the age-predicted max, respiratory quotient >1.15, or a cadence below 60 revolution∙min^-1. Bivariate and multiple linear regression analyses were performed to determine potential relations and contributions among the variables. A pRESULTS: Echo intensity was significantly related (p= .036; r= -.562) and predicted (r²= .316; p= .036; β= -.562) PT but not fatigability (p= .104), PP (p=.156), or VO_2max (p= .168). Stepwise linear regression revealed PT (p=.002, β= 1.226) and fatigability (p=.001, β= -.679) significantly (r²= .872) explained differences in PP. Additionally, fatigability was significantly (r²=.850) explained by PT (p=.001, β= 1.349), PP (p=.034, β= -.607), and VO_2max (p=.047, β= -.389). PP was the only significant (r²=.479; p=.006; β=.692) predictor of VO_2max. CONCLUSION: MQ explained 31.6% of the differences in maximal strength, suggesting that MQ may be more associated with the ability of a skeletal muscle to generate force and power rapidly rather than muscle endurance characteristics. Although aerobic fitness contributed to fatigability, PT was nearly 3.5x more potent of a predictor, likely reflecting the influence of the underlying proportion of skeletal muscle fiber type composition. Our future studies will continue examining relations between MQ, muscle fiber composition, and other functional outcomes in diverse populations.

Recommended Citation

Pennartz, Kase J.; Perlet, Michael R.; Kerr, Marek; and Keller, Joshua L. (2025) "Corrected Echo Intensity Is Not Related to Fatigability or Indices of Aerobic Fitness in Healthy Young Adults: A Pilot Study," International Journal of Exercise Science: Conference Proceedings: Vol. 2: Iss. 17, Article 133.
Available at: https://digitalcommons.wku.edu/ijesab/vol2/iss17/133