The purpose of this study was to evaluate the relationships between echo intensity (EI) and muscular strength (maximal voluntary isometric contraction [MVIC]) and endurance (time-to task-failure [TTF]) in young adults. Ultrasonography was used to examine the dominant vastus lateralis of 15 young men and 15 young women. The participants completed an MVIC to assess muscular strength and sustained a bilateral, leg extension at 45% MVIC to assess muscular endurance. There was a significant (r = -0.354, p = 0.028) correlation between EI and normalized MVIC force for the combined sample (n = 30). There was also a significant (r = -0.520, p = 0.002) correlation between EI and absolute MVIC force for the combined sample. The correlation between EI and TTE was significant for the men (r = -0.449, p = 0.047) and the combined sample (r = -0.477, p = 0.004). Overall, muscle quality as assessed by EI does not appear to be strongly related to muscular strength, but there may be a modest correlation with muscular endurance.
Keywords: Muscle quality; maximal Voluntary Contraction; sex differences; time to task failure; ultrasonography.