Breanna J. Mueller, Paulo H. C. Mesquita, Bradley A. Ruple, Joshua S. Godwin, Casey L. Sexton, Shelby C. Osburn, Mason C. McIntosh, Andreas N. Kavazis, FACSM, Cleiton A. Libardi, Kaelin C. Young, Michael D. Roberts. Auburn University, Auburn, AL.

Background: Two-dimensional cross-sectional analysis is a technique that is widely used to assess skeletal muscle fiber morphology in response to resistance training. While this technique affords some advantages in assessing fiber cross-sectional area (fCSA), fiber typing and other variables, it may not be representative of the whole fiber. A more dimensional analysis is needed to render greater accuracy and insight into the morphological characteristics of a three-dimensional fiber. The purpose of this study was to evaluate single fiber analysis as a valid and comparable technique in analyzing fiber morphology. Methods: Vastus lateralis muscle biopsies from 11 untrained males were collected at pre- and post- of a 7-week total body resistance training protocol. Using two-dimensional cross-sectional analysis and single fiber analysis techniques, we measured fCSA, myonuclear number (MNN), and myonuclear domain (MND). T-tests and correlations were performed with the data to determine any significant changes and relationships between techniques. Results: Two-dimensional cross-sectional analysis revealed a significant increase in myonuclear number (35.51%, p = 0.031) and fCSA (19.81%, p = 0.010), but not in MND (1.15%, p = 0.413). In comparison, single fiber analysis also demonstrated a significant increase in myonuclear number (13.52%, p = 0.011), fCSA (32.55%, p= 0.009), and MND (17.35%, p = 0.118). There was no significant correlation between two-dimensional analysis and single fiber analysis in fCSA (r = -0.074, p = 0.828), myonuclear number (r = 0.326, p = 0.327), or myonuclear domain (r = -0.264, p = 0.435) percent change. Conclusion: In conclusion, the measurements taken with two-dimensional cross-sectional analysis and single fiber analysis did not agree, and statistical analysis showed no correlations between the two measurements. However, these results may have been impacted by our limited sample size. Additional investigation utilizing a greater sample size may provide more promising results. Therefore, future investigation of the longitudinal view provided by single fiber analysis may yet yield an advantage in the morphological assessment of the skeletal muscle fiber. Funding: Participant compensation as well as select reagents related to analyses presented herein were funded by a grant awarded by National Strength and Conditioning Association Foundation to Paulo H.C. Mesquita.

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