Does resistance training increase aponeurosis width? The current results and future tasks

Purpose: The aponeurosis, a sheet of fibrous tissue, is the deep and superficial fascia where muscle fibers attach in pennate muscles. It is quite possible that the aponeurosis size increases in response to resistance training-induced fiber hypertrophy due to an increase in connection area. As a result, it leads to an increase in anatomical muscle cross-sectional area. However, attention has not been paid to aponeurosis area changes. This review sought to determine whether muscle hypertrophy changes aponeurosis width following short-term resistance training using an equation we modified [post/pre changes in aponeurosis width (AW_post/pre) = post/pre changes in anatomical cross-sectional area (CSA_post/pre) ÷ post/pre changes in pennation angle (PA_post/pre) ÷ post/pre changes in fascicle length (FL_post/pre)]. Methods: A search using two electronic databases (PubMed and Google Scholar) was conducted. Nine studies measured CSA_post/pre, PA_post/pre, and FL_post/pre of the vastus lateralis muscle by ultrasound and magnetic resonance imaging. Results: There was a statistically significant 2.73 [95% CI 1.11, 4.36; p = 0.009] cm² increase in CSA_post/pre along with a statistically significant 1.21° [95% CI 0.44, 1.97; p = 0.002] increase in PA_post/pre and a statistically significant 0.36 cm [95% CI 0.19, 0.54; p = 0.0002] increase in FL_post/pre. These results yield an estimated 1% reduction in aponeurosis width. Conclusion: Our results suggest that while muscle CSA, pennation angle, and fascicle length all increase following short-term resistance training, the aponeurosis width is not altered.