Force Enhancement of Quadriceps Femoris in Vivo and Its Dependence on Stretch-Induced Muscle Architectural Changes

in Journal of Applied Biomechanics
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The purpose of this study was to investigate if force enhancement (FE) in vivo is influenced by stretch-induced changes of muscle architecture. Therefore, 18 subjects performed maximum voluntary isometric (100° knee flexion angle) and isometric-eccentric-isometric stretch contractions (80°–100° ω = 60°s−1) whereby pennation angle and fascicle length of vastus lateralis was determined using ultrasonography. We found significant (2-way repeated ANOVA; α = 0.05) enhanced torque of 5–10% after stretch as well as significant passive FE but no significant differences in muscle architecture between isometric and stretch contractions at final knee angle. Furthermore, EMG recordings during a follow-up study (n = 10) did not show significant differences in activation and mean frequency of contraction conditions. These results indicate that FE in vivo is not influenced by muscle architectural changes due to stretch.

Wolfgang Seiberl (Corresponding Author) is with the Department of Biomechanics in Sports, Faculty of Sports Science, Technische Universität München, Munich, Bavaria, Germany. Daniel Hahn is also with the Department of Biomechanics in Sports, Faculty of Sports Science, Technische Universität München, Munich, Bavaria, Germany. Florian Kreuzpointner is also with the Department of Biomechanics in Sports, Faculty of Sports Science, Technische Universität München, Munich, Bavaria, Germany. Ansgar Schwirtz is also with the Department of Biomechanics in Sports, Faculty of Sports Science, Technische Universität München, Munich, Bavaria, Germany. Uwe Gastmann is with the Institute for Sport Science and Sport, Faculty of Educational Science, Universität der Bundeswehr München, Munich, Bavaria, Germany.