Journal
EUROPEAN JOURNAL OF APPLIED PHYSIOLOGY
Volume 113, Issue 11, Pages 2691-2703Publisher
SPRINGER
DOI: 10.1007/s00421-013-2700-1
Keywords
Cross-sectional area; Muscle thickness; Fascicle length; Pennation angle; Regional difference
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Funding
- Japan Society for Promotion of Science [21700630, 24300209]
- Waseda University Global Centre of Excellence (GCOE) program
- Grants-in-Aid for Scientific Research [21700630, 23700745] Funding Source: KAKEN
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Purpose This study aimed to clarify whether resistance training-induced changes in muscle architecture are homogeneous among the quadriceps and over different regions within each muscle. Methods Eleven recreationally active men (27 +/- 2 years) completed a 12-week resistance training program for knee extensors. Before and after the intervention, muscle thicknesses, fascicle lengths, and pennation angles of the four muscles (vastus lateralis, vastus medialis, vastus intermedius, rectus femoris) in several regions (2-4 regions per each muscle) were measured using ultrasonography. Anatomical cross-sectional areas (ACSAs) at the same positions as the ultrasound measurements were determined from magnetic resonance images. Results Relative increases in the ACSA, muscle thickness, and pennation angle of the rectus femoris were significantly greater than those of the vasti. Relative increases in the ACSAs of the vastus lateralis and rectus femoris were significantly greater in the distal than in the proximal region, and those in the muscle thickness and pennation angle of the vastus intermedius were significantly greater in the medial than in the lateral region. Fascicle lengths did not change in any muscles. The interrelations between muscle thickness and pennation angle remained unchanged after the intervention, with a significant association between the relative changes of the two variables. Conclusion The current results indicate that (1) hypertrophy of the quadriceps femoris is associated with a proportional increase in pennation angle but not necessarily in fascicle length, and (2) training-induced changes in muscle size and pennation do not evenly occur among the quadriceps, along or across a muscle.
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