Inhomogeneous architectural changes of the quadriceps femoris induced by resistance training

• Published in: European journal of applied physiology Vol. 113; no. 11; pp. 2691 - 2703
• Main Authors: Ema, Ryoichi, Wakahara, Taku, Miyamoto, Naokazu, Kanehisa, Hiroaki, Kawakami, Yasuo
• Format: Journal Article
• Language: English
• Published: Berlin/Heidelberg Springer Berlin Heidelberg 01-11-2013; Springer Nature B.V
• Subjects: Adult; Biomedical and Life Sciences; Biomedicine; Case-Control Studies; Human Physiology; Humans; Male; Occupational Medicine/Industrial Medicine; Original Article; Quadriceps Muscle - diagnostic imaging; Quadriceps Muscle - physiology; Resistance Training; Sports Medicine; Strength training; Ultrasonography; Japan; Regional difference; Pennation angle; Cross-sectional area; Muscle thickness; Fascicle length
• ISSN: 1439-6319; 1439-6327
• DOI: 10.1007/s00421-013-2700-1

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.