title: Inter- and intramuscular differences in training-induced hypertrophy of the quadriceps femoris: association with muscle activation during the first training session.
abstract: The purpose of this study was to examine whether inter- and intramuscular differences in hypertrophy induced by resistance training correspond to differences in muscle activation during the first training session. Eleven young men completed 12 weeks of training intervention for knee extension. Before and after the intervention, T1-weighted magnetic resonance (MR) images were recorded to determine the volume and anatomical cross-sectional area (CSA) along the length of the individual muscles of the quadriceps femoris. The T2-weighted MR images were also acquired before and immediately after the first training session. The T2 was calculated for each pixel within the quadriceps femoris, from which the muscle activation was evaluated as %activated volume and area. The results showed that the %activated volume after the first training session was significantly higher in the vastus intermedius than the vastus medialis. However, the relative change in muscle volume after the training intervention was significantly greater in the rectus femoris than the vasti muscles (vastus lateralis, intermedius and medialis). Within the rectus femoris, both the %activated area and relative increase in CSA were significantly greater in the distal region than the proximal region. In contrast, the %activated area and relative increase in CSA of the vasti were nearly uniform along each muscle. These results suggest that the muscle activation during the first training session is associated with the intramuscular difference in hypertrophy induced by training intervention, but not with the intermuscular difference.
authors.affiliation: Faculty of Health and Sports Science, Doshisha University, Kyotanabe, Kyoto, Japan.
authors.forename: Taku
authors.initials: T
authors.lastname: Wakahara
authors.affiliation: Graduate School of Engineering and Science, Shibaura Institute of Technology, Saitama-shi, Saitama, Japan.|Japan Society for the Promotion of Science, Chiyoda, Tokyo, Japan.
authors.forename: Ryoichi
authors.initials: R
authors.lastname: Ema
authors.affiliation: National Institute of Fitness and Sports in Kanoya, Kanoya, Kagoshima, Japan.
authors.forename: Naokazu
authors.initials: N
authors.lastname: Miyamoto
authors.affiliation: Faculty of Sport Sciences, Waseda University, Tokorozawa, Saitama, Japan.
authors.forename: Yasuo
authors.initials: Y
authors.lastname: Kawakami
mesh_terms: D000328:Adult; D006801:Humans; D006984:Hypertrophy; D008279:Magnetic Resonance Imaging; D008297:Male; D009119:Muscle Contraction; D009929:Organ Size; D052097:Quadriceps Muscle / Q000000981:diagnostic imaging / Q000502:physiology*; D055070:Resistance Training / Q000379:methods*; D013997:Time Factors; D016896:Treatment Outcome; D055815:Young Adult
keywords: cross-sectional area; knee extensors; magnetic resonance image; muscle volume; transverse relaxation time