title: Medial gastrocnemius muscle growth during adolescence is mediated by increased fascicle diameter rather than by longitudinal fascicle growth.
abstract: Using a cross-sectional design, the purpose of this study was to determine how pennate gastrocnemius medialis (GM) muscle geometry changes as a function of adolescent age. Sixteen healthy adolescent males (aged 10-19 years) participated in this study. GM muscle geometry was measured within the mid-longitudinal plane obtained from a 3D voxel-array composed of transverse ultrasound images. Images were taken at footplate angles corresponding to standardised externally applied footplate moments (between 4 Nm plantar flexion and 6 Nm dorsal flexion). Muscle activity was recorded using surface electromyography (EMG), expressed as a percentage of maximal voluntary contraction (%MVC). To minimise the effects of muscle excitation, EMG inclusion criteria were set at <10% of MVC. In practice, however, normalised EMG levels were much lower. For adolescent subjects with increasing ages, GM muscle (belly) length increased due to an increase in the length component of the physiological cross-sectional area measured within the mid-longitudinal plane. No difference was found between fascicles at different ages, but the aponeurosis length and pennation angle increased by 0.5 cm year(-1) and 0.5° per year, respectively. Footplate angles corresponding to externally applied 0 and 4 Nm plantarflexion moments were not associated with different adolescent ages. In contrast, footplate angles corresponding to externally applied 4 and 6 Nm dorsal flexion moments decreased by 10° between 10 and 19 years. In conclusion, we found that in adolescents' pennate GM muscles, longitudinal muscle growth is mediated predominantly by increased muscle fascicle diameter.
authors: Faculty of Human Movement Sciences, Laboratory for Myology, MOVE Research Institute Amsterdam, VU University Amsterdam, Amsterdam, The Netherlands.|Department of Rehabilitation Medicine, MOVE Research Institute Amsterdam, VU University Medical Center, Amsterdam, The Netherlands.
authors: Guido
authors: G
authors: Weide
authors: Faculty of Human Movement Sciences, Laboratory for Myology, MOVE Research Institute Amsterdam, VU University Amsterdam, Amsterdam, The Netherlands.
authors: Peter A
authors: PA
authors: Huijing
authors: Department of Rehabilitation Medicine, MOVE Research Institute Amsterdam, VU University Medical Center, Amsterdam, The Netherlands.
authors: Josina C
authors: JC
authors: Maas
authors: Department of Rehabilitation Medicine, MOVE Research Institute Amsterdam, VU University Medical Center, Amsterdam, The Netherlands.
authors: Jules G
authors: JG
authors: Becher
authors: Department of Rehabilitation Medicine, MOVE Research Institute Amsterdam, VU University Medical Center, Amsterdam, The Netherlands.
authors: Jaap
authors: J
authors: Harlaar
authors: Faculty of Human Movement Sciences, Laboratory for Myology, MOVE Research Institute Amsterdam, VU University Amsterdam, Amsterdam, The Netherlands.
authors: Richard T
authors: RT
authors: Jaspers
mesh_terms: D000293:Adolescent; D000328:Adult; D002648:Child; D004576:Electromyography; D005260:Female; D005528:Foot / Q000502:physiology; D006801:Humans; D021621:Imaging, Three-Dimensional / Q000379:methods; D007537:Isometric Contraction / Q000502:physiology; D008297:Male; D018482:Muscle, Skeletal / Q000033:anatomy & histology / Q000000981:diagnostic imaging / Q000254:growth & development* / Q000502:physiology; D016059:Range of Motion, Articular; D014463:Ultrasonography; D055815:Young Adult
keywords: adolescents; development; gastrocnemius medialis; growth; hypertrophy; muscle geometry; physiological cross-sectional area; ultrasound imaging