Muscle morphology and architecture of the medial gastrocnemius between typically developing children with different ancestral backgrounds
Authors: Walhain F. , Chin A Fat R. , Declerck M. , Bar-On L. , Van Campenhout A. , Desloovere K. 
Published: January 2023

ABSTRACTIntroductionMuscle ultrasonography is frequently used to improve the understanding of musculoskeletal impairments in children with cerebral palsy. So far, most studies on muscle morphology and architecture have included typically developing children and children with cerebral palsy with similar ancestry, being mainly Caucasian. Less is known about differences in muscle morphology and architecture between children with different ancestral backgrounds. Therefore, the aim of this study was to compare muscle morphology and architecture of the medial gastrocnemius and Achilles tendon of Surinamese typically developing children from African, South Asian and Southeast Asian descent.MethodThis explorative cohort study included 100 typically developing children identified as Maroon (Ghana, African descent), Hindustani (India, South Asian) or Javanese (Indonesia, Southeast Asian), aged 5 to 10 years. A conventional B-mode 2D ultrasound was used to define anatomical cross-sectional area (aCSA), fascicle length and pennation angle (architectural parameters). The muscle belly length, volume and physiological cross-sectional area (pCSA), as well as the tendon length (morphological parameters) were defined using 3D freehand ultrasound, which combines B-mode 2D ultrasound with 3D motion tracking. Muscle and tendon lengths were normalized to the total muscle tendon unit (MTU) lengths and fascicle lengths to muscle belly lengths, while volume, aCSA and PCSA were normalized to body mass. One-way Anova with post hoc t-tests were used to investigate differences between the ancestral groups. A two-way repeated measures Anova was used to define whether the extensibility of the muscle tendon, belly and fascicle differed between ancestral groups for the three conditions, i.e. when applying 0Nm, 1Nm and 4Nm ankle dorsiflexion torque.ResultsThe ancestral subgroups included 34 Hindustani, 34 Javanese and 32 Maroon children. Normalized belly length was 11% shorter in Maroon and 7% shorter in Hindustani children compared to Javanese children (p= <0.001 andp= 0.002, respectively). Normalized fascicle length of Javanese children was 23% longer compared to Maroon and 11% longer compared to Hindustani children (p< 0.001 andp= 0.010, respectively). Normalized muscle volume was significantly higher in Javanese compared to Hindustani children (p= 0.002). The normalized aCSA was higher in Javanese children compared to the Maroon children (p= 0.008), while pCSA was higher for Maroon children compared to the Hindustani children (p= 0.007). The pennation angle of the fascicle with the deeper aponeuroses was larger in Maroon compared to Javanese children (p= 0.015). There were no differences in the extensibility of the muscle belly, tendon and fascicle between ancestral groups.DiscussionAncestry-specific reference data of the morphology of the medial gastrocnemius and Achilles tendon are needed when investigating altered muscle morphology in children with cerebral palsy. The current study showed differences in morphology (muscle belly-, tendon length and muscle volume, aCSA) and architecture (pCSA, fascicle length and deeper pennation angle) between children with different ancestry. These differences were most pronounced for Javanese compared to Maroon or Hindustani children. Future studies should report the ancestral background when describing muscle morphology and architecture of children and ancestral specifications in normative databases should be included.