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Architecture of lower leg muscles in children: Reference curves and potential mechanisms of growth
Brian V Y Chow1,2, Suzanne Davies1, Catherine Morgan3
1Neuroscience Research Australia (NeuRA), Sydney, New South Wales, Australia.
Insights
Childhood muscle growth primarily increases lower leg muscle volume through widening, not lengthening, with significant changes in physiological cross-sectional area (PCSA) and fascicle length from ages 5-15. These findings offer normative data for pediatric muscle development.
Area of Science:
- Pediatric musculoskeletal development
- Human anatomy and physiology
- Biomechanical engineering
Background:
- Muscle architecture parameters like physiological cross-sectional area (PCSA), fascicle length, and pennation angle undergo significant changes during childhood.
- Existing research on pediatric muscle architecture is limited, often focusing on small samples and narrow age ranges, lacking comprehensive developmental analysis.
Purpose of the Study:
- To establish age- and sex-conditional reference curves for the architectural parameters of seven lower leg muscles in typically developing children aged 5-15 years.
- To provide a comprehensive analysis of muscle architectural parameter distribution throughout childhood development.
- To investigate the mechanisms underlying childhood muscle growth.
Main Methods:
- Utilized anatomical and diffusion-weighted magnetic resonance imaging (MRI) to quantify the 3D architecture of seven lower leg muscles in 192 children (aged 5-15).
- Employed quantile regression with b-splines to estimate muscle- and sex-specific reference curves for PCSA, fascicle lengths, and pennation angles.
- Analyzed aponeurosis dimensions and their relationship with muscle architecture.
Main Results:
- Muscle volume increases primarily via transverse (PCSA) growth rather than longitudinal (fascicle length) growth, particularly after age 5.
- Median PCSA increased 3.0-4.7 times and fascicle length 1.1-1.7 times between ages 5 and 15.
- Significant overlap in architectural parameter distributions was observed between sexes across all ages.
- Longitudinal growth of muscle-tendon units is mediated by intramuscular aponeuroses lengthening, with surface area scaling proportionally to PCSA.
Conclusions:
- The developed reference curves provide normative data for lower leg muscle architecture in children.
- Childhood lower leg muscle growth is characterized by significant increases in transverse dimensions (PCSA) and moderate increases in fascicle length.
- Intramuscular aponeuroses play a key role in facilitating longitudinal growth of muscle-tendon units during childhood.
Abstract:
Muscle architecture [i.e. physiological cross-sectional area (PCSA), fascicle length and pennation angle] changes significantly during childhood. Previous studies have described the architecture of selected muscles in small samples of children over narrow age ranges, but a comprehensive analysis of the distribution of muscle architectural parameters during childhood development is currently lacking. The primary aim of this study was to estimate age- and sex-conditional distributions (reference curves) of architectural parameters of seven lower leg muscles (soleus, medial gastrocnemius, lateral gastrocnemius, tibialis anterior, tibialis posterior, flexor digitorum longus and flexor hallucis longus) in typically developing children aged 5-15 years. We used anatomical and diffusion-weighted magnetic resonance imaging to quantify the three-dimensional architecture and aponeurosis dimensions of seven lower leg muscles in 192 typically developing children aged 5-15 years. Quantile regression with b-splines was used to estimate muscle- and sex-specific reference curves for PCSA, fascicle lengths and pennation angles. In the median 15-year-old, PCSAs were 3.0-4.7 times (range is across muscles and sexes), and fascicle lengths were 1.1-1.7 times that of the median 5-year-old, respectively. Thus, lower leg muscle volumes (product of PCSA and fascicle length) increase primarily through transverse growth, rather than longitudinal growth, especially in children above 5 years of age. There was considerable overlap in PCSA, fascicle length and pennation angle distributions between boys and girls at all ages. Further analysis showed that longitudinal growth of muscle-tendon units is achieved primarily by lengthening of intramuscular aponeuroses and that aponeurosis surface areas scale in proportion with PCSA. The reference curves presented here provide normative data for muscle architecture in children and provide insights into the mechanisms of childhood muscle growth.
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