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Histochemical and contractile property changes during human muscle development
1Division of Kinesiology, Dalhousie University, Halifax, Nova Scotia, Canada.
Insights
Infant muscle development shows changes in contractile properties, particularly in plantarflexors, as muscles mature and usage increases. This study tracks these postnatal changes in muscle function and fiber type distribution.
Area of Science:
- Developmental Biology
- Physiology
- Neuromuscular Science
Background:
- Postnatal development involves significant changes in skeletal muscle histochemistry and contractile properties.
- Understanding the interplay between muscle function and its developmental trajectory is crucial for assessing neuromuscular health.
Purpose of the Study:
- To investigate the postnatal changes in histochemical and contractile properties of infant muscles.
- To determine the influence of developing muscle function on these physiological adaptations.
- To correlate muscle property changes with fiber type distribution during development.
Main Methods:
- Contractile properties, including maximal twitch tension (Pt), time to peak tension (TPT), and half-relaxation times (1/2RT), were measured in plantarflexor (PF) and dorsiflexor (DF) muscles.
- Measurements were taken in 19 newborns and 36 infants (5-16 months) over multiple monthly intervals.
- Muscle fiber type distributions (Type I) were analyzed post-mortem from fetal to adult stages.
Main Results:
- Time to peak tension (TPT) in plantarflexors slowed significantly from birth (77 ms) to 110-120 ms by 9-12 months, while dorsiflexors remained unchanged.
- Soleus muscle differentiation coincided with the observed slowing of contractile properties and increased infant muscle usage.
- A trend of higher Type I fiber percentages was noted in children compared to newborns and adults in several muscles.
Conclusions:
- Postnatal maturation leads to distinct changes in infant muscle contractile properties, particularly in plantarflexors, linked to increased functional use.
- The findings suggest a correlation between muscle functional development, contractile property maturation, and shifts in fiber type distribution.
- These insights have implications for evaluating peripheral neuromuscular function in infants and children.
Abstract:
When the histochemical and contractile properties of infant muscles change postnatally, and what influence muscle function has on these changes, were the focus of this study. Contractile properties were measured in the plantaflexor (PF) and dorsiflexors (DF) of 19 newborns and 36 infants aged 5-16 months. Infants were tested between one and four times at monthly intervals. Measurements included maximal twitch tension (Pt), time to peak tension (TPT), and half-relaxation times (1/2RT). TPT was similar in PF (77 ms) and DF (73 ms) at birth, remained unchanged in DF, and slowed in PF to 110-120 ms between 9 and 12 months. Type I distributions were determined at autopsy in fetal through to adult muscles. Completion of differentiation occurred in soleus at about the age that contractile properties slowed and infants started to use these muscles more. A trend of higher percentages of type I distributions was also noted in children than either newborns or adults in other muscles. The implications of these findings and the clinical use of these methods for evaluating peripheral neuromuscular function is discussed.