Skeletal Muscle Development in Premature Infants

Abstract

Biopsies from various skeletal muscles were taken post mortem from 13 infants with conceptional ages between 25 and 40 weeks. Cryostat sections were quantitatively analysed.The growth of the mean fibre diameter follows an exponential curve mainly representing the growth of type 11-fibres which initially predominate.Bcfore the 34th week only isolated large Wohlfart-fibres show type I staining characteristics. A greater numcentage of the total fibre populatioll increases linearly to 40 % at term. I t is suggested that Wohlfart-fibres are a physiologically distinct entity and that typical type I-fibres do not occur before the 34th week. Comparison of muscle groups showed larger fibres in proximal (versus distal) muscles, in cranial (versus caudal) muscles, and in extensors versus flexors. These differences become more pronounced with increasing age. N o differences were found relating to muscle fibre types. ber of smaller type I-fibres appear sud-. -1 Present Adress: Dept. of Paedintrics. Mantilicinl Medidenly around the 34th week. Their per-C~I