Maternal behaviors and exposures affect fetal growth and development. Smoking, malnutrition, sedentary behavior, and stress can each lead to fetal programming and intra-uterine growth restriction. As a result, tissue development may be impaired. Problems with muscle formation can lead to reductions in muscle performance throughout life. The purpose of this study was to determine if in utero effects on muscle mass, muscle function, or both are responsible for the relationship between size at birth and adult muscle strength.
One hundred adults (ages 18-40), who were singletons born at term (37-42 weeks), participated. Birth weight was adjusted for gestational age using neonatal growth reference data. Maximal voluntary contractions (MVC) of dominant and non-dominant handgrip, and right and left leg extension were measured. Linear regression analysis was used to determine the association between adjusted birth weight and muscle strength. Sex and lean body mass were covariates.
Dominant handgrip MVC increased by 1.533 kg per 1 SD increase in adjusted birth weight (p = 0.004). Lean body mass had a significant indirect effect on this relationship. The relationship between handgrip strength and adjusted birth weight was strongest among female subjects. No other muscle strength measures were significantly associated with adjusted birth weight.
Birth size was a significant predictor of handgrip strength in adulthood. Including lean body mass attenuated, but did not remove, the association. Thus, among individuals born to term, having a smaller-than-predicted birth size likely causes both reductions in muscle mass formation and decreased muscle function, ultimately impacting muscle strength in adulthood.

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