Gastrocnemius-Soleus Muscle Tendon Unit Changes Over the First 12 Weeks of Adjusted Age in Infants Born Preterm

BACKGROUND AND PURPOSE: Differences in the gastrocnemius-soleus muscle and tendon have been documented shortly after birth in infants born preterm compared with infants born at term. Knowledge of muscle tendon unit lengths at term age to 12 weeks of age in infants born preterm may be useful in understanding motor development. PARTICIPANTS AND METHOD: Gastrocnemius-soleus muscle tendon unit lengths were compared at term age, at 6 weeks of age, and at 12 weeks of age (preterm adjusted age) in 20 infants born full term and 22 infants born preterm. RESULTS: Significant differences were found between the 2 groups on taut tendon, relaxed muscle length (A(O)); taut tendon, stretched muscle length (A(Max)); and muscle stretch (A(O) to A(Max)). Infants born preterm demonstrated measures of A(O) and A(Max) in positions of greater plantar flexion compared with infants born full term. Significant differences in measurements of A(O) were found between term age and 12 weeks of age, indicating that the tendon lengthens during this period for both groups. DISCUSSION AND CONCLUSION: These results provide knowledge of musculoskeletal development of the gastrocnemius-soleus muscle and tendon. Differences in musculoskeletal measurements are consistent with uterine confinement in the last weeks of full-term gestation. These findings have implications when examining the musculoskeletal system in infants born preterm who are demonstrating functional changes.