Early Upper Limb Function in Infants Under Three Months: Associations with Shoulder Biomechanics and General Movement Patterns

Early identification of neurodevelopmental trajectories is essential for timely intervention in infancy. While joint mobility is often seen as an indicator of motor capacity, its link to early functional performance remains unclear. This study examined whether active shoulder range of motion and the quality of spontaneous movement quality relate to early upper limb function in infants under three months. Thirty-two healthy infants participated in a cross-sectional assessment. Video recordings analyzed with the General Movements Assessment classified movements as Fidgety or Writhing. Fine motor performance was evaluated using five items from the Denver II Screening Test. Active shoulder abduction was measured via two-dimensional frontal-plane analysis with Kinovea^®. Data analysis involved t-tests and Pearson correlations. Results showed that infants with Fidgety movements scored higher on fine motor tests than those with Writhing movements. Shoulder range of motion was slightly higher in infants with Writhing movements, but not significantly. No sex differences were found. Weak, nonsignificant correlations existed between shoulder range of motion and fine motor performance. The findings suggest movement quality, rather than limb mobility, is more connected to early motor function. Combining movement quality assessments with simple tests may improve early detection of subtle neuromotor issues and guide early stimulation strategies.