Development of proximal arm muscle control during reaching in young infants: from variation to selection.
Reaching movements are initiated by activity of the prime mover, i.e. the first activated arm muscle. We aimed to investigate the relationship between prime mover activity and kinematics of reaching in typically developing (TD) infants in supine and sitting position. Fourteen infants were assessed at 4 and 6 months during reaching in supine and supported sitting. Kinematics and EMG-activity of deltoid, pectoralis major, biceps (BB) and triceps brachii were recorded. Kinematic analysis focused on number of movement units (MUs) and transport MU (MU with longest duration). Prime mover use was variable, but at 6 months a dominance of BB emerged in both testing conditions. Kinematics were also variable, but with increasing age the number of MU decreased and the relative proportion of the transport MU increased. BB as prime mover at 6 months was related to a larger transport MU.


CONCLUSIONS
Between 4 and 6 months BB prime mover dominance emerges which is related to relatively efficient reaching characteristics.
Bakker
Hanneke
H
Department Paediatrics - Developmental Neurology, University Medical Center Groningen, University of Groningen, Hanzeplein 1, 9713 GZ Groningen, The Netherlands.
de Graaf-Peters
Victorine B
VB
van Eykern
Leo A
LA
Otten
Bert
B
Hadders-Algra
Mijna
M
D000222:Adaptation, Physiological; D001132:Arm / Q000502:physiology*; D001696:Biomechanical Phenomena; D002657:Child Development / Q000502:physiology*; D004576:Electromyography; D005260:Female; D006801:Humans; D007223:Infant; D008137:Longitudinal Studies; D008297:Male; D009043:Motor Activity / Q000502:physiology*; D009048:Motor Skills / Q000502:physiology*; D024510:Muscle Development; D018482:Muscle, Skeletal / Q000254:growth & development / Q000502:physiology*; D012016:Reference Values; D016683:Supine Position