Vieira da Fonseca M.1, de Souza Oliveira A.L.2, Carregaro R.3,4, Bottaro M.2, Martins de Toledo A.3,4
1SARAH Rehabilitation Hospital Network, Brasília, Brazil, 2Universidade de Brasilia, College of Physical Education, Brasília, Brazil, 3Universidade de Brasília, School of Physical Therapy, Brasília, Brazil, 4Universidade de Brasilia, Rehabilitation Sciences Graduate Program, Brasília, Brazil
Background: Extrinsic restrictions in infants are important because it influences the infant's movement patterns. For instance, the additional weight is an extrinsic restriction that can challenge the infant's abilities. In the manual reaching, the additional weight restriction can improve some kinematic variables in full-term and preterm infants; however, this restriction decreases the object grasping success. Notwithstanding, up to date there are no studies that investigated how the additional weight influences the muscle activation during reaching behavior of low birth weight infants.
Purpose: The aim was to investigate the effects of additional weight on muscle activation of low birth weight preterm infants during reaching.
Methods: Thirty five infants were evaluated at 6 months of corrected age (born weighting less than 2500g, gestational age from 32 to 36 weeks and 6 days). Infants were positioned in a chair at 50º of inclination and performed the reaching behavior in two conditions: P1 (Baseline - Without weight): the object was showed by the examiner during 2 minutes in the middle line at shoulder height and arm length. The object was briefly moved so that the infant could notice and try reaching. After reaching, the object was removed and showed again, to elicit a new reaching movement; P2 (Additional Weight): experimental conditions similar to P1, however, a bracelet weighting 20% of the total mass of the infant´s upper limb was placed on both wrists. Electromyographic data were collected with a Trigno Wireless System (Delsys Inc.) and the electrodes were positioned on the muscle belly of the Biceps Brachii, Triceps Brachii, Deltoid and Pectoralis Major. The following variables were analyzed: a) Muscle Activation: signal amplitude of the muscles (Root Mean Square); and b) Coactivation: Agonist/Antagonist Ratio between the Biceps/Triceps RMS, during the Biceps agonist phase (data presented in %). Muscle activation data was normalized by the baseline muscle contractions and presented as % of this contraction. Independent variable was the condition with or without additional weight. The Wilcoxon Test was used to compare the conditions. Significance was set at 5% (P 0.05) and data are presented as median (Md) and quartiles [25%;75%].
Results: The biceps activation increased significantly in the P2 (4.9 [2.5;7.0]) vs P1 condition (2.6 [1,0;4.7]) (P 0.001). Also, the pectoralis had a greater activation in the P2 (7.5 [4.5;12.5]) vs P1 condition (5.3 [3.1;10.5]) (P=0.001). Triceps activation presented no significant differences. The coactivation decreased significantly in the P2 (53.4 [25.4;113.2]) vs P1 (94.2 [47.0;216.2]) (P=0.004).
Conclusion(s): In the procedure with additional weight, low birth weight premature infants increased their muscle activation of the biceps and pectoralis major muscles, probably due to a higher proprioception and muscle contraction regulation promoted by the additional weight. The decrease of muscle coactivation could be explained by the increase of biceps muscle activation and no modification of triceps brachii muscle activation. Future studies should be conducted in order to elucidate the effects of a long-term training.
Implications: It is suggested that additional weight can be used as an acute intervention strategy focused on the increment of muscle activation of infants.
Funding acknowledgements: The present study was supported by the CNPq (process n. 479202/2011-7)
Topic: Paediatrics
Ethics approval: The Institutional Ethics Committee, Health Sciences Faculty, granted approval (protocol n. 064/12).
All authors, affiliations and abstracts have been published as submitted.
