BACKGROUND:Infants with Down syndrome present with organic and neurological changes that may lead to a delay in the acquisition of motor skills such as kicking, a fundamental skill that is a precursor of gait and is influenced by intrinsic and extrinsic factors. Therefore, this movement should be taken into account in early physical therapy interventions in infants.OBJECTIVE:To analyze and to compare the effect of additional weight on the frequency of kicks in infants with Down syndrome and infants with typical development at 3 and 4 months of age.METHOD:Five infants with Down syndrome and five with typical development at 3 and 4 months of age were filmed. The experiment was divided into four experimental conditions lasting 1 minute each: training, baseline, weight (addition of ankle weight with 1/3 the weight of the lower limb), and post-weight.RESULTS:There were significant differences between groups for all variables (p<0.05), with lower frequencies observed for infants with Down syndrome in all variables. There were significant differences between the experimental conditions baseline and post-weight (p<0.001) for both groups in the frequency of contact and success, with a higher frequency in the post-weight condition.CONCLUSIONS:The weight acted as an important stimulus for both groups, directing the kicks toward the target and improving the infants' performance in the task through repetition, however, the infants with Down syndrome had lower frequencies of kicks.

RESUMO | Durante o processo de aquisição do chute em lactentes, a preferência podal pode ser influenciada de forma diferente pelos fatores extrínsecos e intrínsecos. O objetivo foi comparar a preferência podal e verificar a influência do peso adicional e do Reflexo Tônico Cervical Assimétrico (RTCA) na preferência podal entre lactentes com síndrome de Down e típicos. Participaram do estudo cinco lactentes com síndrome de Down e cinco típicos aos três e quatro meses de idade. O experimento foi subdividido em quatro condições experimentais: Treinamento, Linha de Base, Peso e Pós-Peso. Os lactentes com síndrome de Down apresentaram preferência à esquerda ou indefinida e os típicos, preferência à direita. O RTCA influenciou na preferência podal em ambos os grupos, indicando que o lado de rotação da cabeça orientou o chute do mesmo lado. Nos lactentes com síndrome de Down a correlação entre RTCA e chutes foi positiva, sendo forte aos três meses e moderada aos quatro meses. Para os lactentes típicos foi observada correlação positiva fraca aos três meses, e aos quatro meses a correlação não foi estatisticamente significativa. Lactentes com síndrome de Down apresentam preferência podal contrária aos lactentes típicos. O RTCA exerce influência na preferência podal por um período mais longo em lactentes com síndrome de Down em comparação aos lactentes típicos.Descritores | desenvolvimento infantil; reflexo; lateralidade funcional.ABSTRACT | During the acquisition process of the kick in infants, foot preference may be influenced differently by extrinsic and intrinsic factors. The aim was to compare the foot preference and find the influence of additional weight and Asymmetrical Neck Tonic Reflex (ANTR) on the foot preference of infants with Down syndrome and typical ones. Five infants with Down syndrome and five typical infants at three and four months of age participated of the sudy. The experiment was divided into four experimental conditions: Training, Baseline, Weight and After Weight. Infants with Down syndrome showed preference to the left or indefinite, the typical infants showed preference to the right. ANTR influenced the foot preference in both groups, indicanting that the rotation of head side oriented the kicking for the same side. For infants with Down syndrome the correlation between ANTR and kicking was positive, with a strong positive correlation at three months of age and a moderate positive correlation at four months of age observed. For typical infants it was observed weak positive correlation at three months of age and at four months of age, the correlation was not significant. Infants with Down syndrome have foot preference contrary to typical infants. ATNR influences the foot preference for a longer period in infants with Down syndrome compared to typical infants.