The results of the present study show a significant increase in electromyographic activity of the bíceps brachii muscle in newborns who have been placed in the Kangroo Position. Furthermore this increase was found to be steady and constant. This finding is worthy of note, as it suggests that this position produces a functional alteration in the muscle involved in the anti-gravity posture system.
A previous study showed that early psychomotor stimulation of preterm newborns from the first to fifth corrected month of life improves motor development and that the more stimulation there is, the larger the number of motor skills acquired in the supine, prostrate and sitting positions . Likewise, a meta-analysis published in 2012 shows that vestibular stimuli also improve the psychomotor development of breastfeeding preterm children at a corrected age of six and twelve months .
Although these other studies have examined the effect of psychomotor or sensorial stimulation on the motor development of preterm newborns, they did not specifically investigate the influence of the Kangaroo Position on this development [22–26].
Few studies have been conducted that examine the effect of the Kangaroo Position on motor development [12–14]. Barradas et al.  showed that preterm newborns who were placed in the Kangaroo Position adopted a posture with more flexion. Ferber & Makhoul  showed that, in term children, the Kangaroo Position caused an increase in flexion movements and a decrease in extensor movements compared to those not placed in this position, suggesting that the Kangaroo Position leads to an alteration in the motor system in these babies. More recently, Barradas  studied the influence of the Kangaroo Position on electromyographic activity in preterm newborns and found that, after 24 h of the Kangaroo Position, these newborns exhibited greater electromyographic activity in various muscle groups.
It may be that the stimulation of the kinesthetic and vestibular systems provided by the Kangaroo Position influenced the motor response observed in the aforementioned studies. The hypothesis that the vestibular and kinesthetic systems are involved in this process is backed up by the results presented in meta-analyses of interventions other than the Kangaroo Position [23, 26].
Studies that showed the influence of the Kangaroo Position on the motor skills of newborns also found that this effect is persistent [13, 14]. Ferber & Makhoul  found alterations in the motor skills of term children three hours after interruption of the Kangaroo Position and Barradas  has shown that the effect that the Kangaroo Position has on electromyographic activity in preterm newborns persisted for more than 24 hrs after ceasing to adopt the position. In the present study, the level of electromyographic activity at term equivalent age was no different from that recorded at 96 h, suggesting a more prolonged persistent effect.
Although we cannot rule out the possibility that the growing increase in electromyographic activity observed in the first 96 h of the Kangaroo Position may be due to the natural growth of the child, this is implausible, since there were no correlations between the ages of the newborns or their birth-weight and the level of electromyographic activity. Moreover, the results show that, even after an interval of 21 days between being discharged from hospital and the electromyographic reading at term equivalent age, the electromyographic responses at this point were similar to those found by the reading at 96 h.
Furthermore, since the newborns did not undergo any motor intervention during the data collection period, the results show that the Kangaroo position is associated with the electromyographic responses found.
One limitation of the present study may be the fact there was no comparison with a control group of newborns not placed in the Kangaroo Position, which might have revealed that the increase in RMS is not related to the Kangaroo Position but the result of the natural development/growth of the child. This limitation, however, is minimized by the lack of correlation between the age and the electromyographic activity.
Another limitation is the fact that the results cannot be generalized for newborns with a gestational age of under 27 weeks and it is not known whether the RMS would increase, were the period of adoption of the Kangaroo position shorter than that used for the present study.
The present study is, so far as we are aware, the first follow-up study of the effect of the Kangaroo Position on electromyographic activity in preterm children. Given the results found, it would be particularly interesting to investigate other muscles involved in the postural system, and to conduct a study similar to this one with term children and children who have not been placed in the Kangaroo Position.