Cerebral palsy (CP) refers to a group of persons who had nonprogressive brain damage during their period of fetus or infant, when they were developing. They have limitations in activities due to permanent impairment of motor and postural development (Rosenbaum et al., 2007). Children with CP commonly have trunk instability, which affects postural control and movements (Frank et al., 2013; Son et al., 2017).

Sitting is a vertical position that is taken earliest in normal development. It is an important step that provides postural muscle tone (Park et al., 2001). Independent sitting plays a very important role in facilitating the use of active hands and enabling interactions with the environment (Harbourne et al., 2010). However, children with CP have insufficient ability to control postures compared to normal children due to the lack of stability of the trunk, and show abnormal muscle coordination patterns in the sitting position (Brogren et al., 1998; Liao et al., 2003). Therefore, the abnormal postural control of children with CP leads to the loss of trunk balance and resultant increases in the muscle tone of the upper and lower limbs (Myhr et al., 1993). In addition, they show decreased respiratory function due to uncontrolled trunk stability and weakening of respiratory muscles (Park et al., 2006). It is a common problem of children with CP, which leads to declines in daily living functions (Knox and Evans, 2002; Wang et al., 2012).

Diaphragm is a major muscle that leads respiration and acts as a postural stabilizer to affect the stabilization of vertical positions such as sitting and standing (Noh et al., 2014). Many researchers emphasized about importance of diaphragm movement in patients with musculoskeletal or central nervous system disorder (Kolar et al., 2012; O’Sullivan, 2002; Son et al., 2017). Son et al. (2017) have reported that diaphragm movement was not observed at the initial step of breathing or postural stabilization movement in the children with CP.

In spite of the problems of the diaphragm movement in children with CP, studies on it in children with CP are still limited. Therefore, we were to examine the effects of Vojta approach on diaphragm movements in children with spastic CP.

Children with CP do not experience normal motor development and show neurodevelopmental impairment so that their respiratory functions are remarkably poorer compared to normal children (Ersöz et al., 2006; Son et al., 2017). The reduction in respiratory function may be due to insufficient respiration ability and weakness of respiratory muscles (Kwon and Lee, 2013). On the other hand, children with CP who could walk have better respiratory function than those who could not walk (Lee and Kim, 2014). Ersöz et al. (2006) reported that although the respiratory problems of children with CP are not caused by CP itself but are associated with the deformation of the chest wall structure due to low respiratory muscle strength and decreased movements of the chest wall.

In the present study, we confirmed that the total score of the GMFM-88 for gross motor function showed no significant differences in both groups. However, the GMFM-sitting showed significant difference in the experimental group. In addition, there were significant differences in changes of inspiration between the two groups. The diaphragm affects the trunk control together with abdominal muscles, the abdominal muscle located in front of the abdominal cavity is extended or shortened following inspiration or expiration (Hodges et al., 2001; Kim and Park, 2018). Therefore, the contraction of the diaphragm increases the pressure in the abdominal cavity leading to increases in the spine stability (Hodges and Gandevia, 2000). In the previous studies, postural control and respiratory capacity were correlated with each other (Saunders et al., 2004; Zafar et al., 2018). Shin et al. (2015) reported that sitting posture affects respiratory function. Seat surface inclined anterior 15° had a greater effect on respiratory function than a seat surface inclined posterior 15°. In a study of Son et al. (2017), dynamic neuromuscular stabilization application to children with CP improved the trunk stability and gross motor function by improving diaphragm movement. Ha and Sung (2016) reported the increment of diaphragm area after Vojta approach applied to normal adults. Furthermore, Kolar et al. (2012) reported a decrease in diaphragm movement by using magnetic resonance imaging in patients with low back pain. In our results taken together, indirect stimulation suggest that the diaphragm is involved in respiration and posture maintenance because of increased diaphragm movement of the GMFCS II and III who are poor stability in sitting positions.

We supposed that indirect stimulation of the diaphragm through stimulation point in the Vojta approach would have affected the diaphragm movement during inspiration. This may increase diaphragm movement and abdominal pressure, which affected the improvement of trunk stability in the sitting position. Giannantonio et al. (2010) also suggested that Vojta approach is effective treatment method improving respiratory capacity and motor development of children with CP by activating postural control and respiratory muscles. Therefore, Vojta approach can be presented as an effective treatment for improvement of the diaphragm movement in children with CP.

This study has limitations such as difficulties in generalizing its contents because our sample size was relatively small; also, insufficient findings to explain respiratory functions because the study was limited to the diaphragm area. Future studies should be conducted for the improvement of the overall respiratory and motor functions.