Ballroom dance is a sophisticated, technical and physically strenuous activity. In its competitive form, it is called dancesport. As with most technical sports disciplines, it demands years of dedicated training to achieve mastery. It combines highly energetic processes and neural coordination and places great focus on the aesthetics of movement (Chang et al., 2020, Liiv et al., 2014). International standard dances tournaments are very complex competitions, where male and female partners, as couples, keep a closed position (handhold position) and move in harmony across the dance floor. Judges award the highest marks to couples who act seamlessly in unison (Premelč et al., 2019). Even the untrained eye of a spectator can appreciate the craftsmanship and finesse of the best dancers.

Dancers of various dance styles have been the subject of many research studies. Since spectators admire the harmony and unusual balance among dancers, a larger part of these studies focused on coordination and postural control. Most of these studies involved ballet dancers rather than ballroom dancers. However, it has been proven that dance training, regardless of the style, can influence the postural stability of dancers’ bodies. Dancers may exhibit both increased (Michalska et al., 2018) and decreased (Muelas Pérez et al., 2014) postural sway compared to untrained, age-matched controls and still present excellent balance ability. Usually, balance analyses are conducted on data sets collected from individual dancers. However, undoubtedly, most important, especially in ballroom dancing, is the unison between dance partners. Hence, this study postulates that it is not only especially important but also greatly interesting to assess dancers as a couple rather than as solo dancers.

Information on dance couple stability is limited. Indeed, it is puzzling how the individual partners in a dance couple contribute to the stability of the pair. Based on the fact that a single light touch from an external object might reduce postural sway (Jeka and Lackner, 1994), a dance couple should present different center of foot pressure (COP) characteristics from a solo dancer. One of the ways to answer the above-mentioned issue is to use an advanced COP analysis technique that allows for the extraction of variables reflecting the physiological properties of the postural control system. One of the methods that fulfil this criterion is the rambling (RM) and trembling (TR) decomposition of the COP trajectory (Nematollahi et al., 2017). According to Zatsiorsky and Duarte (2000), this method allows for the decomposition of a COP stabilogram into its slow (RM) and fast (TR) components. The method assumes that the central nervous system sets a reference point (RP) against which balance is maintained. This point is not static and continuously modifies its position. Any deviation from its trajectory triggers mechanisms to restore balance. The trajectory of migratory RP is defined by RM. Other movements resulting from force activity that aim to restore balance within the system are considered as TR. During a balance task, such as quiet standing, with the use of the RM and TR decomposition, it is possible to analyse the contribution of two distinct control mechanisms to postural sway (Zatsiorsky and Duarte, 2000, Zatsiorsky and Duarte, 1999). In essence, RM is a slow non-oscillatory component and may represent a certain amount of natural variability in the central nervous system or an exploratory process updating sensory information, while TR is a faster damped oscillatory component, believed to arise from ‘apparent muscle stiffness’, and may represent the peripheral nervous system’s contribution to postural sway (Zatsiorsky and Duarte, 1999). The postural control system can also be understood as a two-level hierarchical system consisting of supraspinal (RM) and spinal (TR) control. By analysing the decomposed stabilogram, the contribution of each component in posture control can be considered, even without visible changes in the range of postural sway.

The inherent significant differences in RM and TR trajectories can be caused by sport training (Akbaş et al., 2022), aging processes (Ferronato and Barela, 2011), proprioception deficits in the joints (Nematollahi et al., 2017), dyspraxia (Speedtsberg et al., 2017), simulation of varying degrees of somatosensory deficits (Gerber et al., 2022) and external vestibular stimulation (Chen et al., 2021). In general, a reduction in the RM component is reported to indicate a greater efficiency of the postural control system, which is defined as an instantaneous point about which the body is stabilised. A decrease in the TR component is described as reflecting an increased effectiveness provided by an adaptation of spinal reflexes and changes in the intrinsic mechanical properties of muscles and joints (Sousa et al., 2016). Conversely, Degani, Leonard and Danna-dos-Santos (2017) pointed out that an increase in the RM component might reflect impaired sensory reweighting, sensorimotor integration and corrective motor actions, especially among older adults. Likewise, an increase in the TR component might be due to the progressive age-related changes in sensory receptors, muscle mass and properties and modulation of spinal reflex gains. This interpretation corresponds with aging processes and clinical practice and may or may not be related to the postural control of professional competitive dancers.

As previously stated, the scientific literature contains a wide range of studies on the balance of professional dancers, especially ballet dancers. However, these studies typically focus on individual dancers. In this study, the postural stability of ballroom dance couples was examined. The aim was to identify changes in the mechanism of dancers’ postural control between standing solo and standing with a partner during specific international standard dance positions. It was hypothesised that the male partner would stabilise the dance couple. The second hypothesis was that the TR component would increase if the dance partners stood together.