Parkinson’s disease (PD) is a neurodegenerative disorder characterized by cardinal features resting tremor, rigidity, bradykinesia, and postural difficulties which are thought to arise primarily from the loss of dopamine producing neurons and subsequent dysfunction of the basal ganglia-thalamo-cortical pathway (Konczak et al., 2009). Patients with PD have difficulties in performing various motor tasks, such as walking, writing and speaking. Furthermore, PD leads to abnormalities in two main components of postural control: orientation (maintaining a normal postural arrangement and alignment) and stabilization (maintaining equilibrium) (Vaugoyeau & Azulay, 2010). Postural instability (PI) is a disabling disorder, which is associated with sudden falls, progressive loss of independence, immobility and high costs for healthcare systems (Grimbergen et al., 2004). It usually occurs at the later stages of the disease and, unlike gait disorders, responds poorly to medication. Marked alteration of gait is common in advanced PD, although there is evidence suggesting that initial impairment in gait can be detected even early in the course of the disease (Stolze et al., 2005; Baltadjieva et al., 2006). Gait disorders, along with turning and balance disturbances, are the most important determinants of falls, which are recognized to be a major problem among people with PD. Falls occur despite maximal treatment with levodopa, confirming that axial disability in late stage PD is largely dopa-resistant (likely due to extranigral and non-dopaminergic brain lesions). Falls often have dramatic consequences, such as traumas and fractures. The high risk of fractures was demonstrated in a large case control study (Vestergaard et al., 2007), which showed that patients with parkinsonism (not just PD) had a more than two-fold increased risk of sustaining a fallrelated fracture. It has been established that PD has a negative impact on the quality of life (QoL) of patients (Diamond & Jankovic, 2005). Interestingly, in PD, non-motor symptoms such as depression and cognitive impairment are major predictors of QoL (Martinez-Martin, 1998). Although investigators have examined the effect of specific PD symptoms such as tremor, rigidity and bradykinesia (Peto et al., 1995), medication-related complications (Chapuis et al., 2005), insomnia (Caap-Ahlgren & Dehlin, 2001), fatigue (Herlofson & Larsen, 2003) and sweating (Swinn et al., 2003), their relative contributions to the patient’s QoL have