Contents lists available at ScienceDirect Clinical Biomechanics journal homepage: www.elsevier.com/locate/clinbiomech Turning and sit-to-walk measures from the instrumented Timed Up and Go test return valid and responsive measures of dynamic balance in Parkinson's disease Michela Picardi a , Valentina Redaelli a , Paola Antoniotti a , Giuseppe Pintavalle a , Evdoxia Aristidou a , Irma Sterpi a , Mario Meloni b , Massimo Corbo a , Antonio Caronni b, ⁎ a Department of Neurorehabilitation Sciences, Casa di Cura del Policlinico, Via Dezza 48, Milano 20144, Italy b IRCCS Fondazione Don Carlo Gnocchi Onlus, via Alfonso Capecelatro 66, Milano 20148, Italy ARTICLE INFO Keywords: Parkinson's disease Postural balance Neurological rehabilitation Turning Sit-to-walk ABSTRACT Background: Balance impairment is a hallmark of Parkinson's disease with dramatic effects for patients (e.g. falls). Its assessment is thus of paramount importance. The aim of this work is to assess which measures from the instrumented Timed Up and Go test (recorded with inertial sensors) are valid balance measures in Parkinson's disease and evaluate their responsiveness to rehabilitation. Methods: The Mini-BESTest (a criterion-standard balance measure) and the instrumented Timed Up and Go test (with inertial sensors secured to the trunk) were administered to 20 Parkinson's disease patients before and after inpatient rehabilitation (median [IQR]; 76.5 [8.25] years; 5 females; Hoehn and Yahr stage: 2.5 [0.5]). 81 parameters from the instrumented Timed Up and Go test were evaluated. Multiple factor analysis (a variant of principal component analysis for repeated measurements) and effect sizes were used to assess validity and responsiveness, respectively. Findings: Only the first component of the multiple factor analysis correlated with the Mini-BESTest, and 21 measures from the instrumented Timed Up and Go test had large loadings on this component. However, only three of these 21 measures also directly correlated with the Mini-BESTest (trunk angular velocities from sit-to- walk and turning; r = 0.46 to 0.50, P = 0.021 to 0.038). Sit-to-walk angular velocity showed greater respon- siveness than the Mini-BESTest, while turning showed slightly less. Interpretation: Angular velocities from the turning and sit-to-walk phases of the Timed Up and Go test are valid balance measures in Parkinson's disease and are also responsive to rehabilitation. 1. Introduction People suffering from Parkinson's disease (PD) show obvious bal- ance and gait impairments (Lang and Lozano, 1998) that eventually contribute to the increased risk of falls that is typical of this disease (Wood et al., 2002). PD balance impairment affects not only static, but also dynamic balance (the ability to move in an upright stance without falling) (Nardone and Schieppati, 2006), and several PD treatments, including rehabilitation, are actually aimed at improving dynamic balance to eventually reduce the risk of falls (Shulman et al., 2013). On these premises, the importance of assessing balance and gait impair- ments and their changes after treatment is clear and strongly re- commended in PD (Bloem et al., 2016). To date, balance scales are the criterion standard for balance as- sessment (Di Carlo et al., 2016). The Mini-BESTest (MB) (Franchignoni et al., 2010) consists of a set of tasks performed by patients and scored by clinicians. Good balance is required to pass the MB items, most of which assess dynamic balance (e.g. walking with head turns). The MB showed good psychometric properties when used to assess balance in different neurological conditions (Di Carlo et al., 2016). Notably, the MB works well in PD (Schlenstedt et al., 2015). In the Timed Up and Go (TUG) test (Podsiadlo and Richardson, 1991), patients get up from a chair, walk three meters, make a 180° turn, walk back and sit down in the chair. The time taken to complete this sequence (i.e. total TUG duration, TTD) is measured with a con- ventional stopwatch and used as a measure of gross mobility in a range of diseases (PD included), both in everyday clinical practice and in clinical trials (Brusse et al., 2005; Zhu et al., 2011). The Instrumental TUG (ITUG) test is the TUG test completed with an inertial measurement unit (IMU), commonly secured to the patient's lower https://doi.org/10.1016/j.clinbiomech.2020.105177 Received 28 February 2020; Accepted 9 September 2020 ⁎ Corresponding author at: IRCCS Fondazione Don Carlo Gnocchi Onlus, via Alfonso Capecelatro 66, Milano 20148, Italy. E-mail address: acaronni@dongnocchi.it (A. Caronni). Clinical Biomechanics 80 (2020) 105177 0268-0033/ © 2020 Elsevier Ltd. All rights reserved. T