## 1 Introduction  
Parkinson's disease (PD) is a typical neurodegenerative disorder characterized mainly by motor symptoms. Similar to other countries, the number of patients with PD in Japan is rising as the elderly population increases [1]. PD is a heterogeneous disorder, and accordingly the clinical course and responsiveness to levodopa vary among individual patients depending on the age at onset and motor and nonmotor clinical symptoms and signs. Thus, treatment of PD requires adequate assessment of the status of patients as well as consideration of the effects of the disease on their daily lives and social activities. Although several methods for assessment of PD motor symptoms are available, two are widely used in daily clinical practice--the Unified Parkinson's Disease Rating Scale (UPDRS) [2] and the Movement Disorder Society-sponsored revision of UPDRS (MDS-UPDRS) [3]--which allow comprehensive assessment of motor symptoms and difficulties in activities of daily living (ADL). However, evaluation by an expert in the examination room and assessment of the ADL based on patient self-reports have several limitations. In fact, the on-off state is often difficult to assess in routine clinical practice, especially in patients with motor fluctuations.  
In recent years, new technology-based methods for the assessment of PD have been proposed and developed [4; 5; 6; 7; 8; 9]. Some employ wearable sensors, such as accelerometers, gyroscopes, magnometers, barometers, light sensors, and global positioning systems [10]. In fact, some of these new technologies are currently being used in clinical laboratory examinations. Although careful validation is necessary,these sensors have enhanced our understanding of the physical function and activity in daily living that could not be captured previously by clinical observations. Thus, wearable sensors provide new opportunities to gain knowledge with regard to health and function [10].  
It has been postulated that the degree of impairment in daily activities correlates with the severity motor performance deficits, quantified by wearable devices only and not by UPDRS part III, including elemental motor symptoms, such as rigidity and tremor [11]. However, this correlation remains to be investigated.  
In Japan, the portable gait rhythmogram (MIAMORI-Gait; ISI Medience Corporation, Tokyo, Japan) equipped with a triaxial accelerometer has been approved for health insurance reimbursement by the Ministry of Health, Labor, and Welfare. This device is mainly used for the assessment of the amount of overall movement and gait in patients with PD and other neurodegenerative disorders [12; 13; 14; 15]. The amount of overall movement measured with MIMAMORI-Gait is assumed to quantifykinesia/bradykinesia, composite symptoms, combined with elemental motor deficit [12; 13; 14; 15].  
Using the MIMAMORI-Gait, the present study was designed to determine whether the amount of overall movement in PD patients correlates with UPDRS part II-estimated impairments in daily activities. The study also served to examine the correlation between the amount of overall movement measured by the device with the clinical score of elemental motor symptoms, Hoehn and Yahr (mH&Y) stage and UPDRS part III.