## 4 Discussion
Thus, the amount of overall movement measured by the MIMAMORI-Gait seems to be potentially useful parameter in patients with PD for objective assessment of the degree of health-related quality of life. The results of the present study showed that the amount of overall movement was significantly lower in patients with PD, even during the early stage of the disease (mean disease duration of approximately 1.9 years), than healthy subjects. This result suggests that the amount of overall movement measured with MIMAMORI-Gait may help in the diagnosis of early PD. Methodologically, there are some open questions. First, the amount of overall movement measured with MIMAMORI-Gait might not reflect accelerations induced by movements of the upper limbs. The device used in this study is a single-sensor-type accelerometer attached to the lumbar region. Thus, the amount of overall movement measured with this device mainly reflects the movement of the body axis and differs from the amount of movement of the whole body, including the upper limbs. We should carefully interpret the results, although a single-sensor-type device imposes only a slight burden on the patient during long-term continuous recording; thus, it seems to be useful for monitoring activities in the actual daily lives of patients. Second, the effects of external acceleration (e.g., vehicles) may influence the measurement of movements. In this study, the patients were instructed to continue with their usual lifestyle patterns, and therefore the effect of external acceleration (e.g., prolonged transportation) was considered minimal. However, it is important to distinguish between acceleration of the patients themselves and external acceleration, and develop algorithms to exclude such influence. Third, the sensitivity of MIMAMORI-Gait needs to be further examined. While we have determined the high sensitivity of our device for detection of gait-induced accelerations [17; 18; 19], we have not checked its sensitivity in the detection of overall movement-induced accelerations. In other words, a control study that includes simultaneous recordings using the MIMAMORI-Gait and other devices is needed before clinical application. In spite of the lack of a control study for assessment of the amount of overall movement, our algorithm can be a potentially useful tool for quantitative assessment of motor symptoms of PD. The algorithm used in MIMAMORI-Gait for assessment of gait disorders has been validated in a series of studies from our laboratories [12; 13; 14; 17; 18; 19]. The present results confirmed that the algorithm can accurately assess impairment of ADL and gait disorders in PD. Fourth, the duration of monitoring should be examined. Daily activity levels vary among individual patients. Normally, a proper analytical procedure may be to take several measurements and use the mean value as the amount of movement. However, in this study, the amount of overall movement per 24 h was determined by using one measurement in each patient. In this study, the patient was asked to select a day when no special events--such as travel--were scheduled for the measurement, and they were also instructed beforehand to spend the day as usual with regard to physical activities. In a related issue, the present study included untreated patients with PD and healthy control subjects, and the results allowed objective assessment of these patients. However, the study design did not include evaluation of the device in differentiating patients at the initial stage of the illness from those at advanced stage, based on the amount of overall movement over 24 h. It is also not clear at this stage whether the device can be used to evaluate the PD stage of patients under treatment to determine the response to such treatment. Further large-scale studies are needed to evaluate the suitability of the MIMAMORI-Gait device for the above purposes. In summary, the present study measured the amount of overall movement over 24 h using the portable MIMAMORI-Gait device in patients with untreated PD.