Despite the large number of studies that have investigated the use of wearable sensors to detect gait disturbances such as Freezing of gait (FOG) and falls, there is little consensus regarding appropriate methodologies for how to optimally apply such devices. Here, an overview of the use of wearable systems to assess FOG and falls in Parkinson’s disease (PD) and validation performance is presented. A systematic search in the PubMed and Web of Science databases was performed using a group of concept key words. The final search was performed in January 2017, and articles were selected based upon a set of eligibility criteria. In total, 27 articles were selected. Of those, 23 related to FOG and 4 to falls. FOG studies were performed in either laboratory or home settings, with sample sizes ranging from 1 PD up to 48 PD presenting Hoehn and Yahr stage from 2 to 4. The shin was the most common sensor location and accelerometer was the most frequently used sensor type. Validity measures ranged from 73–100% for sensitivity and 67–100% for specificity. Falls and fall risk studies were all home-based, including samples sizes of 1 PD up to 107 PD, mostly using one sensor containing accelerometers, worn at various body locations. Despite the promising validation initiatives reported in these studies, they were all performed in relatively small sample sizes, and there was a significant variability in outcomes measured and results reported. Given these limitations, the validation of sensor-derived assessments of PD features would benefit from more focused research efforts, increased collaboration among researchers, aligning data collection protocols, and sharing data sets.

Freezing of Gait (FOG) is one of the most disabling and least understood symptoms in Parkinson's disease (PD), and is usually observed in the advanced stage of the disease. FOG can be experienced on turning, in narrow spaces, whilst reaching a destination, and in stressful situations. FOG is commonly observed in the "off" state, but it can also be observed in the "on" state. Dual tasking (cognitive load) aggravates FOG. Visual or auditory cues often resolve FOG. Analysis of gait revealed that the rhythm of stepping suddenly jumps into high frequency (4-5 Hz) in FOG (hastening), and that floor reaction forces are disregulated. Stride-to-stride variability is increased in FOG. Hastening phenomenon was reported not only in PD patients but also in patients with striatal lesions. The basal ganglia and its frontal projections may be one of the essential lesion sites for FOG.A recent study using single-photon emission tomography (SPECT) revealed enhanced lateral premotor cortex (PMC) activity during paradoxical gait in PD, suggesting that PMC can compensate for the impaired function of the medial frontal cortex when cued by visual input. Treatment of FOG includes behavioural, medical, and surgical approaches. Tricks of all kinds (including external cues) are effective therapeutic approaches. If FOG occurs predominantly in the "off" state, dopaminergic therapy can be increased. For "on" freezing or if "on" response is otherwise optimised, the dose of the dopaminergic agent may be manipulated, but it could lead to the deterioration of parkinsonism. Deep brain stimulation of the STN often alleviates FOG in the "off" state.

Freezing of gait in Parkinson's disease and related disorders is common and very disabling. It usually occurs in the advanced stages, although mild forms may develop earlier. Freezing can occur on turning, in narrow spaces, immediately before reaching a destination, and in stressful situations. Dual tasking (motor or cognitive load) aggravates the problem. Freezing of gait in Parkinson's disease usually occurs in the 'off' rather than in the 'on' state. It is, therefore, not entirely drug-resistant; the first step in medical treatment is to ensure adequate dopaminergic stimulation to reduce the 'off' state. There is no good evidence for any specific drug to alleviate freezing. Visual or auditory cues are very helpful as behavioural therapy. Assistive devices, such as a wheeled walker sometimes help. Deep brain stimulation of the subthalamic nucleus may alleviate freezing in the 'off' state. Because of the complexity of freezing, individual patients need a careful assessment-particularly in relation to motor fluctuation-to optimise their treatment.

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