## 1 Introduction  
Technology developments towards novel healthcare concepts pave the way for the rising area of digital health, which, according to the U.S. Food and Drug Administration (FDA), includes categories such as mobile health (mHealth), health information technology, wearable devices, telehealth and telemedicine, and personalized medicine. Especially, new smart wearable technologies and the health information technology provided by the internet of things would enable a comprehensive view of an individual's life. In this context, mobility is of the utmost importance, as it defines quality of life in healthy living and chronic diseases. In numerous neurological, musculoskeletal,and cardiovascular disorders, distinct symptoms reduce motor function and/or cardio-pulmonary capacity, and thereby limit the independence and autonomy of individuals. Even though the disease-causing mechanisms and symptomatic patterns are specific to each disorder, impaired mobility is a typical consequence. This fact makes mobility an important surrogate marker for disease severity, progress, and responsiveness to the prescribed therapies, providing opportunities to assist therapeutic decision making.  
The continuous, automatic monitoring of sensor-based information on walking ability and mobility is increasingly exploited to support objective assessment for preventative and proactive disease management and diagnostic workup, and to assist with therapeutic decision-making. In this work, we envision to leverage the emerging Internet of Health Things (IoHT) [1] to enable the application of smart devices for continuous, real-time monitoring. Smart shoes are an attractive form of smart devices for the purpose of mobility assessment for three reasons: (i) smart shoes have a predefined, rigid sensor position on the foot, providing accurate and flexible biomechanical analysis; (ii) smart shoes can be used to monitor gait, a highly stereotype movement that enables the automated assessment of functional biomechanics; and (iii) smart shoes enable a non-obtrusive and non-stigmatizing integration of technology, ultimately improving patient acceptance and long-term adherence. We also envision that the sporting goods industry will produce a growing number of sensor-equipped smart shoes that are capable of monitoring fitness and health conditions. The current limitations of this technology, namely restricted usability to patients, limited battery runtime, and especially restriction to only one shoe model due to a limited availability of instrumentation, will be overcome in the future once this mass-market availability is ensured.  
Mobility monitoring technologies demand research in sensor-based data acquisition and its subsequent analysis to support objective and clinically relevant gait analysis outside of conventional clinical environments [2]. The mounting popularity of this research topic is reflected by the annually increasing number of related articles as shown in Figure 1. Thus, this paper aims to provide an overview of the important engineering aspects of smart-shoe applications in the field of IoHT. It will also highlight the differences and requirements of the related engineering and medical needs (Figure 2), which are critical components for effective biomedical engineering solutions.  
Figure 1: The annual number of publications found using PubMed and Google Scholar on the subject of gait monitoring using smart shoes. The search criteria included “(gait OR shoe OR walking) AND (inertial OR IMU OR sensor OR wearable)”; IMU: Inertial Measurement Unit.