32 Monitoring natural human gait in real-life environments is essential in many 33 applications, including quantification of disease progression, monitoring the effects of 34 treatment, and monitoring alteration of performance biomarkers in professional sports. 35 Walking ground reaction forces are among the key parameters necessary for gait 36 analysis. However, these parameters are commonly measured using force plates or 37 instrumented treadmills which are expensive and bulky and can only be

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... used in a 38 controlled laboratory environment. Despite the importance of real-life gait 39 measurement, developing reliable and practical techniques and technologies necessary 40 for continuous real-life monitoring of gait is still an open challenge, mainly due to the 41 lack of a practical and cost-effective wearable technology for ground reaction force 42 measurement. This paper presents a methodology to estimate the total walking ground 43 reaction force ( ) in the vertical direction using data from a single inertial 44 measurement unit. Correlation analysis of the vertical acceleration of different body 45 segments with ( ) indicated that the 7 th cervical vertebrae is one of the best 46 locations for the sensor. The proposed method improves the accuracy of the state-of-47 the-art ( ) estimation by 25%, by utilising the time-varying ratio of the vertical 48 acceleration of the human body centre of mass and measured C7 vertical acceleration. 49 Results of this study showed that the proposed method estimated consistently the 50 ( ) in both indoor and urban outdoor environment, with a 4-8% peak-to-peak 51 normalised root mean square error. 52