Abstract We present an inertial sensor based moni- toring system for measuring upper limb movements in real time. The purpose of this study is to develop a motion tracking device that can be integrated within a home-based rehabilitation system for stroke patients. Human upper limbs are represented by a kinematic chain in which there are four joint variables to be considered: three for the shoulder joint and one for the elbow joint. Kinematic models are built to estimate upper limb motion in 3-D, based on the inertial mea- surements of the wrist motion. An efficient simulated annealing optimisation method is proposed to reduce errors in estimates. Experimental results demonstrate the proposed system has less than 5% errors in most motion manners, compared to a standard motion tracker. Keywords Inertial measurement Æ Stroke rehabilitation Æ Motion tracking Æ Upper limb Æ Simulated annealing 1 Introduction Stroke is one of the most important causes of dis- ablement among elderly people. In the UK, around 130,000 people each year suffer a stroke, and one-third of them have a severe disability due to the deteriorated motor function in arms and legs. Evidence shows that additional early exercise training may be beneficial [4]. Independent and repetitive exercises could directly strengthen arms and legs, and may help patients re- cover more quickly. Classical treatments primarily rely on the use of physiotherapy, which depends on the trained therapists and their past experience. This suggests that traditional methods lack objective standardised analysis for eval- uating a patient’s performance and assessment of therapy effectiveness. To address this problem, trajec- tories during the rehabilitation course after stroke have to be quantified, and hence appropriate instruments for quantitative measurements are desirable to capture motion trajectories and specific details of task execu- tion. Recently, research has commonly addressed on measurements of upper limb movements. Since upper limbs are frequently used to contact and manipulate objects [5], stroke recovery of functional use of upper limbs is a primary goal of rehabilitation. Successful examples have existed in literature for the applications of inertial sensor based systems in the measurements of upper limb movements [12, 14]. Inertial sensors are sourceless and are able to provide accurate readings without inherent latency. Hence, they are a better option than other sensors in our application. For example, they are able to cope with the occlusion problem bound in the optical tracking systems. However, accumulating errors (or drifts) are This work was supported by the UK EPSRC under Grant GR/ S29089/01. H. Zhou (&) Æ H. Hu Æ Yaqin Tao Department of Computer Science, University of Essex, Colchester CO4 3SQ, UK e-mail: zhou@essex.ac.uk e-mail: ytao@essex.ac.uk H. Hu e-mail: hhu@essex.ac.uk Yaqin Tao e-mail: ytao@essex.ac.uk Med Bio Eng Comput (2006) 44:479–487 DOI 10.1007/s11517-006-0063-z 123 ORIGINAL ARTICLE Inertial measurements of upper limb motion Huiyu Zhou Æ Huosheng Hu Æ Yaqin Tao Received: 18 October 2005 / Accepted: 20 April 2006 / Published online: 31 May 2006 Ó International Federation for Medical and Biological Engineering 2006