Journal of Electromyography and Kinesiology 10 (2000) 1–14 www.elsevier.com/locate/jelekin Time-course analysis of stretch reﬂexes in hemiparetic subjects using an on-line spasticity measurement system Ming-Shaung Ju a , Jia-Jin J. Chen b,* , Hsin-Min Lee b , Thy-Sheng Lin c , Chou-ching Lin c , Yin-Zu Huang c a Department of Mechanical Engineering, National Cheng Kung University, Tainan, Taiwan, ROC b Institute of Biomedical Engineering, National Cheng Kung University, Tainan, Taiwan, ROC c Department of Neurology, National Cheng Kung University, Tainan, Taiwan, ROC Received 18 September 1998; received in revised form 7 May 1999; accepted 18 June 1999 Abstract Spasticity after a stroke is usually assessed in a score form by subjectively determining the resistance of a joint to an externally imposed passive movement. This work presents a spasticity measurement system for on-line quantifying the stretch reﬂex of paretic limbs. Four different constant stretch velocities in a ramp-and-hold mode are used to elicit the stretch reﬂex of the elbow joint in spastic subjects. The subjects are tested at supine position with the upper limb stretched towards the ground, in contrast with the horizontally stretched movement used in other studies. By subtracting the baseline torque, reﬂex torque measured at a selected low stretch velocity of 5 deg/sec, the inﬂuence of gravity torque and inertial in vertical stretching mode can be minimized. The averaged speed-dependent reﬂex torque (ASRT), deﬁned as the measured torque deviated from the baseline torque, is used for quantifying the spastic hypertonia. Four subjects having incurred cerebrovascular accident (CVA) are recruited for time-course study in which the measurements are taken at 72 hours, one week, one month, three months, and six months after onset of stroke. During the development of spasticity, the changes of ASRT and velocity sensitivity of ASRT of the involved and the intact elbow joints are discussed.  2000 Elsevier Science Ltd. All rights reserved. Keywords: Spasticity; Time-course analysis; Hypertonia; Stroke 1. Introduction Spasticity has been deﬁned as a motor disorder characterized by a velocity-dependent increase in tonic stretch reﬂexes with exaggerated tendon jerks [10]. As a component of upper motor neuron syndrome, spasticity or hyperexcitability of stretch reﬂex frequently interferes with the limb functions of patients having suffered from a stroke, traumatic brain injury, or spinal cord injury. For subjects having incurred cerebrovascular accident (CVA), the spasticity changes gradually since the onset of a stroke. As generally known, the lower motor neu- rons lose their control and muscle weakness develops at the acute stage of stroke. After muscle tone decreases at * Corresponding author. Tel.: + 886-6-234-3270; fax: + 886-6-234- 3270. E-mail address: jason@jason.bme.ncku.edu.tw (J.-J.J. Chen) 1050-6411/00/$ - see front matter  2000 Elsevier Science Ltd. All rights reserved. PII:S1050-6411(99)00018-8 the acute stage of a lesion, spasticity typically occurs in a later stage and the tendon reﬂex is also increased [10]. The mechanism of above phenomena still remains unknown. An objective method is highly desired to quantify the changes of spastic hypertonia after the stroke occurs, i.e. time-course analysis, there by improv- ing the treatment and rehabilitation process for spastic patients [29]. For time-course analysis, conventional clinical assess- ments lack a standard reference point to document the changes of spasticity over time. The most widely used approach for assessing spasticity entails feeling the resistance of affected joints to the passive movement imposed by an examiner. Other clinical assessments, e.g. the tendon tap test and various score-based evaluation forms, are semi-quantitative and rely on the examiner’s experience [11]. In addition, these tests are only appro- priate for the same examiner over a short period of time. These limitations become major shortcomings for a