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BioMed Research International
Volume 2017, Article ID 8471546, 13 pages
Research Article

Evidence for Startle Effects due to Externally Induced Lower Limb Movements: Implications in Neurorehabilitation

1Physical Medicine and Rehabilitation Department, Faculty of Medicine, Universidad Complutense de Madrid and National School of Occupational Medicine, Instituto de Salud Carlos III, Madrid, Spain
2Department of Neurology, Hochzirl Hospital, Zirl, Austria

Correspondence should be addressed to Markus Kofler;

Received 24 August 2016; Revised 10 January 2017; Accepted 19 January 2017; Published 16 February 2017

Academic Editor: Prescott B. Chase

Copyright © 2017 Juan M. Castellote et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.


Passive limb displacement is routinely used to assess muscle tone. If we attempt to quantify muscle stiffness using mechanical devices, it is important to know whether kinematic stimuli are able to trigger startle reactions. Whether kinematic stimuli are able to elicit a startle reflex and to accelerate prepared voluntary movements (StartReact effect) has not been studied extensively to date. Eleven healthy subjects were suspended in an exoskeleton and were exposed to passive left knee flexion (KF) at three intensities, occasionally replaced by fast right KF. Upon perceiving the movement subjects were asked to perform right wrist extension (WE), assessed by extensor carpi radialis (ECR) electromyographic activity. ECR latencies were shortest in fast trials. Startle responses were present in most fast trials, yet being significantly accelerated and larger with right versus left KF, since the former occurred less frequently and thus less expectedly. Startle responses were associated with earlier and larger ECR responses (StartReact effect), with the largest effect again upon right KF. The results provide evidence that kinematic stimuli are able to elicit both startle reflexes and a StartReact effect, which depend on stimulus intensity and anticipation, as well as on the subjects’ preparedness to respond.