Force overestimation during tourniquet-induced transient occlusion of the brachial artery and possible underlying neural mechanisms Yudai Takarada a , Daichi Nozaki b , Masato Taira c,d, * a Faculty of Sport Sciences, Waseda University, Saitama 359-1192, Japan b Department of Rehabilitation for the Movement Functions, Research Institute of National Rehabilitation Center for Persons with Disabilities, Saitama 359-8555, Japan c Nihon University, Advanced Research Institute for the Sciences and Humanities, Tokyo 102-8251, Japan d Division of Applied System Neuroscience, Advanced Medical Research Center, Nihon University Graduate School of Medical Science, 30-1 Ohyaguchi-Kamimachi Itabashi, Tokyo 173-8610, Japan Received 13 August 2005; accepted 11 October 2005 Available online 14 November 2005 Abstract A vascular occlusion by a tourniquet inflated at the proximal end of the upper arm is suggested to affect the estimation of exertion force level. In the first part of this study, subjects were asked to estimate the isometric force exerted by the occluded hand with that of the other hand (matching experiment). We found that the perceived force with arterial occlusion was always overestimated. To examine the underlying neural mechanism for this phenomenon, in the second part, the somatosensory evoked potentials (SEPs) and nerve action potential (NAP) were recorded following electrical median nerve stimulation with or without arterial occlusion. Moreover, the maximum motor response (M response) to median nerve stimuli at the axilla was recorded from the skin surface of the thenar eminence muscle of the hand during with arterial occlusion. The N20 of SEP and NAP at Erb’s point were unaffected by the arterial occlusion, and the M response was also unchanged. These results suggest that the tourniquet- induced transient occlusion of the brachial artery does not seriously affect median nerve function. Thus, it is likely that the primary responsible factor for the overestimation of perceived force exertion during arterial occlusion is the centrally generated motor command as previously hypothesized by McCloskey [McCloskey, D.I., Ebeling, P., Goodwin, G.M., 1974. Estimation of weights and tensions and apparent involvement of a ‘‘sense of effort’’. Exp Neurol. 42, 220–232; McCloskey, D.I., 1978. Kinesthetic sensibility. Physiol. Rev. 58, 763–820; McCloskey, D.I., 1981. Corollary discharge and motor commands and perception. In: Brookhart, J.M., Mountcastle, V.B. (Eds.), Handbook of Physiology. American Physiological Society, Bethesda, pp. 1415–1447]. # 2005 Elsevier Ireland Ltd and the Japan Neuroscience Society. All rights reserved. Keywords: Vascular occlusion; Force perception; SEP; M response; Central motor command; Median nerve 1. Introduction It is a common experience to feel a weight heavier than normal when we carry it long enough and when the muscles supporting the weight have been fatigued. McCloskey et al. (1974) have actually shown that weight is determined to be heavier than the usual under experimental muscle fatigue condition by a force matching task. In their study, they also showed that weight is overestimated during the inhibition of the motoneurons of the agonist muscle by vibration of its antagonist muscle. Thus, they suggested that the centrally generated motor command (i.e., effort) is involved in the sensation of heaviness rather than factors in the peripheral nerves and/or muscles (see reviews in McCloskey, 1978, 1981). In preliminary experiments on handgrip contractions with the proximal end of an upper arm occluded by a tourniquet at 250 mmHg, we noticed that subjects reported the need for greater force to keep the same force level during the tourniquet was inflated. However, these were just objective reports. In this study, we first examined how arterial occlusion affects the perception of handgrip force by the force matching experi- ment. The results showed that the subjects always over- estimated their exertion force during arterial occlusion. McCloskey’s idea (1974, 1978, 1981) is thought to be the underlying neural mechanisms for this, however the simplest www.elsevier.com/locate/neures Neuroscience Research 54 (2006) 38–42 * Corresponding author. Tel.: +81 3 3972 8111x2231; fax: +81 3 3972 8292. E-mail address: masato@med.nihon-u.ac.jp (M. Taira). 0168-0102/$ – see front matter # 2005 Elsevier Ireland Ltd and the Japan Neuroscience Society. All rights reserved. doi:10.1016/j.neures.2005.10.004