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Central command and the onset of exercise

2006; Wiley; Volume: 578; Issue: 2 Linguagem: Inglês

10.1113/jphysiol.2006.123950

1469-7793

Niels H. Secher,

Cardiovascular and exercise physiology

The Journal of PhysiologyVolume 578, Issue 2 p. 375-376 Free Access Central command and the onset of exercise Niels H. Secher, Niels H. Secher Department of Anaesthesia, The Copenhagen Muscle Research Centre, Rigshospitalet, University of Copenhagen, DenmarkSearch for more papers by this author Niels H. Secher, Niels H. Secher Department of Anaesthesia, The Copenhagen Muscle Research Centre, Rigshospitalet, University of Copenhagen, DenmarkSearch for more papers by this author First published: 12 January 2007 https://doi.org/10.1113/jphysiol.2006.123950Citations: 5 Email: nhsecher@rh.hosp.dk AboutSectionsPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat Even one small step for man represents a giant challenge for integration of not only motoneurons directly involved in the movement, but also for those involved in regulating ventilation and circulation to enhance oxygen delivery to the muscles. Ventilation and circulation are kept at a low level at rest to allow graded increases to occur during exercise as controlled by feedback from the muscles ('the muscle pressor reflex') as well as by a central nervous influence, termed 'central command'. Such feed-forward control of oxygen transport is important because anaerobic capacity is small as illustrated by reptiles who, after moving very fast from one place to the other, need to sit still in order to eliminate the oxygen deficit because their lungs represent little more than balloons encompassing only few alveoli. For humans it takes a few minutes for steady-state oxygen uptake to be established during exercise illustrating that either feed-forward control of oxygen delivery is a weak influence or that there are considerable energy stores in skeletal muscle. Yet, feed-forward control was addressed by J. E. Johansson (1862–1938) in Stockholm as early as 1893 and from careful experiments in the rabbit, he found convincing evidence for feed-forward control of both heart rate and ventilation (Johannsson, 1983). It had to wait 20 years before the subject was addressed in humans and then through an international collaboration. Krogh & Lindhard (1913) could not monitor heart rate in Copenhagen. In Oxford Miss Buchanan, however, was in possession of an ECG apparatus. In a separate effort both the initial responses of heart rate and ventilation could then be reported and it became clear that the responses were very fast, and variables might even increase in anticipation of exercise. Interestingly, Miss Buchanan was not a co-author on the resulting paper and one can only speculate whether gender bias was of significance in that regard. In numerous follow-up papers, it has been shown that central command is operative at the onset of exercise (Secher, 1999). Partial as well as full neuromuscular blockade, regional anaesthesia and both passive and imagined exercise have been applied as experimental models to separate the central and reflex influences on the investigated variables and in many of these investigations J. H. Mitchell in Dallas has played an important role. It is now established that the first increase in heart rate stems from the central nervous system but that the reflex influence makes its contribution quickly, within the last one third of the first heart beat (Williamson et al. 1995). The responses at the onset of exercise are, however, more complicated. The increase in heart rate, even within the first beat, is proportional to the force developed and a decrease in heart rate is noted at the onset of very weak contraction as exemplified during shooting (Fig. 1). There may also be a transient decrease in blood pressure similar to that seen when humans stand up, and most people have experienced blurred vision in that situation. Figure 1Open in figure viewerPowerPoint Heart rate and blood pressure (Finapress©) responses to rifle shooting at arrow (E. Secher & P. Rasmussen, unpublished observations) The follow-up question is what areas of the brain may be governing central influences on autonomic functions at the onset of exercise. Krogh & Lindhard described their findings in terms of 'cortical irradiation'. The insula is now established as being important while a role for the primary and supplementary motor area has not been ruled out (Nowak et al. 2005). A different approach is taken in the recent report by Green et al. (2007). The authors take advantage of the intracerebral electrodes that are sometimes implated in patients for the treatment of movement disorders or chronic pain. With recording from these electrodes during exercise, it is found that there is enhanced activity in the periaqueductal grey area (PAG) and reduced activity in the subthalamic nucleus, but no change in the globus pallidus in anticipation of exercise. The PAG is of interest because the authors have demonstrated an increase in heart rate and blood pressure with stimulation of that area (Green et al. 2005). Obviously, it was not possible to place the electrodes at will, and the authors had to use the placement that was chosen on medical grounds. Thereby there is no claim that the site of central command is identified, but that areas of the brain that are or are not important relay stations are defined. Refined and often non-invasive techniques allow for human studies on integrative aspects of physiology that previously could be thought of only in an animal preparation. As illustrated in the papers by Green et al. non- or minimally invasive observations can be supplemented by unique observations in patients as pioneered for the study of the central nervous system when W. Penfield (1891–1976) mapped the somatosensory cortex by electrical stimulation during neurosurgical procedures carried out with a local anaesthetic. Penfield is quoted to state that he had 'an experimental preparation' that could talk back to him! References Green AL, Wang S, Owen SLF, Xie K, Liu X, Paterson DJ, Stein JF, Bain PG & Aziz TZ (2005). Deep brain stimulation can regulate arterial blood pressure in awake humans. Neuroreport 16, 1741– 1745. Green AL, Wang S, Purvis S, Owen SLF, Brian PG, Stein JF, Guz A, Aziz TZ & Paterson DJ (2007). Identifying cardiorespiratory neurocircuitry involved in central command during exercise in humans. J Physiol 578, 605– 612. Johansson JE (1983). Ueber die Einwirkung der MuskelthŠtigkeit auf die Athmung und die HŠrzthŠtigkeit. Skand Arch Physiol 5, 20– 66. Krogh A & Lindhard J (1913). The regulation of respiration and circulation during the initial stages of muscular work. J Physiol 47, 112– 136. Nowak M, Holm S, Biering-Sørensen F, Secher NH & Friberg L (2005). "Central command" and insular activation during attempted foot lifting in paraplegic humans. Hum Brain Mapp 25, 259– 265. Secher NH (1999). Cardiovascular function and oxygen delivery during exercise. In Physiological Determinants of Exercise Tolerance in Humans, ed. BJ Whipp & AJ Sargent, pp. 93– 113. Portland Press, Colchester . Williamson JW, Nobrega AC, Winchester PK, Zim S & Mitchell JH (1995). Instantaneous heart rate increase with dynamic exercise: central command and muscle-heart reflex contributions. J Appl Physiol 78, 1273– 1279. Citing Literature Volume578, Issue2January 2007Pages 375-376 FiguresReferencesRelatedInformation