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This Article Full Text Full Text (PDF) All Versions of this Article: 586/11/2753    most recent jphysiol.2007.150060v1 Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Ichinose, M. Articles by Nishiyasu, T. Search for Related Content PubMed PubMed Citation Articles by Ichinose, M. Articles by Nishiyasu, T. Related Collections Cardiovascular Related Article

¹ Faculty of Human Development, Kobe University, Kobe 657-8501, Japan
² Applied Physiology Laboratory, Toyota Technological Institute, Nagoya 468-8511, Japan
³ Institute of Health and Sport Sciences, University of Tsukuba, Tsukuba City, Ibaraki, 305-8574, Japan

We tested the hypotheses that arterial baroreflex (ABR) control over muscle sympathetic nerve activity (MSNA) in humans does not remain constant throughout a bout of leg cycling ranging in intensity from very mild to exhausting. ABR control over MSNA (burst incidence, burst strength and total MSNA) was evaluated by analysing the relationship between beat-to-beat spontaneous variations in diastolic arterial pressure (DAP) and MSNA in 15 healthy subjects at rest and during leg cycling in a seated position at five workloads: very mild (10 W), mild (82 ± 5.0 W), moderate (126 ± 10.2 W), heavy (156 ± 14.3 W), and exhausting (190 ± 21.2 W). The workload was incremented every 6 min. The linear relationships between DAP and MSNA variables were significantly shifted downward during very mild exercise, but then shifted progressively upward as exercise intensity increased. During heavy and exhausting exercise, moreover, the DAP–MSNA relationships were also significantly shifted rightward from the resting relationship. The sensitivity of ABR control over burst incidence and total MSNA was significantly lower during very mild exercise than during rest, and the sensitivity of the burst incidence control remained lower than the resting level at all higher exercise intensities. By contrast, the sensitivity of the total MSNA control recovered to the resting level during mild and moderate exercise, and was significantly increased during heavy and exhausting exercise (versus rest). We conclude that, in humans, ABR control over MSNA is not uniform throughout a leg cycling exercise protocol in which intensity was varied from very mild to exhausting. We suggest that this non-uniformity of ABR function is one of the mechanisms by which sympathetic and cardiovascular responses are matched to the exercise intensity.

(Received 17 December 2007; accepted after revision 3 April 2008; first published online 10 April 2008)
Corresponding author T. Nishiyasu: Institute of Health and Sport Sciences, University of Tsukuba, Tsukuba City, Ibaraki, 305-8574, Japan. Email: nisiyasu{at}taiiku.tsukuba.ac.jp

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