title: Muscle metaboreflex and autonomic regulation of heart rate in humans.
abstract: We elucidated the autonomic mechanisms whereby heart rate (HR) is regulated by the muscle metaboreflex. Eight male participants (22 ± 3 years) performed three exercise protocols: (1) enhanced metaboreflex activation with partial flow restriction (bi-lateral thigh cuff inflation) during leg cycling exercise, (2) isolated muscle metaboreflex activation (post-exercise ischaemia; PEI) following leg cycling exercise, (3) isometric handgrip followed by PEI. Trials were undertaken under control (no drug), β1-adrenergic blockade (metoprolol) and parasympathetic blockade (glycopyrrolate) conditions. HR increased with partial flow restriction during leg cycling in the control condition (11 ± 2 beats min(-1); P < 0.05). The magnitude of this increase in HR was similar with parasympathetic blockade (11 ± 2 beats min(-1)), but attenuated with β-adrenergic blockade (4 ± 1 beats min(-1); P < 0.05 vs. control and parasympathetic blockade). During PEI following leg cycling exercise, HR remained similarly elevated above rest under all conditions (11 ± 2, 13 ± 3 and 9 ± 4 beats min(-1), for control, β-adrenergic and parasympathetic blockade; P > 0.05 between conditions). During PEI following handgrip, HR was similarly elevated from rest under control and parasympathetic blockade (4 ± 1 vs. 4 ± 2 beats min(-1); P > 0.05 between conditions) conditions, but attenuated with β-adrenergic blockade (0.2 ± 1 beats min(-1); P > 0.05 vs. rest). Thus muscle metaboreflex activation-mediated increases in HR are principally attributable to increased cardiac sympathetic activity, and only following exercise with a large muscle mass (PEI following leg cycling) is there a contribution from the partial withdrawal of cardiac parasympathetic tone.
authors.affiliation: School of Sport and Exercise Sciences, College of Life and Environmental Sciences, University of Birmingham, Edgbaston, Birmingham B15 2TT, UK. j.p.fisher@bham.ac.uk
authors.forename: James P
authors.initials: JP
authors.lastname: Fisher
authors.forename: Ahmed M
authors.initials: AM
authors.lastname: Adlan
authors.forename: Alena
authors.initials: A
authors.lastname: Shantsila
authors.forename: J Frederik
authors.initials: JF
authors.lastname: Secher
authors.forename: Henrik
authors.initials: H
authors.lastname: Sørensen
authors.forename: Niels H
authors.initials: NH
authors.lastname: Secher
mesh_terms: D058671:Adrenergic beta-1 Receptor Antagonists / Q000494:pharmacology; D000328:Adult; D062186:Arterial Pressure / Q000187:drug effects; D001642:Bicycling / Q000502:physiology*; D006024:Glycopyrrolate / Q000494:pharmacology; D018737:Hand Strength / Q000502:physiology*; D006339:Heart Rate / Q000187:drug effects / Q000502:physiology*; D006801:Humans; D007511:Ischemia / Q000503:physiopathology*; D008297:Male; D008790:Metoprolol / Q000494:pharmacology; D018727:Muscarinic Antagonists / Q000494:pharmacology; D018482:Muscle, Skeletal / Q000187:drug effects / Q000502:physiology*; D012018:Reflex / Q000502:physiology; D055815:Young Adult
chemical_list: D058671:Adrenergic beta-1 Receptor Antagonists; D018727:Muscarinic Antagonists; D008790:Metoprolol; D006024:Glycopyrrolate