title: Effect of muscle metaboreflex activation on spontaneous cardiac baroreflex sensitivity during exercise in humans.
abstract: We sought to determine whether the activation of metabolically sensitive skeletal muscle afferents (muscle metaboreflex) is a potential mechanism for the decrease in spontaneous cardiac baroreflex sensitivity (cBRS) during exercise in humans. In protocol 1, 15 male subjects (22 ± 1 years) performed steady-state leg cycling at low (26 ± 4 W) and moderate workloads (105 ± 7 W), under free-flow conditions and with partial flow restriction (bilateral thigh cuff inflation at 100 mmHg) to evoke muscle metaboreflex activation during exercise. In protocol 2, rhythmic handgrip exercise at 35% maximum voluntary contraction was performed with progressive upper arm cuff inflation (0, 80, 100 and 120 mmHg) to elicit graded metaboreflex activation. Both protocols were followed by post-exercise ischaemia (PEI) to isolate the muscle metaboreflex. Leg cycling-induced increases in HR and mean BP were augmented by partial flow restriction (P < 0.05 vs. free flow), while HR and mean BP both remained elevated during PEI (P < 0.05 vs. rest). Leg cycling evoked an intensity-dependent decrease in cBRS (16 ± 2, 7 ± 1 and 2 ± 0.2 ms mmHg(-1) at rest, low and moderate workloads, respectively; P < 0.05), which was further reduced with partial flow restriction (by -2.6 ± 0.8 and -0.4 ± 0.1 ms mmHg(-1) at low and moderate workloads). cBRS remained suppressed during PEI following leg cycling with partial flow restriction (4 ± 1 ms mmHg(-1); P < 0.05 vs. rest). cBRS was unchanged during handgrip under free-flow conditions, handgrip with partial flow restriction and PEI following handgrip (P > 0.05 vs. rest). These data indicate that the activation of metabolically sensitive skeletal muscle afferents (muscle metaboreflex) decreases cardiac baroreflex responsiveness during leg cycling exercise in humans.
authors.affiliation: School of Sport and Exercise Sciences, College of Life and Environmental Sciences, University of Birmingham, Edgbaston, Birmingham B15 2TT, UK.
authors.forename: Doreen
authors.initials: D
authors.lastname: Hartwich
authors.forename: William E
authors.initials: WE
authors.lastname: Dear
authors.forename: Jessica L
authors.initials: JL
authors.lastname: Waterfall
authors.forename: James P
authors.initials: JP
authors.lastname: Fisher
mesh_terms: D000293:Adolescent; D000328:Adult; D017704:Baroreflex / Q000502:physiology*; D001794:Blood Pressure; D015444:Exercise / Q000502:physiology*; D018737:Hand Strength; D006321:Heart; D006339:Heart Rate; D006801:Humans; D007866:Leg; D008297:Male; D018482:Muscle, Skeletal / Q000098:blood supply / Q000502:physiology*; D012039:Regional Blood Flow; D055815:Young Adult