Faculty Opinions recommendation of Group III and IV muscle afferents contribute to ventilatory and cardiovascular response to rhythmic exercise in humans.

We investigated the role of somatosensory feedback on cardioventilatory responses to rhythmic exercise in five men. In a double-blind, placebo-controlled design, subjects performed the same leg cycling exercise (50/100/150/325 ± 19 W, 3 min each) under placebo conditions (interspinous saline, L3–L4) and with lumbar intrathecal fentanyl impairing central projection of spinal opioid receptor-sensitive muscle afferents. Quadriceps strength was similar before and after fentanyl administration. To evaluate whether a cephalad migration of fentanyl affected cardioventilatory control centers in the brain stem, we compared resting ventilatory responses to hypercapnia (HCVR) and cardioventilatory responses to arm vs. leg cycling exercise after each injection. Similar HCVR and minor effects of fentanyl on cardioventilatory responses to arm exercise excluded direct medullary effects of fentanyl. Central command during leg exercise was estimated via quadriceps electromyogram. No differences between conditions were found in resting heart rate (HR), ventilation [minute ventilation (V̇e)], or mean arterial pressure (MAP). Quadriceps electromyogram, O2 consumption (V̇o2), and plasma lactate were similar in both conditions at the four steady-state workloads. Compared with placebo, a substantial hypoventilation during fentanyl exercise was indicated by the 8–17% reduction in V̇e/CO2 production (V̇co2) secondary to a reduced breathing frequency, leading to average increases of 4–7 Torr in end-tidal Pco2 ( P < 0.001) and a reduced hemoglobin saturation (−3 ± 1%; P < 0.05) at the heaviest workload (∼90% maximal V̇o2) with fentanyl. HR was reduced 2–8%, MAP 8–13%, and ratings of perceived exertion by 13% during fentanyl vs. placebo exercise ( P < 0.05). These findings demonstrate the essential contribution of muscle afferent feedback to the ventilatory, cardiovascular, and perceptual responses to rhythmic exercise in humans, even in the presence of unaltered contributions from other major inputs to cardioventilatory control.

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On the contribution of group III and IV muscle afferents to the circulatory response to rhythmic exercise in humans

The Journal of Physiology ◽

10.1113/jphysiol.2011.209353 ◽

2011 ◽

Vol 589 (15) ◽

pp. 3855-3866 ◽

Cited By ~ 109

Author(s):

Markus Amann ◽

Sean Runnels ◽

David E. Morgan ◽

Joel D. Trinity ◽

Anette S. Fjeldstad ◽

...

Keyword(s):

Muscle Afferents ◽

Circulatory Response ◽

Group Iii ◽

Rhythmic Exercise ◽

Exercise In Humans

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Reflex cardiovascular responses evoked by selective activation of skeletal muscle ergoreceptors

Journal of Applied Physiology ◽

10.1152/jappl.2001.90.1.308 ◽

2001 ◽

Vol 90 (1) ◽

pp. 308-316 ◽

Cited By ~ 18

Author(s):

B. G. Leshnower ◽

J. T. Potts ◽

M. G. Garry ◽

J. H. Mitchell

Keyword(s):

Skeletal Muscle ◽

Muscle Contraction ◽

Cardiovascular Response ◽

Afferent Fiber ◽

Cardiovascular Responses ◽

Muscle Afferents ◽

Triceps Surae ◽

Muscle Stretch ◽

Group Iii ◽

Passive Muscle

It is well known that the exercise pressor reflex (EPR) is mediated by group III and IV skeletal muscle afferent fibers, which exhibit unique discharge responses to mechanical and chemical stimuli. Based on the difference in discharge patterns of group III and IV muscle afferents, we hypothesized that activation of mechanically sensitive (MS) fibers would evoke a different pattern of cardiovascular responses compared with activation of both MS and chemosensitive (CS) fibers. Experiments were conducted in chloralose-urethane-anesthetized cats ( n = 10). Passive muscle stretch was used to activate MS afferents, and electrically evoked contraction of the triceps surae was used to activate both MS and CS muscle afferents. No significant differences were shown in reflex heart rate and mean arterial pressure (MAP) responses between passive muscle stretch and evoked muscle contraction. However, when the reflex responses were matched according to tension-time index (TTI), the peak MAP response (67 ± 4 vs. 56 ± 4 mmHg, P < 0.05) was significantly greater at higher TTI (427 ± 18 vs. 304 ± 13 kg · s, high vs. low TTI, P < 0.05), despite different modes of afferent fiber activation. When the same mode of afferent fiber activation was compared, the peak MAP response (65 ± 7 vs. 55 ± 5 mmHg, P < 0.05) was again predicted by the magnitude of TTI (422 ± 24 vs. 298 ± 19 kg · s, high vs. low TTI, P < 0.05). Total sensory input from skeletal muscle ergoreceptors, as predicted by TTI and not the modality of afferent fiber activation (muscle contraction vs. passive stretch), is suggested to be the primary determinant of the magnitude of the EPR-evoked cardiovascular response.

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Group III/IV muscle afferents limit the intramuscular metabolic perturbation during whole body exercise in humans

The Journal of Physiology ◽

10.1113/jp272283 ◽

2016 ◽

Vol 594 (18) ◽

pp. 5303-5315 ◽

Cited By ~ 68

Author(s):

Gregory M. Blain ◽

Tyler S. Mangum ◽

Simranjit K. Sidhu ◽

Joshua C. Weavil ◽

Thomas J. Hureau ◽

...

Keyword(s):

Muscle Afferents ◽

Whole Body ◽

Group Iii ◽

Metabolic Perturbation ◽

Exercise In Humans

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Aging alters muscle reflex control of autonomic cardiovascular responses to rhythmic contractions in humans

AJP Heart and Circulatory Physiology ◽

10.1152/ajpheart.00433.2015 ◽

2015 ◽

Vol 309 (9) ◽

pp. H1479-H1489 ◽

Cited By ~ 19

Author(s):

Simranjit K. Sidhu ◽

Joshua C. Weavil ◽

Massimo Venturelli ◽

Matthew J. Rossman ◽

Benjamin S. Gmelch ◽

...

Keyword(s):

Cardiac Output ◽

Cardiovascular Response ◽

Knee Extensor ◽

Cardiovascular Responses ◽

Muscle Afferents ◽

Group Iii ◽

Exercise Pressor Reflex ◽

Pressor Reflex ◽

Exercise Induced ◽

The Impact

We investigated the influence of aging on the group III/IV muscle afferents in the exercise pressor reflex-mediated cardiovascular response to rhythmic exercise. Nine old (OLD; 68 ± 2 yr) and nine young (YNG; 24 ± 2 yr) males performed single-leg knee extensor exercise (15 W, 30 W, 80% max) under control conditions and with lumbar intrathecal fentanyl impairing feedback from group III/IV leg muscle afferents. Mean arterial pressure (MAP), cardiac output, leg blood flow (QL), systemic (SVC) and leg vascular conductance (LVC) were continuously determined. With no hemodynamic effect at rest, fentanyl blockade during exercise attenuated both cardiac output and QL ∼17% in YNG, while the decrease in cardiac output in OLD (∼5%) was significantly smaller with no impact on QL ( P = 0.8). Therefore, in the face of similar significant ∼7% reduction in MAP during exercise with fentanyl blockade in both groups, LVC significantly increased ∼11% in OLD, but decreased ∼8% in YNG. The opposing direction of change was reflected in SVC with a significant ∼5% increase in OLD and a ∼12% decrease in YNG. Thus while cardiac output seems to account for the majority of group III/IV-mediated MAP responses in YNG, the impact of neural feedback on the heart may decrease with age and alterations in SVC become more prominent in mediating the similar exercise pressor reflex in OLD. Interestingly, in terms of peripheral hemodynamics, while group III/IV-mediated feedback plays a clear role in increasing LVC during exercise in the YNG, these afferents seem to actually reduce LVC in OLD. These peripheral findings may help explain the limited exercise-induced peripheral vasodilation often associated with aging.

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