Burgess, Shane, Sidhu, Simranjit, Chalmers, Samuel, Amann, Markus, and Buckley, Jonathan (2026) Feedback from group III/IV afferents in skeletal muscle slows heart rate acceleration when transitioning from rest to low-intensity exercise in males. Experimental Physiology. (In Press)

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Abstract

Group III/IV skeletal muscle afferents respond to intramuscular mechanical and metabolic stimuli and are more active in fatigued muscle. These afferents project onto the brainstem and motor cortex and modulate cardiovascular and motor responses during exercise. The maximal rate of heart rate (HR) increase (rHRI), a marker of HR acceleration during the rest-to-exercise transition, is linearly related to exercise performance across various training and fatigue states, being faster with better exercise performance and vice versa. This study evaluated the effect of feedback from group III/IV afferents on rHRI in non-fatigued muscle. HR data were collected in eight recreationally active male participants (24 ± 1 years) during the transition from rest to 3 min of cycling at 100 W under control (CON) conditions and following lumbar intrathecal fentanyl (FENT) infusion to impair feedback from group III/IV afferents of the leg. rHRI was defined as the maximal first-derivative value of a logistic curve fitted to the HR data. Pre-exercise HR was similar in CON and FENT (CON 91.7 ± 16.7 bpm, FENT 99.8 ± 15.5 bpm, P = 0.250). HR increased more with exercise during CON than FENT (B = 10.01, 95% CI 5.33 to 14.70, P < 0.001) but rHRI was faster during FENT (B = 1.52, 95% CI 0.24 to 2.80, P = 0.020). In non-fatigued muscle, feedback from group III/IV afferents slowed rHRI. Increased feedback when muscle is fatigued may slow rHRI further which may explain the relationship between rHRI and exercise performance seen in previous studies, but further studies on fatigued muscle are required to confirm this.

Item ID:	93766
Item Type:	Article (Refereed Research - C1)
ISSN:	1469-445X
Copyright Information:	© 2026 The Author(s). Experimental Physiology published by John Wiley & Sons Ltd on behalf of The Physiological Society. This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.
Date Deposited:	26 Aug 2026 06:48
FoR Codes:	42 HEALTH SCIENCES > 4207 Sports science and exercise > 420702 Exercise physiology @ 100%
SEO Codes:	20 HEALTH > 2099 Other health > 209999 Other health not elsewhere classified @ 100%
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