Author(s): BUCKLEY, J., BURGESS, S., SIDHU, S.K., CHALMERS, S., AMANN, M., Institution: UNIVERSITY OF SOUTH AUSTRALIA, Country: AUSTRALIA, Abstract-ID: 871

INTRODUCTION:
The maximal rate of heart rate (HR) increase (rHRI), a marker of HR acceleration during the transition from rest to standardised light exercise is linearly related to changes in exercise performance during differing states of training and fatigue (1,2,3,4). It has been hypothesised that rHRI might be linearly related to changes in exercise performance due to feedback from group III/IV skeletal muscle afferents (1). This study evaluated whether feedback from group III/IV skeletal muscle afferents modulates rHRI.
METHODS:
Using a randomised, counter-balanced, cross-over design HR data from eight male recreationally active participants (24 ± 1 years) were collected as R-R intervals during the transition from rest to three minutes of leg cycling at 100 W. Data were collected under control (CON) conditions and following lumbar intrathecal fentanyl (FENT) to impair feedback from group III/IV skeletal muscle afferents of the leg. rHRI was determined as the first-derivative maximum of a logistic curve fit of the HR data.
RESULTS:
Pre-exercise HR was not different between CON and FENT (CON 91.7 ± 16.7 bpm, FENT 99.8 ± 15.5 bpm, p=0.25). HR increased more with exercise during CON compared with FENT (B = 12.2, 95%CI 6.5 to 17.9, p<0.001) but rHRI was faster during FENT compared with CON (B = 1.52, 95% CI = 0.24 to 2.80, p=0.02).
CONCLUSION:
Feedback from group III/IV skeletal muscle afferents increase HR during standardised light exercise but inhibit rHRI at the onset of exercise.

REFERENCES:
1) Nelson et al., Sci Rep, 2020
2) D’Unienville et al., J Sci Med Sport, 2021
3) Nelson et al., Eur J Appl Physiol, 2017
4) Thomson et al., Res Sports Med, 2016