- Title
- Caffeine does not influence persistent inward current contribution to motoneuron firing
- Creator
- Mackay, Karen; Orssatto, Lucas; Polman, Remco; Van der Pols, Jolieke; Trajano, Gabriel
- Date
- 2023
- Type
- Text; Journal article
- Identifier
- http://researchonline.federation.edu.au/vital/access/HandleResolver/1959.17/199067
- Identifier
- vital:19152
- Identifier
-
https://doi.org/10.1152/JN.00350.2023
- Identifier
- ISSN:0022-3077 (ISSN)
- Abstract
- The purpose of this study was to investigate whether caffeine consumption would change persistent inward current (PIC) contribution to motoneuron firing at increased contraction intensities and after repetitive sustained maximal contractions. Before and after the consumption of 6 mg·kg-1 of caffeine or placebo, 16 individuals performed isometric triangular-shaped ramp dorsiflexion contractions (to 20% and 40% of peak torque), followed by four maximal contractions sustained until torque production dropped to 60% of maximum, and consecutive 20% triangular-shaped contractions. Tibialis anterior motor unit firing frequencies were analyzed from high-density surface electromyograms. PIC contribution to motor unit firing was estimated by calculating the delta frequency (DF) using the paired motor unit technique. Motoneuron peak firing frequencies at 20% and 40% contractions and total torque-time integral during the repetitive sustained maximal contractions were also assessed. DF increased 0.69 peaks per second (pps) (95% CI ¼ -0.98, -0.405; d ¼ -0.87) from 20% to 40% contraction intensities and reduced 0.85 pps (95% CI ¼ 0.66, 1.05; d ¼ 0.99) after the repetitive sustained maximal contractions, regardless of caffeine consumption. Participants produced 337 Nm·s (95% CI ¼ 49.9, 624; d ¼ 0.63) more torque integral during the repetitive sustained maximal contractions after caffeine consumption. A strong repeated-measures correlation (r ¼ 0.61; 95% CI ¼ 0.49, 0.69) was observed between reductions of DF and peak firing frequencies after the repetitive sustained maximal contractions. PIC contribution to motoneuron firing increases from 20% to 40% contraction intensities, with no effect of caffeine (on rested tibialis anterior). Repetitive sustained maximal contractions reduced PIC contribution to motoneuron firing, regardless of caffeine or placebo consumption, evidencing that changes in intrinsic motoneuron properties contributed to performance loss. Caffeine-attenuated reduction of torque production capacity was unlikely mediated by PICs. © 2023 American Physiological Society. All rights reserved.
- Publisher
- American Physiological Society
- Relation
- Journal of Neurophysiology Vol. 130, no. 6 (2023), p. 1529-1540
- Rights
- All metadata describing materials held in, or linked to, the repository is freely available under a CC0 licence
- Rights
- Copyright © 2023 American Physiological Society
- Subject
- 42 Health sciences; 52 Psychology
- Reviewed
- Funder
- This work was funded by Queensland University of Technology as part of KM’s PhD candidature.
- Hits: 259
- Visitors: 259
- Downloads: 0