Institutional members access full text with Ovid®

Share this article on:

Neural Correlates to the Increase in Maximal Force after Dexamethasone Administration

Baudry Stéphane; Botter, Alberto; Duchateau, Jacques; Minetto, Marco A.
Medicine & Science in Sports & Exercise: Post Acceptance: September 19, 2017
doi: 10.1249/MSS.0000000000001425
Original Investigation: PDF Only

AbstractPurposeThis study investigated the effects of short-term glucocorticoid administration on voluntary activation and intracortical inhibitory and facilitatory circuits.MethodsSeventeen healthy men participated in a pseudo randomized double-blind study to receive either dexamethasone (8 mg·d-1, n = 9 subjects) or placebo (n = 8 subjects) for 7 days. The ankle dorsiflexion torque, corresponding electromyography (EMG) of the tibialis anterior, and voluntary activation assessed by the interpolated twitch method using transcranial magnetic stimulation (TMS) were measured during a maximal voluntary contraction (MVC). Short-latency intracortical inhibition (SICI) and intracortical facilitation (ICF) were assessed at rest and during submaximal contraction (50% MVC torque) by paired-pulse TMS with the conditioning stimulus set at 0.8x of motor threshold (0.8x MT) and delivered 2 ms (SICI) and 13 ms (ICF) prior to the test stimulus (1.2x MT).ResultsThe MVC torque (+14%), tibialis anterior EMG (+31%) and voluntary activation (+3%) increased after glucocorticoid treatment (p<0.05). The increase in voluntary activation was associated with the gain in MVC torque (r2 = 0.56; p = 0.032). The level of SICI and the duration of the EMG silent period that followed the test TMS decreased (-18.6% and -13.5%, respectively) during the 50% MVC after treatment (p<0.05) while no significant change was observed for ICF. Neither SICI nor ICF changed after treatment when assessed at rest.ConclusionShort-term dexamethasone treatment induced specific decrease in the excitability of intracortical inhibitory circuits that likely contributed to the increase in the voluntary activation and associated MVC torque.

Purpose

This study investigated the effects of short-term glucocorticoid administration on voluntary activation and intracortical inhibitory and facilitatory circuits.

Methods

Seventeen healthy men participated in a pseudo randomized double-blind study to receive either dexamethasone (8 mg·d-1, n = 9 subjects) or placebo (n = 8 subjects) for 7 days. The ankle dorsiflexion torque, corresponding electromyography (EMG) of the tibialis anterior, and voluntary activation assessed by the interpolated twitch method using transcranial magnetic stimulation (TMS) were measured during a maximal voluntary contraction (MVC). Short-latency intracortical inhibition (SICI) and intracortical facilitation (ICF) were assessed at rest and during submaximal contraction (50% MVC torque) by paired-pulse TMS with the conditioning stimulus set at 0.8x of motor threshold (0.8x MT) and delivered 2 ms (SICI) and 13 ms (ICF) prior to the test stimulus (1.2x MT).

Results

The MVC torque (+14%), tibialis anterior EMG (+31%) and voluntary activation (+3%) increased after glucocorticoid treatment (p<0.05). The increase in voluntary activation was associated with the gain in MVC torque (r2 = 0.56; p = 0.032). The level of SICI and the duration of the EMG silent period that followed the test TMS decreased (-18.6% and -13.5%, respectively) during the 50% MVC after treatment (p<0.05) while no significant change was observed for ICF. Neither SICI nor ICF changed after treatment when assessed at rest.

Conclusion

Short-term dexamethasone treatment induced specific decrease in the excitability of intracortical inhibitory circuits that likely contributed to the increase in the voluntary activation and associated MVC torque.

Corresponding author (to whom reprint requests should be addressed): Stéphane Baudry, Ph.D., Laboratory of Applied Biology, Faculty for Motor Sciences, Université Libre de Bruxelles, 808, route de Lennik, CP 640, 1070 Brussels, Belgium, Email : sbaudry@ulb.ac.be, Phone : +32 2 555 3765; Fax: +32-2-555 69 96

Grants: This study was supported by the bank foundations “Compagnia di San Paolo” of Torino, Italy and “Fondazione CARIPLO” of Milano, Italy.

Acknowledgments: The results of the study are presented clearly, honestly, and without fabrication, falsification, or inappropriate data manipulation, and statement that results of the present study do not constitute endorsement by ACSM.

Accepted for Publication: 8 September 2017

© 2017 American College of Sports Medicine