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. 2018 Feb 12;5:6. doi: 10.3389/fnut.2018.00006

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Copyright © 2018 Bowtell, Mohr, Fulford, Jackman, Ermidis, Krustrup and Mileva.

This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

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Voluntary activation (VA) in fresh and fatigued knee extensors. Population average (±SEM, %) values of the peripheral (n = 9) (A) and supraspinal (n = 7) (B) VA were calculated using the standard twitch interpolation equations from the twitch responses to peripheral femoral nerve (PNS) and transcranial magnetic (TMS) stimulation. Stimulation pulses were delivered during and 2 s after the maximal voluntary contractions performed before (PreEx) and after (PostEx) the exercise to task failure. The exercise was completed 1 h after ingestion of either caffeine (filled bars) or placebo (empty bars) supplement; p < 0.05: ^#main condition effect.