Central adaptations during repetitive contractions assessed by the readiness potential

Abstract

Physiological fatigue, a loss of maximal force producing capacity, may originate both from changes at the peripheral and at the central level. The readiness potential (RP) provides a measure to study adaptations to physiological fatigue at the motor cortex. We have studied the RP in the course of repetitive contractions at a high force level. Fourteen female healthy subjects made repetitive force grip contractions at 70% of their maximal voluntary contraction (MVC) for 30 min. Contractions were self-paced and inter-squeeze interval was about 7 s. During the repetitive contractions, the area under the curve of the RP almost doubled at electrode Cz and increased fourfold at electrodes C3' and C4'. The onset of negativity moved forward from 1.5 to 1.9 s before force onset at Cz and from 1.0 to 1.6 s and 1.7 s before force onset at C3' and C4', respectively. EMG amplitude and median frequency did not change significantly and MVC after the fatiguing exercise was 93% of MVC before, indicating relatively little physiological fatigue. The increase of the RP during the repetitive contractions is clearly in excess of the almost absent signs of peripheral fatigue. Because the increase of the RP does not lead to an increased force production, we propose that it is a central adaptation counteracting the decrease of cortical efficiency during repetitive contractions.

Beyond the “Bereitschaftspotential”: Action preparation behind cognitive functions

“…The study confirmed that the pre-motor brain activity increases with muscle fatigue (e.g. Liu et al 2005;Schillings et al, 2006;Falvo et al, 2011) and with the subjectively perceived exertion (Slobounov et al, 2004;de Morree et al, 2012). In particular, they showed that muscle fatigue modulates the activity in the SMA and PMA, as indexed by the larger amplitude of the BP and NS' in the fatigued participants.…”

“…Liu et al, 2005;Schillings et al, 2006). Nevertheless, Liu et al (2005) failed to observe any change during the motor preparation processing, and Schillings et al (2006) did not distinguish between the NS' and the MP components. On the other hand, other authors observed an attenuation of the BP during fatiguing tasks (Kristeva, 1977;Popivanov, Mineva, and Dushanova, 1995), which was interpreted as a decreased intentional involvement and result of habituation processes.…”

“…Several authors replicated these 20 findings (e.g. Liu et al, 2005;Schillings et al, 2006). Nevertheless, Liu et al (2005) failed to observe any change during the motor preparation processing, and Schillings et al (2006) did not distinguish between the NS' and the MP components.…”

Vermoeidheid gezien vanuit het perspectief van de neurofysioloog

“…Tijdens herhaalde willekeurige contracties die tot vermoeidheid leiden kunnen veranderingen in de premotorische potentiaal en daarmee veranderingen in de centrale aansturing gemeten worden. 10 Vermoeidheid is een klacht die bij neurologische patiënten veelvuldig voorkomt.…”

Cortical Activity during a Highly-Trained Resistance Exercise Movement Emphasizing Force, Power or Volume

“…Most investigations have found progressive increases and widespread changes in cortical activity during repetitive movements [4,15,20,21,22,23,24,25,26]. However, these investigations have varied in their use of incremental or non-incremental loading, the biomechanical aspects of movement, and whether or not fatigue was a specific outcome variable.…”