Vol.:(0123456789) 1 3 Exp Brain Res DOI 10.1007/s00221-017-4894-7 RESEARCH ARTICLE Efect of constant, predictable, and unpredictable motor tasks on motor performance and blood markers of stress Laura Kyguoliene 1  · Albertas Skurvydas 1,2  · Nerijus Eimantas 2  · Neringa Baranauskienė 2  · Dalia Mickeviciene 1  · Daiva Urboniene 3  · Margarita Cernych 2  · Marius Brazaitis 1,2   Received: 3 June 2016 / Accepted: 24 January 2017 © Springer-Verlag Berlin Heidelberg 2017 increased dopaminergic activity, which was insufcient to afect central motivation to perform isometric exercise and alter centrally mediated components of fatigue. Keywords Central and peripheral fatigue · Dopaminergic activity · Motor task specifcity · Motor accuracy · Perception Introduction Exercise-induced fatigue can be the result of limitations in skeletal muscles or in the nervous system, or both, and discrimination between central and peripheral mechanisms limiting exercise performance is often complicated because it is not known which of these two (central vs. peripheral) is stressed the most during exercise (Enoka 2008; Bernecke et al. 2015). The performance of prolonged intermittent isometric contractions (IICs) of a knee extensor muscle group at both low (submaximal, 40% maximal voluntary contraction (MVC); until task failure) and high (maximal, 100% MVC; all-out test) intensities induces a failure of the central nervous system (CNS) to activate the muscle at its maximal capacity and of the muscle to generate force (Pethick et al. 2015). CNS failure in voluntary activation of exercising muscle during maximal eforts means that the level of neural drive to the muscle is less than optimal (Gandevia 2001). The extra force evoked by superimposed stimulus to the axons indicates either that the motor units were not all recruited voluntary or that they were discharg- ing at rates that were not high enough to produce full fusion of force (Herbert and Gandevia 1999). Peripheral failure is usually defned as a time-related loss of voluntary force- producing capacity during physical exercise (Enoka and Duchateau 2008; Pethick et al. 2015) and are consistent Abstract An unfamiliar or novel physical stimulus induces activation of dopaminergic neurons within the brain and greater activity in areas involved in emotion; con- sidering this, we aimed to establish whether unpredictable prolonged (fatiguing) motor task (vs. constant vs. predict- able) evokes greater dopaminergic activity, enhances neu- romuscular performance, motor accuracy, and perception of efort, and delays overall central fatigue. Fifteen healthy male volunteers (aged 22 ± 4 years) were required to per- form 1 of 3 exercise trials (at least 1 week apart) of 100 intermittent isometric contraction (IIC) tasks involving knee extensions at 60° fexion. Trials were structured dif- ferently by simulated contraction intensity. A fatigue task involved 5-s contractions and 20-s rest. Variables meas- ured before, during, and after IIC were electrically induced force, maximal voluntary contraction, central activation ratio, intramuscular temperature, and blood levels of dopa- mine, cortisol, and prolactin, and intraindividual motor variability and accuracy (constant and absolute error). We found that IIC increased central and peripheral fatigue, force sensation, and T mu , and decreased absolute and con- stant error without visual feedback, but did not afect motor variability. There were no signifcant diferences between the three IIC tasks. However, only unpredictable tasks * Marius Brazaitis marius.brazaitis@lsu.lt 1 Department of Applied Biology and Rehabilitation, Lithuanian Sports University, Sporto str. 6, 44221 Kaunas, Lithuania 2 Sports Science and Innovation Institute, Lithuanian Sports University, Sporto str. 6, 44221 Kaunas, Lithuania 3 Department of Laboratory Medicines, Medical Academy, Lithuanian University of Health Science, Kaunas, Lithuania