@inproceedings{MartinezValdesCarlsohnHeydenreichetal.2014, author = {Martinez-Valdes, Eduardo Andr{\´e}s and Carlsohn, Anja and Heydenreich, Juliane and Mayer, Frank}, title = {Gastrointestinal complaints following high carbohydrate intake immediately after glycogen depleting exercise: Influence on performance}, series = {Medicine and science in sports and exercise : official journal of the American College of Sports Medicine}, volume = {46}, booktitle = {Medicine and science in sports and exercise : official journal of the American College of Sports Medicine}, number = {5}, publisher = {Lippincott Williams \& Wilkins}, address = {Philadelphia}, issn = {0195-9131}, pages = {160 -- 160}, year = {2014}, language = {en} } @article{LaineMartinezValdesFallaetal.2015, author = {Laine, Christopher M. and Martinez-Valdes, Eduardo Andr{\´e}s and Falla, Deborah and Mayer, Frank and Farina, Dario}, title = {Motor Neuron Pools of Synergistic Thigh Muscles Share Most of Their Synaptic Input}, series = {The journal of neuroscience}, volume = {35}, journal = {The journal of neuroscience}, number = {35}, publisher = {Society for Neuroscience}, address = {Washington}, issn = {0270-6474}, doi = {10.1523/JNEUROSCI.0240-15.2015}, pages = {12207 -- 12216}, year = {2015}, abstract = {Neural control of synergist muscles is not well understood. Presumably, each muscle in a synergistic group receives some unique neural drive and some drive that is also shared in common with other muscles in the group. In this investigation, we sought to characterize the strength, frequency spectrum, and force dependence of the neural drive to the human vastus lateralis and vastus medialis muscles during the production of isometric knee extension forces at 10 and 30\% of maximum voluntary effort. High-density surface electromyography recordings were decomposed into motor unit action potentials to examine the neural drive to each muscle. Motor unit coherence analysis was used to characterize the total neural drive to each muscle and the drive shared between muscles. Using a novel approach based on partial coherence analysis, we were also able to study specifically the neural drive unique to each muscle (not shared). The results showed that the majority of neural drive to the vasti muscles was a cross-muscle drive characterized by a force-dependent strength and bandwidth. Muscle-specific neural drive was at low frequencies (<5 Hz) and relatively weak. Frequencies of neural drive associated with afferent feedback (6 - 12 Hz) and with descending cortical input (similar to 20 Hz) were almost entirely shared by the two muscles, whereas low-frequency (<5 Hz) drive comprised shared (primary) and muscle-specific (secondary) components. This study is the first to directly investigate the extent of shared versus independent control of synergist muscles at the motor neuron level.}, language = {en} } @misc{MartinezValdesNegroLaineetal.2016, author = {Martinez-Valdes, Eduardo and Negro, Francesco and Laine, Christopher M. and Falla, Deborah L. and Mayer, Frank and Farina, Dario}, title = {Identifying motor units in longitudinal studies with high-density surface electromyography}, series = {Converging clinical and engineering research on neurorehabilitation II}, volume = {15}, journal = {Converging clinical and engineering research on neurorehabilitation II}, publisher = {Springer}, address = {Cham}, isbn = {978-3-319-46669-9}, issn = {2195-3562}, doi = {10.1007/978-3-319-46669-9_27}, pages = {147 -- 151}, year = {2016}, abstract = {We investigated the possibility to identify motor units (MUs) with high-density surface electromyography (HDEMG) over experimental sessions in different days. 10 subjects performed submaximal knee extensions across three sessions in three days separated by one week, while EMG was recorded from the vastus medialis muscle with high-density electrode grids. The shapes of the MU action potentials (MUAPs) over multiple channels extracted from HDEMG decomposition were matched across sessions by cross-correlation. Forty and twenty percent of the MUs decomposed could be tracked across two and three sessions, respectively (average cross correlation 0.85 +/- 0.04). The estimated properties of the matched motor units were similar across the sessions. For example, mean discharge rate and recruitment thresholds were measured with an intra-class correlation coefficient (ICCs) > 0.80. These results strongly suggest that the same MUs were indeed identified across sessions. This possibility will allow monitoring changes in MU properties following interventions or during the progression of neuromuscular disorders.}, language = {en} } @article{MartinezValdesGuzmanVenegasSilvestreetal.2016, author = {Martinez-Valdes, Eduardo Andr{\´e}s and Guzman-Venegas, R. A. and Silvestre, R. A. and Macdonald, J. H. and Falla, D. and Araneda, O. F. and Haichelis, D.}, title = {Electromyographic adjustments during continuous and intermittent incremental fatiguing cycling}, series = {Psychotherapeut}, volume = {26}, journal = {Psychotherapeut}, publisher = {Wiley-Blackwell}, address = {Hoboken}, issn = {0905-7188}, doi = {10.1111/sms.12578}, pages = {1273 -- 1282}, year = {2016}, abstract = {We studied the sensitivity of electromyographic (EMG) variables to load and muscle fatigue during continuous and intermittent incremental cycling. Fifteen men attended three laboratory sessions. Visit 1: lactate threshold, peak power output, and VO2max. Visits 2 and 3: Continuous (more fatiguing) and intermittent (less fatiguing) incremental cycling protocols [20\%, 40\%, 60\%, 80\% and 100\% of peak power output (PPO)]. During both protocols, multichannel EMG signals were recorded from vastus lateralis: muscle fiber conduction velocity (MFCV), instantaneous mean frequency (iMNF), and absolute and normalized root mean square (RMS) were analyzed. MFCV differed between protocols (P<0.001), and only increased consistently with power output during intermittent cycling. RMS parameters were similar between protocols, and increased linearly with power output. However, only normalized RMS was higher during the more fatiguing 100\% PPO stage of the continuous protocol [continuous-intermittent mean difference (95\% CI): 45.1 (8.5\% to 81.7\%)]. On the contrary, iMNF was insensitive to load changes and muscle fatigue (P=0.14). Despite similar power outputs, continuous and intermittent cycling influenced MFCV and normalized RMS differently. Only normalized RMS was sensitive to both increases in power output (in both protocols) and muscle fatigue, and thus is the most suitable EMG parameter to monitor changes in muscle activation during cycling.}, language = {en} } @article{MendezRebolledoGaticaRojasMartinezValdesetal.2016, author = {Mendez-Rebolledo, Guillermo and Gatica-Rojas, Valeska and Martinez-Valdes, Eduardo Andr{\´e}s and Xie, H. B.}, title = {The recruitment order of scapular muscles depends on the characteristics of the postural task}, series = {Journal of electromyography and kinesiology}, volume = {31}, journal = {Journal of electromyography and kinesiology}, publisher = {Elsevier}, address = {Oxford}, issn = {1050-6411}, doi = {10.1016/j.jelekin.2016.09.001}, pages = {40 -- 47}, year = {2016}, abstract = {Previous studies show that the scapular muscle recruitment order could possibly change according to the characteristics of the postural task. We aimed to compare the activation latencies of serratus anterior (SA), upper, middle, and lower trapezius (UT, MT and LT, respectively) between an unpredictable perturbation (sudden arm destabilization) and a predictable task (voluntary arm raise) and, to determine the differences in the muscle recruitment order in each task. The electromyographic signals of 23 participants were recorded while the tasks were performed. All scapular muscles showed earlier onset latency in the voluntary arm raise than in the sudden arm destabilization. No significant differences were observed in the muscle recruitment order for the sudden arm destabilization (p > 0.05). Conversely, for voluntary arm raise the MT, LT SA and anterior deltoid (AD) were activated significantly earlier than the UT (p < 0.001). Scapular muscles present a specific recruitment order during a predictable task: SA was activated prior to the AD and the UT after the AD, in a recruitment order of SA, AD, UT, MT, and LT. While in an unpredictable motor task, all muscles were activated after the destabilization without a specific recruitment order, but rather a simultaneous activation. (C) 2016 Elsevier Ltd. All rights reserved.}, language = {en} } @article{MartinezValdesLaineFallaetal.2016, author = {Martinez-Valdes, Eduardo Andr{\´e}s and Laine, C. M. and Falla, D. and Mayer, Frank and Farina, D.}, title = {High-density surface electromyography provides reliable estimates of motor unit behavior}, series = {Clinical neurophysiology}, volume = {127}, journal = {Clinical neurophysiology}, publisher = {Elsevier}, address = {Clare}, issn = {1388-2457}, doi = {10.1016/j.clinph.2015.10.065}, pages = {2534 -- 2541}, year = {2016}, abstract = {Objective: To assess the intra-and inter-session reliability of estimates of motor unit behavior and muscle fiber properties derived from high-density surface electromyography (HDEMG). Methods: Ten healthy subjects performed submaximal isometric knee extensions during three recording sessions (separate days) at 10\%, 30\%, 50\% and 70\% of their maximum voluntary effort. The discharge timings of motor units of the vastus lateralis and medialis muscles were automatically identified from HDEMG by a decomposition algorithm. We characterized the number of detected motor units, their discharge rates, the coefficient of variation of their inter-spike intervals (CoVisi), the action potential conduction velocity and peak-to-peak amplitude. Reliability was assessed for each motor unit characteristics by intra-class correlation coefficient (ICC). Additionally, a pulse-to-noise ratio (PNR) was calculated, to verify the accuracy of the decomposition. Results: Good to excellent reliability within and between sessions was found for all motor unit characteristics at all force levels (ICCs > 0.8), with the exception of CoVisi that presented poor reliability (ICC < 0.6). PNR was high and similar for both muscles with values ranging between 45.1 and 47.6 dB (accuracy > 95\%). Conclusion: Motor unit features can be assessed non-invasively and reliably within and across sessions over a wide range of force levels. Significance: These results suggest that it is possible to characterize motor units in longitudinal intervention studies. (C) 2016 International Federation of Clinical Neurophysiology. Published by Elsevier Ireland Ltd. All rights reserved.}, language = {en} } @article{MartinezValdesNegroLaineetal.2017, author = {Martinez-Valdes, Eduardo Andr{\´e}s and Negro, F. and Laine, C. M. and Falla, D. and Mayer, Frank and Farina, Dario}, title = {Tracking motor units longitudinally across experimental sessions with high-density surface electromyography}, series = {The Journal of Physiology}, volume = {595}, journal = {The Journal of Physiology}, publisher = {Wiley}, address = {Hoboken}, issn = {0022-3751}, doi = {10.1113/JP273662}, pages = {1479 -- 1496}, year = {2017}, abstract = {A new method is proposed for tracking individual motor units (MUs) across multiple experimental sessions on different days. The technique is based on a novel decomposition approach for high-density surface electromyography and was tested with two experimental studies for reliability and sensitivity. Experiment I (reliability): ten participants performed isometric knee extensions at 10, 30, 50 and 70\% of their maximum voluntary contraction (MVC) force in three sessions, each separated by 1 week. Experiment II (sensitivity): seven participants performed 2 weeks of endurance training (cycling) and were tested pre-post intervention during isometric knee extensions at 10 and 30\% MVC. The reliability (Experiment I) and sensitivity (Experiment II) of the measured MU properties were compared for the MUs tracked across sessions, with respect to all MUs identified in each session. In Experiment I, on average 38.3\% and 40.1\% of the identified MUs could be tracked across two sessions (1 and 2 weeks apart), for the vastus medialis and vastus lateralis, respectively. Moreover, the properties of the tracked MUs were more reliable across sessions than those of the full set of identified MUs (intra-class correlation coefficients ranged between 0.63-0.99 and 0.39-0.95, respectively). In Experiment II, similar to 40\% of the MUs could be tracked before and after the training intervention and training-induced changes in MU conduction velocity had an effect size of 2.1 (tracked MUs) and 1.5 (group of all identified motor units). These results show the possibility of monitoring MU properties longitudinally to document the effect of interventions or the progression of neuromuscular disorders.}, language = {en} } @article{MartinezValdesFallaNegroetal.2017, author = {Martinez-Valdes, Eduardo Andr{\´e}s and Falla, Deborah and Negro, Francesco and Mayer, Frank and Farina, Dario}, title = {Differential Motor Unit Changes after Endurance or High-Intensity Interval Training}, series = {Medicine and science in sports and exercise : official journal of the American College of Sports Medicine}, volume = {49}, journal = {Medicine and science in sports and exercise : official journal of the American College of Sports Medicine}, publisher = {Lippincott Williams \& Wilkins}, address = {Philadelphia}, issn = {0195-9131}, doi = {10.1249/MSS.0000000000001209}, pages = {1126 -- 1136}, year = {2017}, abstract = {Purpose Using a novel technique of high-density surface EMG decomposition and motor unit (MU) tracking, we compared changes in the properties of vastus medialis and vastus lateralis MU after endurance (END) and high-intensity interval training (HIIT). Methods Sixteen men were assigned to the END or the HIIT group (n = 8 each) and performed six training sessions for 14 d. Each session consisted of 8-12 x 60-s intervals at 100\% peak power output separated by 75 s of recovery (HIIT) or 90-120 min continuous cycling at similar to 65\% VO2peak (END). Pre- and postintervention, participants performed 1) incremental cycling to determine VO2peak and peak power output and 2) maximal, submaximal (10\%, 30\%, 50\%, and 70\% maximum voluntary contraction [MVC]), and sustained (until task failure at 30\% MVC) isometric knee extensions while high-density surface EMG signals were recorded from the vastus medialis and vastus lateralis. EMG signals were decomposed (submaximal contractions) into individual MU by convolutive blind source separation. Finally, MU were tracked across sessions by semiblind source separation. Results After training, END and HIIT improved VO2peak similarly (by 5.0\% and 6.7\%, respectively). The HIIT group showed enhanced maximal knee extension torque by similar to 7\% (P = 0.02) and was accompanied by an increase in discharge rate for high-threshold MU (50\% knee extension MVC) (P < 0.05). By contrast, the END group increased their time to task failure by similar to 17\% but showed no change in MU discharge rates (P > 0.05). Conclusions HIIT and END induce different adjustments in MU discharge rate despite similar improvements in cardiopulmonary fitness. Moreover, the changes induced by HIIT are specific for high-threshold MU. For the first time, we show that HIIT and END induce specific neuromuscular adaptations, possibly related to differences in exercise load intensity and training volume.}, language = {en} } @article{MartinezValdesNegroFallaetal.2018, author = {Martinez-Valdes, Eduardo Andr{\´e}s and Negro, Francesco and Falla, Deborah and De Nunzio, Alessandro Marco and Farina, Dario}, title = {Surface electromyographic amplitude does not identify differences in neural drive to synergistic muscles}, series = {Journal of applied physiology}, volume = {124}, journal = {Journal of applied physiology}, number = {4}, publisher = {American Chemical Society}, address = {Bethesda}, issn = {8750-7587}, doi = {10.1152/japplphysiol.01115.2017}, pages = {1071 -- 1079}, year = {2018}, abstract = {Surface electromyographic (EMG) signal amplitude is typically used to compare the neural drive to muscles. We experimentally investigated this association by studying the motor unit (MU) behavior and action potentials in the vastus medialis (VM) and vastus lateralis (VL) muscles. Eighteen participants performed isometric knee extensions at four target torques [10. 30. 50, and 70\% of the maximum torque (MVC)] while high-density EMG signals were recorded from the VM and VL. The absolute EMG amplitude was greater for VM than VL (P < 0.001), whereas the EMG amplitude normalized with respect to MVC was greater for VL than VM (P < 0.04). Because differences in EMG amplitude can be due to both differences in the neural drive and in the size of the MU action potentials, we indirectly inferred the neural drives received by the two muscles by estimating the synaptic inputs received by the corresponding motor neuron pools. For this purpose. we analyzed the increase in discharge rate from recruitment to target torque for motor units matched by recruitment threshold in the two muscles. This analysis indicated that the two muscles received similar levels of neural drive. Nonetheless, the size of the MU action potentials was greater for VM than VL (P < 0.001), and this difference explained most of the differences in EMG amplitude between the two muscles (similar to 63\% of explained variance). These results indicate that EMG amplitude, even following normalization, does not reflect the neural drive to synergistic muscles. Moreover, absolute EMG amplitude is mainly explained by the size of MU action potentials. NEW \& NOTEWORTHY Electromyographic (EMG) amplitude is widely used to compare indirectly the strength of neural drive received by synergistic muscles. However, there are no studies validating this approach with motor unit data. Here, we compared between-muscles differences in surface EMG amplitude and motor unit behavior. The results clarify the limitations of surface EMG to interpret differences in neural drive between muscles.}, language = {en} } @article{MuellerMartinezValdesStolletal.2018, author = {Mueller, Juliane and Martinez-Valdes, Eduardo Andr{\´e}s and Stoll, Josefine and Mueller, Steffen and Engel, Tilman and Mayer, Frank}, title = {Differences in neuromuscular activity of ankle stabilizing muscles during postural disturbances}, series = {Gait \& posture}, volume = {61}, journal = {Gait \& posture}, publisher = {Elsevier}, address = {Clare}, issn = {0966-6362}, doi = {10.1016/j.gaitpost.2018.01.023}, pages = {226 -- 231}, year = {2018}, abstract = {The purpose was to examine gender differences in ankle stabilizing muscle activation during postural disturbances. Seventeen participants (9 females: 27 +/- 2yrs., 1.69 +/- 0.1 m, 63 +/- 7 kg; 8 males: 29 +/- 2yrs., 1.81 +/- 0.1 m; 83 +/- 7 kg) were included in the study. After familiarization on a split-belt-treadmill, participants walked (1 m/s) while 15 right-sided perturbations were randomly applied 200 ms after initial heel contact. Muscle activity of M. tibialis anterior (TA), peroneus longus (PL) and gastrocnemius medialis (GM) was recorded during unperturbed and perturbed walking. The root mean square (RMS; [\%]) was analyzed within 200 ms after perturbation. Co-activation was quantified as ratio of antagonist (GM)/agonist (TA) EMG-RMS during unperturbed and perturbed walking. Time to onset was calculated (ms). Data were analyzed descriptively (mean +/- SD) followed by three-way-ANOVA (gender/condition/muscle; alpha= 0.05). Perturbed walking elicited higher EMG activity compared to normal walking for TA and PL in both genders (p < 0.000). RMS amplitude gender comparisons revealed an interaction between gender and condition (F = 4.6, p = 0.049) and, a triple interaction among gender, condition and muscle (F = 4.7, p = 0.02). Women presented significantly higher EMG-RMS [\%] PL amplitude than men during perturbed walking (mean difference = 209.6\%, 95\% confidence interval = -367.0 to -52.2\%, p < 0.000). Co-activation showed significant lower values for perturbed compared to normal walking (p < 0.000), without significant gender differences for both walking conditions. GM activated significantly earlier than TA and PL (p < 0.01) without significant differences between the muscle activation onsets of men and women (p = 0.7). The results reflect that activation strategies of the ankle encompassing muscles differ between genders. In provoked stumbling, higher PL EMG activity in women compared to men is present. Future studies should aim to elucidate if this specific behavior has any relationship with ankle injury occurrence between genders.}, language = {en} }