@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{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}
}