Atividade eletromiográfica como ferramenta para identificar preservação de vias aferentes e eferentes em indivíduos com lesão medular completa e crônica

Abstract

Introduction: It is known that even after a complete spinal cord injury (cSCI) there may be preserved axonal pathways below the lesion level, which can be demonstrated by surface electromyography (sEMG). However, little is known about the transverse and longitudinal behavior of the signal and its spectral properties in response to sensory afferent due to the load associated with the supraspinal descending commands during attempted steps. Objectives: 1) To investigate the presence of preserved efferent axonal pathways in individuals with cSCI by analyzing the temporal and spectral behavior of the EMG signal of muscles below the level of the lesion during attempted voluntary movement in orthostatism; 2) To analyze the behavior of the temporal and spectral properties of the signal sEMG of muscles below the lesion in individuals with cSCI and the presence of afferent and efferent modulation during execution of locomotor tasks Methods: It is an observational analytical study in which 3 individuals with cSCI and chronic (more than 1 year after injury) participated. The sEMG signal of muscles located below the lesion was recorded by repeated measurements during two steps. In the first stage, the EMG signal was recorded in the assisted orthostatic posture concomitant with the attempt to take steps according to 4 verbal cues (FAST, SLOW, HIGH, and LONG). In the second stage, the EMG signal of the same muscle groups was recorded during the Lokomat® robotic orthosis-assisted gait training without commands, concomitant to the attempt to take steps according to 2 verbal commands (HIGH and LONG). It was analyzed the behavior of the EMG signal of the following muscles rectus femoris (RF), biceps femoral (BF), tibialis anterior (TA) and medial gastrocnemius (MG) bilaterally. The collapsed and filtered EMGs signal and the linear envelope were plotted. The representation of the spectral characteristics over time was determined by the spectrogram. From the identification of muscle contractions and myoelectric activity in each cycle of assisted gait, it was determined: duration, RMS, amplitude peak, mathematical integral and median frequency of the EMG signal for each experimental condition. Friedman test was used to compare the dependent variables between the different commands, between measures repeated in orthostatism, over time during assisted walking training and between gait conditions with and without a verbal command. The statistical significance was set at 5 %. Results: 1) It was observed efferent modulation of the left RF and right BF signal EMGs coinciding with the commencement of the voluntary movement attempt was observed. It was identified muscle contractions in the EMG signal, even in the absence of visible muscle contraction, and the amplitude and median frequency of the signal behaved differently according to the verbal command used; 2) It was observed that the efferent modulation of the EMG signal of the left RF and right BF during attempt of voluntary movement of the participant 1 was systematic finding in the longitudinal analysis of the data demonstrating an increase in amplitude (mathematical integral) concomitant to decrease of the median frequency over time; 3) It was identified the afferent modulation of the EMG signal in the three study participants during the assisted gait training. Muscles that did not show modulation during orthostatism with attempt of voluntary movement, presented modulation by the rhythmic sensorial afferent offered by the assisted gait training; 4) The mathematical integral and the median frequency behaved as properties that vary according to the modulations of afferent or efferent origin of the signal sEMG; 5) The graphic visual inspection of the sEMG signal as well as the statistical analysis allowed to identify the presence of afferent and efferent modulation in participants with cSCI confirming the importance of this tool for the evaluation of this population. Conclusion: The presence of afferent and efferent modulation of the sEMG signal suggests the preservation of intact supraspinal and spinal pathways which interfere in the motor output of individuals with cSCI. Such findings direct towards a new paradigm in the process of evaluation and rehabilitation of this population which establishes possible perspectives of neuroplasticity below in the lesion. Therefore, it is considered important the analysis of the EMG signal and its spectral and temporal properties for the development of resources that can optimize the neuroplasticity process in this population.