Reliability of Corticospinal and Motoneuronal Excitability Evaluation During Unfatiguing and Fatiguing Cycling Exercise.

Abstract

Central nervous system excitability depends on the task performed, muscle group solicited, and contraction type. However, little is known on corticospinal and motoneuronal excitability measured during locomotor exercise. This study aimed at determining the reliability of motor-evoked potentials (MEP) and thoracic motor-evoked potentials (TMEP) in dynamic mode during unfatiguing and fatiguing cycling exercise. Twenty-two participants completed four visits. Visit 1 comprised familiarization and a maximal incremental test to determine maximal power output (Wmax). The remaining visits encompassed unfatiguing evaluations, which included 8 brief bouts of moderate (50% Wmax) and high intensity cycling (80% Wmax). In each bout, a set of two TMEPs, five MEPs and one M-max were obtained. Subsequently, a fatiguing exercise to exhaustion at 80% Wmax was performed, with four sets of measurements 3 min through the exercise and 4 additional sets at exhaustion, both measured at 50% Wmax. Intraclass correlation coefficients (ICCs) for 5, 10, 15 and 20 MEP·Mmax-1 revealed excellent reliability at both intensities and during fatiguing exercise (ICC ≥ 0.92). TMEP·Mmax-1 showed ICCs ≥0.82 for moderate and high intensity, and it was not affected by fatigability. Overall standard error of measurement was 0.090 [0.083, 0.097] for MEP·Mmax-1 and 0.114 [0.105, 0.125] for TMEP·Mmax-1. A systematic bias associated to the number of stimulations, especially at high intensity, suggested the evaluation itself may be influenced by fatigability. A mean reduction of 8% was detected in TMEP·Mmax-1 at exhaustion. Motoneuronal and corticospinal excitability measured in dynamic mode presented good to excellent reliability in unfatiguing and fatiguing exercise. Further studies inducing greater fatigability must be conducted to assess the sensitivity of central nervous system excitability during cycling.