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Isokinetic dynamometry (ID) and surface electromyography (SEMG) are two widely used techniques in the study of muscular strength. However, the effectiveness of both is conditioned to the good understanding of their particularities and limitations. For example, resulting data from ID tests must be considered valid only on the load range phase which is the part of the exercise where the dynamometer imposes resistance against the exercising limb in order to keep it at constant angular velocity. Data from acceleration and deceleration phases are often included in analyses and may result in spurious conclusions. Moreover, significant fluctuations of angular velocity in the beginning of the load range can considerably affect the estimate of biomechanical variables such as torque, speed and angular position. Regarding SEMG signals, they can be considered stationary in the broad sense when acquired under isometric conditions. This assumption cannot be directly applied to the case of dynamic contractions since the frequency content of the signal changes over time in this situation. Some techniques are used to minimize non-stationary effects by setting out a range in which the mechanical changes of muscles are cyclic, i.e. they are repeated periodically. Based on the features of ID and SEMG, this study aimed to find out a dynamic range with suitable stationarity conditions for the study of SEMG signals during cyclical isokinetic knee extension tests. The results showed that SEMG analyses should consider only the portion of the load range where angular velocity is stable, i.e. with no significant fluctuations.

Análise da estacionariedade do sinal de eletromiografia de superfície nas fases do exercício isocinético de extensão do joelho