Electromyographic analysis of transient postural responses to anterior-posterior platform translations

Dynamic perturbations of balance have been previously used by various laboratories and the balance patterns have been described in detail. However, these patterns have been analyzed mainly under steady-state condition. In a recent work Schmid et al. [4] investigated the adaptation of balancing behavior during the adaptation to a continuous platform translation. However, this work analyzed only the TA and SOL activity during the adaptation process. Recent studies have shown that movement around the hip joint cannot be negligible, especially under more challenging stance perturbations, and the body behaves like a double-link inverted pendulum. Therefore, in our work the muscle activity analysis during the adaptation to platform translation is extended to include the rectus and biceps femoris (RF and BF, respectively) in order to consider the hip strategy in the postural perturbation response. Eight healthy adults stood on a moving platform that moved in the anterior-posterior direction at two different frequencies (0.2 and 0.8 Hz) with two visual conditions eyes closed and open (EC and EO, respectively). The results showed that the less challenging condition, in this case the platform moving at 0.2 Hz, required more time to adapt. It can be explained by two different possibilities. First, it could be that the initial responses at low frequency platform translations were small and, thus, not so different from the final responses. Second, it can be argued that, as the platform motion did not represent a real threat to postural stance, the subjects did not make an effort to counteract the perturbation.