2014 Volume 59 Issue 2 Pages 577-589
The objective of the present study was to investigate the influences of psychological pressure on initial posture and anticipatory postural adjustment (APA) when performing a single forward step movement. Fourteen participants performed a single step toward a circular target (10 cm in diameter) in response to a beep sound. The trials were conducted under non-pressure and pressure conditions, with 10 attempts for each. In performing the task, participants were required to respond rapidly to the beep sound, to be as brief as possible with the stepping movement, and to place their foot accurately in the landing position on the target. Pressure was induced by a small audience and false instructions of starting over the same experiment on another day and the presentation of video-taped performance in a sports science lecture if performance does not reach a criteria. The results showed that state anxiety (state-trait anxiety inventory: STAI Y-1) increased from 42.4 (±7.0) to 53.7 (±8.7) and that heart rate also increased from 76.2 (±7.0) bpm to 83.4 (±9.3) bpm when the participants were under pressure. Significant increases in mean radial error and bivariate variable error were found, indicating that accuracy of stepping in the landing position was reduced under pressure. Kinematic analysis showed that, in the initial posture phase, significant trunk inclination was observed under pressure. Kinetic data obtained using a force plate showed that mean and maximal force in the posterior direction increased when under pressure. Furthermore, the EMG activity levels of the tibialis anterior muscles increased under pressure. These results indicate that pressure affects both the initial posture and APA when performing a single forward step movement.