Disruption of kinematic coordination in throwing under stress

The present study tested the conscious-control theory of the relationship between stress and performance. Performers under stress conditions consciously attempted to control their movements, disrupting the automaticity of control. Twenty-two male subjects (11 in Experiment 1 and 11 in Experiment 2) performed an underhand ball-throwing task using the non-dominant hand. The inter-trial variability of two kinematic measures was analyzed, namely arm-joint coordination during the throw and hand position at release (release point). Experiment 1 confirmed the validity of regarding these variability measures as indices of automaticity, as they did not vary in spite of resource shortage induced by a dual-task paradigm. In Experiment 2, in which stress led to a detriment in performance, the variability of joint coordination increased, whereas the release point became more fixed. These findings imply that throwing performance is impaired when the coordination is disrupted as a result of inflexible movement executed by conscious control.