The effects of emotion on body movement have been quantified using biomechanical analysis in healthy individuals during gait but the generalizability of these findings to other body movements and to individuals with mood disorders is very limited. Current understanding of emotion effects is limited to spatiotemporal and angular measures in gait but it is not known if emotion affects other movements in similar ways, or how emotion might affect coordination of body movement in any movement task.

Assessment of body movements in individuals with mood disorders is a key criterion for diagnosis, but very little data exist on the effect of mood on body movements. Clinical descriptions defining mood phase in bipolar disorder depend on individuals’ subjective self-descriptions. A few biomechanical studies of bipolar disorder exist, but they do not report participants’ mood phase or they include only one mood phase. Despite the importance of body movement assessment for diagnosis of bipolar disorder, the effects of hypomanic, euthymic and depressed phases on body movements in bipolar disorder have not yet been described quantitatively.

The aim of this dissertation was to investigate the effects of emotion and mood phase on biomechanical characteristics of body movements in healthy individuals and individuals with bipolar disorder. In the first two studies, anger, joy, sadness and neutral emotion were elicited in eighteen healthy individuals while performing sit-to-walk and gait. Movement data were collected using an optoelectronic motion capture system. During sit-to-walk, emotion-related differences were consistent with differences in movement speed so that the shortest durations, greatest velocities and lowest center-of-mass velocity drops (hesitation) were associated with anger and joy, and the longest durations, lowest velocities and largest hesitation were associated with sadness. In contrast to previous studies based on qualitative observations, movement smoothness, measured as normalized jerk of center-of-mass, was greater for anger or joy than sadness, after accounting for speed effects. During gait, emotion affected spatiotemporal measures in a similar way as sit-to-walk, with movement speed and movement smoothness greater for anger and joy than sadness. These studies demonstrate a consistent effect of emotion on spatiotemporal features and movement smoothness across whole-body tasks, and provide new evidence that emotion affects movement coordination assessed by center-of-mass motion.

In the third study, a biomechanical approach was combined with psychiatric assessment to examine the effects of mood phase on gait in individuals with bipolar disorder. Individuals with bipolar disorder in the hypomanic, euthymic or depressed phase, and healthy controls performed gait at self-selected comfortable, slow and fast speeds. An optoelectronic motion capture system and two force plates were used to collect movement data and ground reaction force data. The hypomanic individuals walked at least 28% faster, with at least 18% greater ground reaction force, and at least 50% greater power generation at the ankle compared with the other individuals, with force and power differences beyond the effect of faster speed. Although 20% of the depressed individuals walked as fast as the hypomanic individuals, the majority of the depressed individuals walked at least 15% slower compared with the other individuals. The euthymic individuals walked at the same speed as healthy controls. Study findings demonstrated that gait speed reflects all mood phases well, and ground reaction force and power generation particularly well-reflects hypomania. This study suggests that gait speed may be a promising mood-specific biomarker for bipolar disorder.