Preliminary study investigating influence of anti-depressant medication on diurnal physical activity patterns

We have previously reported that diurnal physical activity patterns are related to certain types of mood disorders. This suggests that a person' s physical activity patterns can be used as a supplementary index for assessing the effects of antidepressants. We investigated the effect of administering selective serotonin reuptake inhibitors (SSRIs) on intraday physical activity patterns of inpatients over a 4 week period, after commencing SSRI. Participants were Inpatients with major depression, or bipolar disorder (n = 90). They were divided into three groups: (1) Patients continuously administered SSRIs (continuous group); (2) Patients discontinued from SSRI during the 4-week period (discontinued group); and (3) Patients taking antidepressants other than SSRIs (non-SSRI group). Participants' activity during the study period was measured by using accelerometers. Each 4-week data block was divided into 1-day-long sections. Fourier series expansion was performed on the activity levels for each section, and principal component analyses (PCA) were performed on the coefficients of expansion. We examined differences in changes of principal component scores between the groups using a state-space model. The results indicated that the group continuously administered SSRIs had a significant increase in their activity level, especially in the mornings, compared to the group that was discontinued from SSRI administration.