A pragmatic randomised controlled trial of preferred intensity exercise in depressed adult women in the United Kingdom: secondary analysis of individual variability of depression.

Background: This study is a secondary analysis of the trial by Callaghan et al. (2011), which reported higher antidepressant effects for preferred intensity (n = 19) vs. prescribed intensity (n = 19) exercise of three sessions/week over four weeks in depressed women. In particular, the present study sought to examine whether greater clinically significant individual change/recovery was observed in the preferred compared to the prescribed exercise group.

Methods: The reliable change index and the C score criteria described by Jacobson and Truax (1991) were employed to determine clinical significance. These criteria examined if individual change in depression scores from pre- to post-intervention in the preferred intensity group were statistically significant beyond the standard error of difference derived from the active comparator prescribed group, and subsequently within a normal population range. Patients fulfilling the first or both criteria were classified as improved or recovered, respectively.

Results: Post-intervention depression scores of six patients in the preferred intensity exercise group (32%) demonstrated statistically reliable improvement (p < 0.05) and recovery. Half of this subgroup started as moderately depressed. No patient demonstrated a reliable deterioration in depression. Due to a small sample size, it was impossible to determine whether patients on psychiatric medication or medication-free patients were equally benefited from preferred intensity exercise. Thirteen patients in the preferred intensity group (68%) displayed non-statistically significant change in post-intervention depression scores (p > 0.05), although eight of them showed a non-significant improvement in post-intervention depression scores and three could not technically show an improvement in depression due to floor effects (baseline depression within normal range).

Conclusions: Preferred intensity exercise of three sessions/week over four weeks led almost a third of the patients to record scores consistent with recovery from depression. Health professionals may consider that short-term preferred intensity exercise provides clinically significant antidepressant effects comparing favourably to exercise on prescription.