It is estimated that depression will be the second most common cause of disability worldwide by 2020 . Postnatal depression (PND) is a serious problem across cultures and affects about 10-15% of women some time in the year after giving birth [2, 3]. Women with postnatal depression can experience disabling symptoms of low mood, irritability, fatigue, insomnia, changes in appetite, anxiety, guilt, inability to cope, feelings of worthlessness and thoughts of suicide. Frequently exacerbating these symptoms are low self-esteem, lack of confidence, and unrealistic expectations of motherhood. Women who have PND are twice as likely to experience subsequent episodes of depression in later life . PND has health consequences not only for the mother but also for the child and family as a whole. Cognitive and emotional development and social behaviour have been shown to be adversely affected in children whose mothers have PND . PND can cause impaired maternal-infant interactions and negative perceptions of infant behaviour . Marital difficulties are not uncommon and the partner may also become depressed . Suicide is a rare but devastating consequence of PND.
After giving birth, many women have excess weight and decreased fitness levels [8, 9]. New mothers have reported weight gain to be a significant concern for them . Studies of pregnant and postpartum women have indicated they are at high risk for inactivity and reductions in previously established levels of activity . These health concerns would also apply to women with PND. The new physical activity guidelines “Start Active Stay Active” published by the Chief Medical Officers in the UK  state that participation in physical activity can have an important role in promoting mental health and well-being. Meta-analyses and reviews [13–15] have concluded that exercise may be effective in reducing depression in adult populations, although concerns have been raised about the methodological quality of trials to date. On the basis of the available evidence in 2009  the National Institute for Health and Clinical Excellence (NICE) in England recommended that people with persistent sub-threshold depressive symptoms or mild to moderate depression should be advised of the benefits of exercise.
Based on evidence of the positive effects of exercise on depression in general populations it seems plausible that regular exercise may also be an effective intervention for the treatment of PND. However, direct extrapolation from research with general populations to those experiencing PND is not necessarily appropriate because the circumstances of early motherhood are sufficiently different to preclude this. Based on general population evidence and findings from two very small trials (total n = 39) that recruited women with PND, in 2006 NICE  recommended in their guidance on the management of antenatal and postnatal mental health, that health professionals should consider exercise as a treatment for PND.
A systematic review and meta-analysis  of randomised and quasi randomised controlled trials has examined the effects of exercise on PND. Five trials (six reports) [19–24] were identified (total N: n = 114 intervention; n = 107 comparators). In three trials, participants were receiving antidepressant medication and/or psychological therapies, one trial excluded participants if they were currently using antidepressants or receiving psychotherapy and one did not provide this information. When compared with no-exercise, exercise significantly reduced symptoms of PND (weighted mean difference in Edinburgh Postnatal Depression Scale  score was −4.00 points (95% CI: -7.64 to −0.35)) (standardised mean difference: -0.81 (95% CI: -1.53 to −0.10)). Whilst the magnitude of this effect might appear initially encouraging, caution is required when interpreting this finding because significant heterogeneity was found and because the effect size was reduced considerably (and became non-significant) when the trial  that included exercise as a co-intervention with social support was excluded (standardised mean difference = −0.42 (CI:-0.90 to 0.05)). Heterogeneity was no longer present either. Therefore it is uncertain whether exercise reduces symptoms of PND and the significant effect size of −0.81 is contingent on the inclusion of one trial where exercise was a co-intervention. We should also remain cognisant that trials were small, confidence intervals were wide, had limited follow-up and included samples of volunteers and not clinically defined cases according to diagnostic criteria. There were no studies on long term effectiveness. Given the paucity of high quality research, it is necessary to evaluate more fully the effectiveness of exercise as a treatment for PND.
In summary, a large trial that compares exercise with standard treatment(s) and which includes longer term follow-up is now essential given the recommendation from NICE  that health professionals should consider exercise as treatment for PND. We are aware of no ongoing trials in this field and therefore the proposed research has the potential to make a significant contribution to the literature. No previous research has investigated the views of depressed postnatal women participating in exercise programmes and a qualitative study will be nested within this trial. The qualitative study will aid our understanding why exercise, in addition to usual care, was or was not superior to usual care in reducing symptoms of PND. These insights could subsequently inform clinical practice and future interventions with women experiencing PND.