Can high intensity interval training improve health outcomes among people with mental illness? A systematic review and preliminary meta-analysis of intervention studies across a range of mental illnesses

High intensity interval training (HIIT) may have beneficial effects among people with mental illnesses. The aim of this systematic review was to establish the benefits, safety and adherence of HIIT interventions across all categories of mental illness. Major databases were searched from inception to 18/2/2019 for intervention studies investigating HIIT among people with mental illnesses. Study quality was assessed via the PEDro scale, intervention characteristics were reported using the TIDier and CERT checklists and findings narratively summarised. A preliminary meta-analysis was undertaken where possible. 12 intervention studies, (including 7 RCTs), were included. Evidence suggested HIIT improved cardiorespiratory fitness (5/8 intervention studies,63%), anthropometric variables (3/4,75%), mental health outcomes (9/12, 75%), cardiovascular fitness (5/9,56%), physical fitness (1/1,100%) and motor skills (1/1,100%), compare to pre-training. The preliminary meta-analysis of pre-post changes found HIIT reduced depression severity (Standardised mean difference (SMD):-1.36 [95%CI-1.63;-1.089], p<0.0001) and possibly improved VO2max (SMD:0.18 [95%CI -0.02; 0.37], p = 0.08) in people with depression. HIIT increased High-Density-Lipoprotein (SMD:0.373 [95%CI 0.18; 0.57], p = 0.0002) and possibly reduced general psychopathology (SMD:-1.58 [95%CI -3.35; 0.18], p = 0.08) in people with schizophrenia-spectrum disorders. No acute injuries were reported, mean adherence to HIIT sessions ranged from 64–94%, and dropout ranged from 0-–50%. Results were limited to a small number of low-to-moderate quality intervention studies. These findings suggest HIIT may improve a range of physical and mental health outcomes among people with mental illnesses. Nonetheless, high-quality well-powered trials are needed to reaffirm these findings, and future research should address the seemingly high rate of dropout.