Table 1 Objectives and hypotheses of the study

Main objective

• To evaluate the effect of a 6-week whole-body vibration-training vs. placebo on clinician-rated severity of depression symptoms in adolescent inpatients experiencing a major depressive episode

Main hypothesis

• In adolescent inpatients experiencing a major depressive episode, the change in the Children’s Depression Rating Scale-Revised raw-scores from baseline to completion of the 6-week intervention differs significantly between the whole-body vibration strength-training group and the control group (hypothesis A)

Secondary objectives

• To evaluate the effect of a 6-week whole-body vibration-training vs. placebo on hypothalamic-pituitary-adrenal axis dysregulation in adolescent inpatients experiencing a major depressive episode

Secondary hypotheses

• In adolescent inpatients experiencing a major depressive episode, the change in cortisol awakening response from baseline to completion of the 6-week intervention differs significantly between the whole-body vibration-training group and the control group (hypothesis B)

• To evaluate the effect of a 6-week whole-body vibration-training vs. placebo on neurotrophin and growth factor expression in adolescent inpatients experiencing a major depressive episode

• In adolescent inpatients experiencing a major depressive episode, the change of brain-derived neurotrophic factor and insulin-like growth factor 1 serum levels from baseline to completion of the 6-week intervention/to 8 weeks’ follow-up differs significantly between the whole-body vibration-training group and the control group (hypothesis C)

• To evaluate the effect of a 6-week whole-body vibration-training vs. placebo on inflammatory-marker expression in adolescent inpatients experiencing a major depressive episode

• In adolescent inpatients experiencing a major depressive episode, the change in tumor necrosis factor-alpha, interleukin-6, C-reactive protein serum levels from baseline to completion of the 6-week intervention/to 8 weeks’ follow-up differs significantly between the whole-body vibration-training group and the control group (hypothesis D)

• To evaluate the effect of a 6-week whole-body vibration-training vs. placebo on self-perceived severity of depression symptoms in adolescent inpatients experiencing a major depressive episode

• In adolescent inpatients experiencing a major depressive episode, the change of Beck’s Depression Inventory-second edition raw-scores from baseline to completion of the 6-week intervention/to 8 weeks’ follow-up/to 20 weeks’ follow up differs significantly between the whole-body vibration-training group and the control group (hypothesis E)

• To evaluate the sustainability of the effect of the 6-week whole-body vibration-training vs. placebo on clinician rated severity of depression symptoms in adolescent inpatients experiencing a major depressive episode

• In adolescent inpatients experiencing a major depressive episode, the change of Children’s Depression Rating Scale-Revised raw-scores from baseline to 8 weeks’ follow-up/to 20 weeks’ follow-up differs significantly between the whole-body vibration-training and the control group (hypothesis F)