Objective: To investigate the effects of high-intensity aerobic exercise on adrenocortical responsiveness and on standard outcome measures in patients with chronic low back pain.

Design: Controlled clinical trial.

Setting: Physical therapy department of a university general hospital.

Subjects: Sixty-four patients with chronic low back pain were randomly allocated into positive and negative suppression test groups and assigned to exercise protocol.

Interventions: Subjects in the positive and negative dexamethasone suppression test groups received a 12-week high-intensity aerobic exercise programme.

Main outcome measures: Dexamethasone suppression test as an index of adrenocortical responsiveness, pain measured with the McGill Pain Questionnaire, functional status measured with the Roland Morris Disability Questionnaire, and psychological strain measured with the Hospital Anxiety and Depression Scale.

Results: Data analysis in the positive group identified a significant reduction of pain by 30% (t ₃₀ = 11.2, P<0.001), a recovery of the lost functioning by 34% (t ₃₀ = 19.7, P<0.001), a reduction of anxiety/depression by 25% (t ₃₀ = 10.2, P<0.001), and a change in adrenocortical responsiveness by 40% (t₃₀ = 14.1, P<0.001). In the dexamethasone suppression test negative group, data analysis identified a significant reduction of pain by 8% (t₃₁ = 4.2, P<0.001), a recovery of lost functioning by 10% (t₃₁ = 4.8, P<0.001), a reduction of anxiety/depression by 11% (t₃₁ = 5.0, P<0.001), and no change in adrenocortical responsiveness (t₃₁ = 1.2, P=0.22). In univariate analysis between-subject differences were significant for dexamethasone suppression test (F₆₁ = 163, P<0.001), and for anxiety/depression (F₆₁ = 21.3, P<0.001).

Conclusion: Exercise alleviated pain, functional disability and anxiety/depression, also improved adrenocortical responsiveness in patients with chronic low back pain with dexamethasone suppression test positive values.