Aerobic exercise can have an antianxiety effect. The physiological changes that occur by exercising can overpower the negative effects of the physiological contributors to anxiety. For example, in one study, the subjects were injected with CCK-4, a chemical that can induce a panic attack even in healthy adults with no history of panic. Thirty minutes of aerobic exercise prior to the injection of CCK-4 lowered the panic scores, whereas resting before the injection did not.