The aim of the current project is to examine the effects of high intensity exercise (by using 1x4 intervals) to reduce symptoms of anxiety in patients in mental health care. The expected benefits for patients are positive health effects, by improving physical fitness and reducing psychological symptom burden. The patients will have the opportunity to learn to use physical activity as a specific measure to be used in their own lives and be a source of coping. Furthermore, knowledge about physical activity and mental health may be applicable in mental health care as a part of a treatment plan.

The study is a randomised controlled trial ("RCT") design with a 1:1 allocation into two groups. The two groups are high intensity exercise (1x4 minutes performed two times per week with a heart rate above 85% of maximal heart rate) and low intensity exercise (45 minutes performed two times per week with a heart rate of approximately 60% of maximal heart rate). The total amount of training sessions for both groups will be eight. The high intensity exercise group will serve as the intervention group, while the low intensity exercise group will serve as an active control group.

The patients will be randomly allocated (randomised) to these groups. An exercise physiologist (holding a master's degree in exercise physiology) will supervise the training sessions. The training sessions will take place in a dedicated room using a treadmill and a heart rate monitor. The training sessions will be individual.

The primary outcome measure will be degree of anxiety symptoms measured by Hospital Anxiety and Depression Scale (HADS) and Beck Naxiety Inventory (BAI) prior to the first (pre) and after the last (post) training session is completed. Secondary outcome measures will be compliance, i.e. to what degree the patient is able to sustain the exercise regimen three months after participating in the project, in addition to the patient's blood pressure.

Inclusion Criteria:

• Patients with mild/moderate anxiety disorders, aged 18-60 years. Anxiety disorders in accordance with F 41 in ICD-10, including generalised anxiety disorder, agoraphobia/panic disorder, social phobia, post-traumatic stress disorder, hypochondria, and obsessive-compulsive disorder.
• Comorbidity will occur, so the patient may also have depression. However, the main disorder should be anxiety.

Exclusion Criteria:

• Somatic diseases that may impede training: cardiovascular disease, severe asthma, severe COPD, cancer, poorly regulated diabetes.
• Schizophrenia or bipolar disease
• Suicidality (prior attempts or ongoing risk of suicide)
• Substance addiction

IPD will not be shared due to various reasons, including concerns about patient privacy and confidentiality, legal or ethical restrictions, the potential risk of re-identifying participants, and the protection of sensitive data.