1. People with severe COVID-19 requiring long stay ICU who develop post-ICU syndrome. These people need rehabilitation and therefore should not be in a RCT in which they may be randomised to no rehabilitation. 2. People with acute symptoms of any illness where exercise is not recommended 3. People who are not medically stable as judged by treating physician 4. Women who are pregnant or post-partum

1. People with severe COVID-19 requiring long stay ICU who develop post-ICU syndrome. These people need rehabilitation and therefore should not be in a RCT in which they may be randomised to no rehabilitation. 2. People with acute symptoms of any illness where exercise is not recommended 3. People who are not medically stable as judged by treating physician 4. Women who are pregnant or post-partum