The Target Temperature Management trial 2 (TTM2) is an international multi-center study, that randomize patients with OHCA of a presumed cardiac or unknown cause to target temperature management at 33°C or normothermia but avoiding fever (37.8°C) for the first 24 hours after the OHCA. The TTM2 study (clinicaltrials.gov Identifier NCT02908308) includes a detailed follow-up of functional outcome, health-related quality of life and neurocognitive function at 6 and 24 months post-arrest. This protocol describes a sub-study within the TTM2 trial that specifically focus on physical activity among the OHCA survivors.

The primary aim of this study is to investigate whether OHCA-survivors have lower levels of self-reported physical activity compared to a non-cardiac arrest (CA) control group who had acute myocardial infarction (MI). Additional aims are to explore potential predictors of physical inactivity (older age, female gender, problems with general physical function, global cognition, mental processing speed/attention, anxiety symptoms, depression symptoms, kinesiophobia, fatigue), and to investigate the relationship between self-reported and objectively measured physical activity among OHCA-survivors.

Inclusion Criteria:

• The TTM2 main trial includes adult, unconscious patients with sustained return of spontaneous circulation after cardiac arrest of a presumed cardiac origin. The aim is to include 100-150 OHCA-survivors to the sub-study.

Exclusion Criteria:

• An exclusion criterion for the TTM2 main trial is an unwitnessed cardiac arrest with initial rhythm asystole, temperature at admission <30°C, on extracorporeal membrane oxygenation (ECMO) prior to return of spontaneous circulation (ROSC), obvious or suspected pregnancy, intracranial bleeding and/or severe chronic obstructive pulmonary disease (COPD) on home oxygen.

An additional exclusion criterion for the sub-study is the inability to speak the local language well enough to complete the test without an interpreter. Patients with major cognitive impairment, patients sitting in a wheel chair, Clinical Frailty Score 8 or 9 (very severely frail or terminally ill), active drug abuse and when a face-to face follow-up is not possible will also be excluded.

Surviving patients in the TTM2-trial are invited to a structured face-to-face follow-up visit at 180 days (+/- 2 weeks). Survivors at selected sites will be invited to an extended study on physical activity at their follow-up visit.