The DVT-Cph RCT aims to investigate: 1. if progressive gait training in combination with standard care is superior to standard care on quality of life in patients with first time lower extremity deep venous thrombosis (clinical effectiveness part). 2. the association between progressive gait training and disease progression, late complications such as post throbotic syndrome, and severity of venous thromboembolism conditions in patients with first time lower extremity deep venous thrombosis (mechanistic part).