Medium work is defined as the ability to lift up to 50 pounds at a time. To qualify for this, you also should be capable of lifting 25 pounds on a consistent basis and be able to both walk and stand for 6 hours in an 8-hour shift. Maximum sustained work capability is determined using medical records and other methods like the questionnaires you fill in the claim process.
SSA will consider only restrictions and ailments in your medical records. In the case that you are found capable of handling medium work, your application will likely be denied. Additionally, you will be considered able to perform occupation classifications below medium work such as sedentary work and light work.