Subjects who pass the visit one screen will be provided the option of participating in ancillary study procedures designed to assess inflammatory biomarkers present in plasma, physical functioning capabilities, and pain and mood status during the pain testing procedures. Subjects will be asked to give blood samples during the pain testing procedures, followed by standardized tests of physical function. Subjects will be also asked to complete additional questionnaire and diary items that ask them to rate their emotions during the pain testing procedures and during the days that they keep their electronic diary for the parent project. At Visit 2, participants will undergo pain testing, an in-home sleep study and optional procedures outlined above. At Visit 3, participants with knee osteoarthritis will have an exam by a rheumatologist.