Inclusion Criteria - Aim 1:  Subjects must be able to provide written consent. Adults 18 years of age and older. Nonsmokers. No recent hospitalization (< 60 days). Ability to perform high-intensity exercise.  Inclusion Criteria - Aim 2:  Subjects must be able to provide written consent to be included in the research study. Adults 18 years of age and older. Nonsmokers. Current ICU patient. Have regular blood samples taken for [lactate] measurements. Have one or more risk factors for sepsis.  Exclusion Criteria - Aims 1 and 2:  History of, or active malignancy. History of HIV with antiretroviral treatment. Smokers. Pregnancy.