Comparing Acute Aerobic and Resistance Exercise

Inclusion Criteria: * "Young" Adults: ages 18-30 * "Older" Adults: ages 55-75 and if a female postmenopausal * Participants classified as "trained" must participate in at least 30 minutes of moderate to vigorous intensity cardiovascular activity at least 3 days per week and engage in resistance training for all of the major muscle groups approximately 2 days / week. They must have upheld this activity for the past 3 months * Participants classified as "untrained" must be participating in less than 30 minutes of moderate to vigorous intensity cardiovascular activity and less than 2 days of resistance training per week for at least the last 3 months. Exclusion Criteria: * Have any contraindications to moderate to vigorous exercise * Range of motion restrictions that would prevent them from participating in aerobic or resistance training with proper form (they must be ambulatory) * aking medications (prescription or over the counter) known to influence immune function, including daily NSAID's, beta blockers, statins, bisphosphonates, or steroids. * Have known cardiovascular, respiratory, metabolic, or renal disease, with the exception of controlled hypertension (as defined by resting BP below 140/90) and/or controlled asthma (self-reported). * Be pregnant * Be unable to complete all visits (i.e. must not be planning to leave the Houston area long-term before concluding their participation in the study which will span several weeks) * Fall outside of a BMI range of (18.5 - 30) * Consume alcohol or recreational drugs for 24h prior to visits * Older women cannot be pre-menopausal (must have not had a menses for at least 12 months) * Unable to speak or read English * Participants must not have scheduling conflicts that would prevent them from reporting to the laboratory of integrated physiology 4 times over the course of the study