Subjects will participate in a 100 min bout of exercise led by an exercise physiologist doing the same exercises as the high-intensity group, but at a lower effort level. Exercise consists of of a mix of running activities (≤ 400 m); body weight exercises, such as burpees and lunges; and exercises, such as crunches and squats utilizing 20.4 kg weight plates, but performed at a pace allowing for in-session recovery. Scheduled 5 min rests will be included at 30, 60, and 85 min and MI subjects will be similarly encouraged to consume water and/or the carbohydrate/electrolyte drink. The researchers will obtain a blood sample from you prior to and immediately following the exercise, as well as one, four and six hours post-exercise.

Subjects in this group will participate in an exercise session that is representative of a training event experienced by cadets preparing for military competitions. All exercises will consist of a mix of running activities (≤ 400 m); body weight exercises, such as burpees and lunges; and exercises, such as crunches and squats utilizing 20.4 kg weight plates; with rapidly occurring exercise transitions to prevent recovery. The exercise bout will last a total of 100 min. Scheduled 5 min rests will be inserted at 30, 60, and 85 min. During the scheduled rest periods, subjects will be encouraged to consume water and/or the carbohydrate/electrolyte drink. The researchers will obtain a blood sample from you prior to and immediately following the exercise, as well as one, four and six hours post-exercise.

Subjects in the two groups preformed 90-100 minutes of exercise at different intensities.

Blood samples were collected using standard venipuncture technique. Blood samples were obtained at baseline, immediately post-exercise (0h), 1 hour post (1h), 4 hours (4h), and 6 hours (6h) post-exercise in heparin vacutainer tubes. Peripheral blood mononuclear cells (PBMC) were isolated using Ficoll-Paque PLUS density gradient centrifugation. Total T cells were purified from washed PBMC by E-rosetting. T cell proliferation was analyzed in response to co-stimulation through CD3+CD28 using plate-bound antibodies, or phytohaemagglutinin (PHA) treatment, or no simulation. Cells were incubated for 6 days at 37˚C in a humidified incubator with 5% CO2 and then analyzed by flow cytometry. Cells were analyzed by flow cytometry using anti-CD3-APC, and anti-CD152-PE antibodies immediately after CD3+ T cell isolation (0 h) and following 6 d in culture using an Accuri C6 flow cytometer.

Blood will be collected in a vial containing EDTA (6 ml) for analysis of catecholamines. Plasma for catecholamine (epinephrine and norepinephrine) analyses was obtained by centrifugation at 2000 g for 10 min at 4˚C. The supernatant was removed and stored at -80˚C until analysis. Catecholamine concentrations will be determined using BI-CAT ELISA kits and performed per the manufacturer's instructions. The samples were measured at 450 nm using a Synergy HT microplate reader. The blood samples will be obtained at the same time as for the primary outcomes (prior to and following exercise as well as one, four and six hours post-exercise.