Enhancing functional capacity in older adults with short session high intensity interval training Frailty is a condition of poor physiological reserve that increases susceptibility to falls, hospitalization, disability and mortality. The incidence of frailty rapidly increases after the age 65, growing from 10% to as many as 50% of those 85 years or older; therefore over 9 million veterans are either frail or at risk for frailty. Exercise has proven benefits for frailty, yet older adults rarely attain the recommended 150 minutes a week of moderate intensity exercise. High intensity interval training (HIIT) is emerging as an alternative as it delivers similar or better gains than moderate intensity exercise in less time. Recently, we published that a 3-day-a-week, 10-minute HIIT regimen in aged mice not only reduces frailty, but leads to both strength and endurance benefits. In addition, our preliminary data demonstrate significant changes in microRNA (miRNA) profiles. Despite the potential of short session HIIT to improve functional capacity and lead to better adherence, the modality has not been tested in individuals 65-85 years of age, and in particular, frail individuals. The goals of this proposal are to: 1) investigate the feasibility of recruiting and administering short session HIIT to frail, pre-frail, and non-frail older veterans and 2) to characterize the physical performance benefits and serum microRNA (miRNA) profiles in those participants. To accomplish our goals we will administer a short session HIIT regimen totaling only 10- minutes, 3-days-a-week for 3 months, using recumbent exercise cycles, to 65-85 year-old participants. We will also utilize next generation RNA-sequence technology to assess HIIT impacts upon microRNA profiles in serum samples. We anticipate our project will demonstrate the feasibility of administering short session HIIT to older individuals, including vulnerable frail and pre-frail populations as well as demonstrate the ability to collect and analyze serum miRNA profiles. The advantages to this program are the ability to maintain or build muscle mass and improve aerobic conditioning, especially in older HIIT enhances physical performance and reduces frailty during aging. patients where frailty and sarcopenia are so prevalent. This pilot project will therefore lay the foundation for future clinical trials that further explore the utility of HIIT to prevent or delay the onset of frailty in larger cohorts, and ultimately lead to the enhancement of functional capacity and quality of life in our aging veteran populations.