A thesis submitted to the School of Graduate Studies in partial fulfillment of the requirements for the degree Master of Science. / Sprint interval training (SIT) is a time-efficient strategy to improve cardiorespiratory fitness; however, most protocols have been studied in a laboratory setting and require specialized equipment. We investigated the efficacy of brief intense stair climbing as a practical model of SIT to improve cardiometabolic health, with a key measure being cardiorespiratory fitness as indicated by peak oxygen uptake (VO2peak). Two separate studies, each consisting of an acute and chronic phase, were conducted in a total of 31 sedentary women (age=24±10 y; BMI=23±4 kg•m-2). The acute phase of Study 1 established that the heart rate (HR), blood lactate concentration (BLa), and rating of perceived exertion (RPE) responses were similar when participants (n=8) performed a SIT protocol that involved 3x20-s “all-out” efforts of either continuous stair climbing or cycling, interspersed with 2 min of recovery. The chronic phase demonstrated that when participants (n=12) performed the 3x20-s stair climbing protocol 3 d•wk-1 for 6 wk, absolute and relative VO2peak increased by 12%, or ~1 metabolic equivalent (1.80±0.25 to 2.02±0.27 L•min-1, p<0.001), as there were no changes in body mass (p=0.35), fat free mass (FFM; p=0.09) or % body fat (p=0.42). There were also no changes in resting systolic and diastolic blood pressure (BP; p=0.82 and p=0.97, respectively), resting HR (p=0.62), and fasting insulin sensitivity (p=0.52). The acute phase of Study 2 established that the HR and RPE responses were similar when participants (n=11) performed three different stair climbing protocols. The protocols investigated include the 3x20-s continuous ascent model used in Study 1 (protocol 1), as well as 3x60-s bouts of ascending and descending either one or two flights of stairs, with 60-s of recovery (protocol 2 and 3, respectively). The chronic phase demonstrated that when the same group of subjects performed the 3x60-s 1-flight protocol 3 d•wk-1 for 6 wk, absolute and relative VO2peak increased by 8 and 7%, respectively (1.79±0.36 to 1.93±0.39 L•min-1, p=0.001; 31.2±4.6 to 33.3±5.3 mL•kg-1•min-1; p=0.01). Despite no changes in % body fat (p=0.10), there was an increase 3% increase in FFM (p<0.001). There was no change in systolic (p=0.50) and diastolic BP (p=1.00), but resting HR improved by 8% after training (p=0.03). The change in insulin sensitivity derived from an OGTT was 7.1±11 mg I2•mmol-1•mIU-1•min-1 (p=0.056). These findings demonstrate that brief intense stair climbing is a practical, time-efficient strategy to improve cardiorespiratory fitness in previously untrained women. / Thesis / Master of Science (MSc) / Sprint interval training (SIT), involving brief bouts of very intense exercise separated by short periods of recovery, is a time-efficient alternative to traditional endurance training for improving fitness. This has largely been established in laboratory settings using specialized equipment, which is impractical for many individuals. This project examined whether brief intense stair climbing was a practical model of SIT to elicit adaptations previously shown with cycling protocols. Subjects performed either three 20-s ascents interspersed with 2 min recovery periods, or three 60-s bouts of ascending and descending one or two flights of stairs, with 60-s recovery periods. Both protocols were 10 min in duration including warm-up and cool-down, and subjects trained three days per week for six weeks. The main finding was that stair climbing is a practical, time-efficient model to improve fitness in previously sedentary individuals.