The purpose of this study was to compare the relationship between immersion running and treadmill running through the measurement of cardiorespiratory parameters. Sixteen subjects completed two exercise protocols to exhaustion. The treadmill running protocol was initiated at 3.08 m*s-l and increased a 0.22 m*s-l every sixty seconds. The immersion running protocol utilized an immersion running Ergometer (IRE). The IRE is similar to a tethered swim machine. The initial weight was set at 1 kg and Increased a 1/2 kg every sixty seconds. Heart rate (HR), oxygen consumption (V02), ventilatory equivalent (VE/V02), and minute ventilation (VE) were determined at ventilatory threshold and at maximal effort, HR, V02, VE/V02 and VE were analyzed by MANOVA (RM). Tidal volume and frequency of breathing were collected for four subjects at ventilatory threshold and at maximal effort (no statistical analysis). Two subjects who had completed the initial exercise protocols volunteered for a follow up study of blood flow distribution testing (no statistical analysis). These subjects were injected with Tc-99 2-methyloxy isobutyl isonitrlle at ventilatory threshold during immersion and treadmill running. Imaging was performed with a Selmans Gamma Camera at the UBC Dept. of Nuclear Medicine. V02 and HR at ventilatory threshold and maximal effort were significantly lower (P < .05) during immersion running. VE/V02 was significantly greater at maximal effort during immersion. Minute ventilation was unaffected by immersion, however, there was a trend towards a smaller tidal volume and greater frequency of breathing. The blood flow distribution data varied considerably partially between subjects. The significant drop in V02 at maximum effort and at ventilation threshold during immersion running may be accounted for by changes in muscle mass recruitment, muscle fibre type recruitment, recruitment pattern and state of peripheral adaptation (muscular). A lower heart rate during immersion may be due to increases in intrathoracic blood volume. The trend towards a higher breathing frequency and lower tidal volume during immersion running may be due to the increased effort to breath caused by hydrostatic chest compression. The significant increase in VE/V02 at maximal effort during immersion running was due to the significant drop in V02. It may be concluded that immersion running causes significant changes in cardiorespiratory parameters at ventilatory threshold and at maximal effort. Research is needed to investigate the significance of the changes. / Education, Faculty of / Curriculum and Pedagogy (EDCP), Department of / Graduate