A growing body of research suggests that the respiratory system may be limited in its ability to meet the demands of increased ventilitory work. This is supported by studies reporting altered contractile properties of the diaphragm in response to increased ventilations. In order to determine if expiratory muscle function is affected by increased ventilitory demand, this study evaluated maximal expiratory pressure, PeMax, in response to two separate short-term, high-intensity exercise trials. Males (n=7) and females (n=5) not currently in active physical training underwent a VO₂ max test and a constant workload of 90% of VO₂ max. PeMax was measured at rest, immediately post exercise, and at one two and five minutes into recovery for both exercise trials. PeMax values were found to decrease 12% and 17% in response to graded and constant workload conditions respectively (P<.05), and this decline persisted throughout the five minute recovery. No Significant relationship was found between magnitude of decline in PeMax and VO₂ max or decline in PeMax and Ve max. These findings suggest that maximal graded exercise as well as exhaustive constant workload exercise corresponding to 90% of VO₂ max provide the ventilitory stimulus great enough to result in a decline in expiratory performance. / Master of Science