The type, intensity and duration of exercise, fitness state, and timing of measurements have been reported to influence the acute vascular responses to exercise. However, little is known regarding the influence of interval training, aging and gender on these responses. The objectives of this study are: 1) to examine the acute vascular responses to continuous low- and moderate-intensity exercise and interval training; and 2) to examine the influence of age and gender on these responses. Subjects will perform the following 3 types of treadmill exercise in a random order: 1) slow-pace walking; 2) moderate-pace walking; and 3) interval training. Flow mediated dilation using high resolution ultrasonography and arterial stiffness using applanation tonometry will be measured before, immediately after and 1-hour after each acute bout of exercise.