The study measured the effectiveness of a predetermined training intensity to induce cardiovascular improvements in sedentary college women. It was an attempt to clarify the question, “When does an exercise become training?” or “What work intensity is necessary for cardiovascular changes?”—quantitatively, an unresolved issue pertaining to the dosage of exercise. Twelve subjects, aged 17 to 21 years, participated in a treadmill training program fifteen minutes daily for four weeks. Six subjects (Group 1), trained at a heart rate of 125 beats per min and six subjects (Group 2), trained at a heart rate of 145 beats per min. Treadmill speeds were regulated during each training session so that the work intensity remained at the predetermined heart rate level. The test battery included basal HR and “all out” treadmill test variables (time at HR 180, max oxygen intake, max HR, and test run time) at pre- and post-training; mid- and post-training re-runs at the second training day treadmill speeds; and treadmill speeds throughout the training. The t test in various forms was used to treat the pre-, pre- to -post, and post-training data. Group 1 showed significant increases in the time required to elicit a heart rate of 180 beats per min and maximal oxygen intake, while Group 2 significantly increased total run time and maximal oxygen intake. It was concluded that a work intensity eliciting a heart rate of 125 beats per min provided sufficient but not minimal stimulus for training effects in sedentary young females.