The purpose of this study was to compare the Karvonen and anaerobic threshold methods for prescribing the intensity component of physical activity exercise prescription in healthy adult males. A performance criterion was utilized to determine both the duration at which the subjects could maintain a physiological steady-state as well as their capacity for sustained exercise at the levels prescribed by the two methods. Subjects were males, ages 22-26 years with a mean VO₂max ±SD of 59.2 ± 5.6 ml•kg⁻¹•min⁻¹ and a predicted body fat of 14.1% ±2.5% (the latter estimated from regression formulas using skinfold measurements). Initially, subjects (N=10) performed graded exercise tests (GXT) to determine the exercise prescription. Each subject started at an initial load of 4 METS and thereafter increments were increased 0.33 METS every 20 seconds until volitional endpoints were reached. The variables measured during the GXT were oxygen uptake, ventilation, heart rate, blood pressure, respiratory exchange values and rating of perceived exertion (RPE). From the subjects' GXT, an exercise prescription was calculated by the Karvonen and anaerobic threshold prescription methods. Afterwards, a micro-computer was utilized to objectively and graphically display a predicted anaerobic threshold. Anaerobic threshold was accepted as the point at which minute ventilation became non-linear with respect to time. From the graded exercise test, anaerobic thresholds were determined in all subjects from the ventilatory responses. Mean anaerobic thresholds (±SD), when expressed as a percentage of the VO₂max were 65.3% ± 5.8%. The Karvonen method was also determined from the GXT data by multiplying a predetermined percentage (65-75% of the individual's cardiac reserve (cardiac reserve = HR_max - HR_rest). After the development of the exercise prescriptions, subjects were assigned to perform continuous exercise in two different training simulation trials. The order of assignment was randomized and administered in a double-blind fashion so that neither the researcher nor the subjects knew of the exercise prescription method being utilized. The subjects performed these trials on alternate days on a motor-driven treadmill for 60 min. To determine if a difference existed between the two exercise prescription methods, a series of dependent t-tests were performed on the following variables: duration of exercise at a prescribed level; the capacity to perform continuous exercise; oxygen uptake during the steady-state level; the rating of perceived exertion (RPE); and respiratory exchange values averaged for the entire simulation trials. The duration that the subjects performed at a prescribed level was significantly longer utilizing the AT method versus the Karvonen method (AT vs. KM, 29.0 vs. 16.4 min, respectively). However, there were no significant differences found in the subjects' oxygen consumption or rating of perceived exertion. When assessing the subjects' maximal capacity to perform continuous exercise during these two training simulation tasks, no significant differences (p ≥ .05) were found between the two training simulations. A statistical significant difference but small mean increase (p ≤ .05) was found in the peak heart rate (KM=l79 and AT=l74 bts·min⁻¹) attained during the training simulation tasks utilizing the two exercise prescription methods. Furthermore, a significant difference (p ≤ .05) occurred in the subjects' duration to exercise during continuous exercise. The subjects' exercised significantly longer utilizing the AT method. These findings reflected that the AT method was a more sensitive technique for allowing individual variability. In conclusion, the results of this study suggest that the anaerobic threshold method is a valid procedure to determine the exercise intensity for young, healthy adult males. / Master of Science