BACKGROUND. High-intensity functional training is a popular form of exercise, but little is known about how it compares to more traditional exercise patterns. METHODS. Thirty healthy, physically active adults (15 males, 15 females) performed a high-intensity functional training workout (HIFT) and a traditional workout (TRAD). Cardiorespiratory responses were measured during and for 15 min after each workout. RESULTS. Peak heart rate (males: 187 +/- 7 vs. 171 +/- 10 bpm, P<0.001; females: 191 +/- 9 vs. 175 +/- 6 bpm, P<0.001), peak VO2 (males: 3.80 +/- 0.58 vs. 3.26 +/- 0.60 L/min, P<0.001; females: 2.65 +/- 0.26 vs. 2.36 +/- 0.21, P<0.001), and average 15 min recovery VO2 (males: 1.15 +/- 0.20 vs. 0.99 +/- 0.17 L/min, P<0.001; females: 0.77 +/- 0.10 vs. 0.71 +/- 0.07 L/min, P=0.019) were significantly higher in HIFT vs. TRAD. Aerobic energy expenditure was significantly higher in HIFT compared to TRAD in males (9.01 +/- 1.43 vs. 8.53 +/- 1.38 kcal/min, P=0.002) but was not significantly different between the two workouts in females (6.04 +/- 0.53 vs. 5.97 +/- 0.50 kcal/min, P=0.395). Postexercise systolic blood pressure (SBP) was significantly higher than pre-exercise SBP following both HIFT (males: 124 +/- 13 mmHg pre to 154 +/- 28 mmHg post, P<0.001; females: 110 +/- 7 mmHg pre to 140 +/- 15 mmHg post, P<0.001) and TRAD (males: 124 +/- 13 mmHg pre to 142 +/- 16 mmHg post, P=0.002; females: 112 +/- 8 mmHg pre to 123 +/- 10 mmHg post, P=0.002), however, HIFT led to a greater increase compared to TRAD in females (P=0.001). Postexercise diastolic blood pressure (DBP) was significantly lower than pre-exercise DBP following both HIFT (males: 77 +/- 9 mmHg pre to 64 +/- 6 mmHg post, P<0.001; females: 71 +/- 8 mmHg pre to 64 +/- 7 mmHg post, P=0.011) and TRAD (males: 82 +/- 7 mmHg pre to 72 +/- 7 mmHg post, P<0.001; females: 73 +/- 8 mmHg pre to 65 +/- 8 mmHg post, P<0.001). Mean arterial blood pressure was unchanged following both workouts. CONCLUSIONS. High-intensity functional training may be an effective form of exercise for caloric expenditure and may elicit greater cardiorespiratory stress than traditional exercise.