PURPOSE:: to determine the effectiveness of brief intense interval training as exercise intervention for promoting health and evaluate potential benefits with reference to common interventions; i.e. prolonged exercise and strength training. METHODS:: 36 untrained men were divided into groups that completed 12 weeks of intense interval running (INT; total training time 40 min a week), prolonged running ( approximately 150 min/week), strength training ( approximately 150 min/week) or continued their habitual life-style without participation in physical training. RESULTS:: The improvement in cardiorespiratory fitness was superior in INT (14+/-2% increase in VO2max) compared to the other two exercise interventions (7+/-2% and 3+/-2% increases). The blood glucose concentration 2 hours following oral ingestion of 75 g of glucose was lowered to a similar extent following training in the INT (from 6.1+/-0.6 to 5.1+/-0.4 mM; P<0.05) and the prolonged running group (from 5.6 +/-1.5 to 4.9+/-1.1 mM; P<0.05). In contrast, INT was less efficient than prolonged running for lowering the subjects resting heart rate, fat percentage and reducing the ratio between total and HDL plasma cholesterol. Furthermore, total bone mass and lean body mass remained unchanged in the INT group, while both these parameters were increased by the strength training intervention. CONCLUSIONS:: INT for 12 weeks is an effective training stimulus for improvement of cardiorespiratory fitness and glucose tolerance, but in relation to the treatment of hyperlipidemia and obesity it is less effective than prolonged training. Furthermore and in contrast to strength training, 12 weeks of INT had no impact on muscle mass or indices of skeletal health.