The present study examined the effect of intense intermittent running with 5 s sprints on body composition, fitness level, and performance in untrained subjects aged 36-53 years. For 7 weeks, the subjects carried out 3 days a week 5-10-15 training consisting of 3-9 blocks of 4 repetitions of 15, 10, and 5 s low-, moderate-, and high-speed running, respectively. Body fat mass was 4.3% lower (P < 0.01), and lean body mass and bone mineral density was 1.1 and 0.9% higher (P < 0.01), respectively, after compared to before the intervention period (INT). The plasma bone turnover markers osteocalcin increased (P < 0.01) by 147%, and procollagen-type I N propeptide and carboxy-terminal collagen crosslinks increased (P < 0.05) by 84 and 76%, respectively. Furthermore, the training improved performance in 1500 m (P < 0.001), 3 km (P < 0.001), Yo-Yo intermittent endurance test (P < 0.01), and incremental treadmill running (P < 0.001) by 8.1, 9.9, 17.2, and 23.9%, respectively. Furthermore, blood lactate after running at 85% of maximal aerobic speed was lower (P < 0.01) after compared to before the INT. Thus, 7 weeks of 5-10-15 training resulted in significant health beneficial changes and better performance in untrained subject.