[Secondary Full Title: Effects of high intensity interval training in plain and uphill regarding physical performance].

Background: As the number of HIITs is increasing in competitive and non-competitive sports, the risk of injuries and overload is increasing. There are no scientific data to support specific recommendations in regard to intensity, duration, number of intervals and gradient for HIIT that result in improved muscular parameters in athletes. Therefore the aim of this study was to compare HIIT in plain and uphill exercise, with respect to exercise tolerance and improvements in performance (VO and 800 m running time in the plain and uphill).

Volunteers And Methods: 17 well-trained sport students (10 females, 7 males; Ø VO: 53.7 ml/min/kg) were randomly assigned to the plain group (plain; GE) (n = 8) or the uphill group (hill, GB) (n = 9). In the four weeks of training, all subjects completed 14 HIIT sessions. Each session consisted of 8 × 2 min running at 90 - 95 % of the maximal heart rate (HR), separated by 2 min recovery periods (work/rest ratio: 1:1). Before the intervention phase, subjects performed treadmill spirometry, a 800 m field test in the plain, as well as an 800 m uphill field test to determine baseline performance. One week after the intervention period, all subjects completed a retest of all measurements and tests. After the intervention, all subjects completed a questionnaire by giving their level of perceived exertion during training, using the BORG scale.

Results: In GE, three subjects dropped out of the study because of overtraining. In GB, two subjects did not complete the study because of time constraints. The evaluation of the perceived exertion of the training in flat terrain showed a trend (p = 0.08; t = - 1.96) towards being perceived as more exhausting then in hilly terrain. A four week HIIT showed significant improvements in VO by 5.2 % (p = 0.02; t = - 2.76), and a reduction in the running time in the plain by 4.6 % (p = 0.01; t = 3.48) and uphill by 6.3 % (p = 0.02; t = 2.77). No significant group effect was detected.

Discussion And Conclusion: In this study, the application of HIIT leads to significant improvements in the performance of well-trained athletes. There is no evidence that the mode of training influenced the running improvements. However, uphill training tends to be better tolerated by the athletes.