Sprint interval training (SIT) is gaining popularity with endurance athletes. Various studies have shown that SIT allows similar or greater endurance, strength, and power performance improvements than traditional endurance training, but demands less time and volume. One of the main limitations in SIT research is that most studies were performed in a laboratory using expensive treadmills or ergometers. The aim of this study was to assess the performance effects of a novel short term and highly accessible training protocol based on maximal shuttle runs in the field (SIT-F). Sixteen (12 male, 4 female) trained trail runners completed a two-week procedure consisting of 4-7 bouts of 30 seconds at maximal intensity interspersed by four minutes of recovery, three times a week. Maximal aerobic speed (MAS), time to exhaustion at 90% of MAS at pre-test (Tmax@90%MAS) and 3000-m Time Trial (TT3000m) were evaluated preand post-training. Data were analyzed using a paired samples t-test and Cohen's (d) effect sizes were calculated. MAS improved by 2.3% (p = 0.01, d = 0.22) while peak power and mean power increased by 2.4% (p = 0.009, d = 0.33) and 2.8% (p = 0.002, d = 0.41) respectively. TT3000m was 6% shorter (p < 0.001, d = 0.35) while Tmax@90%MAS was 42% longer (p < 0.001, d = 0.74). SIT-F significantly improved 3000 m run, time to exhaustion, peak power, and mean power in trained trail runners. SIT-F is a time efficient and cost-free means of improving both endurance and power performance in trained athletes.
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