Masoud Moghaddam1, Carlos A. Estrada1, Tyler W.D. Muddle1, Mitchel A. Magrini1, Nathaniel D.M. Jenkins1, Bert H. Jacobson1, FACSM

1Oklahoma State University, Stillwater, OK

High intensity interval training (HIIT) refers to a group of short bouts separated by rest periods. Intensity and duration of exercise and rest periods are the most significant factors in optimizing HIIT adaptations. Since a 2:1 work-to-rest ratio causes a higher oxygen deficit, a 10s:5s work-to-rest ratio was incorporated to establish a shorter yet potentially effective interval duration. PURPOSE: This study compared the effects of ultrashort (UH) versus short (SH) functional HIIT on body composition, vastus lateralis cross sectional area (VL CSA), anaerobic, and aerobic performance. METHODS: Thirty-four recreationally active participants were randomly assigned to SH (8 males and 9 females) and UH (8 males and 9 females) groups and completed 6 cycles of 6 exercises at ~90% of maximal heart rate (i.e. kettlebell snatches; step-up jumps; jumping jacks; front squat; burpees; high knees) 3 d/wk for 4 weeks. SH was performed with 20s:10s work-to-rest ratio, and a 2-minute recovery between cycles, while UH was completed with 10s:5s work-to-rest ratio, and 1-minute recovery. Fat mass (FM), fat free mass (FFM), VL CSA, Wingate anaerobic capacity (i.e. peak power [PP] and anaerobic power [AP]), and aerobic fitness (i.e. VO2max) were measured before and after the intervention and analyzed with 2-way mixed factorial ANOVAs. RESULTS: FM did not significantly (p>0.05) change, however, both groups significantly (p<0.05) improved FFM (UH: 60.8 ± 15.0 to 61.5 ± 15.2 kg, SH: 54.3 ± 11.5 to 55.5 ± 11.0 kg), as well as VL CSA (UH = 24.8 ± 6.2 to 27.1 ± 6.3 cm, SH = 25.6 ± 5.1 to 27.9 ± 5.5 cm). Additionally, anaerobic (UH: PP = 913 ± 305 to 1033 ± 300 W; AP = 11.5 ± 1.1 to 12.6 ± 1.1 W/kg, SH: PP = 839 ± 162 to 887 ± 181 W; AP = 11.8 ± 1.1 to 12.5 ± 1.2 W/kg) and aerobic capacity (UH: VO2max = 35.8 ± 6.9 to 38.9 ± 6.1 ml/kg/min, SH: VO2max = 39.7 ± 9.3 to 42.6 ± 9.1 ml/kg/min) significantly (p<0.05) increased in both groups. There were no significant (p>0.05) differences between groups. CONCLUSION: These results suggest that HIIT at a 10s:5s work-to-rest ratio can improve physical fitness with a shorter time commitment. Future studies are needed to examine a differential effect of these protocols for men versus women. Since the participants would be best categorized as low-fitness, caution is warranted when extrapolating these results to others with higher-fitness levels.

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