Incline Treadmill Interval Training: Short vs. Long Bouts and the Effects on Distance Running Performance

This study compared 6 weeks of incline treadmill interval training (INC) performed on a 10% treadmill grade using either sprint-like efforts or slower, longer bouts. 24 individuals were randomly assigned between 2 groups that each completed 2 INC and one 30-min level-grade sessions∙wk^-1. Training intensities, bout durations and the number of intervals per INC session were the velocity associated with VO₂max (Vmax), 30 s and 10-14 (INC_Short n=12), and 68%Vmax, ~3 min and 4-6 (INC_Long n=12), respectively. All 30-min sessions were at 65%Vmax. Pre- and post-testing assessed VO₂max; lactate threshold (V_LT); running economy; and time-to-exhaustion at various conditions including 80%Vmax and 20% grade (CF_Mod). Both groups improved significantly in all tests; additionally, INC_Short improved significantly more so in V_LT and CF_Mod despite INC_Long performing more than 2 times the running each INC session (P<0.05). Mean effect size (ES) of the relative improvement in a majority of tests revealed a trivial to very large ES of INC_Short vs. INC_Long training (ES range: 0.05-4.05). We conclude sprint-like INC better than slower, longer INC at improving a key determinant of distance running performance (V_LT), and better at preparing individuals for running on courses with a variety of grades.