Table 4. Acute responses to the short and long HIIT and CE as well as the between-group differences (warm-up and cool-down excluded).
Endurance AthletesMean ± SD Sprint AthletesMean ± SD Difference (sprint – endurance athletes)
Mean;90% CI Inferencea
Mean HR (bpm) HIIT 30 s 158.1 ± 14.2 158.4 ± 17.8 0.4; ± 14.3 trivial
HIIT 3 min 160.5 ± 12.2 163.6 ± 13.4 3.1; ± 11.4 small
CE 133.6 ± 12.0 135.4 ± 11.8 1.8; ± 10.5 trivial
Mean HR(% HRmax) HIIT 30 s 79.7 ± 5.0 80.2 ± 6.5 0.6; ± 5.1 trivial
HIIT 3 min 80.9 ± 4.5 82.9 ± 3.3 1.9; ± 3.5 small
CE 67.4 ± 4.0 68.6 ± 4.3 1.3; ± 3.7 small
Mean O2(mL/kg/min) HIIT 30 s 39.4 ± 2.3 35.1 ± 2.5 -4.4; ± 2.1 large****
HIIT 3 min 43.5 ± 3.4 37.4 ± 2.1 -6.1; ± 2.5 very large****
CE 32.9 ± 2.8 29.7 ± 2.8 -3.2; ± 2.5 moderate***
Mean O2(% O2max) HIIT 30 s 59.7 ± 3.7 62.1 ± 5.8 2.4; ± 4.4 small
HIIT 3 min 66.0 ± 6.6 66.3 ± 5.8 0.3; ± 5.5 trivial
CE 49.8 ± 4.1 52.6 ± 6.3 2.8; ± 4.7 small
Mean RER HIIT 30 s 0.84 ± 0.03 0.86 ± 0.02 0.0; ± 0.0 moderate**
HIIT 3 min 0.93 ± 0.03 0.97 ± 0.02 0.0; ± 0.0 large***
CE 0.81 ± 0.02 0.83 ± 0.04 0.0; ± 0.0 moderate**
RPE HIIT 30 s 12.3 ± 1.5 12.3 ± 1.3 0.0; ± 1.2 trivial
HIIT 3 min 17.3 ± 1.3 15.5 ± 2.4 -1.8; ± 1.7 moderate**
CE 8.6 ± 1.3 8.9 ± 1.6 0.1; ± 1.3 trivial
HIIT – high-intensity interval exercise, CE – constant load exercise, HR – heart rate, V̇O2 – oxygen consumption, RER – respiratory exchange ratio, RPE – rating of perceived exertion.
aMagnitude thresholds (for difference in means divided by average SD): <0.20, trivial; 0.20-0.59, small; 0.60-1.19, moderate; 1.20-2.00, large; 2.01-4.00, very large. Asterisks indicate effects clear at the 90% level and likelihood that the true effect is substantial, as follows: *possible, **likely, ***very likely, ****most likely. No asterisks mean that 90% CL overlapped the thresholds for substantiveness (unclear difference).