High-intensity interval training significantly increased V˙O2max across different regimes compared with nonexercising controls (P<0.001), driven by improvements in maximal cardiac output (P=0.04).
RCT (n=71)
Randomized
Does high-intensity interval training increase maximal oxygen uptake and cardiac output in active men and women?
High-intensity interval training significantly increases maximal oxygen uptake in active individuals, primarily driven by improvements in maximal cardiac output and stroke volume rather than changes in heart rate or arteriovenous oxygen difference.
p-value: p=<0.001
Increases in maximal oxygen uptake (V˙O2max) frequently occur with high-intensity interval training (HIIT), yet the specific adaptation explaining this result remains elusive. PURPOSE: This study examined changes in V˙O2max and cardiac output (CO) in response to periodized HIIT. METHODS: Thirty-nine active men and women (mean age and V˙O2max = 22.9 ± 5.4 yr and 39.6 ± 5.6 mL·kg·min) performed HIIT and 32 men and women (age and V˙O2max = 25.7 ± 4.5 yr and 40.7 ± 5.2 mL·kg·min) were nonexercising controls (CON). The first 10 sessions of HIIT required eight to ten 60 s bouts of cycling at 90%-110% percent peak power output interspersed with 75 s recovery, followed by randomization to one of three regimes (sprint interval training (SIT), high-volume interval training (HIITHI), or periodized interval training (PER) for the subsequent 10 sessions. Before, midway, and at the end of training, progressive cycling to exhaustion was completed during which V˙O2max and maximal CO were estimated. RESULTS: Compared with CON, significant (P < 0.001) increases in V˙O2max in HIIT + SIT (39.8 ± 7.3 mL·kg·min to 43.6 ± 6.1 mL·kg·min), HIIT + HIITHI (41.1 ± 4.9 mL·kg·min to 44.6 ± 7.0 mL·kg·min), and HIIT + PER (39.5 ± 5.6 mL·kg·min to 44.1 ± 5.4 mL·kg·min) occurred which were mediated by significant increases in maximal CO (20.0 ± 3.1 L·min to 21.7 ± 3.2 L·min, P = 0.04). Maximal stroke volume was increased with HIIT (P = 0.04), although there was no change in maximal HR (P = 0.88) or arteriovenous O2 difference (P = 0.36). These CO data are accurate and represent the mean changes from pre- to post-HIIT across all three training groups. CONCLUSIONS: Increases in V˙O2max exhibited in response to different HIIT regimes are due to improvements in oxygen delivery.
Astorino et al. (Sat,) conducted a rct in Healthy active adults (n=71). High-intensity interval training (HIIT) vs. Nonexercising controls was evaluated on V˙O2max and maximal cardiac output (p=<0.001). High-intensity interval training significantly increased V˙O2max across different regimes compared with nonexercising controls (P<0.001), driven by improvements in maximal cardiac output (P=0.04).