High-Intensity Interval Training Increases Cardiac Output and V˙O2max.
Increases in maximal oxygen uptake (V˙O2max) frequently occur with high-intensity interval training (HIIT), yet the specific adaptation explaining this result remains elusive.



This study examined changes in V˙O2max and cardiac output (CO) in response to periodized HIIT.



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.



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.



Increases in V˙O2max exhibited in response to different HIIT regimes are due to improvements in oxygen delivery.
1Department of Kinesiology, California State University, San Marcos, San Marcos, CA; 2Department of Physical Therapy, SUNY, Stony Brook, Stony Brook, NY; and 3National College of Natural Medicine, Portland, OR.
Todd A
TA
Astorino
Ross M
RM
Edmunds
Amy
A
Clark
Leesa
L
King
Rachael A
RA
Gallant
Samantha
S
Namm
Anthony
A
Fischer
Kimi M
KM
Wood
D000328:Adult; D001823:Body Composition / Q000502:physiology; D002302:Cardiac Output / Q000502:physiology*; D005260:Female; D006439:Hemodynamics / Q000502:physiology; D000072696:High-Intensity Interval Training; D006801:Humans; D008297:Male; D010101:Oxygen Consumption / Q000502:physiology*; D011659:Pulmonary Gas Exchange / Q000502:physiology; D055815:Young Adult