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Updated: May 5, 2026
A Real-World High-Intensity Interval Training Protocol for Cardiorespiratory Fitness Improvement
Published on: February 22, 2022
Short-term high-intensity interval and continuous moderate-intensity training improve maximal aerobic power and
Sam Esfandiari1, Zion Sasson, Jack M Goodman
1Faculty of Kinesiology and Physical Education, University of Toronto, 55 Harbord Street, Toronto, ON, M5S 2W6, Canada.
Purpose:
This study examined the effects of short-term high-intensity interval training (HIT) and continuous moderate-intensity training (CMT) on cardiac function in young, healthy men.
Methods:
Sixteen previously untrained men (mean age of 25.1 ± 4.1 years) were randomly assigned to HIT and CMT (n = 8 each) and assessed before and after six sessions over a 12-day training period. HIT consisted of 8-12 intervals of cycling for 60 s at 95-100% of pre-training maximal aerobic power (VO(2max)), interspersed by 75 s of cycling at 10% VO(2max). CMT involved 90-120 min of cycling at 65% pre-training VO(2max). Left ventricular (LV) function was determined at rest and during submaximal exercise (heart rate ~105 bpm) using two-dimensional and Doppler echocardiography.
Results:
Training resulted in increased calculated plasma volume (PV) in both groups, accompanied by improved VO(2max) in HIT (HIT: from 39.5 ± 7.1 to 43.9 ± 5.5 mL kg(-1) min(-1); CMT: from 39.9 ± 5.9 to 41.7 ± 5.3 mL kg(-1) min(-1); P < 0.001). Resting LV function was not altered. However, increased exercise stroke volume (P = 0.02) and cardiac output (P = 0.02) were observed, secondary to increases in end-diastolic volume (P < 0.001). Numerous Doppler and speckle tracking indices of diastolic function were similarly enhanced during exercise in both training groups and were related to changes in PV.
Conclusion:
Short-term HIT and CMT elicit rapid improvements in VO2max and LV filling without global changes in cardiac performance at rest.
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