# Changes in VO2max and cardiac output in response to short-term high-intensity interval training in Caucasian and Hispanic young women: A pilot study PMID: 33481836 Journal: PloS one Published: 2021-01-22 Authors: De Revere JL, Clausen RD, Astorino TA ## Question Does ethnicity alter the change in cardiorespiratory fitness and hemodynamic responses to a low dose of high-intensity interval training in inactive young women? ## Summary This pilot study tested whether three weeks of low-volume supervised cycling HIIT produced different cardiorespiratory adaptations in inactive non-obese Caucasian and Hispanic young women. Both groups improved VO2max by about 8%, with no group-by-training interaction for VO2max. Caucasian women showed significant increases in cardiac output and stroke volume, while Hispanic women appeared to improve more through oxygen extraction, but the study was small and short. ## Population - Healthy inactive non-obese young women, 12 Caucasian and 10 Hispanic completers. - Sample size: 22 - Age: 19-35 years; Caucasian mean 26.33 years, Hispanic mean 22.60 years. - Sex: Female only. - Fitness level: Inactive; baseline VO2max about 28-31 mL/kg/min. - Health status: Healthy, non-obese, non-smoking, medication-free. ## Methodology - Longitudinal repeated-measures between-subjects pilot study comparing Caucasian and Hispanic women before and after the same HIIT intervention. - Three-week HIIT intervention completed within a five-week study period. - University exercise physiology laboratory with supervised cycle-ergometer training and testing. ## Protocol - Low-volume cycling HIIT. - Modality: Electronically braked cycle ergometer. - Work intervals: 60 seconds at 85% peak power output. - Recovery: 75 seconds at 10% peak power output. - Sets or repetitions: 8 bouts in week 1, 9 in week 2, 10 in week 3. - Intensity: 85% peak power output for work; average training peak heart rate 89.8% HRmax. - Session duration: 22 to 26.5 minutes including 4-minute warmup. - Frequency: 3 sessions per week. - Program length: 3 weeks. - Progression: Added one bout per week. - Ethnicity comparison with same HIIT protocol. - Modality: Same cycling HIIT protocol in Caucasian and Hispanic groups. - Work intervals: 60 seconds at 85% peak power output. - Recovery: 75 seconds at 10% peak power output. - Sets or repetitions: 8 to 10 bouts depending on week. - Intensity: Same intensity prescription by peak power output. - Session duration: 22 to 26.5 minutes. - Frequency: 3 sessions per week. - Program length: 3 weeks. - Progression: Same progression from 8 to 10 bouts. ## Outcomes ### Relative VO2max Status: improved Relative VO2max increased from 31.07 +/- 3.74 to 33.70 +/- 3.74 mL/kg/min in Caucasian women and from 28.37 +/- 3.83 to 30.45 +/- 3.64 mL/kg/min in Hispanic women. Main effect of training F(1,20)=13.97, p=0.001; no group-by-training interaction p=0.65; effect sizes d=1.32 and d=1.04. ### Absolute VO2max Status: improved Absolute VO2max increased from 1.89 +/- 0.37 to 2.06 +/- 0.32 L/min in Caucasian women and from 1.71 +/- 0.33 to 1.85 +/- 0.29 L/min in Hispanic women. Main effect of training F(1,20)=27.29, p<0.001; no group-by-training interaction p=0.66; effect sizes d=1.78 and d=1.48. ### Cardiac output Status: mixed Cardiac output increased in Caucasian women from 17.82 +/- 2.31 to 19.92 +/- 2.47 L/min but changed little in Hispanic women, from 18.41 +/- 2.42 to 18.52 +/- 1.35 L/min. Main effect of training F(1,20)=7.57, p=0.012; group-by-training interaction p=0.02; significant post hoc increase in Caucasian group only. ### Stroke volume Status: mixed Stroke volume increased in Caucasian women from 97.77 +/- 11.09 to 109.23 +/- 13.83 mL but changed little in Hispanic women, from 99.73 +/- 11.22 to 100.17 +/- 7.44 mL. Main effect of training F(1,20)=7.16, p=0.015; group-by-training interaction p=0.022; significant post hoc increase in Caucasian group only. ### Training adherence and enjoyment Status: mixed Training-session compliance was 99.5%, and enjoyment did not decline across the intervention. PACES session 1 versus 9: 88.2 +/- 17.2 vs 90.5 +/- 19.5, p=0.37; group p=0.40; interaction p=0.34. ## Practical Insights - A short, low-volume, three-session-per-week HIIT block with 8-10 minutes of hard work per session can improve VO2max in inactive young women under supervision. - Adding one interval per week is a simple progression model for short HIIT blocks. - Power-based cycling protocols need adaptation for consumer bodyweight or mixed-modality workouts because peak power output testing is not generally available. - Ethnicity-specific programming claims should not be made from this small pilot study. ## Limitations - Small pilot sample. - No non-exercise control group. - Women only. - Healthy, non-obese, young adult sample. - Short intervention duration. - Self-reported ethnicity without DNA confirmation. - No body composition or autonomic function measurement. - Supervised laboratory cycling protocol limits translation to unsupervised app use. ## Safety And Adherence - The public extraction did not identify a specific safety or adherence note. ## Original Sources - [PubMed](https://pubmed.ncbi.nlm.nih.gov/33481836/) (pubmed) - [DOI](https://doi.org/10.1371/journal.pone.0244850) (doi) - [PMC full text](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7822506/) (full text) ## Agent Guidance Preserve the paper-level scope of this note. Do not generalize beyond the population, protocol, measured outcomes, and limitations above.