# High-intensity interval training improves respiratory and cardiovascular adjustments before and after initiation of exercise PMID: 38529482 Journal: Frontiers in physiology Published: 2024-03-11 Authors: Ito G, Feeley M, Sawai T, Nakata H, Otsuki S, Nakahara H, Miyamoto T ## Question Does 8 weeks of once-weekly HIIT at 95% WRmax improve time-dependent cardiorespiratory responses before and after initiation of ramp and high-intensity step exercise, maximal exercise performance, and cardiac morphology in healthy young men? ## Summary This randomized controlled study assigned 21 healthy male college students to once-weekly cycle-ergometer HIIT or control for 8 weeks. Each HIIT session used three exhaustive bouts at 95% maximal work rate with 3-min recovery between bouts. Compared with controls, HIIT improved maximal oxygen uptake and maximal work rate in a ramp test, greatly increased time to exhaustion in a 95% WRmax step test, lowered resting systolic blood pressure, and altered heart-rate and ventilatory responses around exercise onset. ## Population - Healthy male college students with no cardiovascular risk factors, normal fitness, and light exercise or sports once or twice weekly. - Sample size: 21 - Age: HIIT 21 +/- 1 years; control 21 +/- 2 years. - Sex: All male. - Fitness level: Normal fitness, not well-trained athletes; baseline ramp VO2max about 3158 +/- 646 mL/min in HIIT and 3134 +/- 470 mL/min in controls. - Health status: Healthy, no cardiovascular risk factors. ## Methodology - Randomized controlled exercise training study with pre-post ramp exercise, high-intensity step exercise, and echocardiography testing. - 8 weeks - Laboratory-based cycle-ergometer training and exercise testing. - Randomized and controlled study design. ## Protocol - Once-weekly 95% WRmax cycling HIIT. - Modality: Bicycle ergometer. - Work intervals: Exercise at 95% maximal work rate until exhaustion; mean time to exhaustion during interval training was 2 min 10 s. - Recovery: 3 minutes between bouts: 2 min active recovery at 0 W, then 1 min rest. - Sets or repetitions: 3 bouts. - Intensity: 95% maximal work rate. - Session duration: Variable; approximately 6 min 30 s mean high-intensity work plus 6 min recovery between bouts, excluding any unreported setup or cooldown. - Frequency: 1 session per week. - Program length: 8 weeks. - No-training control. - Frequency: No exercise training beyond routine activities. - Program length: 8 weeks. ## Outcomes ### Resting systolic blood pressure Status: improved Resting SBP in HIIT decreased from 124 +/- 10 to 116 +/- 11 mmHg; control changed from 123 +/- 7 to 122 +/- 6 mmHg. HIIT pre-post P = 0.004; group x training interaction P = 0.026. ### Ramp VO2max Status: improved Ramp VO2max increased in HIIT from 3158 +/- 646 to 3518 +/- 437 mL/min, while control changed from 3134 +/- 470 to 3087 +/- 365 mL/min. Group x training interaction P = 0.008; table marks HIIT post value P < 0.01 vs pre. ### Ramp maximal work rate Status: improved WRmax increased in HIIT from 294 +/- 40 to 330 +/- 42 W, while control changed from 269 +/- 20 to 270 +/- 24 W. Group x training interaction P = 0.001; table marks HIIT post value P < 0.001 vs pre. ### Step exercise time to exhaustion Status: improved Time to exhaustion increased in HIIT from 130 +/- 16 to 249 +/- 44 s, while control changed from 137 +/- 30 to 151 +/- 29 s. Group x training interaction P < 0.001; table marks HIIT post value P < 0.001 vs pre. ### Dynamic HR and ventilation responses Status: improved HIIT enhanced time-dependent HR before exercise and HR and VE responses during the initial 0-30 s after step exercise onset; the VO2-HR slope during ramp exercise decreased after HIIT. HR resting period -10 to 0 s group x training interaction/main effects P = 0.020; HR 0-10 s P < 0.001, 10-20 s P < 0.001, 20-30 s P = 0.031; VE 0-10 s P = 0.009; VO2-HR slope P = 0.016 in HIIT. ### Left ventricular morphology Status: improved Posterior wall thickness increased from 0.99 +/- 0.13 to 1.09 +/- 0.14 cm and LV mass from 262 +/- 52 to 303 +/- 63 g in HIIT; no comparable control change was observed. Group x training interaction P < 0.001 for PWT and LV mass; HIIT PWT P = 0.001 and LV mass P < 0.001 vs pre. ## Practical Insights - Once-weekly severe-intensity cycling HIIT produced measurable VO2max and performance adaptations in healthy young men, showing that high intensity can partly compensate for low weekly frequency in this narrow context. - The protocol is not a general beginner prescription because work bouts were exhaustive at 95% WRmax and required controlled equipment and strong motivation. - Performance improvements in high-intensity tolerance can be much larger than VO2max improvements, so HIIT outcomes should not be reduced to VO2max alone. ## Limitations - Small sample size. - All participants were healthy young men; women and older participants were excluded. - Findings may not apply to well-trained athletes, low-fitness persons, less motivated users, or clinical populations. - Protocol required maximal work-rate testing and severe exhaustive cycling. - Attendance, completion rate, dropout rate, and adverse event surveillance details were not clearly reported. ## Safety And Adherence - No adverse events were reported in the article. - Authors state less motivated subjects, persons with low fitness, or patients with diseases may have difficulty performing severe-intensity interval training. - All participants were healthy male college students without cardiovascular risk factors. ## Original Sources - [PubMed](https://pubmed.ncbi.nlm.nih.gov/38529482/) (pubmed) - [DOI](https://doi.org/10.3389/fphys.2024.1227316) (doi) - [PMC full text](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC10961378/) (full text) ## Agent Guidance Preserve the paper-level scope of this note. Do not generalize beyond the population, protocol, measured outcomes, and limitations above.