PMID 38529482

Research
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High-intensity interval training improves respiratory and cardiovascular adjustments before and after initiation of exercise

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.

Methodology

  • Healthy male college students with no cardiovascular risk factors, normal fitness, and light exercise or sports once or twice weekly.
  • 21 participants.
  • 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.
  • Intensity: 95% maximal work rate.
  • Variable; approximately 6 min 30 s mean high-intensity work plus 6 min recovery between bouts, excluding any unreported setup or cooldown.
  • 1 session per week.
  • 8 weeks.
  • Randomized controlled exercise training study with pre-post ramp exercise, high-intensity step exercise, and echocardiography testing.
  • Maximal oxygen uptake, Maximal work rate, Time to exhaustion, and Heart-rate and ventilatory dynamics were tracked.

Outcomes

Resting systolic blood pressure

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.

Improved

Ramp VO2max

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.

Improved

Ramp maximal work rate

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.

Improved

Step exercise time to exhaustion

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.

Improved

Dynamic HR and ventilation responses

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.

Improved

Left ventricular morphology

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.

Improved

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

  • 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.