Submaximal exercise cardiac output is increased by 4 weeks of sprint interval training in young healthy males with low initial Q-V O2: Importance of cardiac response phenotype
Question
Does baseline inter-individual variation in the cardiac output-to-oxygen uptake relationship determine cardiovascular adaptation to 4 weeks of sprint interval training, and do changes in submaximal cardiac output affect skeletal muscle oxygenation and perceived exertion?
Summary
This uncontrolled 4-week sprint interval training study tested whether young healthy recreationally active men with different baseline cardiac output-to-oxygen uptake responses adapted differently. The protocol was supervised cycling using 8 x 20-second sprints at 170% of peak VO2 work rate, four times per week. Peak VO2 increased in both lower and higher cardiac-response phenotypes, but submaximal cardiac output relative to oxygen uptake increased only in men who started with a low cardiac output response. Skeletal muscle oxygenation and perceived exertion did not improve despite the higher cardiac response.
Methodology
- Healthy recreationally active young adult males with less than 3 hours per week of structured exercise.
- 22 participants.
- Stationary cycle ergometer.
- Work intervals: 20 seconds.
- Recovery: 10 seconds loadless active recovery.
- Intensity: 170% of work rate at peak VO2; 80 rpm target.
- 5-minute warm-up plus 4 minutes of interval exercise; cooldown not reported.
- 4 sessions per week.
- 4 weeks.
- Uncontrolled 4-week pre-post sprint interval training study with post hoc lower and higher cardiac-response phenotype groups.
- Peak VO2, Submaximal cardiac output-to-oxygen uptake relationship, Skeletal muscle oxygenation, and Ratings of perceived exertion were tracked.
Outcomes
Peak VO2
Both lower and higher cardiac responders increased peak VO2 after SIT.
Both P < 0.01; lower responders 39.7 +/- 6.7 to 44.5 +/- 7.3 ml/kg/min; higher responders 47.2 +/- 4.4 to 52.4 +/- 6.0 ml/kg/min.
Q-V O2 slope
Lower cardiac responders increased Q-V O2 after training; higher cardiac responders were unchanged.
Lower P = 0.02; higher P = 0.5; post-training groups no longer differed, P = 0.3.
Submaximal cardiac output and stroke volume
Lower cardiac responders increased cardiac output at 120, 160, and 185 W because stroke volume increased; higher responders had a smaller mixed response.
Lower delta Q: 120 W P = 0.01, 160 W P = 0.04, 185 W P = 0.001; lower delta SV: 120 W P = 0.04, 160 W P = 0.03, 185 W P = 0.003.
Skeletal muscle oxygenation and perceived exertion
Skeletal muscle saturation, leg RPE, and whole-body RPE were unaffected by SIT.
Skeletal muscle saturation F test P = 0.9; leg RPE F test P = 0.7; whole-body RPE F test P = 0.1.
Insights
- A very short supervised cycling SIT protocol improved peak VO2 over 4 weeks in young healthy men.
- Baseline physiology may influence how a person adapts to SIT, so broad claims about identical HIIT responses should be avoided.
- Improved cardiac output response did not reduce perceived exertion or improve measured muscle oxygenation in this study.
- Direct replication for consumer programming is limited by the need for cycle ergometry and peak VO2-based intensity prescription.
Limitations
- Small sample.
- No non-training control group.
- Post hoc phenotype grouping.
- Male-only young healthy recreationally active sample.
- Attendance among completers not reported.
- Some cardiac output measures above 160 W depended on corrected Finometer estimates.
Safety
- One dropout cited headaches as negative side effects associated with training.
- One dropout did not feel well enough to complete the post-training progressive exercise test.
- Participants were young healthy males without smoking history, cardiovascular disease, or hypertension.