Effect of self-paced sprint interval training and low-volume HIIT on cardiorespiratory fitness: the role of heart rate and power output
Question
Do self-paced SIT and LV-HIIT performed without encouragement improve cardiorespiratory fitness, and do heart-rate or power responses explain adaptation?
Summary
In 82 previously inactive adults, both 6-week self-paced sprint interval cycling and low-volume HIIT cycling improved VO2peak and cardiometabolic markers, with no meaningful difference between protocols. Higher heart-rate responses did not produce superior VO2peak gains, while higher power output during LV-HIIT was associated with larger VO2peak improvement.
Methodology
- Previously inactive adults, mostly women, with low coronary heart disease risk and BMI <=32 kg/m2
- 82 participants.
- Wattbike cycling.
- Work intervals: 30 seconds.
- Recovery: 120 seconds active recovery.
- Intensity: >80% predicted HRmax, all-out recommended.
- 10-20 minutes plus 5-minute warm-up.
- 3 sessions/week.
- 6 weeks.
- Randomized counterbalanced crossover training study
- VO2peak, Body fat, Arterial stiffness, and Glucose tolerance were tracked.
Outcomes
VO2peak
Both SIT and LV-HIIT increased VO2peak, with no protocol difference.
SIT +3.1 +/- 0.4 and LV-HIIT +2.7 +/- 1.2 mL/kg/min; p<0.001.
Cardiometabolic
Body fat percentage, aortic pulse wave velocity, and 120-minute glucose tolerance improved across training.
Body fat p=0.002; aPWV p=0.002; OGTT 120-min glucose p=0.024.
Heart rate
Higher heart-rate tertiles did not show superior VO2peak changes.
Low versus high HR groups p>0.05.
Power output
For LV-HIIT, the highest peak power tertile had greater VO2peak improvement.
Low 1.8 +/- 4.1, medium 1.9 +/- 3.3, high 4.3 +/- 3.6 mL/kg/min; p=0.020.
Insights
- Self-paced hard cycling intervals can improve VO2peak without verbal encouragement.
- Heart-rate targets may help guide effort but do not fully represent training stimulus.
Limitations
- No non-exercise control group
- Lab-based sessions
- Cycling-only
- No long-term adherence follow-up
Safety
- Article did not report adverse events or injuries.
- Participants were screened as low CHD risk by Framingham risk score, BMI <=32 kg/m2, and pregnant/breastfeeding participants were excluded.
- All sessions were lab based with HR monitoring and HR feedback; withdrawal criteria were <90% session completion or <2 sessions/week. Intensity compliance included peak HR >80% HRmax in 81% of SIT and 94% of LV-HIIT sessions.