Effect of self-paced sprint interval training and low-volume HIIT on cardiorespiratory fitness: the role of heart rate and power output
Participants
n=82 previously inactive adults (26M, 56F, age 28 ± 10 yr, BMI 25 ± 3); 6-week crossover with 4-week washout.
Protocol
Two self-paced conditions on WattBikes, 3 sessions/week, without encouragement; a target of >80% HRmax was suggested during intervals: (1) SIT: 4-8 × 30 s with 120 s recovery; (2) LV-HIIT: 6-10 × 1 min with 1 min recovery.
Key Results
VO2peak rose with both: SIT +3.1 ± 0.4, LV-HIIT +2.7 ± 1.2 mL/kg/min (P<0.001); body fat %, aortic pulse wave velocity and 120-min OGTT glucose also improved, with no difference between protocols.
Heart rate reached did not matter: participants in the lowest HR tertile improved VO2peak as much as the highest.
Power reached did matter in LV-HIIT: the top tertile for peak power gained more VO2peak (+4.3 vs +1.8 and +1.9 mL/kg/min, P=0.020).
Practical Application
In 82 previously inactive adults, six weeks of self-paced sprint intervals (4-8 × 30 s) or 1-min intervals (6-10 × 1 min), 3×/week, raised VO2peak by ~3 mL/kg/min with no difference between them; a higher heart rate during the intervals gave no extra gain, while higher peak power in the 1-min format did — for beginners, self-paced intervals work, and pushing the power matters more than chasing a heart-rate number.
Practical flexibility: intervals paced by feel, without fixed power (ERG) targets, still produced meaningful adaptation in untrained people. Whether this holds for trained athletes is untested here.
Limitations
Previously inactive adults — not trained cyclists. Short intervention (6 weeks). No ERG/imposed-power comparison group. The HR and power tertile analysis is secondary and exploratory.
How this entry was checked and changed
Content correction 2026-09-27
Tier 2-3 (trained) -> Tier 0: participants were previously inactive adults.
Added the abstract's numbers (VO2peak +3.1 / +2.7 mL/kg/min) and the secondary finding: higher HR gave no extra VO2peak gain, higher peak power in LV-HIIT did (+4.3 vs ~+1.9).
Sport "cycling, strength, sprint" -> cycling (WattBike intervals).