Higher VO2max fraction during intervals = greater performance gain; %HRmax is an incomplete surrogate
Participants
n=22 well-trained cyclists (19 males, 3 females; VO2max 67.1 ± 6.4 mL/kg/min)
Protocol
9 weeks, 21 interval sessions of 5 × 8 min, conducted at each cyclist's 40-min highest sustainable mean power output (PO40min)
Oxygen uptake measured during every interval session; the % of VO2max attained during the work intervals was related to training adaptations by linear regression
Outcomes: maximal PO in the VO2max test, PO at 4 mmol/L blood lactate, VO2max, and a performance index built from several performance measures
% of maximal heart rate and other session measures were evaluated as alternative markers
full text, checked 2026-09-27: the 8-min work bouts were delivered in more than one intra-interval format (e.g. 30/15, 60/60, constant) with 3 min recovery between bouts
Key Findings
Higher % VO2max during the work intervals → larger improvements in maximal PO during the VO2max test (R² adj = 0.44, p = 0.009), PO at 4 mmol/L lactate (R² adj = 0.25, p = 0.035), the performance index (R² adj = 0.36, p = 0.013) and VO2max itself (R² adj = 0.54, p = 0.029)
% HRmax was related to fewer outcome variables and showed poorer session-to-session repeatability than % VO2max
Authors' conclusion: % VO2max was the measure that best reflected the magnitude of training adaptations
Mechanism — why %HRmax ≠ %VO2max as a marker of HIT effectiveness (interpretation, not measured here)
1
HR is only one component of cardiac output (Q̇ = HR × SV). Stroke volume is not measured by any wearable, so two sessions at the same average HR can differ in Q̇ and VO2 (inference, not tested).
2
VO2 is a more direct measure of the stress on the oxygen transport and utilisation system — closer to the adaptive signal.
3
HR carries day-to-day noise from hydration, residual fatigue, temperature, stress, caffeine and sleep — consistent with the poorer session-to-session repeatability the study reports for % HRmax.
4
Cardiac drift and HR plateauing at very high power can dissociate % HRmax from % VO2max within a session (inference, not tested).
Practical Application
In n=22 well-trained cyclists (VO2max 67.1) doing 21 sessions of 5 × 8 min at 40-min power over 9 weeks with VO2 measured in every session, the % of VO2max sustained in the work intervals predicted the gains: VO2max (R² = 0.54), maximal aerobic power (R² = 0.44), performance index (R² = 0.36) and 4-mmol power (R² = 0.25); % HRmax related to fewer outcomes and repeated worse session to session — the aerobic dose of an interval session is how close to VO2max it runs, and heart rate is only a rough read of that.
Format choice should be guided by which one maximises time near VO2max for the individual (see REF-046 for 30/15 vs 60/60 vs constant at equal mean power).
% HRmax is a usable proxy when no metabolic cart is available — but read it as an *indirect, incomplete* marker. When comparing two HIT sessions by HR, control for confounders first: hydration, ambient temperature, caffeine timing, prior-day load, sleep.
Power-based dose (time at/above a set % of PO40min or MAP) is the most robust field-side surrogate; HR provides complementary internal-load context.
Limitations
Well-trained, mostly male sample (19M/3F, VO2max 67) — generalisation to masters athletes (≥40 yrs) and lower-trained athletes should be cautious; HR–VO2 dissociation may be stronger in older athletes due to reduced HRmax and altered β-adrenergic responsiveness (inference).
Single-arm regression design: the % VO2max–adaptation link is correlational within one programme, not a randomised comparison of formats.
Same 5×8-min framework throughout — the relationship may differ for very short or very long formats.
Stroke volume not measured directly → mechanism for %HRmax under-prediction inferred, not proven.
Lab measurement of VO2 during every session is impractical in the field — practical implementation still relies on imperfect HR/power proxies.
How this entry was checked and changed
Why this level
regraded 2026-09-27 from A: single-arm training study, n=22
Content correction 2026-09-27
n=30, "~21 yrs, VO2max ~70" -> n=22 (19 males, 3 females), VO2max 67.1 ± 6.4; age is not in the abstract.
"Three alternating formats", "~9 h/wk, 2-3 HIT/wk", "3 min recovery at 35% PO40min" -> not in the abstract; the formats are kept only as a full-text note.
"%HRmax did not reach significance" -> the abstract says %HRmax related to fewer outcome variables with poorer session-to-session repeatability. Added: performance index R² = 0.36 and VO2max R² = 0.54. Tier set to 3.
Cross-reference descriptions checked against the cited entries' current content; wrong years, wrong entries and claims the cited entry does not make were corrected.
Lines labelled "full text; not checked against the abstract" were checked against the open-access full text (PMC11534653): every number in them appears there; relabelled "full text, checked 2026-09-27".
Full text (checked 2026-10-12)
Thirty participants were recruited and eight withdrew (sickness n = 5, injury n = 1, personal reasons n = 2), leaving 22 (19 men, 3 women) with 3.7 (2.9) years of competitive cycling and a mean age of 22.6 (6.0) years (full text, Table 1).
The 8-min work intervals changed by 3-week period: 30-s at 118% and 15-s at 60% of PO40min, then 60-s alternating 110% and 90% of PO40min, then constant at 100% of PO40min, with 3-min active recovery at 35% of PO40min; each participant averaged 20.6 (0.8) sessions (full text).
If RPE after the fifth work interval was ≤15, the % of PO40min at the next session was raised by 2%-points (full text).
Average % of VO2max during the work intervals ranged from 74.2%–90.8% across participants, with means of 86.2 (3.8)% in the HIGH%VO2max half and 79.9 (4.0)% in the LOW%VO2max half (full text).
HIGH%VO2max vs LOW%VO2max gained more VO2max (5.23 (2.76) versus 1.78 (1.72) mL·min−1 kg−1; p = 0.003), Wmax (0.51 (0.33) versus 0.23 (0.14) W·kg−1; p = 0.022) and PO4mmol (0.31 (0.15) versus 0.12 (0.18) W·kg−1; p = 0.015) (full text).
Session-to-session ICC across the 21 sessions was 0.61 for % of VO2max, 0.56 for time ≥90% of VO2max, 0.31 for % of HRmax and 0.24 for time ≥90% of HRmax (full text).
% of HRmax during intervals was positively related only to the change in the performance index, with a tendency for PO4mmol (full text).
Mean total training during the intervention was 08:41 (02:36) h:m per week, including 00:30 (00:21) h:m in zone 5 (>106% of PO40min) (full text, Table 2).