REF-180 · Stevenson et al., 2024 · European Journal of Applied Physiology, · Paper

Prolonged Exercise Shifts Ventilatory Parameters at the Moderate-to-Heavy Intensity Transition

Blimited evidenceMeasured on trained to highly trained athletesWritten before October 2026, being re-checked

Continuation of Stevenson 2022 (REF-179). Fourteen endurance-trained cyclists and triathletes (one female) had the moderate-to-heavy transition (first ventilatory threshold, VT1) assessed before and after two hours of moderate-intensity cycling. As previously reported, power at VT1 fell by ~10% from PRE to POST.

Minute ventilation (VE) at VT1 was unchanged (72 ± 12 vs 69 ± 13 L/min; Δ −3 ± 5 L/min, −4 ± 8%, P = 0.075) and consistent within subjects (CV 5.4% [3.7, 8.0%]).

That same VE was produced differently after two hours: breathing frequency rose (27.6 ± 5.8 → 31.9 ± 6.5 breaths/min, +16 ± 11%, P = 0.0002) and tidal volume fell (2.62 ± 0.43 → 2.19 ± 0.36 L/breath, −16 ± 7%, P = 0.0002).

Conclusion: prolonged exercise shifts the ventilatory pattern at the boundary, but VE itself stays stable, so real-time VE monitoring may be a useful way to judge proximity to the moderate-heavy transition late in a ride — flagged by the authors as worthy of further research.

Participants

n=14 endurance-trained cyclists and triathletes (one female)

Protocol

Within-subject pre/post design: fourteen endurance-trained cyclists and triathletes (one female) (from the abstract).
The moderate-to-heavy intensity transition, determined as the first ventilatory threshold (VT1), was assessed before (PRE) and after (POST) two hours of moderate-intensity cycling.
Measures at VT1, PRE and POST: power output, minute ventilation (VE), breathing frequency and tidal volume; within-subject coefficient of variation of VE at VT1.

Key Results

Parameter at VT1PREPOST (2 h)Changep
Power output——~ −10% (as previously reported)significant
VE (L/min)72 ± 1269 ± 13−3 ± 5 (−4 ± 8%)0.075 (NS)
Breathing frequency (breaths/min)27.6 ± 5.831.9 ± 6.5+4.3 ± 3.1 (+16 ± 11%)0.0002
Tidal volume (L/breath)2.62 ± 0.432.19 ± 0.36−0.44 ± 0.22 (−16 ± 7%)0.0002
Within-subject CV of VE at VT15.4% (3.7-8.0%)

Practical Application

After 2 h of moderate cycling in 14 trained cyclists/triathletes, power at the first ventilatory threshold fell ~10% but ventilation at VT1 did not move (72 ± 12 → 69 ± 13 L/min, P = 0.075; within-subject CV 5.4%), achieved with faster (+16%) and shallower (−16%) breaths — so breathing volume, not watts, is the stable marker of the moderate-heavy boundary late in a long ride (pre/post study, Stevenson 2024).
Do not trust a fixed wattage as a domain marker after 2+ hours: the power that sat in the moderate domain early can be heavy late. The boundary moved, not the athlete's discipline.
Inference, not tested here: because VE at the boundary is stable while breathing gets faster and shallower, a talk test (full sentences = still moderate; laboured, broken speech = heavy) is a reasonable field proxy for the VE signal the authors propose monitoring; the study measured VE, not speech.
Not from this paper; the base's own practice: HR/power decoupling (a drift above ~5%) and RPE are used as cross-checks for the same moderate→heavy shift; this study reports neither.

Limitations

From the design as the abstract reports it: a single-group pre/post comparison with no control condition described; fourteen participants, only one of them female.
One exposure tested: two hours of moderate-intensity cycling; other durations and intensities were not examined.
The power drop at VT1 (~10%) is given "as previously reported", without its own values in this abstract.
Real-time VE monitoring is the authors' proposal, "worthy of further research" in their words — it was not tested as a guidance tool here.
How this entry was checked and changed
Why this level

regraded 2026-09-27 from B+: uncontrolled pre-post design, n=14

Content correction 2026-09-27
Table row "Power at VT1 … p <0.001" -> abstract reports only "significantly decreased by ~10%, as previously reported"; p-value removed.
Added the abstract's breathing-frequency (27.6 → 31.9/min) and tidal-volume (2.62 → 2.19 L) shifts, both P = 0.0002.
Talk test relabelled as inference; ~5% decoupling rule relabelled as the base's own practice.
Level B+ -> B (uncontrolled within-subject pre/post, n=14).
2026-09-28: added Protocol and Limitations from the abstract (Europe PMC, DOI 10.1007/s00421-023-05285-2, PMID 37495864).