REF-1555 · Torvik et al., 2025 · Frontiers in Physiology · Paper · PubMed · Free full text

How much does 2 h easy drift?

In 12 national-level women on roller skis, little by what was reported: breathing up about 2 breaths/min in one gear, RPE up about 0.6. No heart rate in the abstract, no split comparison, one session.

Main caveat: Abstract only for now. The article is open (CC BY) in PubMed Central, but the copy could not be opened when this entry was written, so methods, heart-rate data…
limited, mixed evidenceMeasured on highly trained athletes

Twelve national-level female cross-country skiers did one 2-hour low-intensity session, roller-ski skating in the laboratory and alternating between Gear-2 and Gear-3.

Oxygen uptake, carbon dioxide output, ventilation, breathing frequency, exchange ratio, blood lactate, RPE, cycle length and cycle rate were collected at four consecutive points (T1 to T4) in each gear, with a questionnaire afterwards. Changes were small for most physiological measures.

The most pronounced were main effects of time on two measures; whether others also had one is not stated. Breathing frequency: in Gear-3, 45.5 ± 7.7 at both T2 and T3 against 43.2 ± 7.3 breaths/min at T1. RPE: 12.1 ± 1.0 and 12.2 ± 1.1 at T2 and T3 against 11.5 ± 1.2 at T1 in Gear-2, and 11.2 ± 1.6 at T2 and T3 against 10.6 ± 1.2 at T1 in Gear-3.

Cycle length and rate showed no clear difference across time points, and neither did perceived total, ventilatory or mental exertion or perceived quality between the two halves. Our reading: at this low intensity for 2 h, these women moved little by the measures reported.

That limits how far the drift seen in harder continuous work (REF-159, moderate intensity, men, running) can be carried into easy volume, though the two studies differ in sex, sport, intensity and measures, so it is a limit on transfer and not a contradiction.

Protocol

Who: as above.
Session: 2 h at low intensity, roller-ski skating in the laboratory, alternating Gear-2 and Gear-3.
Measures: VO2, VCO2, ventilation, breathing frequency, respiratory exchange ratio, blood lactate, RPE, cycle length, cycle rate at T1 to T4 for each sub-technique; a post-session questionnaire on total, ventilatory and mental exertion and on training quality.
Not in the abstract: how intensity or speed was set, feeding, hydration, temperature, the lengths of each gear block, or the timing of T1 to T4.
Funding and interests: the authors declare no potential conflict of interest (PubMed). Funding is not in the abstract.

Key Results

MeasureT1T2T3Test
Breathing frequency, Gear-3 (breaths/min)43.2 ± 7.345.5 ± 7.745.5 ± 7.7time F(3,30) = 3.52, ηp2 = 0.260, P = 0.027
RPE, Gear-211.5 ± 1.212.1 ± 1.012.2 ± 1.1time F(3,33) = 4.43, ηp2 = 0.287, P = 0.010
RPE, Gear-310.6 ± 1.211.2 ± 1.611.2 ± 1.6same main effect
Cycle length, cycle rateno clear difference T1 to T4
Perceived total, ventilatory, mental exertion; perceived qualityno clear difference between halves
T4 is not printed. The abstract gives no T4 values, so whether breathing or RPE kept rising, or settled, is not known from what was read.
Other physiology is only summarised. "Relatively small" changes are not given as numbers for VO2, ventilation, lactate or exchange ratio.
Degrees of freedom (our reading). F(3,30) for breathing frequency implies 11 participants in that test, against 12 for RPE.
Identical values appear at T2 and T3 for Gear-3 breathing frequency and RPE, as printed; they could be a coincidence or a slip.

Mechanisms

Measured: small shifts in breathing and perception with duration, and no clear change in technique markers.
Authors' interpretation: the session could be held for 2 h with little physiological, perceptual or technical change.
Not measured, on the abstract: heart rate, muscle glycogen, any marker of adaptation, performance afterwards, and what happens beyond 2 h.

Practical Application

How much does 2 h easy drift? In 12 national-level women on roller skis, little by what was reported: breathing up about 2 breaths/min in one gear, RPE up about 0.6. No heart rate in the abstract, no split comparison, one session.
Good for: reassurance that a 2-h low-intensity session need not move much within itself, for trained women on skis and on the measures reported (no heart rate, no printed T4), and for limiting a claim that a long easy session must produce large drift.
Not good for: deciding on one long session against two short ones. That was not tested here; see REF-1331 for skiers.
Not good for: claiming long easy sessions have no extra effect. No adaptation or fatigue test was done; small drift within a session does not speak to what the session builds.
Not good for: cyclists or men, or sessions past 2 h.
Not from this paper: how long an easy session should be. That judgement stays with the base's durability guide.

Limitations

Abstract only for now. The article is open (CC BY) in PubMed Central, but the copy could not be opened when this entry was written, so methods, heart-rate data if any, T4 values and funding were not read. Rechecking is needed.
Single session, no control. No matched rest or split condition; time and gear are the only factors.
No men, and women's cycle phase is not addressed in the abstract.
n = 12, with a null by questionnaire between halves that cannot prove equality.
Sport and laboratory. Skating on roller skis in a laboratory, with switching between gears, is not cycling or running, and the switches themselves could change the load (inference).
Measures differ from the drift literature: with no heart rate reported in the abstract, comparison with heart-rate drift studies is indirect.
How this entry was checked and changed
Why this level

(from the abstract) — an uncontrolled single-group study earns B by design, lowered one step because it describes the response to one session rather than performance or adaptation, and because the open copy in PubMed Central could not be opened when this entry was written, so methods beyond the abstract were not read