REF-1331 · Kjøsen Talsnes et al., 2022 · International Journal of Sports Physiology and Performance · Paper · PubMed

One 3-hour easy session or two 1.5-hour ones?

13 national-level skiers skied the split 1.9% faster, no significant heart-rate difference; RPE rose late in the long one as speed rose; stress 7 and 23 h later did not differ. Acute.

Main caveat: Abstract only: the skiers' sex, age and fitness, how low intensity was defined, the course, timing of sessions, food and drink, absolute values and the stress…
limited, mixed evidenceMeasured on highly trained athletes

Kjøsen Talsnes and colleagues (Meråker High School, Nord University, NTNU) compared one long low-intensity training (LIT) session with the same distance done as two shorter sessions in one day.

Thirteen national-level cross-country skiers did both, in counterbalanced order, on classical roller skis: one session of about 3 h (1LIT) or two of about 1.5 h with 7 h of recovery between them (2LIT). Speed was self-selected; speed, heart rate, RPE and blood lactate were measured, and perceived training stress (1-10) was rated after the sessions.

The split was skied at a 1.9% (SD 2.0%) higher speed than the long session (P ≤ .01); speed also rose from the first to the second session of 2LIT (1.9% [3.2%]) and from the first to the second half of 1LIT (3.2% [3.6%]). Heart rate did not differ between the two formats.

RPE rose 0.9 (0.8) point from the first to the second half of the long session, and lactate fell by about 0.16 (0.20) mmol/L from the first to the second part in both formats. Perceived muscular exertion was 2.0 (1.1) points higher straight after the long session, but perceived training stress 7 and 23 h after training did not differ.

The authors conclude that skiers do a split LIT day slightly faster for the same physiological response, with minor differences in perceived stress.

Our reading: at low intensity the long session's extra cost was small and short-lived — unlike the moderate-intensity version (REF-159), where the single session left more next-morning fatigue — so the choice between one long and two short easy sessions can rest on what each is for.

Protocol

Design: counterbalanced crossover; two LIT types on separate days, matched for distance.
Participants: n = 13 national-level cross-country skiers; sex, age, VO2max and training volume are not given in the abstract.
Conditions: 1LIT — one session of approximately 3 h; 2LIT — two sessions of approximately 1.5 h each with 7 h of recovery between them; classical roller-skiing; speed self-selected (the abstract does not say how "low intensity" was instructed or verified, nor the terrain).
Measures: speed, heart rate, RPE and blood lactate during the sessions; perceived training stress (1-10) after the sessions, at 7 h and at 23 h; perceived muscular exertion directly after.
Funding and interests: not given in the abstract; Crossref lists no funder.

Key Results

ComparisonResult (mean [SD])P
Speed, 2LIT vs 1LIT2LIT 1.9% (2.0%) faster≤ .01
Speed, second vs first session of 2LIT+1.9% (3.2%)≤ .01
Speed, second vs first half of 1LIT+3.2% (3.6%)≤ .01
Heart rate, 2LIT vs 1LITno significant difference—
RPE, second vs first half of 1LIT+0.9 (0.8) point≤ .01
Blood lactate, second vs first part (both formats)about −0.16 (0.20) mmol/L≤ .05
Perceived muscular exertion, directly after2.0 (1.1) points higher after 1LIT≤ .01
Perceived training stress 7 h and 23 h afterno difference between formats—
What the abstract does not report: absolute speeds, heart rates, RPE or lactate values; whether heart rate rose within the long session; the stress scores themselves; sex and fitness of the skiers.

Mechanisms

Measured (abstract): with no significant heart-rate difference the skiers chose a slightly higher speed when the distance was split; within the long session both speed and RPE rose from the first to the second half while lactate fell.
Authors' interpretation: the split elicits the same physiological response at slightly higher self-selected speed, with minor differences in perceived training stress.
Inference: because speed was free, any extra cost of the long session showed as a slightly slower overall speed and a higher RPE late on, not as a higher heart rate. The RPE rise in the second half came with a 3.2% faster speed, so it cannot all be read as fatigue.
Inference: in REF-159 (moderate intensity, fixed external load, well-trained runners) heart rate, lactate and RPE drifted up within the long session and next-morning fatigue was higher; here, at low intensity and self-selected speed, lactate fell and stress at 7 and 23 h did not differ. Intensity, not only duration, seems to set how costly the long version is.

Practical Application

One 3-hour easy session or two 1.5-hour ones? 13 national-level skiers skied the split 1.9% faster, no significant heart-rate difference; RPE rose late in the long one as speed rose; stress 7 and 23 h later did not differ. Acute.
At low intensity, the long session cost no more the next day than the same distance split: perceived training stress at 7 and 23 h did not differ between formats and heart rate showed no significant difference (B-, from the abstract, national-level skiers; one day each; no evidence of a difference, not proof of none). Inference: an easy long session need not sit further from an ordinary training day than an easy double.
The split buys a little speed with no significant heart-rate difference, the long session buys time on the feet: the double was skied 1.9% faster; what the long session alone gives (hour three, fuelling and pacing late) was not measured.Not from this paper; the base's own practice: choose by purpose — drift and fatigued work, keep it whole; volume at low cost before a key day, split (SYNTH-84 rule 3, which rests on the moderate-intensity REF-159) — and the long session's need scales with event duration (optional up to about 2 h, SYNTH-84).
Expect easy effort to feel harder late in a long session: RPE rose about one point in the second half (the skiers also went 3.2% faster then; the abstract does not say whether heart rate rose within the session). Not from this paper; the base's own practice: cap long easy days by breathing and talk rather than by the opening speed (SYNTH-51).
This is not the moderate-intensity result: where the long session left more next-morning fatigue, the work was 6 × 10 min between the thresholds (REF-159); do not carry that cost over to easy work.

Limitations

Abstract only: the skiers' sex, age and fitness, how low intensity was defined, the course, timing of sessions, food and drink, absolute values and the stress scores are not given; nothing beyond the abstract's statements could be checked.
Small and acute: 13 skiers, one day per condition; no training block, so nothing about adaptation, durability or performance over weeks.
Self-selected speed: the formats were matched for distance, not for speed or time, so the long session was also slightly slower; a fixed-speed comparison might show a heart-rate drift this design hides.
Who and what: national-level skiers on classical roller skis; recreational athletes, cyclists and runners were not studied.
Funding and interests: not given in the abstract.
How this entry was checked and changed
Why this level

(from the abstract) — a crossover of 13 is B under the rubric (crossover under 15); held at B- because it is an abstract-only small study with key details missing (sex, age, fitness, how "low intensity" was defined or checked, the course and the fuelling) and its outcomes are acute responses on one day each, not adaptation. Closed access; no open copy via Europe PMC or OpenAlex