REF-1432 · Fontana et al., 2009 · European Journal of Applied Physiology · Paper · PubMed

If I ride my threshold session instead of running it, what carries over?

In 15 moderately trained men at MLSS, effort (7.2 vs 7.2) and time to exhaustion matched across modes, but heart rate was 10 bpm lower on the bike. Abstract.

Main caveat: Abstract only; the repository copies OpenAlex lists were behind a bot check or a rate limit.
moderate evidenceMeasured on recreational to trained athletes

Fontana, Boutellier and Knöpfli-Lenzin (ETH Zurich) compared time to exhaustion at MLSS between cycling and running, asked whether oxygen uptake, ventilation, lactate and perceived exertion differ between the modes at MLSS, and whether the same criteria can define MLSS in both.

Fifteen moderately trained men (30 ± 6 years, 77 ± 6 kg) had MLSS determined in each mode by several constant-load tests to exhaustion. Time to exhaustion (37.7 ± 8.9 vs 34.4 ± 5.4 min) and perceived exertion (7.2 ± 1.7 vs 7.2 ± 1.5) were similar for cycling and running.

Heart rate (165 ± 8 vs 175 ± 10 per min, P < 0.01), oxygen uptake (3.1 ± 0.3 vs 3.4 ± 0.3 L/min, P < 0.001) and ventilation (93 ± 12 vs 103 ± 16 L/min, P < 0.01) were lower in cycling, and blood lactate higher (5.6 ± 1.7 vs 4.3 ± 1.3 mmol/L, P < 0.05).

The authors explain the similar endurance by a relatively equal cardiorespiratory demand at MLSS and conclude that the same criteria can be used to determine MLSS in both modes.

Our reading: at the same physiological ceiling the effort felt the same and lasted about as long in both modes, while heart rate was 10 bpm lower on the bike — the cleanest evidence in the base that RPE carries across cycling and running at threshold and heart rate does not.

Protocol

Participants: n = 15 moderately trained men; 30 ± 6 years; 77 ± 6 kg.
MLSS: determined separately for cycling and running by several constant-load tests to exhaustion.
Measures: heart rate, oxygen uptake and ventilation recorded continuously; blood lactate and perceived exertion every 5 min; time to exhaustion at MLSS.
Funding and interests: none listed in the PubMed or Crossref record; no conflict statement in the abstract record.

Key Results

At MLSSCyclingRunningP
Time to exhaustion (min)37.7 ± 8.934.4 ± 5.4similar
Perceived exertion7.2 ± 1.77.2 ± 1.5similar
Heart rate (per min)165 ± 8175 ± 10< 0.01
VO2 (L/min)3.1 ± 0.33.4 ± 0.3< 0.001
Ventilation (L/min)93 ± 12103 ± 16< 0.01
Blood lactate (mmol/L)5.6 ± 1.74.3 ± 1.3< 0.05
Individual spread: the abstract gives group SDs, not the SD of each man's cycling-minus-running difference, so how far one athlete's gap strays from 10 bpm cannot be read here.

Mechanisms

Measured: at each mode's MLSS, similar endurance time and perceived exertion; lower heart rate, oxygen uptake and ventilation and higher lactate in cycling.
Authors' interpretation: the similar time to exhaustion reflects a relatively equal cardiorespiratory demand at MLSS in both modes, which also allows the same MLSS criteria in both.
Inference: cycling reaches its steady-state limit with less total oxygen uptake (smaller active muscle mass, a seated, non-weight-bearing posture), so the same relative strain comes at a lower heart rate; the higher lactate at the cycling MLSS means a lactate number does not transfer between modes either.

Practical Application

If I ride my threshold session instead of running it, what carries over? In 15 moderately trained men at MLSS, effort (7.2 vs 7.2) and time to exhaustion matched across modes, but heart rate was 10 bpm lower on the bike. Abstract.
Threshold on the substitute: ride or run at the same perceived effort and expect a lower heart rate on the bike; on these group means, an athlete who holds their running threshold heart rate on the bike is likely riding above threshold; one athlete's own gap may be smaller or larger (REF-1431). The 10 bpm is a group mean in moderately trained men; triathletes averaged 3 bpm with a 12-bpm individual error (REF-1431).
Lactate does not transfer: MLSS lactate was 5.6 mmol/L cycling vs 4.3 running; a lactate target from one mode is not the other's.
What it does not show: women, highly trained athletes, interval sessions, or whether training at matched RPE on the bike keeps running fitness (REF-1428).

Limitations

Abstract only; the repository copies OpenAlex lists were behind a bot check or a rate limit.
Men only, moderately trained, main sport not stated; one laboratory.
Exertion scale not named in the abstract (values near 7 suggest a 0-10 scale).
Group means; no paired differences or limits of agreement.
Funding and interests: not stated in the record.
How this entry was checked and changed
Why this level

(from the abstract) — a within-subject comparison of 15 (the rubric's B+ floor for crossovers); men only, one laboratory, the exertion scale not named in the abstract