REF-241 · Liedl et al., 1999 · Medicine & Science in Sports & Exercise, Vol. · Paper · PubMed

Physiological effects of constant versus variable power during endurance cycling

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

Participants

n=8 trained male cyclists (age 28 ± 2 yr, mass 74.4 ± 2.3 kg, VO2max 4.24 ± 0.13 L/min, weekly training 277 ± 44 km); three 1-h ergometer trials.

Protocol

Three conditions: (1) self-paced maximal 1-h effort; (2) constant power (CP) = mean power of the self-paced trial; (3) variable power (VP) = alternating ±5% of that mean every 5 min. CP vs VP compared at identical mean power.

Key Results

Parameter	Constant Power	Variable Power (±5%)
Mean VO₂	3.33 ± 0.11 L/min	3.26 ± 0.12 L/min
Mean HR	158 ± 3 bpm	159 ± 3 bpm
Mean blood lactate	4.2 ± 0.7 mM	4.3 ± 0.7 mM
Mean RPE	13.9 ± 0.4	14.1 ± 0.4

No differences between constant and variable (±5%) power in VO2, HR, lactate or RPE during a strenuous 1-h effort (78% of VO2max).

Mechanism

Inference, not tested: power fluctuations of ±5% every 5 min do not measurably alter metabolic cost or perceived effort at this intensity — the system tolerates minor variability without additional stress. The study measured the outcome, not the reason.

Practical Application

n=8 trained male cyclists, 1 h at 78% of VO2max: alternating power ±5% every 5 min produced the same VO2 (3.26 vs 3.33 L/min), HR (159 vs 158 bpm), lactate (4.3 vs 4.2 mM) and RPE (14.1 vs 13.9) as holding the mean power constant — small power variation carries no extra physiological cost.

Inference, not tested: the natural ±5% wobble of a non-ERG ride is physiologically benign at this amplitude, so a rider does not need ERG to "protect efficiency" in steady Z2 or tempo work; the training stimulus is the same.

Inference, not tested: the study's motivation was time-trial pacing — varying power slightly against wind or gradient need not cost anything physiologically. Larger swings than ±5% were not tested.

Together with REF-240 (enforced constant pace was MORE stressful than self-paced rowing), the base's reading is that strictly constant power is not automatically the better stimulus.

Limitations

Small sample (n=8). Only ±5% variability tested (larger swings may differ). Single intensity (78% VO₂max). 1999 study — older equipment. RPE was measured (no difference); no neuromuscular fatigue measure. No DOI on the entry; verified against the PubMed abstract (PMID 10527322).

How this entry was checked and changed

Content correction 2026-09-27

Lead Practical bullet was an ERG argument -> now the study's finding with the abstract's values (incl. RPE 13.9 vs 14.1, which the entry had omitted; the Limitations wrongly said RPE was not measured).

Tier line said "mixed ... (review ...)" -> this is a single crossover study; tier set from the abstract's population (trained male cyclists, VO2max 4.24 L/min, 277 km/week).

Participant characteristics from the abstract added (age, mass, VO2max, weekly km). ERG/free-ride bullets labelled as inference.