REF-1340 · Coyle & González-Alonso, 2001 · Exercise and Sport Sciences Reviews · Paper · PubMed

Why does my heart rate climb at the same watts on long rides?

Drift: after 10-20 min stroke volume falls; this leading lab blames the rising heart rate itself, not blood sent to the skin. A contested mechanism (B+, abstract).

Main caveat: Abstract only, one sentence. The full text is behind the publisher's paywall and is not in PubMed Central or any repository listed by OpenAlex.
moderate evidenceMeasured on recreational to highly trained athletes

The whole abstract is one proposal: cardiovascular drift, characterised by a progressive decline in stroke volume after 10-20 min of exercise, is primarily due to increased heart rate rather than to a progressive increase in cutaneous (skin) blood flow as body temperature rises.

In other words, Coyle and González-Alonso put the rising heart rate first and the falling stroke volume as its consequence, against the classic view (the abstract names only skin blood flow; the rest of this sentence is the standard account, not the abstract's) that blood moved to the skin for cooling lowers central blood volume and the heart's filling, and heart rate rises to make up for it.

The abstract gives no data, no study count and no mechanism for how a faster heart rate lowers stroke volume, and does not mention dehydration.

Our reading: the base already holds that drift is real extra strain — heart rate rises, stroke volume and VO2max fall, most in the heat (REF-3495, REF-3496); this entry adds the leading laboratory's position on the cause; the base's only statement of the cause so far is the other side, "skin-blood-flow steal", given as reasoning without a source in SYNTH-16, which this entry now contests.

It does not settle the dispute, and it cannot carry dehydration's share of drift.

Protocol

Design: narrative review / perspective of the authors' experiments on drift; search method, inclusion rules and studies are not given in the abstract (n = not applicable).
Scope (from the abstract): the cause of the decline in stroke volume during prolonged exercise — heart rate versus cutaneous blood flow.
Not given in the abstract: any data, populations, exercise intensities or environments; the role of dehydration; funding or conflicts. The abstract record in PubMed and Europe PMC contains the typo "tahn" for "than".

Key Results

Definition (abstract): cardiovascular drift is a progressive decline in stroke volume after 10-20 min of exercise.
The proposal (abstract): the decline is primarily due to increased heart rate.
What it is set against (abstract): a progressive increase in cutaneous blood flow as body temperature rises.
No numbers: the abstract gives no size of drift, no heart-rate or stroke-volume values, and no conditions.

Mechanisms

Authors' interpretation (abstract): the heart-rate rise drives the stroke-volume fall during prolonged exercise, rather than skin blood flow pulling volume away from the heart. How a faster rate lowers stroke volume is not stated in the abstract.
The other side (not sourced in the base): the classic explanation holds that as body temperature rises more blood goes to the skin, central blood volume and cardiac filling fall, stroke volume drops and heart rate rises to hold cardiac output. The base has no review that argues it.
Elsewhere in the base: a review states that drift begins at roughly 10 min and comes with a fall in VO2max, most in the heat (REF-3495, abstract), and an experiment measured it; at the same watts with fluid replaced, heart rate drifted 11% and VO2max fell 15% at 35 °C against 2% and no significant change at 22 °C (REF-3496).
Inference: for reading a session the cause does not change the reading — on either account a heart rate that climbs at fixed power means the same work is costing more of a shrinking capacity (REF-3495); the mechanism matters for physiology, not for the decision.

Practical Application

Why does my heart rate climb at the same watts on long rides? Drift: after 10-20 min stroke volume falls; this leading lab blames the rising heart rate itself, not blood sent to the skin. A contested mechanism (B+, abstract).
What it is good for as a source: naming one side of the drift-mechanism dispute in its authors' words. It does not measure drift, does not size the effect of heat or fluid loss, and cannot be cited for any number.
What it means for training (the base's reading, not this paper's): compare heart rate at fixed power only between like sessions, and in the heat cap easy work by heart rate, talk test or RPE, and late in a long cool ride by talk test and RPE (SYNTH-38); do not read big drift alone as dehydration (SYNTH-68).

Limitations

Abstract only, one sentence. The full text is behind the publisher's paywall and is not in PubMed Central or any repository listed by OpenAlex; the experiments, the size of the effects, the role of dehydration and the authors' funding and conflicts could not be read.
One side of a dispute, argued by the laboratory whose experiments support it; the opposing view has no review in the base.
2001. Later work on drift, heat and VO2max (REF-3495, REF-3496) is not considered.
How this entry was checked and changed
Why this level

authoritative narrative review from a leading group on cardiovascular drift (Coyle, University of Texas at Austin, with González-Alonso), the rubric's line; read from a one-sentence abstract, so nothing quantitative may be cited from this entry, and it states one side of a disputed mechanism. Graded as the base's other leading-group reviews read from the abstract (REF-1196, REF-1207, REF-1208); REF-3495 (Cureton group, same journal), once downgraded to C+ for being read from the abstract, is now B+ on the same grounds