REF-1733 · Bommarito et al., 2026 · American Journal of Physiology - Heart and Circulatory Physiology, · Paper · PubMed

After one night cut to 40% of normal sleep by early waking, 25 young adults cycling 60 min at a moderate fixed power (81 ± 35 W) showed no significant difference in heart rate or blood pressure from normal sleep, but a lower cardiac output at the 60th minute (11.5 vs 12.3 L/min) and in recovery, not at 30 min, which the authors attribute to a blunted stroke volume (itself only a trend), with a smaller rise in noradrenaline and adrenaline, in a randomised crossover; haemodynamic measures, not performance, and abstract only

Main caveat: Haemodynamic and hormonal outcomes only; no performance measure.
limited evidenceMeasured on non-athletes and recreational peopleRead from the abstract only

Bommarito and colleagues asked why a short night can lower systolic blood pressure during exercise, testing whether cardiac output is reduced. Twenty-five young adults (13 women) took part in a randomised crossover: once they slept normally and once they were woken early so that they slept 40% of their normal duration.

Each time they rested, cycled 60 min at a moderate fixed power (81 ± 35 W) and recovered, while blood pressure, cardiac output (impedance cardiography) and cerebral blood velocity (transcranial Doppler) were measured. Blood pressure did not differ at rest or during exercise.

Cardiac output was the same at rest and at 30 min, but lower after the short night at 60 min of cycling (11.5 vs 12.3 L/min) and in recovery (7.2 vs 7.7 L/min). Heart rate and estimated end-diastolic volume did not differ; stroke volume tended to be lower, estimated ejection fraction was lower and total peripheral resistance higher after the short night.

Noradrenaline and adrenaline were unchanged at rest but rose less by 60 min of cycling. The authors conclude that a short night can lower cardiac output after 30 min of moderate cycling through a smaller stroke volume, without a compensating rise in heart rate.

Participants

n = 25 adults, 13 F / 12 M, age 22 ± 3 y, aerobic fitness 40.1 ± 7.7 mL/kg/min (the variable's symbol is lost in the PubMed text; by its units an oxygen uptake, probably peak).
Training status, sport and habitual sleep: not in the abstract.

Protocol

Randomised crossover: normal sleep versus acute partial sleep deprivation by early waking, to 40% of normal sleep duration.
Measurements at rest, throughout 60 min of moderate-intensity cycling at 81 ± 35 W, and in recovery: blood pressure, cardiac output (impedance cardiography), heart rate, stroke volume, estimated end-diastolic volume and ejection fraction, total peripheral resistance, middle and posterior cerebral artery blood velocity (transcranial Doppler), plasma noradrenaline and adrenaline.
Not in the abstract: how sleep was measured, the actual sleep hours in each condition, time of day of testing, how intensity was set, the washout, and the cerebral blood velocity results.

Key Results

MeasureControlShort nightP
Systolic and diastolic BP, rest and exerciseno difference≥ 0.19
Cardiac output, rest (L/min)5.0 ± 0.94.9 ± 0.7> 0.99
Cardiac output, 30 min cycling (L/min)11.5 ± 2.711.0 ± 2.50.16
Cardiac output, 60 min cycling (L/min)12.3 ± 3.111.5 ± 2.60.003
Cardiac output, recovery (L/min)7.7 ± 1.97.2 ± 1.40.04
Heart rate; estimated end-diastolic volumeno difference≥ 0.82
Stroke volumetended lower0.07
Estimated ejection fractionlower0.02
Total peripheral resistancehigher0.04
Noradrenaline and adrenaline, restunchangednot given
Noradrenaline and adrenaline, 60 min cyclingsmaller rise≤ 0.045
Effect sizes and confidence intervals are not in the abstract.

Practical Application

After one short night (40% of normal sleep, woken early), heart rate during a steady 60-min ride at the same power did not differ significantly from normal sleep (the abstract gives no time point for it), while the heart pumped less blood per minute by the end of the hour and in recovery. Young adults of modest fitness; haemodynamic measures, no performance outcome.
Against SYNTH-38: the guide lists heavy sleep debt among the days when heart rate stops being comparable, as base practice; it cites this study for one short night and says no cited entry measures sleep debt over several nights.In this study one short night did not significantly change heart rate at a fixed moderate power, so heart-rate-at-power looked normal while cardiac output and stroke volume were lower after 30 min. That qualifies the guide rather than contradicting it: the heart rate number stayed comparable, but here it did not reveal a change in the heart's output.
Inference, not tested here: after a short night a steady ride's heart rate may look normal, so a normal heart rate is not evidence that the night cost nothing; the base reads the warm-up and first hard reps for that (SYNTH-07).
Inference, not tested here: whether the lower cardiac output limits performance, and whether the same holds in trained athletes, at higher intensities or after several short nights, was not measured.

Limitations

Haemodynamic and hormonal outcomes only; no performance measure.
Impedance cardiography estimates cardiac output and stroke volume; the abstract does not describe its validation in this setting.
Stroke volume was only a trend (P = 0.07); the cardiac output difference appeared at 60 min, not at 30 min.
One night, one moderate fixed-power ride; young adults of modest fitness, training status not reported.
Actual sleep obtained, testing time and cerebral blood velocity results are not in the abstract.
Written from the abstract and the PubMed record; full text not read.
How this entry was checked and changed
Why this level

a randomised crossover of 25 (the rubric's B+ band) lowered one step because the outcomes are haemodynamic and hormonal markers, not performance (rule 3); read from the abstract, which gives means and SDs for the main outcome