Background Changes in cardiac output, driven by increased heart rate and stroke volume, are crucial for oxygen delivery during acute exercise and influence maximal oxygen uptake (VO₂max). Thoracic electrical bioimpedance provides a non-invasive alternative to traditional invasive methods by estimating stroke volume through impedance changes during ventricular filling and emptying. However, its test-retest reliability remains uncertain, requiring further investigation for use in acute and long-term training assessments.

Methods Inclusion: 12 healthy individuals (six males, six females) Exclusion: Known ischaemic heart disease, known heart failure, symptoms of disease within 2 weeks prior to the study, known malignant disease, claudication, pregnancy, unstable cardiac arrhythmic disease, renal or liver dysfunction, known chronic lung disease Design: Test-retest study of thoracic electrical bioimpedance-based stroke volume

Intervention: Acute exercise bout on a bicycle ergometer Statistical design: Rest-to-exercise changes, as well as between-day smallest real difference, coefficient of variation and intraclass correlation coefficient Sample size: Since this is a pilot study, the sample size is set at 12 in accordance with current recommendations.

Perspective The results are relevant for designing future studies in which stroke volume is measured and compared in response to various interventions at rest and during exercise.

Inclusion criteria

• Men and women
• 18-70 years

Exclusion criteria

• Known chronic lung disease
• Known ischaemic heart disease
• Known heart failure
• Symptoms of disease within 2 weeks prior to the study
• Known malignant disease
• Claudication
• Pregnancy
• Unstable cardiac arrhythmic disease
• Renal or liver dysfunction