{ "abstract": "Background/Objectives: Short-term bed rest may reduce cardiorespiratory capacity for mobility and rehabilitation, but gas-exchange-assessed fitness has not been synthesised in older adults. We characterised immediate V.O2peak/V.O2max change, recovery, and countermeasures. Methods: This PROSPERO-registered review (CRD420261431685) searched seven databases and two trial registries through 24 May 2026, with Embase and SPORTDiscus through 26 May. Eligible studies imposed 5-14 days of horizontal bed rest (HBR) or 6° head-down tilt bed rest (HDBR) in cohorts with mean age ≥ 60 years or ageing-focused programmes enrolling adults aged 55-65 years. Reports sharing participants and protocol formed one cohort/protocol unit. Body-mass-normalised V.O2 was primary; absolute V.O2 was separate. Risk of bias was assessed with RoB 2 or the revised JBI tool, and certainty with GRADE. Meta-analysis was not undertaken because three independent, comparable effects were unavailable. Results: Of 1964 records, 15 reports formed six units representing four to six independent participant groups. Across four HBR units (n = 9-19), V.O2peak/V.O2max declined by 4.9-15.3%; two percentages were directly reported, one was calculated from a reported change, and one from unit-adjudicated means (low certainty for direction; very low for magnitude). In one HDBR trial, changes were -13.4% ± 12.5% SD in controls (n = 9) and -3.5% ± 5.2% SD with multimodal exercise (n = 10). Single leucine, approximately 2000 steps/day, and whey comparisons provided insufficient evidence of V.O2 preservation. Recovery evidence from three programmes was heterogeneous and very uncertain; only one small HDBR cohort had approximately four-week follow-up. Conclusions: V.O2peak/V.O2max consistently declined after short-term HBR, but a precise decline, duration-response relationship, specific countermeasure prescription, and universal recovery time are not established. Minimising avoidable immobility is a plausible clinical implication, not a directly tested intervention. No external funding.", "abstract_shown": true, "affiliations": [ "Laboratory of Epidemiology and Morphological Sciences, Instituto de Biología, Pontificia Universidad Católica de Valparaíso, Valparaíso 2373223, Chile.", "Departamento de Morfología, Facultad de Medicina, Universidad Andrés Bello, Viña del Mar 2520000, Chile.", "Departamento de Ciencias Químicas y Biológicas, Facultad de Ciencias de la Salud, Universidad Bernardo O'Higgins, Santiago 8370993, Chile.", "Facultad de Ciencias de la Salud, Universidad Autónoma de Chile, Santiago 8910060, Chile.", "Faculty of Health and Social Sciences, University of the Americas, Santiago 8370040, Chile.", "Escuela de Medicina, Universidad Finis Terrae, Santiago 7501015, Chile.", "Facultad de Medicina y Ciencia, Universidad San Sebastián, Lota 2465, Santiago 7510157, Chile.", "Carrera de Odontología, Facultad de Medicina, Universidad Católica de la Santísima Concepción, Av. Alonso de Ribera 2850, Concepción 4090541, Chile.", "Facultad de Medicina, Universidad Católica del Maule, Talca 3460000, Chile.", "Escuela de Ciencias de la Salud, Universidad Viña del Mar, Viña del Mar 2520000, Chile.", "Cerebro, Emoción y Conducta (CEC) Research Group, Escuela de Medicina, Universidad de las Américas (UDLA), Quito 170521, Ecuador.", "GIAVAL Research Group, Faculty of Medicine, University of Valencia, 46001 Valencia, Spain.", "Physiology Laboratory, Department of Biological Sciences, Faculty of Life Sciences, Universidad Andrés Bello, Viña del Mar 2520000, Chile.", "Departamento de Ciencias Básicas, Facultad de Medicina, Universidad de La Frontera, Temuco 4811230, Chile.", "Departamento de Ciencias y Geografía, Facultad de Ciencias Naturales y Exactas, Universidad de Playa Ancha, Valparaíso 2360072, Chile." ], "article_type": "review article", "arxiv": null, "author_total": 13, "authors": [ { "affs": [ 0 ], "name": "Gustavo Vega-Fernández", "orcid": "0000-0003-3088-0638" }, { "affs": [ 1, 2 ], "name": "Juan José Valenzuela-Fuenzalida" }, { "affs": [ 3 ], "name": "Yasna Jeria-Pizarro" }, { "affs": [ 4 ], "name": "Gustavo Oyanedel-Amaro", "orcid": "0009-0009-9092-3469" }, { "affs": [ 5, 6 ], "name": "Mathias Orellana-Donoso", "orcid": "0000-0002-1781-062X" }, { "affs": [ 7 ], "name": "Gloria Cifuentes-Suazo", "orcid": "0000-0002-6497-3480" }, { "affs": [ 8 ], "name": "Juan Jose Cabezas-Salgado" }, { "affs": [ 9 ], "name": "Christopher Blackwood-Espinoza" }, { "affs": [ 10 ], "name": "José E León-Rojas", "orcid": "0000-0002-8130-6460" }, { "affs": [ 11 ], "name": "Juan Sanchis-Gimeno", "orcid": "0000-0002-2599-8474" }, { "affs": [ 12 ], "name": "Rodrigo Cañas-Jamett", "orcid": "0000-0003-0429-255X" }, { "affs": [ 13 ], "name": "Nicolás Vidal-Seguel", "orcid": "0000-0001-5284-4262" }, { "affs": [ 1, 14 ], "name": "Alejandro Bruna-Mejías", "orcid": "0000-0002-7697-419X" } ], "bibtex": "https://research.draconitic.com/paper/cdmfmja0dmc9v.bib", "cited_by": 0, "doi": "10.3390/healthcare14203459", "fulltext_url": "https://europepmc.org/articles/PMC13704191", "id": "cdmfmja0dmc9v", "issns": [ "2227-9032" ], "landing_url": "https://europepmc.org/article/MED/42940503", "language": "eng", "licence": "CC-BY", "licence_label": "CC BY", "licence_source": "article", "licence_url": "https://creativecommons.org/licenses/by/4.0/", "metadata_licence": null, "native_subjects": [ [ "openalex", "2737|Spaceflight effects on biology" ] ], "openalex": "W7222294175", "pdf_url": "https://europepmc.org/articles/PMC13704191?pdf=render", "pmcid": "PMC13704191", "pmid": "42940503", "published": "2026-10-15", "publisher": null, "ris": "https://research.draconitic.com/paper/cdmfmja0dmc9v.ris", "sources": [ { "first_seen": "2026-10-30T12:22:12Z", "native_id": "MED:42940503", "source": "europepmc", "url": "https://europepmc.org/article/MED/42940503" } ], "subjects": [ { "field": "medicine", "origin": "openalex:2737|Spaceflight effects on biology", "subfield": "physiology" } ], "title": "Cardiorespiratory Fitness Decline After Short-Term Experimental Bed Rest in Older Adults and Ageing-Focused Cohorts Aged 55-65 Years: A Systematic Review.", "title_text": "Cardiorespiratory Fitness Decline After Short-Term Experimental Bed Rest in Older Adults and Ageing-Focused Cohorts Aged 55-65 Years: A Systematic Review.", "type": "peer-reviewed", "updated_at": "2026-10-30T12:22:12Z", "url": "https://research.draconitic.com/paper/cdmfmja0dmc9v", "venue": "Healthcare (Basel, Switzerland)", "versions": [] }