Muscle & aerobic fitness
Also: Reduced fitness risk
Gravity FieldsMusculoskeletalCardiovascularIn-flightEVA & Surface OpsPostflight RecoveryLEO long-durationLunar surfaceMars transit & surfacePublicClinicianResearcher
- About 600 minutes per week of exercise doesn't fully prevent deconditioning on 6-month missions, and individual responses vary widely. ◆◆◆◇ Moderate · F
- Many astronauts aren't back to preflight fitness 30 days after landing. ◆◆◆◇ Moderate · F
- For Mars, NASA rates this risk 5×4, requiring mitigation. ◆◆◆◆ High · E
Proposed certainty (◆ High → ◇ Very low) and evidence-type tags: F flight · A analog · M model/animal · C computational · E expert/operational/standards. AI-proposed, pending reviewer confirmation. How to read the grades.
NASA risk title (verbatim)
Risk of Mission Performance Decrements and Adverse Health Outcomes Resulting from Reduced Cardiorespiratory and Musculoskeletal Fitness
NASA short title: Muscle and Aerobic · HRP element: Human Health Countermeasures (HHC) · Status: Active [current research ongoing] [1]
What it is
This risk is about losing the heart, lung and muscle fitness needed for mission tasks such as spacewalks, emergency egress and surface exploration, and about long-term health effects [1].
Current evidence
- Despite in-flight exercise, fitness falls during and after flight. People vary widely, and adherence doesn’t fully explain the differences [1].
- Some ISS astronauts don’t meet fitness standards for weightless operations, and many wouldn’t meet the standards for surface spacewalks. Many aren’t back to preflight fitness by the end of the standard 30-day reconditioning program [1].
- In 46 long-duration astronauts, about 600 minutes per week of aerobic and resistance exercise didn’t fully prevent multisystem deconditioning. Responses varied widely between individuals [4].
- Peak aerobic capacity fell about 17% early in flight, then partly recovered [5].
- In 4 crew members after about 6 months, calf muscle volume fell 10–16% and thigh volume 4–7% [6].
- There are few data for missions longer than 4–6 months, for women, or for partial gravity. Exercise hardware will be smaller on exploration vehicles [1].
NASA’s risk posture
NASA scores each risk for each design reference mission (DRM) as likelihood × consequence (LxC). Both run from 1 (lowest) to 5 (highest) on the HSRB’s 5×5 matrix [1][3]. Each score comes with a disposition, such as “Accepted”, “Requires Characterization” or “Requires Mitigation”. These ratings were last approved by NASA’s Human System Risk Board (HSRB) in 4/2024 [1].
| Mission | Duration | In-mission (operations) | Long-term health |
|---|---|---|---|
| LEO | Short (under 30 d) | 5x1 · Accepted with Optimization | 3x1 · Accepted |
| LEO | Long (30 d–1 yr) | 5x1 · Requires Characterization | 5x2 · Accepted with Optimization |
| Lunar orbit | Short | 5x1 · Accepted with Optimization | 3x1 · Accepted |
| Lunar orbit | Long | 5x1 · Requires Characterization | 5x2 · Accepted with Optimization |
| Lunar orbit + surface | Short | 5x2 · Requires Characterization | 3x1 · Accepted with Optimization |
| Lunar orbit + surface | Long | 5x3 · Requires Mitigation | 5x2 · Requires Characterization |
| Mars preparatory | Under 1 yr | 5x2 · Requires Mitigation | 5x2 · Requires Characterization |
| Mars planetary | 730–1,224 d | 5x4 · Requires Mitigation | 5x3 · Requires Mitigation |
NASA carries this as two HSRB risks, one for aerobic fitness and one for muscle; the HRR shows a combined rating [1].
Copied from the Human Research Roadmap on 2026-10-14. Ratings change. Check the live record before citing.
Open knowledge gaps
NASA lists 5 knowledge gaps for this risk, 4 of them open as of 2026-10-14 [1]. Each gap ID links to its page on the Human Research Roadmap (HRR).
Show NASA’s gap list (verbatim)
| Gap | NASA gap statement | Status |
|---|---|---|
| MA-101 | Characterize the effects of the spaceflight environment, including reduced gravity (i.e., weightlessness, partial gravity), countermeasures, and individual variability, on physiological and functional measures of muscular and cardio-respiratory fitness and performance. | Open |
| MA-102 | Determine the relationship between physiological and functional measures of muscular and cardio-respiratory fitness or performance and mission-specific task performance and crew health outcomes. | Open |
| MA-201 | Determine the required exercise countermeasure or countermeasures (i.e., modality or modalities, prescription, monitoring) to protect mission-specific task performance and crew health outcomes. | ? |
| MA-202 | Determine whether adjunct or supplementary countermeasures (e.g., nutrition, pharmaceuticals, novel devices, sensorimotor training) improve the efficacy of the exercise countermeasures to protect mission-specific task performance and crew health outcomes. | Open |
| MA-301 | Evaluate an integrated exercise countermeasure system(s) and the potential impact of other physiological countermeasure(s) to protect mission-specific task performance and crew health outcomes. | Open |
See also Open questions.
Active countermeasure research
- New exercise systems. Novel exercise systems are being evaluated on the ISS, Orion and Gateway, and in analogs [1].
- Task-specific fitness. Studies measure the metabolic cost and strength needed for spacewalk tasks to set fitness requirements (gaps MA-101 to MA-301) [1].
Project-level detail, including status, investigators and results, is in the NASA Task Book and on each HRR gap page.
Clinical articles
For practical, clinic-facing guidance, see:
Evidence profile
- Overall certainty
- ◆◆◆◇ Moderate (proposed)
- Evidence types
- F · Flight dataE · Expert / operational / standards
- Literature through
- 2026-10-14
- NASA source
- Human Research Roadmap risk page (last published 05/13/25; read 2026-10-14)
Requirements referenced 5
| Requirement | Title | Plain-language meaning |
|---|---|---|
| [V1 4001]–[V1 4002] | EVA Aerobic Capacity | Minimum VO2max for microgravity and surface EVAs. |
| [V1 4003] | In-Mission Aerobic Capacity | Maintain at least 80% of preflight VO2max. |
| [V1 4023] | Muscle Strength | Table 4.6-1 minimum deadlift and bench press as multiples of body weight. |
| [V1 4024] | In-Mission Muscle Strength | Maintain at least 80% of preflight strength. |
| [V2 7038] | Physiological Countermeasures Capability | Vehicles must provide countermeasure capability (e.g., exercise hardware) to meet crew health standards. |
IDs as published in NASA-STD-3001 Vol. 1 Rev C (2023-09-15) and NASA-STD-3001 Vol. 2 Rev F (2026-07-14). NASA-STD-3001 binds NASA programs; it is not a regulation for commercial flights. Paraphrased. Standards quick reference.
References 6
- NASA Human Research Roadmap. Risk record: “Risk of Mission Performance Decrements and Adverse Health Outcomes Resulting from Reduced Cardiorespiratory and Musculoskeletal Fitness”. Accessed 2026-10-14. humanresearchroadmap.nasa.gov/Risks/?i=180 NASA E
- NASA Human Research Program. Evidence report for the aerobic and muscle fitness risk (2024). humanresearchroadmap.nasa.gov/evidence/reports/Evidence%20re… NASA E
- Antonsen EL, et al. Updates to the NASA human system risk management process for space exploration. NPJ Microgravity. 2023;9:72. doi:10.1038/s41526-023-00305-z PMID:37679359 Peer-reviewed E
- Scott JM, et al. Effects of exercise countermeasures on multisystem function in long duration spaceflight astronauts. NPJ Microgravity. 2023;9:11. doi:10.1038/s41526-023-00256-5 PMID:36737441 Peer-reviewed F
- Moore AD Jr, et al. Peak exercise oxygen uptake during and following long-duration spaceflight. J Appl Physiol. 2014;117(3):231–238. doi:10.1152/japplphysiol.01251.2013 PMID:24970852 Peer-reviewed F
- Gopalakrishnan R, et al. Muscle volume, strength, endurance, and exercise loads during 6-month missions in space. Aviat Space Environ Med. 2010;81(2):91–102. doi:10.3357/ASEM.2583.2010 PMID:20131648 Peer-reviewed F
Machine-checked on 2026-10-14: each URL resolved, each DOI's title/journal/year matched via Crossref, and claims were checked against the source text (abstract or full NASA page). Human verification against full text is still required before review. NASA documents are U.S. Government works (public domain) and are summarized with attribution; journal articles are summarized, not reproduced.
Article info
- Authors
- Pending (AI-assisted draft)
- Reviewer
- Pending review
- Last reviewed
- Pending review
- Literature through
- 2026-10-14
- AI-assisted
- Yes (disclosed)
- COI
- Pending
- License
- CC BY-SA 4.0
- Use
- Educational only · Disclaimer
- Cite this version
- Pending first edition