Changes in muscle size, architecture, and neural activation after 20 days of bed rest with and without resistance exercise
Abstract
Nine healthy men carried out head-down bed rest (BR) for 20 days. five subjects (TR) performed isometric, bilateral leg extension exercise every day, while the other four (NT) did not. Before and after BR, maximal isometric knee extension force was measured. Neural activation was assessed using a supramaximal twitch interpolated over voluntary contraction. From a series cross-sectional magnetic resonance imaging scans of the thigh, physiological cross-sectional areas (PCSA) of the quadriceps muscles were estimated (uncorrected PCSA, volume/estimated fibre length). Decrease in mean muscle force after BR was greater in NT [-10.9 (SD 6.9)%, P < 0.05] than in TR [0.5 (SD 7.9)%, not significant]. Neural activation did not differ between the two groups before BR, but after BR NT showed smaller activation levels. Pennation angles of the vastus lateralis muscle, determined by ultrasonography, showed no significant changes in either group. The PCSA decreased in NT by -7.8 (SD 0.8)% (P < 0.05) while in TR PCSA showed only an insignificant tendency to decrease [-3.8 (SD 3.8)%]. Changes in force were related more to changes in neural activation levels than to those in PCSA. The results suggest that reduction of muscle strength by BR is affected by a decreased ability to activate motor units, and that the exercise used in the present experiment is effective as a countermeasure.
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Due to the low number of participants and large SD in bed rest studies, the a priori decision was made to summarize results as relative deltas.
“Due to the nature of bed rest studies (low number of participants and large SD; e.g., Ref. 19), the priori decision was made to summarize the results of muscle atrophy and strength decline as relative deltas.”
From Nonuniform loss of muscle strength and atrophy during bed rest: a systematic review (2021) · cites this paper as [19]
Scientific evidence manifests discrepancies in the magnitude and degradation rates between atrophy and the functional decline of skeletal muscles as a response to bed rest.
“Scientific evidence manifests discrepancies in the magnitude and degradation rates between atrophy and the functional decline of skeletal muscles as a response to bed rest (18–20).”
From Nonuniform loss of muscle strength and atrophy during bed rest: a systematic review (2021) · cites this paper as [19]
The small sample size and large interindividual variability raise the question of the relevance of a meta-analytic summary, but open new perspectives for investigating individual-specific mechanisms of bed rest-induced deterioration.
“Finally, the small sample size and the large interindividual variability (e.g., Ref. 19) of the responses raise the question of the relevance of a meta-analytic summary of the results, but at the same time open new perspectives for the investigation of individual-specific mechanisms of bed rest-induced deterioration.”
From Nonuniform loss of muscle strength and atrophy during bed rest: a systematic review (2021) · cites this paper as [19]
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- Authors
- Kawakami, Y., Akima, H., Kubo, K., Muraoka, Y., Hasegawa, H., Kouzaki, M., Imai, M., Suzuki, Y., Gunji, A., Kanehisa, H., & Fukunaga, T.
- Affiliations
- The University of Tokyo (JP)
- Seigakuin University (JP)
- Venue
- European Journal of Applied Physiology
- Published
- 2001-02-16
- Volume
- 84
- Issue
- 1-2
- Pages
- 7-12
- ISSN
- 0020-9376 (ISSN-L)
- 1439-6319
- 1439-6327
- OpenAlex
- W1985902477
- Cited by
- 214
- References
- 0
- Citations by year
- 2026: 3 · 2025: 4 · 2024: 10 · 2023: 9 · 2022: 3 · 2021: 12 · 2020: 11 · 2019: 11 · 2018: 11 · 2017: 10 · 2016: 6 · 2015: 6 · 2014: 15 · 2013: 9 · 2012: 4
- FWCI
- 2.19
- Type
- journal article
- Language
- en
- Open access
- closed
- Licence
- www.springer.com/tdm (tdm)
- Locations
- European Journal of Applied Physiology (publishedVersion)
- PubMed (publishedVersion)
- Topics
- Health Sciences › Medicine › Physiology › Spaceflight effects on biology
- Life Sciences › Biochemistry, Genetics and Molecular Biology › Molecular Biology › Muscle Physiology and Disorders
- Health Sciences › Medicine › Complementary and alternative medicine › Cardiovascular and exercise physiology
- Keywords
- bed rest, resistance training, muscle atrophy, neuronal activation, motor unit activation, physiological cross-sectional area, quadriceps, countermeasures, microgravity
- MeSH terms
- Adolescent, Adult, Atrophy, Bed Rest, Humans, Knee Joint, Male, Muscle Contraction, Exercise, Muscle, Skeletal
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