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Neuromuscular Adaptations Following 90 Days Bed Rest With or Without Resistance Exercise

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INTRODUCTION: This study examined the effects of long-term bed rest with or without a concurrent resistance exercise protocol on different muscle function indices of the knee extensors and their influence on previously shown atrophy, neural impairment, and slow-to-fast phenotype shift.

METHODS: Nine men underwent 90 d of bed rest only (BR), while eight men in addition performed maximal supine squats every third day (BRE). Before and at day 1 and 5 following bed rest, surface quadriceps electromyographic (EMG) activity was measured during a sustained (60-s) submaximal isometric action and rate of force development (RFD) was assessed during a maximal isometric action, both in the supine squat position. Maximal torque was measured during isokinetic knee extensions at different angular velocities before and after (day 2 and 11) bed rest.

RESULTS: EMG amplitude at a fixed submaximal load increased in BR, but not in BRE. The increase in amplitude during the sustained action was elevated in BR but not in BRE. RFD decreased in BR; this effect was attenuated day 1 and normalized day 5 in BRE. RFD expressed relative to maximal force was maintained in both groups. Angle-specific torque decreased equally for all velocities in BR. The decrease in isokinetic strength was attenuated day 2 in BRE.

DISCUSSION: Phenotype changes were not reflected in muscle function measurements, probably because they were overridden by the effects of atrophy and neural adaptation. The protective effect of resistance exercise was more pronounced in tasks similar to the training action, inferring great impact of neural mechanisms.

Alkner BA, Norrbrand L, Tesch PA. Neuromuscular adaptations following 90 days bed rest with or without resistance exercise. Aerosp Med Hum Perform. 2016; 87(7):610–617.
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Keywords: electromyography; fatigue; force-velocity; rate of force development; spaceflight

Document Type: Research Article

Affiliations: Department of Orthopaedics, Eksjö, Region Jönköping County, and Department of Clinical and Experimental Medicine, Linköping University, Linköping, Sweden

Publication date: July 1, 2016

More about this publication?
  • This journal (formerly Aviation, Space, and Environmental Medicine), representing the members of the Aerospace Medical Association, is published monthly for those interested in aerospace medicine and human performance. It is devoted to serving and supporting all who explore, travel, work, or live in hazardous environments ranging from beneath the sea to the outermost reaches of space. The original scientific articles in this journal provide the latest available information on investigations into such areas as changes in ambient pressure, motion sickness, increased or decreased gravitational forces, thermal stresses, vision, fatigue, circadian rhythms, psychological stress, artificial environments, predictors of success, health maintenance, human factors engineering, clinical care, and others. This journal also publishes notes on scientific news and technical items of interest to the general reader, and provides teaching material and reviews for health care professionals.

    To access volumes 74 through 85, please click here.
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