Head-down tilt bed rest with or without artificial gravity is not associated with motor unit remodeling.
PURPOSE
The objective of this study was to assess whether artificial gravity attenuates any long-duration head-down 60 bed rest (HDBR)-induced alterations in motor unit (MU) properties.


METHODS
Twenty-four healthy participants (16 men; 8 women; 26-54 years) underwent 60-day HDBR with (n = 16) or without (n = 8) 30 min artificial gravity daily induced by whole-body centrifugation. Compound muscle action potential (CMAP), MU number (MUNIX) and MU size (MUSIX) were estimated using the method of Motor Unit Number Index in the Abductor digiti minimi and tibialis anterior muscles 5 days before (BDC-5), and during day 4 (HDT4) and 59 (HDT59) of HDBR.


RESULTS
The CMAP, MUNIX, and MUSIX at baseline did not change significantly in either muscle, irrespective of the intervention (p > 0.05). Across groups, there were no significant differences in any variable during HDBR, compared to BDC-5.


CONCLUSION
Sixty days of HDBR with or without artificial gravity does not induce alterations in motor unit number and size in the ADM or TA muscles in healthy individuals.
['Attias|Julia|J|http://orcid.org/0000-0003-3420-7977', 'Grassi|Andrea|A|', 'Bosutti|Alessandra|A|http://orcid.org/0000-0002-8651-818X', 'Ganse|Bergita|B|http://orcid.org/0000-0002-9512-2910', 'Degens|Hans|H|http://orcid.org/0000-0001-7399-4841', 'Drey|Michael|M|http://orcid.org/0000-0001-6709-9672']
D000328:Adult D001510:Bed Rest D005260:Female D018475:Head-Down Tilt D006801:Humans D008297:Male D008875:Middle Aged D018485:Muscle Fibers, Skeletal D011897:Random Allocation D018474:Weightlessness Simulation
Bed rest Motor unit MUNIX Microgravity Muscle strength Neuromuscular Spaceflight