Human skeletal muscle protein breakdown during spaceflight

T. P. Stein, M. D. Schluter

Research output: Contribution to journalArticlepeer-review

38 Scopus citations


Human spaceflight is associated with a loss of body protein. Excretion of 3-methylhistidine (3-MH) in the urine is a useful measurement of myofibrillar protein breakdown. Bed rest, particularly with 6°head-down tilt, is an accepted ground-based model for human spaceflight. The objectives of this report were to compare 3-MH excretion from two Life Sciences shuttle missions (duration 9.5 and 15 days, n = 9) and from 17 days of bed rest (n = 7) with 6°head-down tilt. The bed rest study was designed to mimic an actual Life Sciences spaceflight and so incorporated an extensive battery of physiological tests focused on the musculoskeletal system. Results showed that nitrogen retention, based on excretion of nitrogen in the urine, was reduced during both bed rest [from 22 ± 1 to 1 ± 5 mg N·kg-1·day-1 (n = 7; P < 0.05)] and spaceflight [from 57 ± 9 to 19 ± 3 mg N·kg-1·day- 1 (n = 9; P < 0.05)]. 3-MH excretion was unchanged with either bed rest [pre-bed rest 5.30 ± 0.29 vs. bed rest 5.71 ± 0.30 μmol 3-MH·kg-1·day -1, n = 7;P = not significant (NS)] or spaceflight [preflight 4.98 ± 0.37 vs. 4.59 ± 0.39 μmol 3-MH·kg-1·day-1 in-flight, n = 9; P = NS]. We conclude that 1) 3-MH excretion was unaffected by spaceflight on the shuttle or with bed rest plus exercise, and 2) because protein breakdown (elevated 3- MH) was increased on Skylab but not on the shuttle, it follows that muscle protein breakdown is not an inevitable consequence of spaceflight.

Original languageEnglish (US)
Pages (from-to)E688-E695
JournalAmerican Journal of Physiology - Endocrinology and Metabolism
Issue number4 35-4
StatePublished - Apr 1997
Externally publishedYes

All Science Journal Classification (ASJC) codes

  • General Medicine


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