title: Effects of exercise on soleus in severe burn and muscle disuse atrophy.
abstract: BACKGROUND
  Muscle loss is a sequela of severe burn and critical illness with bed rest contributing significantly to atrophy. We hypothesize that exercise will mitigate muscle loss after burn with bed rest.
  
  
  METHODS
  Male rats were assigned to sham ambulatory (S/A), burn ambulatory (B/A), sham hindlimb unloading (S/H), or burn hindlimb unloading (B/H). Rats received a 40% scald burn or sham and were ambulatory or placed in hindlimb unloading, a model of bed rest. Half from each group performed twice daily resistance climbing. Hindlimb isometric forces were measured on day 14.
  
  
  RESULTS
  Soleus mass and muscle function were not affected by burn alone. Mass was significantly lower in hindlimb unloading (79 versus 139 mg, P < 0.001) and no exercise (103 versus 115 mg, P < 0.01). Exercise significantly increased soleus mass in B/H (86 versus 77 mg, P < 0.01). Hindlimb unloading significantly decreased muscle force in the twitch (12 versus 31 g, P < 0.001), tetanic (55 versus 148 g, P < 0.001), and specific tetanic measurements (12 versus 22 N/cm(2), P < 0.001). Effects of exercise on force depended on other factors. In B/H, exercise significantly increased twitch (14 versus 8 g, P < 0.05) and specific tetanic force (14 versus 7 N/cm(2), P < 0.01). Fatigue index was lower in ambulatory (55%) and exercise (52%) versus hindlimb (69%, P = 0.03) and no exercise (73%, P = 0.002).
  
  
  CONCLUSIONS
  Hindlimb unloading is a significant factor in muscle atrophy. Exercise increased the soleus muscle mass, twitch, and specific force in this model. However, the fatigue index decreased with exercise in all groups. This suggests exercise contributes to functional muscle change in this model of disuse and critical illness.
authors.affiliation: Department of Surgery, University of Texas Southwestern Medical Center, Dallas, Texas. Electronic address: Melody.Saeman@UTSouthwestern.edu.
authors.forename: Melody R
authors.initials: MR
authors.lastname: Saeman
authors.affiliation: Department of Surgery, University of Texas Southwestern Medical Center, Dallas, Texas.
authors.forename: Kevin
authors.initials: K
authors.lastname: DeSpain
authors.affiliation: Department of Surgery, University of Texas Southwestern Medical Center, Dallas, Texas.
authors.forename: Ming-Mei
authors.initials: MM
authors.lastname: Liu
authors.affiliation: Department of Surgery, University of Texas Southwestern Medical Center, Dallas, Texas.
authors.forename: Brett A
authors.initials: BA
authors.lastname: Carlson
authors.affiliation: Department of Surgery, University of Texas Southwestern Medical Center, Dallas, Texas.
authors.forename: Juquan
authors.initials: J
authors.lastname: Song
authors.affiliation: Department of Surgery, University of Texas Health Science Center at Houston, Houston, Texas.
authors.forename: Lisa A
authors.initials: LA
authors.lastname: Baer
authors.affiliation: Department of Surgery, University of Texas Health Science Center at Houston, Houston, Texas.
authors.forename: Charles E
authors.initials: CE
authors.lastname: Wade
authors.affiliation: Department of Surgery, University of Texas Southwestern Medical Center, Dallas, Texas.
authors.forename: Steven E
authors.initials: SE
authors.lastname: Wolf
mesh_terms: D000818:Animals; D002056:Burns / Q000150:complications* / Q000503:physiopathology; D006614:Hindlimb / Q000503:physiopathology; D008297:Male; D018482:Muscle, Skeletal / Q000503:physiopathology*; D020966:Muscular Disorders, Atrophic / Q000209:etiology*; D010805:Physical Conditioning, Animal; D051381:Rats; D017207:Rats, Sprague-Dawley
keywords: Bed rest; Burn; Critical illness; Muscle atrophy