M. R. Saeman1, K. DeSpain1, M. Liu1, B. Carlson1, L. A. Baer2, J. Song1, C. E. Wade2, S. E. Wolf1 1University Of Texas Southwestern Medical Center,Surgery,Dallas, TEXAS, USA 2University Of Texas Health Science Center At Houston,Surgery,Houston, TEXAS, USA
Introduction:
Muscle loss is a known sequela of severe burn and critical illness that increases the risk of complications such as sepsis and prolonged recovery time. A prior study in a rat model of hindlimb unloading after burn supports that bedrest contributes significantly to muscle atrophy. The aim of our study was to evaluate if exercise mitigates the loss of muscle in this animal model.
Methods:
Two groups of 24 Sprague-Dawley rats were randomly assigned to burn ambulatory (B/A), burn hindlimb unloading (B/H), sham ambulatory (S/A), or sham hindlimb unloading (S/H). One group was trained to perform twice daily weighted resistance climbing of 1 meter with 5 repetitions; the other group had no exercise. Rats received a full thickness scald burn of 40% total body surface area or sham and were allowed to ambulate or were placed in a tail traction system for hindlimb unloading. On day 14 in situ isometric forces were measured on the left soleus muscle. Statistical analysis was performed with Sigma Plot using Student’s t-test, Mann Whitney, or ANOVA with Holm-Sidak method where appropriate.
Results:
The soleus wet weight was lower in the hindlimb (144 mg) and the exercise (136 mg) versus the ambulatory (190 mg, p<0.001), and no exercise (180 mg, p=0.01) groups. There was no difference in weights between burn and sham. Twitch was significantly lower in the hindlimb group: 31 vs 12 g (p<0.001). Compared to no exercise, the B/H exercise group had a significantly higher twitch force 14 vs. 8 g (p=0.04). Across all other factors there was no significant difference in the twitch between exercise and no exercise. There was a significantly lower tetanic force in the hindlimb group: 55 vs 148 g (p<0.001). B/A had a lower tetanic force in the exercise group versus no exercise: 118 vs 165g (p=0.02). In B/H no difference in tetanic force was seen with or without exercise. All hindlimb groups had significantly lower specific tetanic force than ambulatory: 12 vs. 22 N/cm2 (p<0.001). The specific tetanic force in B/H was significantly higher in exercise versus no exercise: 14 vs. 7 N/cm2 (p=0.008). Fatigue index was significantly lower in the ambulatory (55%) and exercise (52%) groups versus hindlimb (69%) and no exercise (73%) groups (p=0.03, p=0.002 respectively). Muscle function of all groups included in table.
Conclusion:
Hindlimb unloading is a significant factor in muscle atrophy with or without burn. Exercise increased soleus twitch and specific force in this model. However, there was a surprising decrease in muscle mass with exercise in all groups and a decrease in the fatigue index. These findings suggest that exercise contributes to a functional muscle change in a model of disuse and critical illness.
