M. R. Saeman1, K. DeSpain1, L. A. Baer2, J. Song1, C. E. Wade2, S. E. Wolf1 1University Of Texas Southwestern Medical Center At Dallas,Surgery,Dallas, TEXAS, USA 2University Of Texas Health Science Center At Houston,Surgery,Houston, TEXAS, USA
Introduction: Muscle loss is a consequence of severe burn and critical illness increasing sepsis risk and recovery time. Previously, a rat model of hindlimb unloading after burn found bedrest contributes significantly to atrophy. In this model, we found that exercise increased the function and changed the fiber composition of slow-twitch muscle. We hypothesize that insulin with exercise will further diminish the loss of muscle function in burn with bedrest.
Methods: Twenty-four male Sprague-Dawley rats received a full thickness 40% total body surface area (TBSA) burn and were randomly assigned (n=6) to vehicle without exercise (V/No), insulin (pro zinc 40U daily) without exercise (I/No), vehicle with exercise (V/Ex), or insulin with exercise (I/Ex). All animals were placed in a tail traction system for hindlimb unloading to mimic bed rest immediately following burn. The exercise group was trained to perform twice daily weighted resistance climbing of 1 meter with 5 repetitions. On day 14 in situ isometric forces of the left soleus and plantaris muscles were measured. Fatigue measurement was performed in only the soleus. Statistical analysis was performed with Sigma Plot using Student’s t-test or ANOVA where appropriate.
Results: There was no significant change in animal body mass between treatments. The physiological cross sectional area (PCSA) of the plantaris increased with combined insulin and exercise. The tetanic (Po) and twitch (Pt) muscle functions were significantly elevated in the plantaris of I/Ex. However, there was no change in the tetanic force when normalized to PCSA (Po/CSA). The soleus had significant elevation of Po, Pt, Po/CSA, fatigue maximum, and fatigue minimum in I/Ex. Please refer to the table for specific values and significance.
Conclusion: Insulin and resistance exercise have a positive combined effect on the hindlimb muscle function in this model of critical illness. The plantaris muscle demonstrated increased physiological cross sectional area with increased force suggesting a net increase in muscle fibers. Previously, we found no change in plantaris with exercise only. The soleus demonstrated a change in the specific force of the muscle and fatigue functions indicating a change in the composition of muscle fiber types.
