Journal Article

220 A Long-term of Resistant Exercise Decreased Rat Muscle Function in Fast Twitch Myofiber Dominated Plantaris

J Song, K DeSpain, L Baer, J Burchfield, K Nutall, S Vincent, C Wade and S E Wolf

in Journal of Burn Care & Research

Volume 39, issue suppl_1, pages S77-S77
Published in print April 2018 | ISSN: 1559-047X
Published online April 2018 | e-ISSN: 1559-0488 | DOI: http://dx.doi.org/10.1093/jbcr/iry006.142
220 A Long-term of Resistant Exercise Decreased Rat Muscle Function in Fast Twitch Myofiber Dominated Plantaris

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Abstract

Introduction

We previously showed muscle function was impaired with hindlimb unloading in burned rats which was alleviated by insulin treatment and resistance exercise. In the current study, we investigated the role of continued resistance exercise to further improve function in a model designed to mimic the late recovery period akin to the rehabilitation phase in patients.

Methods

Twenty-four Sprague-Dawley rats received a full thickness 40% total body surface area (TBSA) burn and hindlimb unloading (HLU) to mimic severe burn with muscle disuse. All animals underwent exercise training twice a day with 5 climbs per training session. Resistance exercise was achieved by adding weight to the base of the tail and increased every 3 days. All rats were given a subcutaneous injection of either saline or pro zinc insulin 5U/kg daily. On day 14, all rats were removed from HLU and all injections stopped. Then, rats within each exercise treatment group were separated into no exercise (NEX) and exercise (EX) groups (n=6 per group) for an additional 14 days. On day 28, in situ isometric forces of the left soleus and plantaris muscles were measured. Values are presented as mean ± SD. Statistical analysis was by two-way ANOVA.

Results

Plantaris isometric twitch tension force (Pt) and muscle optimal length (Lo) significantly decreased with exercise treatment for 28 days (149.40 ± 16.95g NEX vs Pt: 131.99 ± 17.84g EX)(p=0.028); (39.42 ± 1.77mm NEX vs Lo: 37.08 ± 1.99mm EX)(p=0.008). However, soleus tetanic force (Po) increased significantly in those treated with insulin previously with or without continued exercise (183.01 ± 33.33g vehicle vs 220.61 ± 26.01g insulin)(p=0.01). Further, the ratio of single twitch force to maximal tetanic force (Pt/Po) significantly decreased in the soleus with exercise treatment (0.32 ± 0.08 NEX vs. 0.26 ± 0.02 EX)(p=0.037).

Conclusions

In our previous study, we found the combination of insulin treatment and exercise after burn and hindlimb unloading improved muscle function in both plantaris and soleus. In the current study, the effect of previous insulin treatment further augments improvements at 28 days after injury in slow twitch muscle. However, continued resistance exercise actually decreased muscle isometric force in the fast twitch myofiber dominated plantaris with no change in the slow-twitch soleus. The decrease in Pt/Po ratio in slow-twitch myofiber dominated soleus suggests a myofiber type change in response to continued resistance exercise.

Applicability of Research to Practice

The current study provides evidence of appropriate type of exercise in burn patient rehabilitation.

Journal Article.  0 words. 

Subjects: Medicine and Health ; Acute Medicine ; Emergency Medicine ; Critical Care ; Surgery

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