AUTHOR=McMahon Gerard , Morse Christopher I. , Winwood Keith , Burden Adrian , Onambélé Gladys L. 

TITLE=Circulating Tumor Necrosis Factor Alpha May Modulate the Short-Term Detraining Induced Muscle Mass Loss Following Prolonged Resistance Training

JOURNAL=Frontiers in Physiology

VOLUME=10

YEAR=2019

URL=https://www.frontiersin.org/journals/physiology/articles/10.3389/fphys.2019.00527

DOI=10.3389/fphys.2019.00527

ISSN=1664-042X

ABSTRACT=<sec><title>Introduction</title><p>Tumor necrosis factor alpha (TNFα) is a pro-inflammatory cytokine that has been shown to modulate muscle mass, and is responsive to exercise training. The effects of resistance training (RT) followed by a short period of detraining on muscle size, architecture and function in combination with circulating TNFα levels have not been previously investigated in a young, healthy population.</p></sec><sec><title>Methods</title><p>Sixteen participants (8 males and 8 females) were randomly assigned to a training group (TRA; age 20 ± 3 years, mass 76 ± 7 kg), whilst fourteen participants (7 males and 7 females) age 22 ± 2 years, mass 77 ± 6 kg were assigned to a control group (CON). Measures of vastus lateralis (VL) muscle size (normalized physiological cross-sectional area allometrically scaled to body mass; npCSA), architecture (fascicle length; L<sub>F</sub>, pennation angle Pθ), strength (knee extensor maximal voluntary contraction; KE MVC), specific force, subcutaneous fat (SF) and circulating TNFα were assessed at baseline (BL), post 8 weeks RT (PT), and at two (DT1) and four (DT2) weeks of detraining.</p></sec><sec><title>Results</title><p>Pooled BL TNFα was 0.87 ± 0.28 pg/mL with no differences between groups. BL TNFα tended to be correlated with npCSA (<italic>p</italic> = 0.055) and KEMVC (<italic>p</italic> = 0.085) but not specific force (<italic>p</italic> = 0.671) or SF (<italic>p</italic> = 0.995). There were significant (<italic>p</italic> &lt; 0.05) increases in npCSA compared to BL and CON in TRA at PT, DT1, and DT2, despite significant (<italic>p</italic> &lt; 0.05) decreases in npCSA compared to PT at DT1 and DT2. There were significant (<italic>p</italic> &lt; 0.05) increases in L<sub>F</sub>, Pθ and KE MVC at PT but only L<sub>F</sub> and torque at DT1. There were no significant (<italic>p</italic> &gt; 0.05) changes in SF, specific force or TNFα at any time points. There was a significant correlation (<italic>p</italic> = 0.022, <italic>r</italic> = 0.57) between the relative changes in TNFα and npCSA at DT2 compared to PT.</p></sec><sec><title>Discussion</title><p>Neither RT nor a period of short term detraining altered the quality of muscle (i.e., specific force) despite changes in morphology and function. TNFα does not appear to have any impact on RT-induced gains in muscle size or function, however, TNFα may play a role in inflammatory-status mediated muscle mass loss during subsequent detraining in healthy adults.</p></sec>