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Purpose: To examine the effects of 7-d of beetroot juice (BRJ) supplementation on SkM contractile characteristics and function. Methods: Recreationally active males (n=8) underwent transcutaneous electrical muscle stimulation of the vastus lateralis for evaluation of contractile characteristics before (pre) and after (post) 7-d of BRJ supplementation (280 mL/day, ~26 mmol NO3-). An additional group of individuals (n=8) followed the same supplementation protocol but underwent SkM biopsies pre/post supplementation for determination of proteins associated with calcium handling via Western blotting, and the ratio of reduced/oxidized glutathione (GSH:GSSG), an indicator of cellular redox state, via HPLC. Results: Following supplementation, there was no change in maximal voluntary force production (602 ± 50 vs 596 ± 56 N), or electrically-induced tetanic contractions. In contrast, force production was increased at 10 Hz electrical stimulation (41.1 ± 2.3 vs 37.6 ± 2.4% of peak force, p < 0.05), as was peak twitch tension (164.0 ± 12.5 vs 136.5 ± 7.2 N, p < 0.01) and maximal rates of force development and relaxation (3582.8 ± 382.3 vs 2575.7 ± 196.2 and -2752.4 ± 423.9 vs -2104.4 ± 249.0 N/s, respectively, p < 0.05). Despite these measurements implicating a change in calcium handling, the content of associated proteins (SERCA1a, SERCA2a, dihydropyradine receptor, ryanodine receptor, calsequestrin), and the GSH:GSSG ratio were unaltered by BRJ. Conclusion: BRJ supplementation increases force production at low stimulation frequencies, however in human SkM this is independent of changes in redox stress or the expression of protein targets associated with calcium handling.


Mary MacKillop Institute for Health Research

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