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Liver and muscle glycogen oxidation and performance with dose variation of glucose-fructose ingestion during prolonged (3 h) exercise.

PMID: 30840136 (view PubMed database entry)
DOI: 10.1007/s00421-019-04106-9 (read at publisher's website )
PMCID: PMC6469629 (free full text version available)

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Andy J King, John P O'Hara, Nicola C Arjomandkhah, Josh Rowe, Douglas J Morrison, Thomas Preston, Roderick F G J King,

<h4>Purpose</h4>This study investigated the effect of small manipulations in carbohydrate (CHO) dose on exogenous and endogenous (liver and muscle) fuel selection during exercise.<h4>Method</h4>Eleven trained males cycled in a double-blind randomised order on 4 occasions at 60% [Formula: see text] for 3 h, followed by a 30-min time-trial whilst ingesting either 80 g h<sup>-1</sup> or 90 g h<sup>-1</sup> or 100 g h<sup>-1 13</sup>C-glucose-<sup>13</sup>C-fructose [2:1] or placebo. CHO doses met, were marginally lower, or above previously reported intestinal saturation for glucose-fructose (90 g h<sup>-1</sup>). Indirect calorimetry and stable mass isotope [<sup>13</sup>C] techniques were utilised to determine fuel use.<h4>Result</h4>Time-trial performance was 86.5 to 93%, 'likely, probable' improved with 90 g h<sup>-1</sup> compared 80 and 100 g h<sup>-1</sup>. Exogenous CHO oxidation in the final hour was 9.8-10.0% higher with 100 g h<sup>-1</sup> compared with 80 and 90 g h<sup>-1</sup> (ES = 0.64-0.70, 95% CI 9.6, 1.4 to 17.7 and 8.2, 2.1 to 18.6). However, increasing CHO dose (100 g h<sup>-1</sup>) increased muscle glycogen use (101.6 ± 16.6 g, ES = 0.60, 16.1, 0.9 to 31.4) and its relative contribution to energy expenditure (5.6 ± 8.4%, ES = 0.72, 5.6, 1.5 to 9.8 g) compared with 90 g h<sup>-1</sup>. Absolute and relative muscle glycogen oxidation between 80 and 90 g h<sup>-1</sup> were similar (ES = 0.23 and 0.38) though a small absolute (85.4 ± 29.3 g, 6.2, - 23.5 to 11.1) and relative (34.9 ± 9.1 g, - 3.5, - 9.6 to 2.6) reduction was seen in 90 g h<sup>-1</sup> compared with 100 g h<sup>-1</sup>. Liver glycogen oxidation was not significantly different between conditions (ES < 0.42). Total fat oxidation during the 3-h ride was similar in CHO conditions (ES < 0.28) but suppressed compared with placebo (ES = 1.05-1.51).<h4>Conclusion</h4>'Overdosing' intestinal transport for glucose-fructose appears to increase muscle glycogen reliance and negatively impact subsequent TT performance.

Eur J Appl Physiol (European journal of applied physiology)
[2019, 119(5):1157-1169]

Cited: 6 times

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