Application of 13C MRS demonstrates carbohydrate feeding spares muscle but not liver glycogen utilisation during high-intensity interval exercise

Hannon, SC, Henthorn, L, Vadher, J, Montgomery, C ORCID: 0000-0003-2805-5807, Pavis, GF, Stephens, FB, Wall, BT, Hodson, N, Morton, JP ORCID: 0000-0003-2776-2542, Kennerley, AJ and Hearris, MA (2026) Application of 13C MRS demonstrates carbohydrate feeding spares muscle but not liver glycogen utilisation during high-intensity interval exercise. American Journal of Physiology. Endocrinology and Metabolism, 331 (3). E320-E334. ISSN 0193-1849

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Abstract

We examined liver and muscle glycogen utilization during high-intensity interval cycling, and the impact of carbohydrate (CHO) feeding, using noninvasive 13C magnetic resonance spectroscopy (MRS). Following 24 h of standardized dietary intake, nine male cyclists completed 8 × 5-min intervals (1-min recovery), ingesting either placebo (PLA), 60 g maltodextrin (CHO), or 60 g maltodextrin plus caffeine, taurine, l-theanine, l-citrulline, and citicoline (CHO+) in a randomized crossover design. 13C MRS and 1H imaging were performed pre- and postexercise to determine liver and muscle glycogen and liver volume, respectively. Liver glycogen utilization was not significantly different between trials (P = 0.101) despite lower postexercise plasma glucagon concentrations in CHO and CHO+ (P = 0.001). In contrast, muscle glycogen utilization was significantly lower (∼40%) with CHO feeding compared with PLA (P = 0.006), yet this sparing effect was not evident with CHO+ (P = 0.073) in accordance with a higher mean power output during the late intervals (+2.8%, P = 0.046). Plasma glucose was comparable between trials (P = 0.175), whereas plasma lactate was higher in CHO+ versus CHO (P = 0.003), alongside lower blood bicarbonate (P = 0.005), base excess (P < 0.001), and total CO2 (P = 0.004). These findings demonstrate preferential use of skeletal muscle glycogen during high-intensity interval training (HIIT), which is attenuated under conditions of CHO feeding. This sparing effect is, however, not evident with the coingestion of a caffeine-containing multi-ingredient blend, potentially due to an increased capacity to sustain higher power outputs resulting in greater glycogen utilization.
NEW & NOTEWORTHY Using 13C MRS, we provide data demonstrating preferential use of skeletal muscle glycogen during HIIT. Furthermore, data show muscle glycogen utilization is attenuated with CHO feeding, yet sparing is not evident when coingesting a caffeine-containing formulation, potentially reflecting increased capacity to perform more total work rather than a direct metabolic effect of caffeine. In contrast, liver glycogen utilization was not significantly different with CHO feeding despite a modest reduction of ∼5 g versus placebo.

Item Type:	Article
Uncontrolled Keywords:	Muscle, Skeletal; Liver; Humans; Carbon Isotopes; Caffeine; Glycogen; Liver Glycogen; Dietary Carbohydrates; Polysaccharides; Magnetic Resonance Spectroscopy; Cross-Over Studies; Adult; Male; Young Adult; Carbon-13 Magnetic Resonance Spectroscopy; High-Intensity Interval Training; 13C magnetic resonance spectroscopy; HIIT; exercise; glycogen; liver; Male; Humans; Muscle, Skeletal; Liver; Dietary Carbohydrates; High-Intensity Interval Training; Glycogen; Adult; Cross-Over Studies; Caffeine; Liver Glycogen; Magnetic Resonance Spectroscopy; Polysaccharides; Carbon Isotopes; Carbon-13 Magnetic Resonance Spectroscopy; Young Adult; 32 Biomedical and Clinical Sciences; 42 Health Sciences; 4207 Sports Science and Exercise; Digestive Diseases; Liver Disease; Nutrition; Clinical Research; Clinical Trials and Supportive Activities; Biomedical Imaging; Male; Humans; Muscle, Skeletal; Liver; Dietary Carbohydrates; High-Intensity Interval Training; Glycogen; Adult; Cross-Over Studies; Caffeine; Liver Glycogen; Magnetic Resonance Spectroscopy; Polysaccharides; Carbon Isotopes; Carbon-13 Magnetic Resonance Spectroscopy; Young Adult; 06 Biological Sciences; 11 Medical and Health Sciences; Endocrinology & Metabolism; 31 Biological sciences; 32 Biomedical and clinical sciences; 42 Health sciences
Subjects:	B Philosophy. Psychology. Religion > BF Psychology T Technology > TX Home economics > TX341 Nutrition. Foods and food supply R Medicine > RC Internal medicine
Divisions:	Psychology (from Sep 2019) Sport and Exercise Sciences
Publisher:	American Physiological Society
Date of acceptance:	25 July 2026
Date of first compliant Open Access:	21 September 2026
Date Deposited:	21 Sep 2026 10:11
Last Modified:	21 Sep 2026 10:11
DOI or ID number:	10.1152/ajpendo.00139.2026
URI:	https://researchonline.ljmu.ac.uk/id/eprint/29475

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