Author(s): MARTYN, H., STELLINGWERFF, T.2,3, GONZALEZ, J.4, BURKE, L.5, OWENS, D.1, PUGH, J.1, MORTON, J.1, Institution: LIVERPOOL JOHN MOORES UNIVERSITY , Country: UNITED KINGDOM, Abstract-ID: 2556

INTRODUCTION:
Recent data suggest athletes may benefit from carbohydrate (CHO) ingestion rates ≥120 g.h-1 (1). However, alternative views suggest as little as 10 g.h-1 is sufficient to prevent hypoglycaemia (<4 mmol.L-1) during prolonged sub-maximal exercise and promote endurance performance (2). Accordingly, the aim of this study was to evaluate the effects of CHO intakes of 10, 90, 120 and 150 g.h-1 on substrate metabolism and exercise capacity.
METHODS:
In a randomised crossover design (after a 24 h CHO intake and pre-exercise meal of 8 and 2 g.kg-1, respectively), eight male cyclists (VO2max; 73 ± 7 ml.kg-1.min-1) ingested 90, 120 and 150 g.h-1 CHO during 3 h cycling (consisting of 2 h at 95% of their power output at lactate threshold (LT), a subsequent 1 h period where 3 x 5 min intervals at lactate turn-point were interspersed with 15 min periods at 95% of LT) followed by exercise to exhaustion at 150 % LT. CHO was consumed in fluid form and doses of 90–150 g.h-1 comprised a 1:0.8 ratio of maltodextrin to fructose ([U13C]-glucose and [U13C]-fructose enriched). Participants completed an initial familiarisation trial where they consumed 10 g.h-1 (maltodextrin only).
RESULTS:
Blood glucose during exercise was not different between 90, 120 and 150 g.h-1 (4.6 ± 0.4, 4.6 ± 0.4, 4.8 ± 0.4 mmol.L-1 respectively; all P > 0.05), but was lower in the 10 g.h-1 trial (3.8 ± 0.3 mmol.L-1, all P < 0.01) compared with all other doses. Whole-body CHO oxidation (2.6 ± 0.5; 2.3 ± 0.6; 1.7 ± 0.8 g.min-1, respectively) increased in a dose dependent manner such that 120 > 90 > 10 g.h-1 (all P < 0.01), though 150 (2.6 ± 0.5 g.min-1, P = 0.99) was not different to 120 g.h-1. Mean exogenous CHO oxidation during hour 3 was greater in 120 (1.80 ± 0.07 g.min-1; P < 0.01) compared to 90 g.h-1 (1.44 ± 0.07 g.min-1) though differences between 150 (1.94 ± 0.12 g.min-1) and 120 g.h-1 did not achieve significance (P = 0.07). The contribution of CHO towards whole-body energy expenditure during hour 3 was not different between 120 and 150 g.h-1 (57 ± 7 vs 57 ± 4 %, P = 0.96), though both doses achieved greater CHO dependency compared to the 90 (45 ± 5 %, both P < 0.01) and 10 g.h-1 trials (27 ± 5 %, all P < 0.01). Total exercise duration was not different between 90, 120 and 150 g.h-1 (3:04:59 ± 0:01:52, 3:05:24 ± 0:03:28, 3:00:39 ± 0:07:00 h:min:sec; all P > 0.05), though was less in the 10 g.h-1 trial (2:41:28 ± 0:24:47, all P < 0.05) compared to all other doses.
CONCLUSION:
We conclude 1) 150 g.h-1 CHO does not increase whole body CHO oxidation (despite small increases in exogenous oxidation) nor provide any ergogenic advantage over and above 120 g.h-1, 2) 120 g.h-1 maintains CHO dependency to a greater extent than 90 g.h-1, and 3) 10 g.h-1 does not prevent hypoglycaemia, impairs exercise capacity compared to 90-150 g.h-1, and is not recommended for optimal endurance performance.

1. Hearris et al., 2022. J Appl Physiol, 132; 1394–1406
2. Prins et al., 2025. Am J Physiol Cell Physiol, 328: C710–C727