Effects of 10, 90, 120 and 150 G.H -1 CHO on Substrate Metabolism, Exogenous Oxidation and Exercise Capacity: Implications for CHO Personalization

Purpose: Given recent controversy surrounding the optimal CHO intake during exercise, we assessed the effects of CHO ingestion at rates of 10, 90, 120 and 150 g.h -1 on substrate metabolism and exercise capacity. Methods: Eight trained males cycled for 3 hours, followed by an exercise capacity test (150% lactate threshold). Participants completed an initial familiarization comprising 10 g.h -1 (maltodextrin) with subsequent trials randomized (90, 120 and 150 g.h -1 : 1:0.8 ratio of maltodextrin to fructose drinks enriched with [U 13 -C] glucose-fructose). Results: Mean exogenous CHO oxidation increased in a dose dependent manner where 150 > 120 > 90 g.h -1 (1.62 ± 0.45; 1.48 ± 0.44; 1.23 ± 0.35 g.min -1 , respectively, all P<0.05), though substantial variation was observed within trials (range of 0.3, 0.6 and 0.9 g.min -1 for 90, 120 and 150 g.h -1 , respectively). Whole-body CHO oxidation did not differ (P=0.97) between 150 and 120 g.h -1 (both trials = 2.6 ± 0.3 g.min -1 ), with both trials greater than 90 and 10 g.h -1 (2.3 ± 0.5; 1.7 ± 0.7 g.min -1 , respectively). Blood glucose was lower in 10 g.h -1 (3.8 ± 0.2, P<0.01) versus 90, 120 and 150 g.h -1 (4.6 ± 0.2, 4.6 ± 0.1, 4.8 ± 0.2 mmol.L -1 ; P>0.05 between higher doses). Total exercise duration was lower in 10 g.h -1 (2:41:28 ± 0:24:47 h:min:secs,) versus 90 (3:04:59 ± 0:01:52), 120 (3:05:24 ± 0:03:28, both P<0.05) and 150 g.h -1 (3:00:39 ± 0:07:00, P=0.06), with no differences (P>0.05) between higher rates. Optimal exercise capacity was achieved with 107 g.h -1 (95 % CI: 92-122 g.h -1 ) Conclusions: Data demonstrate 150 g.h -1 does not increase whole-body CHO oxidation versus 120 g.h -1 , though variations in ergogenic dose and exogenous CHO oxidation rates support CHO personalization.