Table 1.

Some potential ‘barriers’ to carbohydrate ingestion and glucose infusion

Potential ‘Barrier’	Carbohydrate ingestion		Glucose infusion
	Issues	Potential solutions	Issues	Potential solutions
Gastric emptying	GI problems with high osmolality/hypertonic solutions	Isotonic or ↓CHO content solutions (> 60 min) Trainable	Not applicable
Intestinal absorption	Probable major barrier ↓Transportation (saturation of SGLT1 and GLUT5)	Upregulation with ↑CHO diet Multiple CHO transporter	Not applicable
Bypass liver	Uptake of Fructose by the liver Fructose → Glucose delay	Glucose or Multiple CHO transporters	Not applicable
Splanchnic blood flow	↓during exercise ↑gut permeability	↑flow in trained individuals	Not applicable
Muscle blood flow	Limited Q̇ Unable to provide all muscles with maximal flow during whole body exercise	↑with training adaptations	Limited Q̇ Unable to provide all muscles with maximal flow during whole body exercise	↑with training adaptations Possible ↑with high insulin
Muscle uptake	↓ Blood flow and GLUT4	↑with training adaptations ↑with increased insulin		↑with training adaptations ↑with insulin stimulation greater than ingested CHO
Muscle oxidation	CHO oxidation ↓with endurance training Limited number of protein carriers	Promoted by CHO intake Potential to supplement with probiotics to ↑oxidation	↓with endurance training	Significantly ↑with infusion