Whilst theoretically, body size should influence the capacity for intestinal carbohydrate absorption and thus exogenous oxidation rates during exercise, there is currently little empirical evidence to support this hypothesis. Accordingly, current nutrition guidelines for carbohydrate intake during exercise do not take body mass into account. Therefore, there is a need to establish whether body mass is related to exogenous carbohydrate oxidation rates during exercise. If such a relationship is established, this would lay the foundation to revise the current sports nutrition guidelines regarding carbohydrate intake during exercise.

The aims of this study are, therefore, to: 1) establish whether larger individuals display higher rates of exogenous carbohydrate oxidation than smaller individuals; and 2) establish if such a difference can be explained by the higher absolute exercise intensity, and thus the energy demand of exercise. It is hypothesised that larger individuals will demonstrate higher exogenous carbohydrate oxidation rates than smaller individuals, and that this difference will be partly (but not completely) diminished when the absolute intensity of exercise is matched.

Inclusion Criteria:

• Able to cycle continuously for 2 hours at a moderate intensity
• VO2max of between 40-75 mL/kg/min
• Fat-mass index (determined by dual energy x-ray absorptiometry) < 5.5 kg·m-2

Exclusion Criteria:

• Diagnosed disorders of the gastrointestinal tract (e.g. crohn's, colitis etc.)
• People following a low-carbohydrate, high-fat diet
• Pregnant or lactating
• Diagnosed cardiovascular disease
• Possible symptoms of cardiovascular disease
• Diagnosis of diabetes of any type
• Hypercholesterolaemia (total cholesterol ≥ 6.2 mmol/L
• Hypertension (systolic blood pressure ≥140 mmHg or diastolic blood pressure ≥90 mmHg)
• Current smoker
• Family history of coronary artery disease (first-degree relative <60 years)
• Prevalence of vascular disease
• Autonomic neuropathy
• Kidney disease
• Diagnosed pulmonary disease (e.g. chronic obstructive pulmonary disease, asthma, interstitial lung disease or cystic fibrosis)
• Blood borne disease or infection
• Osteoporosis
• Osteoarthritis
• Blood clotting disorders
• Food intolerances/allergies (these may not specifically exclude you- please talk to the investigator)
• Sensitivity or allergy to anaesthetic

Trained cyclists or triathletes