Purpose: To compare fuel selection during prolonged arm (AE) and leg exercise (LE) with water or glucose ingestion.
Methods: Ten subjects (V˙O2max: 4.77 ± 0.20 and 3.36 ± 0.15 L·min−1 for LE and AE, respectively) completed 120 min of LE and AE at 50% of the mode-specific maximal power output (353 ± 18 and 160 ± 9 W, respectively) with ingestion of water (20 mL·kg−1) or 13C-glucose (2 g·kg−1). Substrate oxidation was measured using indirect respiratory calorimetry corrected for urea excretion and 13CO2 production at the mouth.
Results: The contribution of protein oxidation to the energy yield (%En) was higher during AE than LE (∼8% vs ∼4%) because of the lower energy expenditure and was not significantly modified with glucose ingestion. With water ingestion, the %En from CHO oxidation was not significantly different during LE and AE (64 ± 2% and 66 ± 2%, respectively). Glucose ingestion significantly increased the %En from total CHO oxidation during AE (78 ± 3%) but not during LE (71 ± 2%). Exogenous glucose oxidation was not significantly different in AE and LE (56 ± 4 and 65 ± 3 g, respectively), but the %En from exogenous glucose was higher during AE than LE (30 ± 1% and 24 ± 1%) because of the lower energy expenditure. When glucose was ingested, the %En from endogenous CHO oxidation was significantly reduced during both AE (66 ± 2% to 48 ± 3%) and LE (64 ± 2% to 47 ± 3%) and was not significantly different in the two modes of exercise.
Conclusions: The difference in fuel selection between AE and LE when water was ingested was modest with a slightly higher reliance on CHO oxidation during AE. The amount of exogenous glucose oxidized was lower but its %En was higher during AE because of the lower energy expenditure.