The effect of a carbohydrate beverage on the physiological responses during prolonged load carriage

Abstract

Effects of a carbohydrate beverage on the physiological responses to load carriage were examined. Ten fit male participants (age: 28 ± 9 years, body mass: 81.5 ± 10.5 kg, $\dot{V}$O_2max: 55.0 ± 5.5 mL kg⁻¹ min⁻¹) completed two test conditions in random order, walking on a treadmill (6.5 km h⁻¹) for 120 min, carrying a 25-kg backpack. At 0 and 60 min of exercise participants consumed 250 mL of a placebo (flavoured water) (PLA) or 6.4% carbohydrate (CHO) beverage. There were no differences in $\dot{V}$O_2, respiratory exchange ratio (RER), heart rate or EMG activity of m. rectus femoris, m. vastus lateralis, m. semitendinosus and m. biceps femoris between conditions at minute 5 of exercise. The increase in $\dot{V}$O₂ between minutes 5 and 120 was less during CHO than PLA (8 ± 5 vs. 14 ± 6%, P = 0.036). RER decreased during PLA, from 0.96 ± 0.05 at minute 5 to 0.87 ± 0.04 at minute 120 (P < 0.001), but not during CHO (P = 0.056). Heart rate increased between minutes 5 and 120 during PLA (16 ± 10%, P < 0.001) and CHO (12 ± 6%, P < 0.001), with no difference between conditions (P = 0.251). EMG peak RMS did not change between minutes 7 and 107 during PLA or CHO for the leg muscles. However, individual responses in EMG were highly variable (i.e. both increases and decreases in RMS). It was concluded that carbohydrate intake during load carriage reduced the $\dot{V}$O₂ drift, which could be partially attributed to higher carbohydrate oxidation rates. Despite muscle fatigue/damage previously being identified as a cause of $\dot{V}$O₂ drift, it appears that carbohydrate had no effect on neuromuscular responses during load carriage.