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, VO(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 VO(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 VO(2) 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 VO(2) drift, which could be partially attributed to higher carbohydrate oxidation rates. Despite muscle fatigue/damage previously being identified as a cause of VO(2) drift, it appears that carbohydrate had no effect on neuromuscular responses during load carriage.

Effects of load carriage and footwear on spatiotemporal parameters, kinematics, and metabolic cost of walking

“…Maintaining balance and supporting a larger mass while loaded requires additional muscular efforts that increase the steady state cost of walking [6]. The short bouts of loaded walking in this study did not induce fatigue, but longer durations of loaded walking have been suggested to decrease stability and possibly increase risk of falls [23] as lower limb muscles fatigue and the cost of walking continues to increase [24]. Besides tripping, load carriage may elevate the risk of lower limb trauma as a result of the increased demands placed on the lower limbs [3] and/or be associated with the incidence of low back pain in college students [1].…”

Negative, Null and Beneficial Effects of Drinking Water on Energy Intake, Energy Expenditure, Fat Oxidation and Weight Change in Randomized Trials: A Qualitative Review

“…Blacker et al [ 112 ] compare 250 mL flavored water (placebo) with 250 mL 6.4% carbohydrate beverage in healthy men walking on a treadmill, carrying a 25-kg backpack. The placebo results in greater oxygen consumption and lower RER than the carbohydrate beverage.…”

Preloaded Time Trial to Assess Load Carriage Performance

“…whilst on patrol) and also at highintensity levels (e.g. during engagement) (6). Although it is inherently difficult to devise a laboratorybased protocol which precisely reflects operational requirement as the load, intensity, duration, terrain and environment vary with each scenario; protocols should more closely reflect the physiological characteristics of activities encountered in military situations such as during training or pre-deployment assessments.…”