Article

Carbohydrate availability and muscle energy metabolism during intermittent running.

Institute of Food, Nutrition and Human Health, Massey University, Auckland, New Zealand.
Medicine &amp Science in Sports &amp Exercise (impact factor: 4.43). 01/2008; 40(1):96-103. DOI:10.1249/mss.0b013e3181586b2c pp.96-103
Source: PubMed

ABSTRACT To examine the influence of ingesting a carbohydrate-electrolyte (CHO-E) solution on muscle glycogen use and intermittent running capacity after consumption of a carbohydrate (CHO)-rich diet.
Six male volunteers (mean +/- SD: age 22.7 +/- 3.4 yr; body mass (BM) 75.0 +/- 4.3 kg; V O2 max 60.2 +/- 1.6 mL x kg(-1) x min(-1)) performed two trials separated by 14 d in a randomized, crossover design. Subjects consumed either a 6.4% CHO-E solution or a placebo (PLA) in a double-blind fashion immediately before each trial (8 mL x kg(-1) BM) and at 15-min intervals (3 mL x kg(-1) BM) during intermittent high-intensity running to fatigue performed after CHO loading for 2 d. Muscle biopsy samples were obtained before exercise, after 90 min of exercise, and at fatigue.
Subjects ran longer in the CHO-E trial (158.0 +/- 28.4 min) compared with the PLA trial (131.0 +/- 19.7 min; P < 0.05). There were no differences in muscle glycogen use for the first 90 min of exercise (approximately 2 mmol of glucosyl units per kilogram of dry matter (DM) per minute). However, there was a trend for a greater use in the PLA trial after 90 min (4.2 +/- 2.8 mmol x kg(-1) DM x min(-1)) compared with the CHO-E trial (2.5 +/- 0.7 mmol x kg(-1) DM x min(-1); P = 0.10). Plasma glucose concentrations were higher at fatigue in the CHO-E than in the PLA trial (P < 0.001).
These results suggest that CHO-E ingestion improves endurance capacity during intermittent high-intensity running in subjects with high preexercise muscle glycogen concentrations. The greater endurance capacity cannot be explained solely by differences in muscle glycogen, and it may actually be a consequence of the higher plasma glucose concentration towards the end of exercise that provided a sustained source of CHO for muscle metabolism and for the central nervous system.

0 0
 · 
0 Bookmarks
 · 
23 Views
  • Source
    Article: Carbohydrate ingestion during team games exercise: current knowledge and areas for future investigation.
    Shaun M Phillips, John Sproule, Anthony P Turner
    [show abstract] [hide abstract]
    ABSTRACT: There is a growing body of research on the influence of ingesting carbohydrate-electrolyte solutions immediately prior to and during prolonged intermittent, high-intensity exercise (team games exercise) designed to replicate field-based team games. This review presents the current body of knowledge in this area, and identifies avenues of further research. Almost all early work supported the ingestion of carbohydrate-electrolyte solutions during prolonged intermittent exercise, but was subject to methodological limitations. A key concern was the use of exercise protocols characterized by prolonged periods at the same exercise intensity, the lack of maximal- or high-intensity work components and long periods of seated recovery, which failed to replicate the activity pattern or physiological demand of team games exercise. The advent of protocols specifically designed to replicate the demands of field-based team games enabled a more externally valid assessment of the influence of carbohydrate ingestion during this form of exercise. Once again, the research overwhelmingly supports carbohydrate ingestion immediately prior to and during team games exercise for improving time to exhaustion during intermittent running. While the external validity of exhaustive exercise at fixed prescribed intensities as an assessment of exercise capacity during team games may appear questionable, these assessments should perhaps not be viewed as exhaustive exercise tests per se, but as indicators of the ability to maintain high-intensity exercise, which is a recognized marker of performance and fatigue during field-based team games. Possible mechanisms of exercise capacity enhancement include sparing of muscle glycogen, glycogen resynthesis during low-intensity exercise periods and attenuated effort perception during exercise. Most research fails to show improvements in sprint performance during team games exercise with carbohydrate ingestion, perhaps due to the lack of influence of carbohydrate on sprint performance when endogenous muscle glycogen concentration remains above a critical threshold of ∼200  mmol/kg dry weight. Despite the increasing number of publications in this area, few studies have attempted to drive the research base forward by investigating potential modulators of carbohydrate efficacy during team games exercise, preventing the formulation of optimal carbohydrate intake guidelines. Potential modulators may be different from those during prolonged steady-state exercise due to the constantly changing exercise intensity and frequency, duration and intensity of rest intervals, potential for team games exercise to slow the rate of gastric emptying and the restricted access to carbohydrate-electrolyte solutions during many team games. This review highlights fluid volume, carbohydrate concentration, carbohydrate composition and solution osmolality; the glycaemic index of pre-exercise meals; fluid and carbohydrate ingestion patterns; fluid temperature; carbohydrate mouthwashes; carbohydrate supplementation in different ambient temperatures; and investigation of all of these areas in different subject populations as important avenues for future research to enable a more comprehensive understanding of carbohydrate ingestion during team games exercise.
    Sports Medicine 07/2011; 41(7):559-85. · 5.16 Impact Factor
Data provided are for informational purposes only. Although carefully collected, accuracy cannot be guaranteed. The impact factor represents a rough estimation of the journal's impact factor and does not reflect the actual current impact factor. Publisher conditions are provided by RoMEO. Differing provisions from the publisher's actual policy or licence agreement may be applicable.

Keywords

6.4% CHO-E solution
 
body mass
 
CHO loading
 
CHO)-rich diet
 
CHO-E
 
CHO-E ingestion
 
CHO-E trial
 
crossover design
 
double-blind fashion
 
dry matter
 
endurance capacity
 
greater endurance capacity
 
higher plasma glucose concentration
 
intermittent high-intensity
 
male volunteers
 
muscle glycogen use
 
muscle metabolism
 
PLA trial
 
preexercise muscle glycogen concentrations
 
trials