Muscle glycogenolysis and resynthesis in response to a half Ironman triathlon: a case study.
OBJECTIVE
To describe the degrees of muscle-glycogen depletion and resynthesis in response to a half Ironman triathlon.


METHODS
One male subject (38 years of age) completed the Grand Columbian half Ironman triathlon (1.9-km swim, 90-km bike, 21.1-km run, Coulee City, Wash). Three muscle biopsies were obtained from his right vastus lateralis (prerace, immediately postrace, and 4 hours postrace). Prerace and postrace body weight were recorded, in addition to macronutrient consumption before, during, and after the race. Energy expenditure and whole-body substrate oxidation were estimated from linear regression established from laboratory trials (watts and run pace relative to VO2 and VCO2).


RESULTS
Body weight decreased 3.8 kg from prerace to postrace. Estimated CHO energy expenditure was 10,003 kJ for the bike segment and 5759 kJ for the run segment of the race. The athlete consumed 308 g of exogenous CHO (liquid and gel; 1.21 g CHO/min) during the race. Muscle glycogen decreased from 227.1 prerace to 38.6 mmol . kg wet weight-1 . h-1 postrace. During the 4 hours postrace, the athlete consumed a mixed diet (471 g CHO, 15 g fat, 64 g protein), which included liquid CHO sources and a meal. The calculated rate of muscle-glycogen resynthesis was 4.1 mmol . kg wet weight-1 . h-1.


CONCLUSIONS
Completing a half Ironman triathlon depends on a high rate of muscle glycogenolysis, which demonstrates the importance of exogenous carbohydrate intake during the race. In addition, rates of muscle-glycogen resynthesis might be dampened by the eccentric damage resulting from the run portion of the race.
Gillum
Trevor L
TL
Human Performance Laboratory, University of Montana, Missoula, MT 59812, USA.
Dumke
Charles L
CL
Ruby
Brent C
BC
D000328:Adult; D001642:Bicycling; D001706:Biopsy; D004040:Dietary Carbohydrates / Q000008:administration & dosage / Q000378:metabolism*; D004041:Dietary Fats / Q000008:administration & dosage / Q000378:metabolism; D004044:Dietary Proteins / Q000008:administration & dosage / Q000378:metabolism; D004734:Energy Metabolism; D006003:Glycogen / Q000096:biosynthesis / Q000378:metabolism*; D050261:Glycogenolysis; D006801:Humans; D016014:Linear Models; D008297:Male; D009119:Muscle Contraction; D018763:Muscle Fatigue; D009752:Nutritional Status; D010101:Oxygen Consumption; D010807:Physical Endurance; D052097:Quadriceps Muscle / Q000378:metabolism* / Q000473:pathology; D012420:Running; D013550:Swimming; D013997:Time Factors; D015431:Weight Loss
D004040:Dietary Carbohydrates; D004041:Dietary Fats; D004044:Dietary Proteins; D006003:Glycogen