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[RC] Improved endurance performance - Ridecamp Guest

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Authors HGL Rauch, AS Gibson, EV Lambert, TD Noakes
Title   A signalling role for muscle glycogen in the regulation of pace during 
prolonged exercise
Full source     British Journal of Sports Medicine, 2005, Vol 39, Iss 1, pp 
34-38

Introduction: In this study we examined the pacing strategy and the end muscle 
glycogen contents in eight cyclists, once when they were carbohydrate loaded 
and once when they were non-loaded. Methods: Cyclists completed 2 hours of 
cycling at similar to73% of maximum oxygen consumption, which included five 
sprints at 100% of peak sustained power output every 20 minutes, followed 
immediately by a 1 hour time trial. Muscle biopsies were performed before and 
immediately after exercise, while blood samples were taken during the 2 hour 
steady state rides and immediately after exercise. Results: Carbohydrate 
loading improved mean power output during the 1 hour time trial (mean (SEM) 219 
(17) v 233 (15) W; p<0.05) and enabled subjects to use significantly more 
muscle glycogen than during the trial following their normal diet. 
Significantly, the subjects, kept blind to all feedback except for time, 
started both time trials at similar workloads (&SIM;30 W), but after 1 minute 
of cycling, the workload average 14 W higher throughout the loaded compared 
with the non-loaded time trial. There were no differences in subjects' plasma 
glucose and lactate concentrations and heart rates in the carbohydrate loaded 
versus the non-loaded trial. Of the eight subjects, seven improved their time 
trial performance after carbohydrate loading. Finishing muscle glycogen 
concentrations in these seven subjects were remarkably similar in both trials 
(18 (3) v 20 (3) mmol/kg w/w), despite significantly different starting values 
and time trial performances (36.55 (1.47) v 38.14 (1.27) km/h; p<0.05). The 
intra-subject coefficient of variation ( CV) for end glycogen content in these 
seven subjects was 10%, compared with an inter-subject CV of 43%. Conclusions: 
As seven subjects completed the time trials with the same end exercise muscle 
glycogen concentrations, diet induced changes in pacing strategies during the 
time trials in these subjects may have resulted from integrated feedback from 
the periphery, perhaps from glycogen content in exercising muscles.


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