Performance and exercise capacity in prolonged continuous exercise has been shown
to be enhanced by the ingestion of dilute (-6%) carbohydrate-electrolyte (CHO-E)
solutions during exercise. There is a wealth of literature on the effects of CHO-E
solutions on prolonged, continuous exercise however this is not the case for highintensity
intermittent exercise. One reason for this is the difficulty of replicating the
demands of multiple-sprint sports within the laboratory. The development of the
Loughborough Intermittent Shuttle Running Test (LIST), a protocol that simulates the
physiological demand of multiple-sprint sports, has allowed for further study in this
Sports drinks contain a variety of different types of carbohydrate, including synthetic
polymers of maltodextrins. The rationale for these is two-fold; firstly there is some
evidence to suggest that these glucose polymers of low osmolality may empty faster
than isoenergetic glucose solutions especially at dilute (-6%) concentrations.
Secondly CHO-E solutions formulated from maltodextrins with low dextrose
equivalents are less acidogenic and have lower cariogenic potential than simple
glucose solutions, thus making them preferable for tooth health. Therefore the
purpose of this thesis was to examine the effects of a 6.4% hypotonic synthetic
polymer maltodextrin CHO-E solution on muscle metabolism and physiological
performance during prolonged high-intensity intermittent running (LIST).
This thesis contains four experimental studies. From the results of study 1 it was
concluded that the ingestion of a 6.4% hypotonic CHO-E solution provided no
ergogenic benefit to running capacity during the LIST despite blood and hormonal
data suggesting that the solution was effective at delivering glucose. As isotonic
CHO-E solutions have shown to have ergogenic properties during LIST running the
purpose of study 2 was to compare isoenergetic hypotonic and isotonic CHO-E
solutions during LIST running. The results from this study suggested that
performance, as measured by exercise capacity and sprint speed, was not affected by
In study 3 the protocol was modified to extend the exercise duration so that a greater
demand was placed on the subjects' glycogen reserves. The results from this study
further confirmed that exercise capacity in LIST running was not influenced by CHO
provision during exercise however the habitual CHO intake of the subjects may have
masked any ergogenic properties of the CHO-E solution and led to increased
performance in the control trials.
In the final study the subjects' pre-trial exercise and dietary CHO intake was
manipulated to increase endogenous glycogen concentrations. The results showed that
in these subjects the ingestion of a 6.4% hypotonic CHO-E solution increased
exercise capacity during the LIST by 21%. Muscle biopsy analyses revealed a lower
net muscle glycogen utilisation in the CHO trial post-90 min (p=0.07).
There is evidence in the literature to suggest that there is an ergogenic effect of CHO
ingestion during the LIST. However the results presented in this thesis suggest that
when endogenous glycogen stores are moderate the ingestion of a CHO-E solution
may suppress lipid oxidation without a concomitant increase in CHO oxidation and
thus LIST capacity is not enhanced. In contrast, when endogenous glycogen
concentrations are elevated through dietary manipulation there is an ergogenic benefit
from the ingestion of hypotonic CHO-E solutions during LIST exercise.
Doctoral Thesis. Submitted in partial fulfilment of the requirements for the award of Doctor of Philosophy of Loughborough University.