Thesis-2003-Bilzon.pdf (12.17 MB)
Influence of heat stress and carbohydrate availability on substrate metabolism and exercise tolerance time in humans
thesis
posted on 2010-12-08, 16:38 authored by James L.J. BilzonWhilst the effects of environmental heat stress on the physiological responses
of humans during exercise have been investigated for over half a century, the
mechanisms responsible for fatigue during exercise in the heat are not well
understood. There is increasing evidence that heat stress increases the reliance on
carbohydrate (CHO), particularly muscle glycogen, as a fuel for prolonged exercise.
The provision of CHO during exercise and during short-term recovery from exercise
in the heat may theoretically offer some benefit. However, the literature available on
the efficacy of CHO feedings during prolonged running in the heat is scarce. The aim
of the experiments that are reported in this thesis were to investigate the effects of
heat stress and CHO feeding regimens on substrate metabolism and exercise tolerance
during prolonged running. An initial investigation revealed that the heat stress
imposed by wearing a military protective clothing ensemble during prolonged running
impaired exercise tolerance time and increased the reliance on CHO as a fuel. This
response was associated with increases in circulating adrenaline and lactate
concentrations, which may be indicative of an enhanced ß-adrenergic receptor
stimulation of muscle glycogenolysis. Thus, further studies into the efficacy of CHO
supplementation regimens during exercise and recovery from exercise in the heat
were performed. Rehydration with a carbohydrate-electrolytes olution (CES) during a
4-h recovery period markedly increased total CHO utilisation and exercise tolerance
during subsequent exercise in the heat (35°C) compared to a sweetened placebo.
Whilst there was no difference in post-recovery exercise tolerance time after ingesting
55-g or 220-g of CHO within a CES, ingesting 220-g lead to a five-fold increase in
estimated glycogen synthesis during recovery, which increased CHO availability and
utilisation during subsequent exercise. Ingesting a 12.5% glucose solution attenuated
the increased reliance on endogenous CHO stores during exercise in the heat, but the
associated increases in thermal and cardiovascular strain and gastric discomfort may
have been responsible for the impairment of exercise capacity. These findings suggest
that increases in endogenous CHO metabolism occur in response to exogenous heat
stress during prolonged running. Whilst CHO ingestion during short-term recovery
periods are associated with favourable changes in glycogen synthesis and tolerance to
subsequent exercise in the heat, ingestion of a hypertonic glucose solution during
exercise in the heat, may impair exercise capacity.
History
School
- Sport, Exercise and Health Sciences
Publisher
© J.L.J. BilzonPublication date
2003Notes
Doctoral Thesis. Submitted in partial fulfilment of the requirements for the award of Doctor of Philosophy of Loughborough University.EThOS Persistent ID
uk.bl.ethos.402964Language
- en