The effect of environmental and nutritional factors on time trial performance in trained cyclists

Backx, Karianne (2002) The effect of environmental and nutritional factors on time trial performance in trained cyclists. (PhD thesis), Kingston University, .


The studies described in this thesis examine the effect of environmental and nutritional factors on cycling time trail (TT) performance. The first investigation determined the effect of ambient temperature (T[sub]a) on 1-h TT performance and physiological responses. A curvilinear relationship was found between T[sub]a and performance, with the optimal distance covered at 18.6[degrees]C. A linear increase in physiological parameters (heart rate, core temperature, mean body temperature, sweat loss and self-selected fluid intake) was found with increasing T[sub]a. During the second study fluid intake and sweat loss were recorded during 40.2-km TT under competitive conditions. Whilst 43 of 75 riders consumed a pre-ride bolus, few chose to drink during racing. A significant relationship was found between pre-ride bolus volume and race speed (speed increase by 0.3km h[sup]-1 for each 100ml of fluid consumed). Despite moderate environmental conditions sweat losses were high (1.5[plus or minus]0.5 and 1.2[plus or minus]0.3 L h[sup]-1). As the actual type and beverage volume was not controlled in this study, and there is clear evidence to suggest that carbohydrate (CHO) consumption will assist performance, an investigation to determine whether different volumes of fluid, with identical CHO content, consumed before and during exercise, had an effect of 1-h TT performance under thermoneutral conditions was conducted. Although differences in stomach fullness ratings were found, there were no differences in either performance parameters or physiological variables (heart rate or sweat loss) between trails. These results suggest that when a pre-exercise CHO bolus is consumed there is no effect of subsequent consumption of different CHO beverages. Further, due to abdominal discomfort associated with high fluid consumption it might be neither advisable nor practical to consume high volumes of fluid during 1-h TT performance. The last investigation examined alterations in TT performance within a simulated three-day stage race when a moderate and high dietary CHO intake was consumed, observations were of any alterations in metabolism and immune function. Despite being well trained and ingesting more than 6 g kg[sup]-1 of CHO per day two subjects did not manage to complete the performance trials on the third day with the moderate CHO diet. There was a trend for a larger reduction in mean distance covered and mean power output when the moderate was compared to the high CHO trial. A shift in substrate use was detected during both treatments with a greater reliance on fat as a fuel towards the end of the trial. This shift appeared to occur earlier with moderate CHO ingestion.

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