Date of Award


Document Type


Degree Name

Doctor of Philosophy (PhD)



First Advisor

Arnold G. Nelson


The effect of caffeine ingestion upon endurance performance while walking at 45% VO$\sb{2\rm max}$ in a warm environment (27$\sp\circ$C, 48% rh) was examined. Eight moderately trained subjects (aged 21-25 years) walked on a treadmill on 4 separate occasions until exhaustion under 4 different treatment regimens. Two of the treatments consisted of caffeine-containing beverages, while the other 2 included non-caffeine-containing beverages. One hour prior to the start of exercise, the subjects consumed a GatorPro drink with either 5 mg/kg of caffeine, if caffeine was the randomized drink, or placebo (flour). At the start of exercise and every half hour until exhaustion, the subjects consumed either 2.5 mg/kg of caffeine mixed in 150 ml of placebo (PC) or Gatorade (GC), or 150 ml of placebo only (PO) or Gatorade only (GO), if they were on the caffeine or non-caffeine trials, respectively. The GO treatment significantly (p $\leq$ 0.05) increased time to exhaustion by 14.2% compared to PO (GO = 251.4 min, PO = 220.1 min), and was also significantly greater than GC (215.9 min) and PC (206.0 min). No treatment differences were found for performance variables, such as heart rate, tympanic temperature, and weight loss. Additionally, markers for substrate utilization such as glucose, RER, and FFA showed no treatment differences. There were significant increases (p $\leq$ 0.05) for the caffeine treatment compared to the non-caffeine treatment for the other substrate utilization markers, glucose, lactate, and triglycerides. The indicators of fluid loss and dehydration showed no treatment differences for Na$\sp+$, Cl$\sp-$, hematocrit, hemoglobin, and plasma volume. There was a significant increase (p $\leq$ 0.05) for the non-caffeine treatment for K$\sp+$. These data suggest that differences in performance times between the GC and PC trials versus the GO trial were not a result of intensity, fluid shifts, hypoglycemia, or substrate utilization. Subjects reported serious gastric distress during the caffeine trials. This unanticipated and previously unreported side effect may account for the reduced performance in these trials and may have negated any ergogenic effects of caffeine during prolonged submaximal exercise.