Effects of Caffeine Ingestion on Metabolic Responses to Prolonged Walking in Sedentary Males

This study examined the effects of a single dose of caffeine (5 mg.kg-1) on energy metabolism during 60-min treadmill walking at light (30% VO2max) and moderate (50% VO2max) aerobic intensities in eight sedentary (VO2max) 39.6 +/- 3.1 ml.kg-1 x min-1) males. Caffeine intake 60 min prior to walking exercise increased pre- and postexercise FFA, glycerol, and lactate concentrations (p < 0.05). Blood glucose levels following walking trials were lower than preexercise values (p < 0.05). Gas exchange indicated that caffeine did not change exercise oxygen uptake, RER values, and carbon dioxide production (p > 0.05). In contrast, a small but statistically significant effect of caffeine on exercise minute ventilation was noted (p < 0.01). It is concluded that ingestion of 5 mg.kg-1 caffeine increases the mobilization of energy substrate from fat sources; however, the present data do not provide evidence of a caffeine-induced shift in energy substrate usage. Caffeine is not an effective means for enhancing the energy cost of prolonged walking.