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% ) and moderate (50% ) aerobic intensities in eight sedentary ( 39.6 ±t3.1 ml.kg−1.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 (p0.05). 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 caffeineinduced shift in energy substrate usage. Caffeine is not an effective means for enhancing the energy cost of prolonged walking.
Hermann-Josef Engels is with the Div. of HPR-Exercise Science, 257 Matthaei Bldg., Wayne State University, Detroit, MI 48202. Emily M. Haymes is with the Dept. of Nutrition, Food, and Movement Sciences, 203 Montgomery Gym, Florida State University, Tallahassee, FL 32306.