Retention of intravenously infused [13C]bicarbonate is transiently increased during recovery from hard exercise

Exercise Physiology Laboratory, Department of Integrative Biology, University of California, Berkeley, California Submitted 19 March 2007 ; accepted in final form 13 August 2007 The effects of exercise on energy substrate metabolism persist into the postexercise recovery period. We sought to derive bicarbonate retention factors ( k ) to correct for carbon tracer oxidized, but retained from pulmonary excretion before, during, and after exercise. Ten men and nine women received a primed-continuous infusion of [ 13 C]bicarbonate (sodium salt) under three different conditions: 1 ) before, during, and 3 h after 90 min of exercise at 45% peak oxygen consumption ( O 2peak ); 2 ) before, during, and 3 h after 60 min of exercise at 65% O 2peak ; and 3 ) during a time-matched resting control trial, with breath samples collected for determination of 13 CO 2 excretion rates. Throughout the resting control trial, k was stable and averaged 0.83 in men and women. During exercise, average k in men was 0.93 at 45% O 2peak and 0.94 at 65% O 2peak , and in women k was 0.91 at 45% O 2peak and 0.92 at 65% O 2peak , with no significant differences between intensities or sexes. After exercise at 45% O 2peak , k returned rapidly to control values in men and women, but following exercise at 65% O 2peak , k was significantly less than control at 30 and 60 min postexercise in men (0.74 and 0.72, respectively, P < 0.05) and women (0.75 and 0.76, respectively, P < 0.05) with no significant postexercise differences between men and women. We conclude that bicarbonate/CO 2 retention is transiently increased in men and women for the first hour of postexercise recovery following endurance exercise bouts of hard but not moderate intensity. prior exercise; postexercise; exertion; physical activity; NaHCO 3 ; correction factor; glucose oxidation; fatty acid oxidation; leucine oxidation Address for reprint requests and other correspondence: G. A. Brooks, Exercise Physiology Laboratory, Dept. of Integrative Biology, 5101 Valley Life Sciences Bldg., Univ. of California, Berkeley, Berkeley, CA 94720-3140 (e-mail: gbrooks{at}berkeley.edu )