Blood ammonia response to treadmill and bicycle exercise in man

Nine male healthy and physically active volunteers performed four different exercise tests: an incremental load exercise test to exhaustion and a constant load exercise test of 15 min at 65% VO2max, both on the bicycle ergometer and on the treadmill. During the incremental exercise test, blood ammonia levels were significantly higher on the bicycle ergometer as compared to the treadmill at the same submaximal VO2 (p < 0.05 at 80% of VO2max) and at the VO2max, which was identical in the two modes of exercise. Plasma lactate levels were also significantly higher on bicycle ergometer at high submaximal exercise intensity but not at VO2max. During the constant load exercise test blood ammonia levels increased continuously and showed no differences between cycling and running, in contrast to plasma lactate accumulation, which was higher on the bicycle ergometer. The finding that blood ammonia accumulation during exercise is critically dependent upon the test procedure has to be taken into account whenever blood ammonia measurements are used in the physiological monitoring of athletes.