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Cerebral metabolism during upper and lower body exercise

Department of Anesthesia, The Copenhagen Muscle Research Center, Rigshospitalet, University of Copenhagen, Copenhagen, Denmark

Submitted 28 April 2004 ; accepted in final form 15 June 2004

When continuation of exercise calls for a "will," the cerebral metabolic ratio of O₂ to (glucose + lactate) decreases, with the largest reduction (30–50%) at exhaustion. Because a larger effort is required to exercise with the arms than with the legs, we tested the hypothesis that the reduction in the cerebral metabolic ratio would become more pronounced during arm cranking than during leg exercise. The cerebral arterial-venous differences for blood-gas variables, glucose, and lactate were evaluated in two groups of eight subjects during exhaustive arm cranking and leg exercise. During leg exercise, exhaustion was elicited after 25 ± 6 (SE) min, and the cerebral metabolic ratio was reduced from 5.6 ± 0.2 to 3.5 ± 0.2 after 10 min and to 3.3 ± 0.3 at exhaustion (P < 0.05). Arm cranking lasted for 35 ± 4 min and likewise decreased the cerebral metabolic ratio after 10 min (from 6.7 ± 0.4 to 5.0 ± 0.3), but the nadir at exhaustion was only 4.7 ± 0.4, i.e., higher than during leg exercise (P < 0.05). The results demonstrate that exercise decreases the cerebral metabolic ratio when a conscious effort is required, irrespective of the muscle groups engaged. However, the comparatively small reduction in the cerebral metabolic ratio during arm cranking suggests that it is influenced by the exercise paradigm.

arm cranking; central fatigue; cerebral metabolism; lactate

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