Skeletal muscle glycolysis during submaximal exercise following acute β‐adrenergic blockade in man

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Abstract
The present study describes the influence of β‐adrenergic blockade on glycogen utilization and lactate accumulation in skeletal muscle of exercising man. Twelve physically active men were examined during 25 min of continuous cycle exercise equivalent to 65% of their maximal oxygen uptake both with and without oral administration of 80 mg of propranolol (Inderal®). Heart rate, oxygen uptake, rate of perceived exertion (RPE) and blood lactate concentration were measured during exercise. Muscle biopsies were obtained from m. vastus lateralis after 5 and 25 min of exercise, β‐adrenergic blockade decreased steady state exercise heart rate by (mean + SD) 35 ± 10 beats min‐1 (P < 0.001) and oxygen uptake from 2.47 to 2.39 1‐min‐1 (P < 0.01). Muscle glycogen decreased from the 5th to the 25th min of exercise, and β‐blockade had no significant effect on this decrease. In contrast to without drug, β‐blockade resulted in a decrease (P < 0.05) in muscle lactate concentration from the 5th (6.9 mmolkg‐1 w./w.) to the 25th min (4.8 mmolkg‐1 w./w.). Similarly blood lactate levels were lower (P < 0.05) with than without β‐blockade in the last but not the first 10 min of exercise. The alteration in muscle lactate concentration pattern following β‐blockade, may imply that adrenergic effects per se contribute to the stimulation of glycolysis during submaximal exercise, except in its earliest phase. Nevertheless, the effect is not great enough to produce substantial differences in glycogen utilization.

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