Effects of Acute β-Adrenergic Blockade on Blood and Muscle Lactate Concentration during Submaximal Exercise

Abstract

Heart rate and blood and muscle lactate concentrations were studied in 15 physically active males during submaximal exercise before and after oral administration of 80 mg propranolol (Inderal^®). First, a cycle exercise protocol, with a stepwise increased exercise intensity (30 W every 4 min until voluntary exhaustion) was performed before and after β-blockade. Blood samples for lactate determination were obtained before each exercise intensity increase. In a second set of experiments, the procedure was repeated before and after β-blockade, but exercise was terminated at the exercise corresponding to a blood lactate concentration of 4 mmol·l^-1 l^-1, as determined beforehand without β-blockade (i.e., the same absolute work load was compared with and without β-blockade), and a muscle biopsy was taken from m. vastus lateralis for subsequent lactate analyses. Following β-blockade at low and high work loads, the heart rate decreased similarly by 22%-26%. Blood lactate concentration was unchanged at exercise intensities up to 150 W. At higher exercise intensities (180-240 W), a significant increase (P < 0.05 - P < 0.01) in blood lactate concentration occurred after β-blockade. Muscle lactate concentration was unaffected by β-blockade at a work load (130-230 W) where blood lactate was higher with than without blockade. Assuming a reduced blood flow to the exercising muscle, there are reasons to speculate that lactate production was diminished following β-blockade even though blood lactate increased probably as a result of reduced lactate uptake by other organs.

Key words

exercise - heart rate - muscle lactate - blood lactate - β-blockade