Beta-Blockade and Response to Exercise: Influence of Training

In brief: Beta-blockers and exercise training are recommended for treating cardiovascular disease and hypertension, and researchers have tried to determine the interaction of these two treatment modalities. Data from four studies conducted on 93 subjects over the past five years show that beta-blockade exerts a differential effect on the exercise capacity of subjects of different levels of health and fitness: It increases the capacity of angina patients; decreases the capacity of highly trained, fit individuals; and has little or no effect on the capacity of healthy, untrained individuals.

Metabolic adaptations to exercise: a review of potential beta-adrenoceptor antagonist effects

Human skeletal muscle contains 2 muscle fiber types: slow twitch (type I) and fast twitch (type II). They have different profiles including their biochemical, metabolic, O2 diffusion, microcirculatory and neuromotor characteristics. The slow twitch fiber represents endurance, high combustive potential and recruitment during moderate activity; in contrast, the fast twitch represents explosiveness, force, high capacity for phosphate splitting and lactate formation, but is more fatiguable. A muscle rich in slow twitch fibers is confined to low peripheral resistance at rest and during exercise, higher exercise leg blood flow and higher maximal oxygen uptake (VO2 max). During graded exercise lactate has been shown to be a good marker for the metabolic and circulatory characteristics of the contracting muscle and the exercise intensity (W) eliciting a blood lactate concentration of 4 mmol/liter-1 [(WOBLA) from onset of blood lactate accumulation] integrated for peripheral metabolic, neuromotor and central circulatory potentials both in health and disease. It is well known that a blood lactate level greater than 4 mmol/liter-1 represents a major increase in sympathetic tone and is incompatible with endurance or prolonged exercise. With prolonged exercise and sympathetic regulation both circulation and metabolism adapt. Adipose tissue is stimulated and fatty acids are released. Muscle tissue lipoprotein lipase activity is enhanced; that is, there is increased utilization of blood triglycerides for local lipolysis in the capillary bed of the contracting muscle. Both mechanisms will increase fatty acid availability and induce a "glycogen-sparing effect" resulting in a reduced respiratory exchange ratio. Studies have shown that both the magnitude of the initial glycogen stores and these adaptive responses will determine performance time. With age, changes take place in heart rate regulation, neuromotor control and muscle fibers. Thus VO2 max is decreased, but partly compensated for by a fast motor unit and fiber loss leading to a muscle more rich in slow twitch fibers--an "endurance training-like effect." Relative endurance is also increased with age; however, lactate metabolism is still a critical feature. The OBLA concept describes capacity for both occupational and leisure-time physical activity.

Effect of beta 1-selective and nonselective beta blockade on blood pressure relative to physical performance in men with systemic hypertension

Eleven physically active men with systemic hypertension were studied after 5 weeks of treatment with placebo, atenolol or propranolol. A double-blind, crossover randomized design was used. Blood pressure (BP), heart rate (HR), physical performance capacity, rate of perceived exertion and blood lactate concentrations were measured during rest, exercise to exhaustion and postexercise, at 8 and 24 hours after intake of the last dose. Blood pressure at rest and during exercise was similarly decreased with both drugs (8 and 24 hours), and there was no difference between 8 and 24 hours with any of the treatments. Heart rate (8 hours) was decreased similarly by both drugs, but after 24 hours, HR at increased workloads (above 120 watts) was higher with atenolol compared with propranolol. Maximal HR was lower with propranolol than atenolol at both 8 and 24 hours. Maximal exercise loads (8 and 24 hours) were 231 and 232 watts with placebo, 211 and 212 with propranolol and 228 and 227 with atenolol. That is, maximal workload was decreased with propranolol compared with placebo and atenolol at both 8 and 24 hours. No difference was found between placebo and atenolol at either 8 or 24 hours. The rate of perceived exertion values were higher with propranolol than atenolol. Blood lactate concentrations did not differ according to treatments. The results indicate that atenolol, when given in a dose that decreases resting and exercise BP to the same extent as propranolol, limits physical performance less than propranolol.

Acute response to submaximal and maximal exercise consequent to beta-adrenergic blockade: implications for the prescription of exercise

Forty-seven healthy male subjects, 17 to 34 years old, completed a test to exhaustion on a motor-driven treadmill to determine their maximal oxygen uptake. A second test was administered 2 days later during which the subject walked for 20 to 25 minutes at a steady-state level representing 60% of the maximal oxygen uptake as determined in the first test. The grade was then increased every 2 minutes until the subject reached the state of exhaustion. After the second test, the subjects were randomly assigned, in a double-blind manner, to either placebo, propranolol (160 mg/day), or atenolol (100 mg/day) treatment for 7 days. Exactly 1 week from the time of the second test, and 3 hours after the last medication, the subjects completed the final exercise test using the same treadmill protocol administered in the second test. Heart rate and systolic blood pressure at rest and during submaximal steady-state exercise were significantly reduced by both drugs, whereas diastolic pressure was unaffected. During submaximal steady-state exercise, cardiac output was reduced in both the placebo and atenolol groups, stroke volume was increased in both atenolol and propranolol groups, oxygen uptake was reduced in the atenolol group, pulmonary ventilation was reduced in both propranolol and atenolol groups, and the respiratory exchange ratio remained unchanged. With maximal exercise, treadmill time was significantly reduced with propranolol, pulmonary ventilation and heart rate were reduced significantly with both drugs, but maximal oxygen uptake remained unchanged. Thus, beta blockade does not appear to limit ability to exercise. However, there appears to be a significant advantage to using a cardioselective rather than a nonselective beta-blocking agent.

Effects of cardioselective and nonselective beta-adrenergic blockade on the performance of highly trained runners

Twenty-five highly trained runners with a maximal oxygen uptake (VO2 max) of 64.7 +/- 4.3 ml . kg-1. min-1 were administered clinically equivalent doses of a nonselective (propranolol) and a cardioselective (atenolol) beta-blocking agent as well as a placebo. The subjects performed a horizontal treadmill test on the eighth day and a 10-km track race on the tenth day of each treatment. Beta blockade decreased submaximal heart rate and propranolol caused the largest decrease. Beta blockade caused a decrease in maximal heart rate, VO2 max, maximal ventilation, maximal respiratory exchange ratio and treadmill time. Propranolol caused a greater decrease than atenolol in each of these values. The 10-km race times were significantly slower during beta blockade, and propranolol race times were significantly slower than atenolol race times. It is concluded that the performance of highly trained distance runners is significantly altered by beta-adrenergic blockade and that nonselective agents reduce performance to a greater extent than cardioselective agents.

Maximal aerobic power and blood pressure in normotensive subjects after acute and chronic administration of metoprolol

The acute and long-term effects of the beta 1-adrenoceptor blocking agent metoprolol on blood pressure and maximal aerobic power (Wmax) were studied in 10 healthy subjects. Progressive maximal bicycle ergometer tests were performed after intravenous administration of placebo and metoprolol (0.15 mg . kg-1 and 0.30 mg . kg-1), and at the end of 4-week treatment periods with placebo, conventional metoprolol (C-M) and slow-release metoprolol (SR-M). The reduction in maximal exercise heart rate (HRmax) was correlated with the log plasma metoprolol concentration. Despite a reduction in HRmax of 23 beats/min after 0.15 mg . kg-1 metoprolol, Wmax was unaffected. After 0.30 mg . kg-1 HRmax was reduced by 40 beats/min and Wmax by 5.0%. During chronic treatment, the reductions in HRmax and Wmax were 48 beats/min and 7.5% (C-M) and 45 beats/min and 6.9% (SR-M), respectively. Resting systolic blood pressure was not changed after acute administration of metoprolol but it was reduced during chronic beta-blocker treatment. Resting diastolic blood pressure was not affected after acute or chronic treatment. Exercise systolic blood pressure remained unchanged after 0.15 mg . kg-1 metoprolol i.v. The fall in exercise systolic pressure after 0.30 mg . kg-1 metoprolol i.v. (18 +/- 5 mmHg) was significantly smaller than that during chronic treatment (30 +/- 6 mmHg C-M; 30 +/- 6 mmHg, SR-M). During chronic metoprolol treatment a certain % HRmax corresponded to a higher % Wmax than during placebo treatment, but the shift appeared to be of minor practical importance.(ABSTRACT TRUNCATED AT 250 WORDS)