How do beta blockers affect exercisers and exercise performance? How does exercise affect the action of beta blockers? Since you are unable to reach target heart rates, is weight loss possible while on beta blockers?
Beta-adrenoreceptor blocking drugs, more commonly called beta blockers, affect the hemodynamic parameters, reducing blood pressure and heart rate at rest and during exercise. They work by blocking the action of noradrenaline. Noradrenaline is a chemical that transmits messages between muscles and nerves or between two sets of nerves. By blocking this action, beta blockers can decrease the force of contraction of the heart. This leads to a decrease in blood pressure and overall reduction of workload by the heart.
Heart rate training has been used for quite some time as a guide to exercise intensity because of the linear relationship between heart rate and oxygen uptake. It is well established that beta blockers have a dose response related to the potential depressive effect on VO2peak by reducing cardiac output. Some prescribe exercise intensity for individuals taking beta blockers based on a cardiopulmonary graded exercise test while others rely on estimates using the Karvonen formula.
One research study compared target heart rate prescription, calculated by the Karvonen formula, to heart rate at anaerobic threshold, calculated by a conventional graded exercise test with gas exchange. The results indicated that predicting exercise intensity with the Karvonen formula failed to accurately determine a target heart rate that would allow a training effect close to the anaerobic threshold in individuals receiving beta blocker therapy. The authors concluded that this may lead to exercise below the upper limit of aerobic capacity and may result in an under training effect.
Because of the lower heart rate during exercise experienced in those taking beta blockers, accurate heart rate prescription should be determined using a graded exercise test or the modified Karvonen formula. This will allow the individual the ability to exercise at appropriate intensities to improve aerobic parameters.
Since exercise intensity can be underestimated based on the method of determination, it can have a significant impact on individuals who seek weight loss. Beta blockers are considered to lower resting metabolic rate (RMR). Total energy expenditure may be reduced as much as four to 12 percent for those on beta blocker therapy. This in itself poses a challenge for weight loss, especially considering that research also indicates that beta blocker therapy is often associated with a 1.1 to 7.7 pound increase in body weight with chronic treatment.
A research study with the purpose of determining the effect of a 12-week moderate intensity aerobic exercise program on the RMR of overweight sedentary individuals taking beta blockers found that RMR remained unchanged in those treated with beta blockers, which indicated that individuals treated with beta blockers could have more difficulty obtaining a negative energy balance from aerobic training alone. Modest weight loss can be obtained in individuals taking beta blockers, but energy intake should be a major focus in addition to accurate determination of target heart rates for aerobic physical activity.
Creating a negative energy balance through calorie reduction and focusing on the proper portions of lean proteins, fruits and vegetables and whole grains would be most prudent for producing weight loss in individuals undergoing beta blocker therapy.
- Belanger, M. & Boulay, P. (2005). Effect of an aerobic exercise training program on resting metabolic rate in chronically beta-adrenergic blocked hypertensive patients. Journal of Cardiopulmonary Rehabilitation, 25: 354-360.
- Chaloupka, V. et al. (2005). Exercise intensity prescription after myocardial infarction in patients treated with beta-blockers. Journal of Cardiopulmonary Rehabilitation, 25: 361-365.
- Tabet, J. et al. (2006). Determination of exercise training heart rate in patients on beta-blockers after myocardial infarction. European Journal of Cardiovascular Prevention and Rehabilitation, 13: 538-543.