By: Thomas Pickering, MD, DPhil, FRCP, Director of Integrative and Behavioral Cardiology Program
of the Cardiovascular Institute at Mount Sinai School of Medicine, New York.

The benefits of aerobic exercise are well established, but the effects of muscular-strength training (weight lifting) are less understood. Strength training involves sudden and sustained contraction of muscles against resistance and causes a dramatic increase of both systolic and diastolic pressure, which in the long run can cause thickening of the heart muscle (technically referred to as concentric ventricular hypertrophy). These effects are thought to be unhealthy from a cardiovascular point of view. Aerobic exercise enlarges the chamber of the heart, but does not make the muscle thicker, and it also makes the arteries less stiff. These changes are thought to be beneficial.

An Australian study compared 19 young weight lifters (average age 26) with 19 healthy sedentary subjects. The weightlifters did at least 3 sessions per week to build their muscle strength, but did not do regular aerobic exercise. A number of measurements were made, which included blood pressure, muscle strength (measured by a handgrip test), aerobic fitness (maximum oxygen consumption), heart size (by echocardiography), and arterial stiffness (measured from the pressure and flow waveform recorded noninvasively from the arteries).

The weightlifters were slightly shorter, but weighed more than the sedentary subjects, and had a greater grip strength, but their aerobic fitness was the same. Their systolic pressure was higher and their diastolic lower than the sedentary subjects (120/59 versus 109/63 mmHg). Their pulse pressure was thus also greater (60 versus 50 mmHg). The weight lifters had larger hearts, but not when allowance was made for their greater body size. Their arteries were about 25% stiffer than the arteries of the sedentary subjects.

Doctor’s comments

The subjects in this study were carefully chosen in that they did weightlifting but not aerobic exercise. It showed that strength training results in stiffer arteries, which also explains why the pulse pressure was wider in the weightlifters. When arteries are stiff the pressure wave gets reflected more readily from the periphery of the circulation (just as the waves resulting from a stone dropped in a pool get reflected at the edge of the pool), and the combination of the outgoing wave and the reflected wave results in a sharper pressure waveform, and hence a wider pulse pressure.

Several studies have shown that increased stiffness of the arteries is associated with aging, with hypertension and with coronary heart disease. There is also extensive evidence that a wide pulse pressure is a risk factor for heart disease and strokes. All in all, these findings suggest that in contrast to aerobic exercise, weightlifting may be harmful to the cardiovascular system.

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