Introduction

Exercise programs for health purposes have traditionally emphasized aerobic exercise, with the intent of improving cardiovascular function, myocardial vigor, metabolic processes, and psychosocial well-being. Recently, however, resistance training has been found to offer more than a means of developing and maintaining muscle strength and mass. An advisory committee of the Council on Clinical Cardiology has recently published a statement outlining the benefits, rationale, and safety of resistance training for healthy men, and for men with mild to moderately severe cardiovascular disease.

The effects of resistance compared to aerobic training

The main measure of successful aerobic training is an increase in the maximum oxygen uptake (VO2max), together with improvements in associated cardiopulmonary variables that have been shown to modify cardiovascular risk factors associated with coronary artery disease. The metabolic benefits include improved carbohydrate metabolism, decreased low-density lipoprotein cholesterol and increased high-density lipoprotein cholesterol levels.

Resistance training, in addition to developing muscle strength, endurance and mass, also assists in elevation of the basal metabolic rate, in a similar way to aerobic training - through effects on glucose tolerance and insulin sensitivity. Thus resistance training can also assist in weight control programs, and in staving off the risk of type 2 diabetes. Moreover, it promotes physical independence and helps to prevent falls in the elderly, through improved muscle strength and function.

Both types of training have similar beneficial effects on bone mineral density.

Recommended resistance training programs

Moderate-to-high intensity resistance training, done two or three days a week for 3 to 6 months, improves muscle strength and endurance by 25% to 100%. Appropriate resistance training programs have been summarized elsewhere on this site.

Physiological responses to resistance exercise

The cardiovascular pressor response to resistance exercise (increased heart rate and blood pressure) is proportional to the percent of maximal voluntary contraction (MVC%), so that increased muscle strength by training results in a lowered pressor response to any given load, as the load now represents a lower percentage of the MVC. Resistance training therefore allows older people to undertake strength-related activities of daily living, such as carrying groceries or firewood, with a lessened increase in the blood pressure and heart rate.

Although resistance training produces little or no improvement in the VO2max, subjects who have undergone 12 weeks of strength training improve their submaximal walking time by over 30%, their submaximal endurance time to exhaustion while cycling by 40%, and while running by 10%. Thus improved endurance is not a function of aerobic exercise alone, but can be enhanced by the increased muscle strength.

Safety of resistance training

Many studies in healthy adults and low-risk cardiac patients (i.e. those without resting or exercise-induced myocardial ischemia, severe left ventricular dysfunction or complex ventricular dysrhythmias) have yielded hardly any adverse cardiovascular events. Thus complete one-repetition maximum strength testing (i.e. lifting the greatest possible weight, once) in over 6,000 healthy subjects aged 20 - 69 was shown to be free of cardiac events. Intra-arterial blood pressures measured in cardiac patients during weight lifting at 40% - 60% of one-repetition maximum strength were within clinically acceptable ranges.
Twelve different studies have reported on the use of resistance training in the rehabilitation of male coronary disease patients. After approximately three months resistance training was added to aerobic conditioning of men with coronary disease in one major study. Upper- and lower-body resistance exercises were done using relatively light weights (40% - 60% of one-repetition maximum strength) with little rest between sets. The training ranged from 30 - 60 minutes, 6 - 26 weeks. The improvement in muscle strength and endurance was similar for both high and moderate training intensities. There was a total absence of angina symptoms, ischemic ST-segment depression, abnormal hemodynamics, complex ventricular dysrhythmias or indeed any cardiovascular complications.

Criteria for participation

The contraindications to resistance training are the same as those for aerobic training in cardiac exercise programs. They include unstable angina, uncontrolled hypertension (above 160/100 mmHg), uncontrolled dysrhythmias, recent congestive heart failure, severe stenotic or regurgitant valvular disease, and hypertrophic cardiomyopathy. Some authorities suggest that moderate to good left ventricular function and cardiorespiratory fitness without angina or ischemic ST-segment depression should be added as prerequisites to resistance training. Cardiac medications should be continued, as clinically necessary.
Subjects with low-to-moderate-risk of cardiac events who wish to start resistance training should complete at least 2 - 4 weeks of aerobic training first. This allows cardiorespiratory and muscular adaptation to occur that may reduce the potential for complications of resistance exercise. Usually older, more frail individuals and cardiac patients will start at a very low resistance, progress quite slowly, and never exercise to exhaustion. The number of repetitions should range between 10 and 15 at a low relative resistance, to prevent injury that can occur in older persons. Patients after coronary artery bypass surgery are eligible for resistance training, provided appropriate stretching or flexibility exercises precede each session, and the repetitions/level of resistance are carefully monitored.

Blood pressure benefits

Resistance training has received additional support from a meta-analysis of 11 studies in which blood pressure was measured before and after a course of progressive exercises¹;. In those subjects who exercise regularly, there was a 2% reduction in systolic, and 4% reduction in diastolic pressure at rest. Although small, both changes were statistically significant and clinically important, according to the researchers. Further studies need to be done in patients with hypertension.

Summary

Easy--to-moderately intense resistance training can help cardiac patients by improving muscle strength and endurance, preventing chronic medical conditions, modifying coronary risk factors, and improving psychosocial well-being. Moreover, weight training will reduce the pressor response (heart rate-blood pressure) to a given load, thereby decreasing myocardial demands during daily activities of a physical nature.

The safety of resistance exercise has been demonstrated widely in healthy men and in men with low-risk cardiovascular disease. The extent to which this safety can be extrapolated to other populations (e.g. women, older patients with low aerobic fitness, and those with significant left ventricular dysfunction) is unclear. However, patients should be able to proceed with such training provided it is done under appropriate close monitoring, as the benefits are likely to exceed the possible risks of cardiovascular injury.