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Cardiac Patients and Weight Training
Robert S. McKelvie
Career Scientist of the Ontario Ministry of Health
Hamilton General Hospital
Hamilton, Ontario, Canada
L8L 2X2
Coronary artery disease (CAD) results from atherosclerosis which produces stenosis and frequently occlusion of the arteries providing blood flow to the myocardium. Patients afflicted with CAD can suffer from exertional chest pain (angina), heart attack (myocardial infarction), heart failure (congestive heart failure), and death. Although there are other forms of cardiac disease (such as disorders related to heart valves), CAD and the associated complications account for the greatest proportion of heart disease in our society. Billions of health care dollars are spent each year in the assessment and treatment of patients with cardiovascular disease. As these patients are often young and active in the work force further money is spent on disability programs due to time lost from their employment.
A significant component of the disability is related to the inappropriately reduced levels of activity resulting in physical deconditioning rather than due to primary limitations imposed by the cardiac disease. The recognition of this situation many years ago led to the development of cardiac exercise rehabilitation programs which provided guidelines for exercise training and advice regarding CAD (9). In these programs the approach has been to involve large muscle groups in aerobic activities such as walking and stationary cycling. The well documented training effects of these activities include an increase in maximal oxygen uptake (O2max), an increase in exercise tolerance, a reduction in myocardial oxygen demand (MO2) at submaximal loads and an increase in the intensity of exercise needed to precipitate angina (7). Cardiac exercise rehabilitation has become an accepted form of therapy with the goals to improve the physical fitness and psychological well being of patients. More recently studies that have used meta-analysis to examine the trials of cardiac exercise rehabilitation have found that a further benefit is a reduction in mortality (8). Finally, a sedentary life style is now recognized as a risk factor for CAD and these findings, in combination with those from patients, emphasize the importance of regular physical activity in both the primary and secondary prevention settings (2).
Many occupational, recreational or daily living activities require muscular strength (3,7). Recent studies have demonstrated that a decrease in muscle strength may be quite common among cardiac patients (7). Aerobic training does not directly address this very important aspect of rehabilitation, however weight training is an activity which can be used to improve muscle strength (7). The initial reluctance to use weight training was probably based on the unfounded concern that the cardiovascular response to weightlifting would be similar to that found during isometric exercise. Studies of the acute cardiovascular response to weightlifting have demonstrated a different response, compared to that found with isometric exercise, suggesting that weight training is appropriate in patients with uncomplicated CAD. This has led to the more generalized acceptance of this form of training and the recommendation that weight training be included as an adjunct to the aerobic training program of patients with stable CAD (3,7).
Cardiovascular Response To Weightlifting
The cardiovascular responses to isometric or dynamic exercises have been well described (7). Dynamic exercise results in an increase in cardiac output, heart rate, stroke volume and mean arterial pressure (related to the rise in systolic blood pressure) with a decline in peripheral vascular resistance. There is usually an increase in end diastolic volume with a decrease in end systolic volume. In contrast isometric exercise invokes an increase in cardiac output, heart rate and mean arterial pressure (related to an increase in systolic and diastolic pressures), with no change or a decrease in stroke volume and no change or a slight increase in peripheral vascular resistance. The left ventricular end diastolic and end systolic volumes either increase or do not change during isometric exercise.
Systolic Blood Pressure Response
The response to weightlifting has not been well documented and only a few studies have used intra-arterial blood pressure monitoring to measure blood pressure (4,11). Frequently the assumption is made that isometric and weightlifting exercise are similar however there is a significant difference between the two types of exercise. Isometric exercise consists of a sustained static muscle contraction which obstructs blood flow to the contracting muscle during the activity. In contrast weightlifting is a static-dynamic activity which does not produce significant obstruction of blood flow to the working muscle during the activity.
Initial studies of weightlifting, performed in healthy individuals, reported large increases in blood pressure up to values as great as 330/250 mmHg (7,10). However, in the studies where large increases in blood pressure were found the subjects performed at 95% of 1 repetition maximum (1 RM) to failure and this would account for the hemodynamic response observed during this type of lifting. Patients with cardiac disease perform weightlifting exercise at much lower intensities and because of this the blood pressure response would be expected to be lower.
The blood pressure response has been examined in relation to weightlifting in a number of studies (7,10). Most of these studies reported relatively small increases in systolic blood pressure with values usually not exceeding 150-160 mmHg (10). Even during double leg press exercise with intensities of 80% 1 RM the observed systolic blood pressures in aerobically trained cardiac rehabilitation patients were found to be acceptable (7,10). These studies measured blood pressure using a sphygmomanometer and usually immediately following exercise (7). This would have led to an underestimation of the arterial blood pressure response during weightlifting exercise. A recent study performed by Wiecek et al. (11) demonstrates how the indirect (sphygmomanometer) measurement of blood pressure significantly underestimates the pressure response during this type of exercise. The results demonstrated that the blood pressure decreases very quickly following termination of weightlifting making it difficult to draw any conclusions about the pressure changes during exercise from the post exercise assessment (Figure 1). Furthermore, compared to direct (intra-arterial) blood pressure measurements the indirect measurements consistently underestimated the systolic blood pressure response during weightlifting by 14 to 20%. Finally this study demonstrated that during a single-arm military press the systolic blood pressure response (170 ± 14.6 mmHg) was much greater than previously reported using indirect measurement of blood pressure during this exercise (10).
Another study by Haslam et al. (4) measured the systolic blood pressure using an intra-arterial catheter during different weightlifting exercises. The highest systolic pressures attained were in the order of 200 mmHg for double leg press at 80% 1 RM (Figure 2). For all the exercises performed in this study the increases in systolic pressure were greater than those found in studies where blood pressure was measured with a sphygmomanometer (7,10). However, except for single-leg press at 80% 1 RM and double-leg press at 60 and 80% of 1 RM, the rate pressure product (RPP) was the same as that observed during aerobic exercise at less than 85% of O2 (Figure 3). It was concluded that the responses were within a clinically acceptable range except perhaps for single-leg and double-leg press activities at high intensities, where some caution may be advised in prescribing these exercises for patients with CAD.
Diastolic Blood Pressure Response
The diastolic blood pressure during weightlifting exercise has been variously reported to remain unchanged or to increase during the exercise (10). In our laboratory (Figure 2) using intra-arterial blood pressure monitoring a significant increase in diastolic blood pressure is observed during weightlifting (4,11).
Heart Rate Response
The heart rate response during weightlifting in most studies has been found to be in the range of 50-60% of the values observed during maximal graded exercise (10). This represents a heart rate response during weightlifting that is about 10% below that prescribed for aerobic training. The amount of weight lifted and the rest intervals between exercise stations both affect the heart rate response (4,10). An increase in weight lifted or a decrease in the rest interval between exercise sets will produce an increase in heart rate during weightlifting exercise.
Comparison of The Cardiovascular Response of Weightlifting to Cycling
Recently a study completed in our laboratory compared the cardiovascular response during single leg press exercise at 70% of 1 RM to cycling at 70% of peak power output in patients with CAD (unpublished data). Compared to cycling during weightlifting the diastolic blood pressure was significantly greater while the systolic blood pressure, RPP and heart rate were significantly lower (Figure 4). It can be argued that a lower RPP reflects a lower myocardial oxygen requirement during weightlifting. Furthermore, it is well known that coronary blood flow occurs mainly during diastole so that during weightlifting the slower heart rate (longer diastolic period) and higher diastolic pressure (increased coronary artery perfusion pressure) could potentially improve myocardial perfusion as long as left ventricular end diastolic pressure did not increase in parallel. Studies to investigate this possibility are currently under way in our laboratory.
Cardiac Wall Motion and Volumes During Weightlifting
Information about myocardial wall motion and the change in cardiac volumes during weightlifting exercise in patients with CAD is limited. Butler et al. (1) used echocardiography to compare changes in wall motion between weightlifting and traditional aerobic exercise. The echocardiographic studies were begun within 1 minute after exercise and were completed within 5 minutes. With aerobic exercise a worsening of wall motion occurred in 5 of 61 left ventricular segments, while the motion in only 1 segment was found to deteriorate following weightlifting. We recently have extended the investigation of the effects of weightlifting on the cardiovascular response to patients with left ventricular dysfunction (unpublished data). For this study we recruited 10 patients with a mean ejection fraction of 31 ± 2%. Echocardiographic measurements, to determine cardiac volumes, and intra-arterial blood pressure were recorded while the patients cycled for 5 minutes at 70% of their previously determined peak power output and then performed 10 repetitions of single leg press exercise at 70% 1 RM. The results demonstrated the same changes for blood pressure, heart rate and RPP that we have found in previous studies. Compared to cycling the weightlifting exercise did not produce any significant differences in end diastolic volume, end systolic volume, ejection fraction or peak systolic pressure end systolic volume relationship (Table 1). These findings would suggest the load on the cardiovascular system during weightlifting is no greater than occurs during aerobic exercise.
The studies to date have demonstrated that weightlifting should not be equated to isometric exercise. Systolic blood pressure does not appear to be excessive when the exercise loads are properly prescribed. Compared to aerobic exercise the combination of a higher diastolic blood pressure, lower heart rate and RPP during weightlifting exercise may have a very beneficial effect in terms of myocardial perfusion in patients with CAD. However, despite these findings, further research is required to confirm and further define the cardiovascular responses during weightlifting exercise.
Safety Of Weightlifting Training
The results from studies examining the cardiovascular response to weightlifting would suggest this form of exercise is safe for patients with CAD. A number of studies have shown that weight training programs in patients with CAD are not associated with symptoms of angina, ST segment depression, or dysrhythmias (3,7). In fact the study by Butler et al. (1), using echocardiography to assess wall motion changes, found a worsening of wall motion abnormalities in 5 of 61 segments during aerobic exercise while in the same patients this was observed in only 1 segment during weightlifting.
There is very little data regarding the long term safety of weight training. However, the available data would support the safety of this form of training as a recent report describes 73 patients that uneventfully completed 7,422 circuit weight training sessions (3).
There is some concern that weightlifting training may not be advisable for patients with poor left ventricular function as they may develop further wall motion abnormalities, life threatening arrhythmias or both (3). It should be emphasized that these concerns are based on results from studies which used isometric exercise and they may not apply to weightlifting exercise. Further research is required before conclusions can be drawn regarding the safety of weight training in patients with poor left ventricular function.
Although the cardiovascular response observed during weightlifting is acceptable it must be remembered that the response is related to the intensity of the prescribed exercise. Data from healthy male bodybuilders performing double-leg presses at 95% of 1 RM to failure emphasizes this point as they were found to develop blood pressures of 330/250 mmHg (7). Therefore formal weightlifting to failure in patients with cardiac disease can not be classified as safe.
The studies to data would suggest that weightlifting training in patients with cardiac disease is safe but this must be qualified by stating the number of studies have been limited and that most have involved small numbers of patients followed over a relatively short (e.g. 12 weeks) period of time. Furthermore, these studies have been performed in patients with stable CAD and aerobic exercise capacities of greater than 6 METS (1 MET = 3.5 ml ¥ kg-1 ¥ min-1). Therefore at the present time the safety of weightlifting training can not be supported for patients with poor left ventricular function, a low aerobic functional capacity or symptoms of angina at low aerobic workloads.
Benefits Of Weightlifting Training
Effects on Muscular Strength, Endurance and Maximum Dynamic Power Output
In healthy individuals weightlifting training has been repeatedly found to produce an improvement in strength of 20-50% (7,10). The improvement in strength has been found to be in a similar range for patients with cardiac disease (7,10).
A recent study by McCartney et al. (5) highlights the benefits when weight training is used as an adjunct to an aerobic training program. In this study the patients had all aerobically trained for 3 months prior to initiation of weight training. The control group continued aerobic training and the treatment group performed both aerobic and weight training for 10 weeks with both groups completing the same amount of total exercise. After training, strength was significantly increased only in the combined training group and, in addition, the number of times the initial 1 RM could be performed increased to 14 in the weight trained patients, but only to 4 in the control group. Following training a significant 15% improvement in maximal power output in cycle ergometer performance occurred in the treatment group while no change was observed in the control group. Symptom-limited endurance while cycling at 80% of the initial maximum power output increased in the treatment group following training with the time to reach a Borg scale rating of perceived exertion of 7 (very severe) increasing from 541 seconds before training to 1128 seconds after training. Endurance for the control group increased from 604 seconds to 672 seconds following training.
Weightlifting when used as the only form of exercise training has been observed to produce either a small increase or no increase in O2 (10). There are a number of possible reasons for this finding including: (i) the relatively low level of oxygen consumption required during weightlifting exercise; (ii) the differences in training protocols; (iii) duration of rest intervals between lifting; (iv) characteristics of the population examined; (v) total volume of work performed; (vi) specificity of muscle training; and (7) the initial exercise capacity of the subjects examined (10). Therefore, it is important to realize that weight training should be used as an adjunct to aerobic training in patients with cardiac disease.
Effects on the Circulatory Response During Lifting
Weight training has been found to result in a reduction in the blood pressure recorded at rest in healthy middle aged adults, borderline hypertensive adults and hypertensive adolescents (10). However, this has not been a consistent finding in all studies (10).
We recently examined the effects of weight training on the circulatory response to weightlifting in a healthy group of males aged 60-70 years (6). In this study the subjects were assessed before and after 12 weeks of progressive weight training. Following training the systolic pressure, diastolic pressure, heart rate and RPP responses were significantly lower during the lifting of identical submaximal loads. This response has not been examined in patients with CAD and studies need to be designed to assess the circulatory response following training. However, if the response is similar to that found in healthy males then the potential exists that following training patients would be able to perform strength requiring activities of daily living (ADL) at a lower RPP and possibly with greater safety.
Effects on Risk Factors For Coronary Artery Disease
A number of studies have examined whether weight training has an effect on blood lipid levels. These studies have provided results which are in conflict with each other, some demonstrate a reduction in lipid levels while others indicate no significant change following weightlifting training (7,10). The main reason for the lack of agreement among studies is due to their design. In these studies there has not been adequate control for age, body fat, training regimen, anabolic steroid use and diet. Future studies need to control for the amount of weightlifting exercise, subject fitness level, sex, baseline lipoprotein values, plasma volume status, medication use and dietary regimen. Only after studies which have controlled for these variable have been completed can definitive conclusions be drawn about whether weight training alters blood lipid levels.
Although weight training does not appear to alter glucose tolerance it does alter the insulin response to glucose. Lower insulin levels are observed for any given blood glucose level and this may be protective against atherosclerosis (7).
Conclusions