Resistance Training for Older Adults in Cardiac Rehabilitation

Abstract

Cardiac Rehabilitation (CR) plays a key role in the care of older patients after a coronary event. Hospitalizations are prevented and quality of life, exercise capacity, and physical function are improved. Almost 50% of CR participants are older adults (>65 years), many of whom are frail or deconditioned. Resistance training, as a component of CR, improves muscle strength, endurance, and physical function. The purpose of this review is to describe the effects of resistance training in CR for older adults with a particular focus on physical function.

Background/Introduction:

The prevalence of atherosclerotic cardiovascular disease (ASCVD) and chronic heart failure (HF) rise with age and accounts for more than 50% of cardiovascular related deaths in the United States.¹ Cardiac rehabilitation (CR) plays a key role in improving clinical outcomes, quality of life, exercise capacity, and physical function in older patients with heart disease. Participation in CR is recommended for patients after an acute myocardial infarction, coronary revascularization (percutaneous or surgical), or for patients with chronic stable angina pectoris, systolic HF (EF ≤35%), or heart valve surgery. This multidisciplinary program promotes a comprehensive and individualized treatment program of aerobic exercise, resistance training (RT), lifestyle modifications, and counseling which can be particularly valuable for the aging population. The purpose of this review is to focus on the effects of RT on physical function for older participants in CR.

Physiologic Response in Resistance Training:

Resistance training is a form of anaerobic exercise which utilizes repeated movements against resistance to stimulate a stronger muscle contraction. It is generally guided by exercise intensity as defined by the single-repetition maximal lift (1-RM) which can be safely determined in older adults by an experienced exercise specialist. 1-RM is the maximum amount of weight that can be lifted once while maintaining proper form.

Gains in strength result from an “overload” beyond a minimal threshold of resistance. In the initial phase of RT (weeks), there is an increase in strength due to neuromuscular adaptation.² Over time (months), the muscle fibers respond to the repeated resistance stimulus by increasing in size (muscle hypertrophy) leading to improvements in function and efficiency. The acute cardiovascular response during RT is an augmented pressure load on the heart that can transiently increase heart rate and blood pressure (BP).³ The BP effect from RT depends on the load intensity and the magnitude of resistance.

Breathing techniques to avoid “straining” and rest between sets can help attenuate the BP response to RT. Breath holding (Valsalva maneuver) during exertion should be avoided to mitigate increases in intrathoracic pressure and an exaggerated BP response. By exhaling during the exertion phase of RT, destabilizing hemodynamic responses are minimized.³

Resistance Training in Frail Older Adults:

Sarcopenia, the loss of muscle mass and strength due to aging or chronic disease such as HF and cancer, often leads to frailty and physical impairment. Frailty is a clinical syndrome due to age-associated declines in function and physiologic reserve, leading to increased vulnerability to acute stressors.⁴ Frailty consists of five domains: physical exhaustion, mobility, muscular strength, low energy expenditure, and nutrition. The physical frailty phenotype is widely used as a screening tool to assess frailty in the elderly.⁵ Frail patients with cardiovascular disease (CVD) which includes coronary heart disease, stroke, and HF have twice the morbidity and mortality compared to non-frail individuals.⁶ Furthermore, frailty in CVD patients is associated with higher disability and hospitalization rates. RT can help combat frailty by improving several components of physical function including muscular strength, walking endurance, and balance.³

Fiatarone et al studied the effects of RT in a cohort of frail adults aged 72 to 98 years who participated in high intensity progressive RT of the hip and knee extensors. ⁷ Muscle strength and size improved with RT, allowing for better mobility and increased level of physical activity. Similarly, a randomized controlled trial in forty nonagenarians aged 90–97 years assessed the effects of an 8-week RT program consisting of light to moderate intensity RT characterized as 30–70% of 1-RM three times a week and found an increase in muscle strength and a reduction in fall risk.⁸

Another study examined the efficacy of RT at different intensities in older, frail adults. Individuals participating in RT, starting at 20% and increasing to 80% of 1-RM over a 12 week period, had greater increase in muscle strength compared to those who trained exclusively at 20% of 1-RM.⁹ No training related adverse events occurred in either groups. Thus, RT in frail, older adults is well tolerated and can improve gait speed, strength, and balance, thereby reducing the number of falls and fractures.^7–9

Functional benefits of RT in CR patients

The functional benefits of RT on measures of physical performance were carefully evaluated in 42 disabled female cardiac patients age 65 or older. Subjects were randomized to either high intensity RT (i.e. 80% of 1-RM) or light yoga (control).^10,11 RT improved the performance on a wide range of physical activities such as simulated grocery carrying or lifting heavier luggage onto a bus more rapidly. There was a close relationship between increases in muscle strength and increases in the total physical function score (Figure 1). ¹⁰ Additionally, there were measured improvements in endurance activities such as the stair climb and 6-minute walk and tasks involving flexibility and coordination such as pouring milk or vacuuming. Thus, RT safely improves performance on a wide variety of daily activities in older women with coronary heart disease.

Figure 1:

Association between percent changes in total Continuous-Scale Physical Functional Performance test (CS-PFP) physical performance score and percent changes in maximal strength on the bench press. Pre, before exercise; Post, after exercise.

From Brochu M, Savage P, Lee M, et al. Effects of resistance training on physical function in older disabled women with coronary heart disease. J Appl Physiol 2002;92:676.

Patients with HF have reduced exercise tolerance for many reasons including diminished cardiac function, autonomic dysfunction, and skeletal muscle abnormalities.^3,12 For those with HF, exercise intolerance is strongly associated with quality of life, morbidity, and mortality.¹² Historically, there has been apprehension regarding RT in patients with systolic HF due to a theoretical concern of adverse remodeling of the left ventricle (LV) due to increased afterload with exertion. This, however, has not been the case. Two studies randomized patients with systolic HF to RT versus usual care and noted that LV volumes remained unchanged without deterioration of ejection fraction in the RT group.^13,14

The relationship of RT and muscle function in older women with HF was examined in a randomized control trial.¹⁵ Participants had significantly lower muscle strength, but similar aerobic capacity compared to age matched peers without HF. High intensity RT resulted in improvements in muscle strength, endurance, and exercise performance due to peripheral muscle adaptations seen on biopsy. These benefits occurred despite a lack of change in skeletal muscle mass or cardiac function. Another study measured performance in activities of daily living and muscle strength before and after an 18-week RT program in patients 71–75 years of age with HF.¹⁶ At baseline, measured performance of daily activities was 30% lower in HF patients compared with healthy age-matched controls due to reduced aerobic capacity and diminished muscle strength. RT resulted in significant improvements in activities of daily living such as carrying groceries, loading and unloading a washing machine and dryer and picking up items off the floor, without change in aerobic capacity. Muscle weakness, therefore, is a key determinant of physical disability in individuals with HF and RT can improve physical functioning.^15,17,18 While much research has centered on abnormalities of skeletal muscle in patients with HF and relative benefits of exercise training, recent efforts highlight similar skeletal muscle changes associated with diastolic HF, and similar benefits of exercise training.¹⁹

Metabolic benefits of RT in Older CR patients

The loss of muscle mass due to aging diminishes total body glucose utilization and lowers caloric expenditure thus contributing to insulin resistance, diabetes mellitus type 2 (T2DM), hypertension, dyslipidemia, and obesity. Strength is inversely associated with the prevalence of metabolic syndrome independent of aerobic activity.²

i. Insulin Resistance

Insulin resistance and T2DM are significant risk factors for development and progression of ASCVD. In one study, the combined prevalence of insulin resistance and T2DM for individuals enrolled in CR was remarkably high at 67%.²⁰

RT is associated with increase insulin sensitivity and glucose uptake in patients with abnormal glucose tolerance, improving glycosylated hemoglobin levels, and should, therefore, be considered in patients with insulin resistance and/or T2DM.^21,22 A large prospective cohort study followed 32,000 men aged 40 to 75 over eighteen years to examine the role of RT in primary prevention of T2DM.²³ Engaging in RT alone, for at least 150 minutes per week, had a 34% risk reduction in developing T2DMs; but for participants in combined RT and aerobic exercise, a 59% risk reduction was observed. Therefore, RT is an important intervention for the prevention and management of insulin resistance and T2DM.

ii. Blood Pressure

The effect of RT on BP has been examined in two meta-analyses.³ An analysis of 11 studies found that following RT, both resting systolic blood pressure (SBP) and diastolic blood pressure (DBP) decreased 3–3.5 mm Hg.²⁴ Similarly, another meta-analysis of RT reported resting reductions of 3mm Hg and 6 mm Hg in DBP and SBP, respectively.²⁵A caveat to both of these analyses, however, is that only a third of the study patients were deemed to be hypertensive at baseline (i.e. initial resting SBP of > 140 mm Hg or DBP > 90 mm Hg). While reductions appear minimal at the individual level, an SBP reduction of 3 mm Hg has been associated with reducing stroke and cardiac morbidity and overall mortality at the population level.³

For patients with hypertension, there is more benefit when RT is combined with aerobic exercise. 104 individuals between ages 55 to 75 with untreated mild hypertension (SBP of 130–159 mm Hg or DBP of 85–99 mm Hg) were randomized to combined aerobic and RT versus usual care.²⁶ A reduction of 5 mm Hg and 3 mm Hg in SBP and DBP, respectively, was observed in the intervention group. While the evidence for RT alone as a form of exercise to reduce BP is limited, the American Heart Association has recommended moderate intensity RT as an adjunct to aerobic exercise in treating and preventing hypertension.³

iii. Effects of RT on Dyslipidemia

Resistance training appears to have no significant effects on lipid metabolism.³ One large study which consisted of approximately 1190 women and 5460 men found no association between muscle strength and low density lipoprotein cholesterol (LDL) or total cholesterol (TC).²⁷ A randomized control trial examining the effects of high intensity RT (85–90% of 1-RM) in men aged 60–75 years and found no significant improvement in lipid profiles.²⁸ In another study, 15 post-menopausal women underwent low intensity RT and no significant alterations in LDL or TC were seen.²⁹ Based on these studies, there is no good evidence that RT affects dyslipidemia.

iv. RT and Weight Management

Over 80% of participants in CR are overweight.³⁰ While aerobic activity is greatly emphasized regarding weight management due to an increase in caloric expenditure, RT plays a role as well. Several studies have reported an increase in lean body mass and a decrease in adipose tissue for older adults undergoing RT.³ For example, Hunter et al examined the effects of RT on fat distribution in older men and women aged 61–77 years.³¹ Interestingly, there appears to be sex specific differences. Women lost a significant amount of visceral adiposity while men did not. Both men and women, however, had significant increase in muscle mass and similar loss of total body fat. This increase in muscle mass will increase basal metabolic rate which is responsible for up to two thirds of total energy expenditure in healthy adults.^3,30 Furthermore, given that visceral fat has been associated metabolic syndrome, T2DM and hypertension, a reduction in visceral adipose tissue is beneficial in older adults at CR.

Effect of Resistance Training on Aerobic Capacity

Aerobic capacity defined by peak oxygen consumption (VO₂), reflects the overall functional capacity of the cardiorespiratory system. It has been postulated that increased muscle strength, resulting from RT, would improve peak aerobic capacity. However, studies examining the link between RT and measures of peak VO₂ have been equivocal.

In a randomized control trial of 24 healthy older adults who underwent RT, a significant improvement in leg strength and walking endurance was seen, but peak VO₂ remained unchanged.³² A recent meta-analysis of 34 studies examined the effects of RT on aerobic fitness and strength in older adults with coronary heart disease and found that while RT improved muscle strength, peak VO₂ and work capacity remained the same.³³

Another review, however, examined whether RT enhanced peak VO₂ in older patients and 6 of the 9 studies reported an improvement in peak VO₂ following RT regardless of the intensity.³⁴ Interestingly, a negative correlation was seen between the initial peak VO₂ and RT induced change in peak VO₂ suggesting that the increase in VO₂ from RT is dependent on the VO₂ at baseline. Older adults with an initial peak VO₂ of less than 25ml*kg⁻¹*min⁻¹* were more likely to increase peak VO₂ with RT. While the data remains mixed regarding the effect of RT on peak VO_2, RT clearly improves walking endurance and muscle strength thereby increasing physical function among older adults.

Combination of aerobic exercise and Resistance Training more beneficial than Resistance Training alone

Decreases in muscle mass and strength due to aging affects the performance of daily living and leisure activities, mobility, and aerobic fitness. While RT, alone, can help to counteract some of the changes associated with aging, the combination of RT with aerobic exercise has proven to be more beneficial. Several randomized control trials have demonstrated improvement in muscle strength, endurance, and quality of life in cardiac patients with the combination of RT and aerobic exercise.^35,36

The effects of high intensity RT on quality of life were studied in 34 older CR participants.³⁷ Among those randomized to RT with aerobic training, a significant improvement was seen in exercise treadmill time, muscle endurance, and self-reported ability to lift weights, to do push-ups, and to climb stairs.

Furthermore, combined RT and aerobic exercise in cardiac patients was more effective at improving peak VO₂ and upper/lower body strength compared to isolated RT or aerobic exercise alone.³⁸ Thus, the combination of aerobic and RT can ameliorate the effects of frailty and improve physical function. Given the overall benefits, all CR programs should be incorporating both RT and endurance exercise.

Safety of Resistance Training

Supervised RT appears to be quite safe even amongst the elderly in CR. Nonetheless, a small risk for injury remains and is likely associated with an individual’s age, baseline fitness level, intensity of RT, and the quality of supervision.

Absolute and relative contraindications to RT and CR overlap and include decompensated HF, severe and symptomatic aortic stenosis, uncontrolled hypertension (≥180/110 mm Hg), unstable coronary heart disease, Marfan’s syndrome, enlarging aortic aneurysms, and severe pulmonary hypertension (mean arterial pressure >55 mm Hg).³ Patients with recently implanted pacemakers or defibrillators should consult their physician prior to initiating a RT program as upper body activity can cause lead fractures or dislodgment. For patients who recently underwent valvular or coronary artery bypass surgery with a full sternonotomy, upper body RT should be delayed 12-weeks from the date of surgery to ensure proper healing of the sternum.³

Patients following an acute MI can engage in weight lifting activity as early as 4–6 weeks post event. In one study, RT combined with aerobic exercise was implemented in patients 6 weeks after an MI and improvement in strength was seen with no adverse events.³⁹

While very intense RT can temporarily elevate BP substantially, such increases are not seen when RT is performed with proper technique and avoidance of Valsalva maneuver in the CR setting. Even for those with controlled hypertension, no adverse events were observed when RT was performed at low to moderate intensity.⁴⁰

Many older patients who enter CR may have co-morbidities such as osteoporosis, neuropathy, arthritis, or complications from prior stroke. While individuals with co-morbid conditions are at an increased risk for physical complications, they can still benefit from RT. With appropriate guidance, the RT program can be adapted to accommodate patients with physical limitations.³

Prescription of RT in older CR patients

The critical components of RT prescription include intensity, frequency, type and the number of sets and repetitions. The primary types of RT are weight lifting stations, free weights, wall pulleys, resistance bands, and weight cuffs/hand weights.³ (Table 1)

Table 1:

Types of Resistance Training

	Advantages	Disadvantages
Weight lifting machines	• Low risk of injury with proper technique • Able to target specific muscle groups • Proper form fostered by going through a machine dictated range of motion • Requires less counseling	• More expensive • Space consuming or requires “facility membership” • Range of motion is not individualized and is dictated by the constraints of the machine • May not be appropriate for individuals that are on the extremes for body habitus • Not versatile (each station is muscle group specific) • Machine may allow for dominate limb to compensate for strength deficiencies in the other limb • Requires maintenance/repairs
Free weights	• Relatively compact • Allows for free range of motion • Requires engaging axillary stabilizing muscles • Versatile (same equipment can be used for multiple exercises) • Exercise can be more functional (recreating “everyday” activities)	• May cause injury if weight is mishandled • May be difficult to target specific muscle groups without adjunct equipment (i.e. bench) • Need to master proper form • Requires more counseling
Resistance bands	• Inexpensive • Portable, compact • Allows for free range of motion • Requires engaging axillary stabilizing muscles • Low risk of equipment being mishandled • Versatile	• May not provide a sufficient resistance for some muscle groups. • With repeated use, bands lose resistance • Bands need to be replaced when broken • Need to master proper form
Resistance balls, sand bags	• Inexpensive • Portable, relatively compact • Allows for free range of motion • Requires engaging axillary stabilizing muscles	• Difficult to target specific muscle groups • May not provide an adequate resistance for some muscle groups
Individual’s body weight	• No expense • Portable • Allows for free range of motion • Requires engaging axillary stabilizing muscles	• May not provide an adequate resistance for some muscle groups • Need to master proper form • Difficult to target specific muscle groups

Once RT is initiated, proper technique and progression need to be prioritized. Initially, patients should perform single-set of 8–10 lifts per station at least twice a week and strength intensity should be 30–40% of 1-RM in the upper body and 50–60% of 1-RM in the legs and

hips.^3,41 Participants should work to a perceived exertion of 11–14 (“fairly light to somewhat hard”) on the Borg scale.² Periodically during the workout, heart rate, BP and perceived exertion should be assessed. If adverse signs or symptoms such as dizziness, angina equivalent, and heart rhythm irregularities occur, RT should be temporarily terminated.

As the individual adapts, parameters can be advanced to further facilitate improvement. Once the upper limit of a prescribed repetition range is achieved, for example 10–12 repetitions, resistance or weight load can be increased up to 80% of 1-RM. Typically, this translates to increases of 2–5 lb for arm exercises and 5–10 lb for leg exercises.³ Over time, the prescription can include multiple set programs to ensure all major muscle groups are being trained. For many older people in CR, RT is often a new form of exercise and should be counseled as to when it is appropriate to make these changes.

Summary

Many patients entering CR are older with diminished muscle mass and reduced strength and functional capacity. RT can play a pivotal role as it enhances muscular strength and exercise capacity, allowing for improvement in physical function and quality of life. The benefits of RT are distinct yet complementary to aerobic exercise. Under appropriate guidance and supervision, RT is safe and can be implemented with minimal adverse events in the CR setting. It is, therefore, a safe and effective way to improve exercise capacity, ameliorate cardiovascular risk factors, and reduce disability in older CR patients.

Key points:

• Resistance training has been shown to increase muscle strength, endurance, exercise performance and physical function in older adults with coronary heart disease and heart failure.

• Resistance training can help improve selected cardiovascular risk factors.

• The combination of aerobic exercise with resistance training in cardiac patients is more effective at improving muscle strength and cardiorespiratory fitness compared to isolated aerobic or resistance training.