People living with cardiovascular disease often present with low muscle mass, poor cardiac contractility function, increased adiposity, and a host of cardiovascular problems such as hypertension and poor glucose control. Additionally, most adults with cardiovascular disease are older people who have lower bone mineral density and are more susceptible to falls and have a higher risk of fracture. Exercise training is an important therapy in the treatment of associated comorbidities.
While aerobic and strength exercise training is highly recommended for cardiac patients, resistance exercise training is underutilized and often poorly prescribed.
Strength training is an exercise modality that involves exerting muscular force against an external load and leads to important health outcomes not optimally achieved with aerobic exercise, such as an increase in muscle mass, maintenance of density bone mineral and an increase in muscle fitness parameters (i.e. muscle strength, power and endurance)
Aerobic interval training involves repeated bouts of moderate to high intensity aerobic activity interspersed with periods of passive or active recovery. It is often incorporated into clinical practice for cardiac patients who have a severe condition and low cardiorespiratory fitness to improve the patient’s tolerance to an exercise session.
Similarly, group sets can be used to prescribe interval resistance training, which uses regular planned passive rest in addition to the passive rest periods between sets found in traditional resistance training. Group sets are a strength training practice model commonly applied in athletic populations to maximize performance and/or reduce cumulative fatigue, but may also be an appropriate mode of resistance training for chronically ill populations, including those with cardiovascular diseases.
This review aims to provide support for the use of group sets as a method for prescribing interval strength training in clinical cardiac rehabilitation exercise programs. The safety, practical application, and limitations of this resistance exercise training method will also be discussed.
| Benefits of strength training for cardiac patients |
Common clinical presentations in cardiac patients include cardiac cachexia (up to 42% of patients with heart failure), skeletal muscle atrophy, and peripheral muscle weakness ; There are no pharmacological interventions available to treat such presentations and they are not effectively addressed by aerobic training.
Preserving or improving muscle function should be the primary goal when addressing skeletal muscle health in cardiac populations.
Systematic reviews and meta-analyses have demonstrated the positive impact of participating in chronic resistance training (3 to 26 weeks, 1 to 5 sessions per week including 1 to 12 exercises at 25-80% 1 repetition maximum [1RM] 1 to 10 sets of 2 to 30 repetitions) to increase muscle function (i.e., muscle strength, muscle endurance, and muscle power) in patients with coronary artery disease and heart failure compared to inactive controls.
Greater muscle function improves the ability to perform activities of daily living and is strongly associated with reduced physical disability and continued independence, providing additional rationale for integrating training with high-quality resistance exercises for cardiac populations. .
There is limited evidence on the effect of strength training alone on muscle mass in cardiac patients. Combined exercise training approaches (aerobic and strength training) appear successful in improving muscle mass in patients with coronary artery disease.
Cardiorespiratory fitness is a predictor of prognosis and survival for people with cardiovascular diseases.
Therefore, it is pertinent to consider how strength training may affect changes in cardiorespiratory fitness. Meta-analyses have shown that resistance training can improve cardiorespiratory fitness in patients with coronary artery disease and heart failure.
Combined strength and aerobic training , compared with aerobic training alone, led to near-significantly greater improvements in cardiorespiratory fitness, suggesting that strength training should be incorporated into the exercise programs of people with cardiovascular disease.
Some authors found that in a cohort of 1171 patients with coronary artery disease, 23% did not experience an improvement in cardiorespiratory fitness with traditional cardiac rehabilitation: consisting of 30-40 min of aerobic conditioning and light hand weights for training of strength. Given these findings, a strength training prescription with moderate to high loads may help improve cardiorespiratory fitness in people with poor response to aerobic training.
It is clear that strength training can provide a host of health benefits for cardiac patients ( Figure 1 ). Greater efforts are warranted to include strength training as part of patient care.
Figure 1. A summary of the known benefits of performing strength training for cardiac patients. Possible benefits that are unclear are preceded by a question mark.
Since improving cardiorespiratory fitness is the primary goal of physicians working with cardiac patients, strength training is anecdotally underprescribed, with aerobic training taking priority. Furthermore, acceptance of resistance training is poor. In a retrospective analysis of a 12-month home cardiac rehabilitation program, 50% of patients discontinued the strength training program. Participants reported that they “lacked motivation,” did not have “enough time,” were “too fatigued,” and found resistance training “boring.”
| Safety Concerns with Resistance Exercise in Cardiac Cohorts |
Although strength training is a Class I Level A recommendation for cardiac patients, aerobic training remains the dominant feature of cardiac rehabilitation.
In fact, recommendations for strength training are often poorly defined in guidelines, and strength exercise accounts for less than one-third of a typical cardiac rehabilitation session.
Historically, strength training, particularly high-intensity strength training, has been considered a potentially unsafe exercise modality for cardiac patients. This has been attributed to the notion that acute resistance exercise leads to large hemodynamic responses (increased blood pressure and heart rate), which may increase the risk of an adverse event or chronically increase afterload, leading to adverse cardiac remodeling.
While this acute increase in blood pressure is concerning, a comparatively high relative load (i.e., >80% of 1RM and repetitions performed to failure) is unlikely to be used in clinical practice in cardiac patients. In fact, the recommended strength training load for outpatient cardiac rehabilitation is 40% to 60% 1RM, with some guidelines progressing the load up to 80% 1RM.
| Interval resistance training exercise prescription models |
We propose two models of interval strength training that may be practical and safe options for cardiac patients:
(a) Basic series in groups.
(b) The method of redistribution of rest.
A basic group set interval strength training approach integrates the use of short rests within the set. intervals (i.e. after a "set" of reps) plus a longer rest period between sets.
In stable, low-risk cardiac patients and in those patients moving into the maintenance phase of cardiac rehabilitation (i.e., exercising within the community setting), the use of group sets may allow higher loads (>70% 1RM ) are well tolerated and reduce exercise intensity and the transient hemodynamic response during resistance exercise. This can be done by prescribing group sets away from muscle failure (i.e. a large number of repetitions in reserve).
While group sets may currently be employed haphazardly in clinical settings, providing these models may provide practitioners with a framework to improve the quality of exercise prescription of strength training for cardiac patients and, more specifically, strength training. interval resistance.
| The benefits, usefulness and limitations of interval resistance training for cardiac patients |
Compared to traditional strength training, including additional rest periods within sets, between repetitions, or spread out in interval strength training can mitigate fatigue, improve patient perception of strength exercise, and ultimately Importantly, reduce the hemodynamic response and cardiac load. These benefits are particularly important for cardiac patients, as many have poor exercise tolerance and task self-efficacy regarding resistance exercise and in some cases possible hypertensive responses to exercise.
> Hemodynamic response and cardiac load
Recent evidence has suggested that longer sets occurring with higher repetition ranges, rather than load, may be the training factor leading to greater hemodynamic responses in resistance training.
These preliminary findings suggest that an interval strength training approach may result in lower or comparable hemodynamic response and cardiac loading (i.e., myocardial oxygen demand) in people with cardiovascular disease by reducing repetition ranges, incorporating rest more frequent and reduce the density of the exercise. Future research should focus on hemodynamic responses and cardiac loading during interval resistance exercise to determine acute responses.
> Cardiorespiratory fitness, musculoskeletal fitness and functional capacity
The effectiveness of traditional strength training in increasing muscle function is widely documented in healthy young and older adults and in populations with cardiovascular disease. However, it is important to evaluate whether interval strength training may be a viable method to improve muscle function in cardiac patients to mitigate reductions in muscle strength, especially with increasing age (1-2% per year to from 50 years old).
It was recently shown in a meta-analysis that there is no difference in muscular endurance, strength, power, or hypertrophy between traditional sets and interval sets (i.e., in groups) in apparently healthy and athletic populations.
Research in clinical and healthy populations suggests that interval strength training may be a suitable alternative resistance exercise prescription to increase muscle mass and improve muscle fitness parameters. Based on these findings, interval strength training may allow for higher quality repetitions (e.g., better movement quality/range of motion, higher movement speeds, and power production) due to reduced fatigue. This may be particularly important in cardiac patients given low exercise tolerance and peripheral muscle weakness that can hinder performance using traditional strength training methods.
These findings suggest that improvements in muscle strength are not dependent on the magnitude of fatigue accumulated during strength training.
Furthermore, interval strength training may be a more appropriate exercise prescription alternative, compared to traditional strength training, since its implementation can reduce the perception of effort, exacerbation of symptoms such as dyspnea, and cardiovascular load.
Alternatively, prescribing higher loads, due to more frequent rest periods, may increase the total “load volume” of work performed to potentially facilitate greater adaptations in cardiac patients. The effectiveness of higher loads and lower repetitions also appears to be superior compared to lower loads and high repetitions when strength training volumes are equalized.
> Practical limitations of interval strength training and high-intensity interval resistance training
A key limitation of interval strength training is the additional time required to complete the training session if a basic group interval strength training model is applied, particularly because many international cardiac rehabilitation guidelines suggest that exercise programs include 6 to 8 resistance exercises.
High-intensity interval strength training may also be an option to reduce session duration but achieve the same load volume, as the total repetitions needed to achieve a comparable load volume are lower. Therefore, if strength exercise sessions are limited by time constraints, as is common in cardiac rehabilitation, then a rest redistribution model or high-intensity interval strength training may be more appropriate than sets. basic in groups.
Since cardiac rehabilitation uses group classes, the integration of high-intensity interval strength training may be limited by the equipment available at the respective facility. This could be mitigated by using a circuit-style strength exercise class, where patients alternate between exercises, which may allow for more effective use of limited resistance training equipment.
| Clinical considerations and recommendations |
First, it is important that exercise professionals instruct cardiac patients on proper exercise technique and encourage free breathing or establish breathing patterns (such as inhaling during the eccentric component and exhaling during the concentric component of the exercise) when performing strength exercises. This will reduce the risk of musculoskeletal injury and attenuate unwanted acute hemodynamic responses to help ensure the patient is safe.
| Valsalva maneuver : Clinicians should monitor possible adverse responses that may occur during strength training. Specifically, when high loads are used there is an increased risk of a patient performing the Valsalva maneuver ; this is difficult to avoid with loads ≥80% maximum voluntary contraction. This increases intrathoracic pressure and may impede venous return during exercise. Significant reduction in cardiac output may cause syncope or dizziness . |
In low-to-moderate risk patients, it would be reasonable to implement interval strength training for people with cardiovascular disease, as long as the load remains the same or is only modestly higher than recommended in guidelines using traditional structures. This interval strength training approach appears to result in a lower acute hemodynamic load, which may make it a safer method of prescribing strength exercise from a cardiac perspective.
| Conclusion |
- Interval strength training is a promising rehabilitation method for cardiac patients.
- Implementation of group sets (rest periods within sets or rest redistribution technique) to prescribe interval strength training appears to reduce hemodynamic load, neuromuscular fatigue, and perceived exertion, which may optimize prescription and adherence. to strength exercise.
- If applied in people with cardiovascular disease, the relative load used should be consistent with current guideline recommendations until more evidence is available.
