Physical activity and structured exercise in patients with type 2 diabetes mellitus and heart failure
Patients with type 2 diabetes mellitus (T2DM) or heart failure (HF) are encouraged to adopt a physically active lifestyle and participation in structured exercise is endorsed as a safe and effective adjunct to medical therapy in both conditions. This article aims to provide health care professionals with the information required to tailor guidance relating to physical activity and exercise for individuals with T2DM and HF by: (1) presenting an overview of current guidelines, and (2) providing practical suggestions for their implementation.
‘Traditional’ forms of exercise training include moderate to vigorous-intensity aerobic exercise and dynamic resistance exercise. Benefits of exercise training include improved cardiorespiratory fitness and physical function, more favourable body composition, lower metabolic risk and enhanced quality of life. Before engaging in structured exercise, medical clearance may be required for certain types of activities, and precautions should be taken to minimise the risk of hypoglycaemia and left-ventricular overload in patients with T2DM and HF. Importantly, patients with HF should be educated to distinguish severe adverse symptoms during exercise from expected feelings of breathlessness and fatigue. The latter should not be a reason to discourage patients from engaging in as much physical activity and structured exercise as possible.
In order to optimise adherence, exercise prescription should be driven by patient preferences, motivations and individual circumstances. Consideration should also be given to more novel approaches, such as reducing sedentary behaviour and high-intensity interval training.
The coexistence of heart failure (HF) and type 2 diabetes mellitus (T2DM) is common and has important implications for clinical management and prognosis.1
Exercise has been promoted as an effective and safe adjunct to optimal medical treatment in the management of both T2DM and HF.2–5 However, exercise intolerance can trigger acute exacerbation of dyspnoea and fatigue5 which are also common symptoms of worsening HF status. This can lead to confusion for patients and clinicians as to the cause of these symptoms and there is a need for a better understanding that feelings of dyspnoea and fatigue may, in fact, be evidence of important physiological adaptations6 and not a reason to discourage patients with HF from engaging in an active lifestyle.
This article discusses the role of physical activity and structured exercise in the management of patients with T2DM and HF, focusing on current recommendations, evidence and clinical implications. Specifically, we aim to provide health care professionals with the information needed to tailor physical activity and exercise advice and prescription to this growing clinical population.
Current recommendations for physical activity
In order to provide a frame of reference, the definitions of physical activity, physical inactivity, sedentary behaviour and exercise are listed in Box 1.
Box 1. Definitions of key terms used throughout this article
The American College of Sports Medicine (ACSM) provides physical activity recommendations for the general adult population.7 Further guidelines from the American Diabetes Association (ADA) and a consensus group of the Heart Failure Association (HFA) and the European Association for Cardiovascular Prevention and Rehabilitation (EACPR) provide specific recommendations for patients with diabetes or HF (New York Heart Association [NYHA] class I to III), respectively.4,6
These guidelines, which are summarised in Table 1, share some common themes. Most prominently, they each fully endorse the use of a personalised, patient-centred approach to promote physical activity within the personal limitations, preferences and circumstances of a given individual. Importantly, while increasing light-intensity physical activity and limiting sedentary behaviours should be encouraged in all individuals, certain types or intensities of structured exercise may be contraindicated in some patients. Some of these contraindications may be readily apparent upon clinical review, but others may only be detected during specific pre-participation testing. As such, appropriate screening of patients, particularly those who are previously inactive, is essential prior to engaging in a structured exercise programme. This is particularly important for patients with HF where establishing haemodynamic tolerance to exercise is pivotal. Pre-participation screening procedures are discussed in more detail below.
Mechanisms underlying the effects of physical activity in patients with T2DM and HF
Type 2 diabetes mellitus
Several reviews and meta-analyses have summarised the health benefits of exercise training in T2DM.8,9 In a pooled analysis of 23 randomised controlled trials, 12–52 weeks of aerobic, resistance or combined (aerobic plus resistance) exercise training elicits significant reductions in HbA1c compared to non-exercising control participants (mean difference -0.73%, -0.57% and -0.51%, respectively).9 Regardless of exercise mode, interventions with a total duration >150 minutes/week have the greatest effect on HbA1c (-0.89%), but even those below this threshold elicit significant benefits (-0.36%).9 These results suggest that any form of sustained exercise training is likely to be worthwhile for patients with T2DM.
Aerobic exercise interventions are also repeatedly found to induce clinically significant benefits on cardiorespiratory fitness (mean improvement in peak oxygen uptake [V.O2 peak] 11.8%), with higher intensity exercise providing additional benefits on both fitness and metabolic control.8,10 Resistance exercise is generally found to improve insulin sensitivity and glucose tolerance, while improving lean body mass and parameters of strength.11,12 Both forms of exercise, and their combination, can also induce several metabolic benefits in skeletal muscle to improve glycolytic and oxidative substrate metabolism, including enhanced capillary density and greater mitochondrial capacity.4,7,11 Chronic adaptations to training also include the lowering of whole-body and ectopic lipid stores, improvements in endothelial function, reduction of systolic and diastolic blood pressure (-6.0mmHg and -3.6mmHg, respectively), and promotion of a more favourable circulating lipid profile.4,7,13 Improved physical function and enhanced performance in tasks of daily living may also mediate improvements in quality of life (QoL).7
As little as one bout of exercise transiently improves glycaemic control for up to 72 hours, through both insulin-dependent and insulin-independent mechanisms.14,15 However, a dose–response relationship exists whereby exercise of greater intensity, duration or frequency will likely result in greater benefits.16,17 For example, even small amounts of high-intensity exercise, such as those promoted through high-intensity interval training (HIIT), have been shown to improve glucose regulation in individuals with T2DM.16 In a small study, HIIT was also shown to increase cardiac volumes, stroke volume and ejection fraction, with no effect on myocardial strain.18 Furthermore, this occurred with a corresponding increase in peak early diastolic filling rate measured using MRI.18 Whether such changes result in a lower risk of subsequent heart failure is not known.
It is important to note that, while higher-intensity exercise elicits a greater range and magnitude of physiological adaptations, any form of increased movement is likely to induce beneficial effects on health. Mounting evidence shows that breaking prolonged sitting time with slow walking or other forms of light-intensity physical activity elicits substantial, acute improvements in postprandial glucose metabolism in individuals with or at high risk of T2DM.19–21 Longer-term benefits have also been demonstrated with supervised interventions employing light-intensity exercise training. Interestingly, when matched for energy expenditure, prolonged continuous light-intensity exercise training was equally as effective as continuous moderate- to high-intensity training in lowering HbA1c and increasing whole-body and skeletal muscle oxidative capacity in patients with obesity and T2DM.22
Despite both falling under the umbrella term of HF, the underlying pathophysiological differences between HFrEF and HFpEF (HF with reduced ejection fraction and HF with preserved ejection fraction, respectively) may have important implications for clinical management and the identification of effective exercise therapies. In HFrEF, exercise training is generally associated with central adaptations, such as improved cardiac output and stroke volume.5,23,24 Conversely, in HFpEF, the limited research alludes to improvements in peripheral muscle function, with little evidence of altered cardiovascular structure.25,26
A wealth of evidence supports the potential for exercise training to elicit meaningful benefits in patients with HF without adverse effects on left ventricular (LV) remodelling.2,6,24,27–30 In this patient group, regular aerobic exercise elicits significant improvements in exercise capacity and QoL, with meta-analyses reporting 13% and 12% improvements in V.O2 peak and 6-minute walking distance, respectively, and a 9.7 point improvement in the Minnesota Living with Heart Failure Questionnaire.29–31 These benefits may be mediated by both central and peripheral adaptations.2,6,24,27–31
Furthermore, a recent Cochrane review (including 4740 patients with HF from 33 exercise training studies) reported a reduction in overall (25%) and HF-specific hospitalisation (39%) with exercise, compared to standard clinical care.29,30 This review also reported lower all-cause mortality with exercise training when patients were followed up for more than one year, but this did not reach statistical significance (p=0.09).29,30 Interestingly, patients with HF and T2DM have lower functional capacity, an increased rate of hospitalisation and a reduced response to aerobic exercise training in comparison to patients with HF alone.32
Evidence surrounding the effects of dynamic resistance exercise in patients with HF is limited. However, when appropriately prescribed, resistance exercise appears to be safe and effective and, in combination with aerobic exercise, improves skeletal muscle strength and function.27,33,34
These peripheral benefits may have particular importance for individuals with HF (with or without T2DM) as these patients are often hindered by skeletal muscle weakness,27 and muscular strength and cross-sectional area (particularly of the lower body) are independent predictors of exercise tolerance, clinical prognosis and long-term survival.35 Greater upper body strength may also lead to greater performance in tasks of daily living, which may in turn improve QoL.27 Combined aerobic and resistance training has also been shown to improve exercise capacity and elicit anti-inflammatory effects.27,34,36 Moreover, improvements in submaximal exercise capacity may be greater than in those with aerobic training alone.34
High-intensity interval training has also been shown to yield improvements in exercise capacity and QoL for patients with HF with no apparent deleterious effects to LV remodelling.28,37,38
Furthermore, although the evidence to date is limited, one study reports that improvements in cardiorespiratory fitness with HIIT may be greater than those seen with continuous aerobic training (46% versus 14% increase in V.O2 peak, respectively).37
Practical implications for employing different modes of exercise in T2DM and HF
While the risk of cardiovascular events (sudden cardiac death and acute myocardial infarction) are transiently increased during vigorous-intensity exercise, the overall absolute and relative risks remain low and the benefits of an active lifestyle far outweigh the modest increase in risk of these adverse events.39–41 Previously inactive individuals and patients with T2DM are, however, at a higher relative risk of such events and should therefore receive medical clearance from a health care professional prior to engaging in structured exercise. The ACSM provides guidelines for pre-participation screening,39 but stresses that these should be considered in conjunction with the clinical assessment of each given individual to identify their specific risk, requirements and limitations. Importantly, screening should be appropriate for the intensity of activity prescribed and categorising exercise intensity is discussed in more detail below. Medical evaluation may include symptom-limited exercise testing, at the discretion of the health care professional, while cardiovascular disease (CVD) risk should also be considered.39 Stratifying individuals purely on the number of CVD risk factors present should be avoided, however, as this approach may result in unnecessary barriers to participation.39 Notably, the ADA suggests that necessitating medical clearance for all individuals with T2DM may be excessive. Clinical assessment beyond ongoing diabetes management may be reserved for individuals wishing to engage in activities above the demands of brisk walking or tasks of daily living, or when adverse symptoms are experienced at these lower intensities.4
Ideally, each patient’s exercise capacity should be determined (or at least predicted using validated methods) prior to engaging in an exercise programme, allowing the prescription of exercise intensity in relative terms (Table 2). Where possible, light-intensity physical activity, moderate- to vigorous-intensity aerobic exercise and HIIT may be prescribed at an intensity relative to cardiorespiratory fitness (%V.O2 peak) or maximal heart rate (%HR max). However, given the practical limitations within primary care (namely time and cost), physical activity or exercise can also be prescribed according to the absolute energy demands of the activity, which may be presented as ‘metabolic equivalents of task’ (METs). The ‘Compendium of Physical Activities’42 details the intensity (in METs) of numerous different activities, ranging from very light to maximal. Practical examples are outlined in Table 2. Moreover, rating of perceived exertion (RPE),43 assessed using a scale that ranges from 6 (no exertion at all) to 20 (maximal exertion), is an easily implemented measure to monitor subjective perceptions of exercise intensity. RPE may also be used in a prescriptive capacity when asking patients to self-select the intensity of a given exercise (e.g. ‘please walk at a speed with an RPE of 9’). Despite its simplicity, however, it is important that patients are familiarised with RPE to ensure its effective use.
(Click table for full size image)
Table 2. Categories of exercise intensity for use when prescribing light-intensity physical activity, moderate to vigorous aerobic exercise training or high-intensity interval training. (Adapted from: Garber CE, et al. Med Sci Sports Exerc 2011;43:1334–59)7
Resistance exercise can also be prescribed relative to a 1-repetition maximum (1-RM), which is the heaviest weight that can be successfully lifted once through the complete range of motion and using the correct technique. 1-RM should be determined for each exercise that is contained within a resistance training programme.
For longer exercise programmes, exercise capacity should be reassessed at appropriate intervals to ensure progression. Assessments of exercise capacity and subsequent exercise prescription should be done in conjunction with a clinical assessment of the patient and their individual stability/limitations.
Practical considerations (mode of exercise)
Table 3 presents a summary of example exercise training regimens for patients with T2DM and HF, specifically light-intensity physical activity, moderate- to vigorous-intensity aerobic exercise, HIIT and dynamic resistance exercise.
Given the relative equivalency of metabolic benefits across aerobic and resistance exercise modalities for patients with T2DM44 (and to an extent HF), choice of exercise should be primarily driven by patient preferences, motivations and circumstances. The presence of other comorbidities may also be an important factor. For example, some form of resistance training in combination with aerobic exercise may be strongly encouraged in patients with sarcopenia, given their higher risk of falling and other peripheral limitations. Patient age should also be considered as this may have important implications on the precise nature of physical activity performed. While T2DM is prevalent in younger adults (18–40 years),45,46 and these individuals may display some extent of cardiovascular dysfunction, older individuals constitute a high proportion of patients with T2DM and/or HF.47,48
Moderate- to vigorous-intensity aerobic exercise
Continuous moderate- to vigorous-intensity aerobic exercise remains the most prevalent form of exercise training, due to its well-demonstrated efficacy and safety.24,49–52 Typically, it is performed on a stationary cycle ergometer or motorised treadmill and is characterised by steady-state moderate- to vigorous-intensity exercise (50–80% V.O2 peak), with the ultimate aim of enabling individuals to perform prolonged training sessions (45–60 minutes duration). The improvement in exercise capacity after continuous aerobic exercise training is primarily determined by the total energy expenditure of training, which results from the intensity, duration and frequency of exercise. Session duration should be progressed according to patient tolerance, with a minimum target of 30 minutes per session, at least three times per week.53,54 However, patients with recent haemodynamic instability, lower exercise capacity or greater fatigue should start with shorter exercise bouts (i.e. 10 minutes), which can be repeated several times a day.27
Light-intensity physical activity
In previously inactive patients with T2DM and HF, ensuring safety during exercise is paramount. The implementation of lower-intensity exercise, at least during the early stages of exercise training, may lower the risk of adverse events and reduce the reliance on risk stratification and monitoring. Light-intensity physical activity may also be more acceptable to a broader population, including older adults or those with physical limitations. Light-intensity activity corresponds to approximately 40% V.O2 peak (RPE 9–11) and individuals should aim for a minimum of 30 minutes per session, at least three times per week.
For patients with severe HF, or those that are severely deconditioned, gradual mobilisation (‘calisthenic exercises’) may be warranted as a prerequisite to more formal exercise.6 Practically, this consists of a range of simple muscular movements for the purpose of physical conditioning, performed without weights or equipment and intended to increase body strength and flexibility. For these individuals, it is recommended to start even lower and progress even slower (i.e. low-intensity exercises for 5–10 minutes twice a week). If well tolerated, session duration and frequency may be gradually increased towards the guidelines outlined above.6
All individuals should also be encouraged to increase their total daily incidental (non-exercise) physical activity to gain additional health benefits.4,55–57 This includes various activities that are conducted in both occupational and leisure time such as light walking, gardening and housework. Increasing unstructured physical activity increases daily energy expenditure, while also reducing total daily sitting time. Increasing unstructured physical activity should be encouraged as part of a whole-day approach, or at least initially as a stepping stone for individuals who are sedentary/deconditioned and who are unable/reluctant to participate in more formal exercise.
High-intensity interval training
Low adherence to exercise training programmes remains a major concern in clinical care. New and refined strategies are thus warranted to further improve the effectiveness of exercise training in patients with HF and T2DM. One such strategy is HIIT, which is typically divided into two main categories: sprint and aerobic types.37,58 Sprint protocols are characterised by very short bursts (10–30 seconds) of maximal activity and are thus particularly physically demanding. As a result, evidence in clinical populations is limited. Aerobic HIIT protocols are more practical alternatives for patients with T2DM and/or HF and, while several protocols exist, low-volume HIIT (LV-HIIT) and aerobic interval training (AIT) are the most widely studied. LV-HIIT consists of 10 x 1-minute intervals performed at near-maximal aerobic capacity (80–95% V.O2 peak), which are alternated with 1-minute periods of low-intensity active recovery. AIT is characterised by 4 x 4-minute bouts at 85–95% of maximal heart rate (HR max), interspersed by 3-minute recovery intervals at 50–75% HR max.37,58 Given the high-intensity nature of HIIT, caution regarding its use in patients with HF is understandable. However, as highlighted in Table 3, a personalised approach whereby interval intensity and duration begin low, before progressing according to patient tolerance, should be implemented. If implemented in this manner, HIIT appears to be safe and feasible for patients with T2DM and/or HF.
While improving endurance capacity in patients with HF and T2DM is important, aerobic exercise training alone does not address the multi-domain deficits present in this population. Typically, these patients may also be at risk of sarcopenia, impaired balance and reduced flexibility,59 all of which may limit functional capacity and QoL. Initiating exercise training of any kind without addressing these deficits may also increase risk of injury and aggravate outcomes. As such, the inclusion of resistance training is now accepted practice when designing an exercise programme for patients with HF.33 Training should be initiated with a low weight and number of repetitions, and emphasis should be placed on the quality of exercise technique. Intensity may then be progressed as tolerated. Chosen exercises should include both upper and lower body muscle groups, with a focus on functional improvements relevant to tasks of daily living rather than skeletal muscle hypertrophy (increasing muscle mass) per se.
Type 2 diabetes mellitus
For the large majority of people with T2DM, exercise is a valuable therapeutic aid to optimise health that can be undertaken at their convenience. Depending on specific circumstances – such as the characteristics of exercise, the timing in relation to meals, the patient’s habitual glycaemic control and the suitability/effectiveness of any precautions undertaken – the risk of hypo- or hyperglycaemia may be increased both during and after exercise, particularly in patients on insulin therapy.4
However, implementing appropriate precautions (including changes to insulin regimens, carbohydrate intake and the timing of activity), along with regular monitoring of blood glucose before, during and after exercise should effectively minimise risk.4 These precautions should be discussed with patients prior to initiating exercise training.
Other temporary contraindications include acute systemic infections, severe exacerbations of inflammatory joint disease or musculoskeletal injury, severe hypertension or unstable HF. Physical activity undertaken with peripheral neuropathy necessitates proper foot care to detect, or ideally prevent, problems early to avoid ulceration and the increased risk of amputation.4 Such individuals may still participate in moderate weight bearing exercise and moderate-intensity walking is unlikely to increase the risk of foot ulcer development or reulceration.60 Similarly, the presence of autonomic neuropathy may complicate an active lifestyle, so patients should obtain physician approval and discuss symptom-limited exercise testing before commencing exercise.4
Caution is vital when patients with HF (with or without diabetes) wish to undertake resistance exercise, to avoid pressure and/or volume overload of the left ventricle.61 It is therefore recommended that short-duration exercise is performed to provide a sufficient peripheral muscular stimulus, but with sufficient rest intervals to avoid high cardiovascular stress. Ultimately, the intensity and duration of exercise prescribed should reflect the clinical stability of the patient and the size of the working muscle mass. The aim of resistance training in this population should not be to significantly increase muscle strength or size but instead to maintain a more normal skeletal muscle mass and reverse or delay adverse functional changes. As such, heavy weights should be avoided. For example, individuals with low cardiovascular reserve may benefit from the use of small hand weights (e.g. 0.5, 1 or 3kg). Furthermore, the guidelines outlined in this article are focused at patients in NYHA class I–III. At present, evidence of the safety and efficacy for resistance exercise in NYHA class IV patients is extremely limited, but patients should be encouraged to maintain functional strength, range of movement and balance through participation in modified programmes.6 Absolute contraindications to exercise for patients with HF, regardless of activity type, include unstable angina, uncontrolled HF or arrhythmias, uncontrolled hypertension or diabetes and acute systemic illness or fever, as well as severe and symptomatic valvular heart disease.6
Importantly, patients should be educated to recognise the adverse signs and symptoms associated with exercise and to report these promptly to their primary health care professional. This is vital because caution regarding unexpected adverse events should be intricately balanced with education of acceptable and expected levels of fatigue and exertion. Patients should be reassured that feelings of breathlessness associated with the initiation of exercise may be a product of signalling between the periphery and central haemodynamic performance and not necessarily an unhelpful exacerbation of symptoms.62 Those with HF and T2DM should also monitor and self-manage their blood glucose levels before, during (if deemed necessary) and after exercise in order to reduce the risk of hypoglycaemia.
Collectively, the evidence suggests that exercise training yields both central and peripheral adaptations for patients with T2DM and HF, which are clinically translated into anti-remodelling effects, increased exercise capacity and reduced morbidity. Furthermore, patients actively involved in any kind of exercise training may benefit from improved prognosis, QoL and anatomic function. However, there is extremely limited data in patients with HFpEF and further studies are needed.
Exercise is clearly an effective but neglected treatment for many chronic conditions, including T2DM and HF. However, as is the case with surgical and pharmacological treatments, exercise is not a single entity and must be tailored to the specific conditions of the individual. This is important, as preliminary data suggest that the clinical benefit of exercise may be reduced (but, importantly, not abolished) in patients with T2DM and HF. Therefore, the agreed exercise strategy for a given individual should be based on clinical evaluation and personal preference, to increase long-term adherence and the magnitude of benefits elicited. Individuals may also benefit from regular follow-up with a multidisciplinary team in order to prevent re-hospitalisation.
Although there are few absolute contraindications to exercise in patients with chronic conditions, it is important that patients receive a thorough assessment before undertaking exercise, which should be done in consultation with a multidisciplinary team of health care professionals. It should also be ensured that previously inactive individuals start by performing short sessions of low-intensity exercise before the duration and intensity of exercise are increased progressively, as tolerated, towards desired targets. Sedentary individuals may benefit most from a stepped approach whereby they first aim to reduce sitting time through increasing standing, light ambulation or simple resistance exercises.19–21 If tolerated, light ambulation may then progress to purposeful exercise.
Finally, guidelines promote minimum targets but patients should be encouraged to engage in as much physical activity and structured exercise as possible. Conversely, in patients where 150 minutes/week of moderate exercise may not be achievable, any activity is likely to be of benefit and should therefore be encouraged.
Funding/declaration of interests
This work is funded by the National Institute for Health Research (NIHR) Leicester Biomedical Research Centre, UK.
There are no conflicts of interest declared.
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