Physical activity is widely recommended as an essential non-pharmacological therapeutic strategy to the prevention and control of type 2 diabetes and cardiovascular risk. Microvascular and macrovascular complications associated with the natural progression of the disease and typical age and anthropometric profile of individuals with type 2 diabetes may expose these patients to an increased risk of injury and acute adverse events during exercise. These injuries and adverse events can lead to fear of new injury and consequent physical inactivity. Preventative measures are essential to reduce risk, increase safety and avoid the occurrence of exercise-related injuries in people with type 2 diabetes. This population can exercise safely if certain precautions are taken and if exercise is adapted to complications and contraindications of each individual. Conditions such as diabetic foot, diabetic retinopathy, diabetic nephropathy, diabetic autonomic neuropathy, cardiovascular risk factors, musculoskeletal disorders, hypoglycaemia, hyperglycaemia, dehydration and interactions between medication and exercise should be taken into consideration when prescribing exercise.
- Sports Medicine
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Diabetes is a chronic disease that affects approximately 8.3% of world's population1 and is associated with complications such as poor metabolic control, diabetic foot, retinopathy, nephropathy, autonomic neuropathy, coronary artery disease and cerebrovascular disease.2 Type 2 diabetes accounts for 90%–95% of those with diabetes.3
Physical activity is widely recommended as an essential non-pharmacological therapeutic strategy to the prevention and control of type 2 diabetes and cardiovascular risk.2 ,4 ,5 The success of regular exercise in improving glycemic control, insulin sensitivity and body composition in people with type 2 diabetes likely results from adaptations that occur in several organs and tissues, including adipose, skeletal muscle, liver and pancreas.6 Major international organisations4 ,7 ,8 recommend a weekly accumulation of a minimum of 150 min of aerobic exercise of moderate to vigorous intensity, spread over a minimum of 3 days per week. Resistance exercise is also recommended at least 2 days a week, in addition to aerobic exercise, as well as flexibility exercises integrated in all exercise sessions.
Recent studies conducted in several countries9–12 revealed that most people with type 2 diabetes do not engage in exercise on a regular basis and those who exercise do not meet the international recommendations described above. Therefore, promotion of exercise training in people with type 2 diabetes should represent a priority in strategies related to lifestyle modification.
Exercise counselling and prescription for the patient with diabetes is difficult due to microvascular and macrovascular complications associated with the natural progression of the disease and also because of the typical age and anthropometric profile of individuals with type 2 diabetes. They are generally sedentary older individuals who are overweight or obese, with low-exercise capacity and a high risk of falling (figure 1).1 ,4 ,13 ,14 Overweight and obesity are also related to musculoskeletal and cardiovascular complications, which may have future implications in exercise training.15 All of these conditions and complications can expose diabetic patients to an increased risk of injuries and acute adverse events related to exercise training when compared with healthy subjects.16 ,17 One of the effects associated with the rise of exercise training among the population is the increased incidence of injury.18 ,19 Injuries and adverse events associated with exercise can lead to fear of new injury and consequent physical inactivity.20 It is fundamental that implementation of measures promoting physical activity take into account aspects related to injury prevention.17 ,19 ,20
Therefore, the purpose of this paper is to outline diabetes conditions and complications that may be aggravated by exercise and to highlight the main preventative measures essential to reduce risk, increase safety and prevent the occurrence of injuries and adverse events related to exercise participation in people with type 2 diabetes.
Risks to feet
Diabetic foot is a consequence of the interaction between peripheral neuropathy, peripheral vascular disease, deformity and trauma, resulting in increased risk of injury, ulceration and amputation.2 ,21 ,22
All patients with diabetes should wear appropriate sports footwear (comfortable sneakers made of soft and stretchable leather, with a cushioned sole and a wider toe box) and examine their feet daily, especially before and after exercise, to detect early damage.7 ,8 Individuals with peripheral neuropathy and without active feet ulcers can engage in weight-bearing exercises of moderate intensity, such as brisk walking.7 Although walking may expose the feet to impacts that can contribute to the development and maintenance of ulceration,8 walking at moderate intensity does not appear to increase the risk of foot ulcers or re-ulceration in individuals with peripheral neuropathy.2 ,7 Patients with active feet lesions or ulcers should restrict exercise to non-weight-bearing activities such as bicycle exercise, rowing, swimming and other water activities, exercises in chairs and exercises with upper limbs.7 ,8 ,23
Foot examination of patients with diabetes should be performed by a health professional regularly at least once a year. These examinations for the presence of the predisposing factors for ulcerations and amputation should include inspection of the skin status, infections, ulcerations, calluses, musculoskeletal deformities, assessment of pinprick sensation, temperature and vibration perception (using a 128 Hz tuning fork), 10 g monofilament pressure sensation, ankle reflexes and foot pulses.21 ,22
People with proliferative diabetic retinopathy, severe non-proliferative diabetic retinopathy or macular degeneration need to take particular care with exercise and should receive specific counselling about the risk of exercise to sight. This group should avoid activities that significantly raise intraocular pressure—such as vigorous intensity aerobic or resistance exercise and high-impact activities with jumps or any exercise that results in Valsalva manoeuvre—as this increases the risk of vitreous haemorrhage and retinal detachment.2 ,7 ,8
In addition, physical contact sports, ball sports or any sports in which there is a risk of eye injury should be avoided in those whose sight is in jeopardy. For this group, recommended exercises include walking, jogging and running.24 Other non-contact and low-impact activities such as cycling and swimming require certain precautions like helmet use and swimming goggles, respectively.
Diabetic nephropathy, characterised by the excretion of increased amounts of albumin in the urine, high blood pressure and renal failure, represents one of the major complications related to diabetes and is associated with other complications such as cardiovascular disease and retinopathy.25
Patients with nephropathy and microalbuminuria do not require exercise restrictions,2 ,8 which may be performed even during dialysis sessions.7 Individuals with established nephropathy should undergo a detailed medical evaluation before starting exercise. A stress test may be important to detect coronary artery disease and abnormal responses of heart rate and blood pressure to exercise.7
Since blood pressure has been identified as one of the most important factors influencing the degree of albuminuria associated with exercise,26 vigorous intensity exercise and activities that promote Valsalva manoeuvre should be avoided in order to prevent sudden increases in blood pressure.7
Diabetic autonomic neuropathy
Autonomic neuropathy can affect any system of human body and may increase the risk of acute adverse events due to exercise intolerance, postural hypotension, abnormal thermoregulation, decreased night vision and changes in supply of carbohydrates due to gastroparesis, predisposing to hypoglycaemic episodes.2
Cardiovascular autonomic neuropathy is the most important form of autonomic dysfunction due to the life-threatening consequences and can be manifested by resting tachycardia (>100 bpm), orthostatic hypotension (drop in systolic blood pressure >20 mm Hg upon standing) without an appropriate heart rate response or other disturbances in autonomic nervous system function.21
The presence of autonomic neuropathy may limit exercise capacity and increase the risk of an acute cardiovascular adverse event during exercise.2 Hypotension and hypertension after vigorous exercise are more likely to develop in patients with autonomic neuropathy, particularly when starting an exercise programme.21 Since these individuals may have difficulty with thermoregulation, they should be advised to avoid exercise in hot or cold environments and should undertake proper hydration.17
Patients with cardiovascular autonomic neuropathy should be submitted to a detailed medical evaluation before beginning exercise training, which may include a stress test and a battery of autonomic tests that evaluate both branches of autonomic nervous system.2 ,7 ,21 Due to possible resting tachycardia, decreased exercise tolerance and reduced maximum heart rate, aerobic exercise intensity should be prescribed using the heart rate reserve method with direct measurement of maximum heart rate through a stress test.7
The risk of a cardiovascular event during exercise is low, and the overall benefits of exercise largely exceed its risks in the general population.27–30 Although this ratio is still not adequately studied in people with type 2 diabetes, whose prevalence of symptomatic or asymptomatic coronary artery disease is higher, cardiovascular diseases are not an absolute contraindication to exercise training.8
Patients with diabetes and established coronary artery disease should begin exercise training in supervised cardiac rehabilitation programmes, at least initially.7 These individuals have indication to perform a stress test before starting exercise,2 ,8 and the maximum training heart rate should be 10 bpm below the ischaemic threshold.27 Such patients should be encouraged to start exercise training with short periods of low intensity and increase intensity and duration slowly and progressively.2
All people with type 2 diabetes should be educated about the typical and atypical symptoms of myocardial ischaemia (chest pain/angina, burning discomfort, exertional dyspnoea, increasing fatigue, sweating, light-headedness, nausea, etc.) and stroke (sudden numbness or weakness of face, arm or leg; sudden confusion, trouble speaking or understanding; sudden trouble walking, dizziness, loss of balance or coordination; sudden severe headache with no known cause, etc.) and instructed to report these symptoms to exercise professionals and to a physician for further evaluation.27 Exercise professionals who supervise exercise programmes should have current training in cardiac life support and emergency procedures.28
High blood pressure is a major risk factor for coronary artery disease and cerebrovascular diseases,31 and it is particularly important in patients with diabetes.32 In poorly controlled hypertensive patients, blood pressure should be regularly monitored at rest before exercise (figure 2) and exercise should be avoided if the values are equal or greater than 200 mm Hg of systolic blood pressure or 100 mm Hg of diastolic blood pressure.27 ,33 In order to prevent sudden increases in blood pressure during exercise, Valsalva manoeuvre should be averted,7 ,27 especially when performing resistance and flexibility exercises.
Musculoskeletal injuries and other traumatic lesions are the main potential adverse outcomes of exercise training in the general population.20 Musculoskeletal injury includes acute injuries and chronic injuries due to overuse and is mainly associated with vigorous exercise and contact sports.19 ,20
Age and anthropometric profile of people with type 2 diabetes can predispose to a higher risk of injury of the musculoskeletal system.23 Individuals with overweight or osteoarthritis may have difficulties in weight-bearing exercises such as walking or jogging. Low-impact activities such as bicycle exercise, water activities or resistance exercises are advisable alternatives.15 Shock-absorbing insoles, joint external support materials and joint strengthening exercises seem to have a preventive effect on reducing musculoskeletal injuries.19
Although exercise may increase risk of hypoglycaemia, only the individuals medicated with insulin or insulin secretagogues (sulfonylureas and meglitinides) seem to be at risk during, immediately after or several hours after exercise.2 ,7 ,35 Hypoglycaemia associated with exercise is rare in patients medicated with other types of oral antidiabetic drugs. However, all patients with diabetes should recognise early symptoms of hypoglycaemia (tremulousness, palpitations, anxiety, sweating, hunger, paresthesias, weakness, fatigue, confusion, seizures, lost of consciousness and others) and know how to treat them in an effective way, thus avoiding severe consequences.34 It is important to understand that these symptoms are non-specific and may differ from individual to individual.
Self-monitoring of blood glucose levels appears to be the most effective preventative measure. Capillary blood glucose should be assessed before, during, immediately after and up to several hours after exercise, especially in people treated with insulin or insulin secretagogues.7 ,35 Monitoring capillary blood glucose several hours after exercise is particularly important in the case of poorly controlled diabetes, during the first sessions of exercise, after sessions of vigorous or long-term exercise, when exercise programmes are modified or when there are changes in medication.23 The recommendation of ingesting 15–20 g of carbohydrates if capillary glycaemia before exercise is equal to or less than 100 mg/dL (5.6 mmol/L) in patients treated with insulin or insulin secretagogues2 ,7 depends on what the person’s insulin regimen is, when insulin (and what type) was last given, when food was last ingested, the time of day, exercise intensity and duration, and other factors. However, with prolonged exercise (more than 1 h), carbohydrate intake during and immediately after exercise (up to 30 min) minimises the risk of hypoglycaemia.7
Risk of hypoglycaemia associated with exercise appears to be related to hypoglycaemia-associated autonomic failure, which causes a defective counterregulation response to exercise and hypoglycaemia unawareness.2 ,35 ,36 Thus, exercise should be avoided for 24 h following an episode of hypoglycaemia because of the risk of recurrent hypoglycaemia.35
The timing of exercise must also be considered in patients treated with insulin or insulin secretagogues. Exercise is not recommended neither during the peak insulin action due to the increased risk of hypoglycaemia nor before bed rest because of the risk of delayed postexercise hypoglycaemia.27
Although it is not possible to define hypoglycaemia in patients with diabetes based on a specific value of blood glucose, it seems important to maintain values above 72 mg/dL (4.0 mmol/L).37 Glucagon emergency kits should be prescribed to all patients with significant risk of severe hypoglycaemia , and healthcare providers, exercise professionals and family members should be instructed in their administration.2
Hyperosmolar hyperglycaemic state and ketoacidosis are the most serious acute metabolic complications of diabetes, although they are rare in patients with type 2 diabetes in the absence of certain precipitating events, such as infection or inadequate insulin therapy.38 Common symptoms associated with hyperglycaemia include polyuria, fatigue, weakness, increased thirst and acetone breath.27
People with type 2 diabetes do not need to postpone exercise due to high blood glucose (>300 mg/L or 7.16 mmol/L), provided they feel well, are properly hydrated and there is no ketosis.2 However, due to increased production of catecholamines, vigorous exercise should be avoided in case of hyperglycaemia because of the risk of increasing blood glucose levels and ketosis.7 ,27 Exercise is contraindicated in the presence of hyperglycaemia (>300 mg/dL or 7.16 mmol/L) with urine or blood ketones, and appropriate medical care must be established.2 ,7 ,38
Patients with poorly controlled diabetes often have polyuria, and so they are particularly susceptible to dehydration with exercise. That risk is greater especially in hot environments.7 ,27 All patients should begin exercising properly hydrated and should drink about 0.4–0.8 L of water per hour during exercise depending on exercise intensity and environment temperature. Carbohydrates can be added to the beverage if exercise is prolonged (more than 1 h) in those with hypoglycaemia risk.39
Interactions between medication and exercise
Adjustments in medication dosage to prevent exercise-related hypoglycaemia are only necessary with insulin or insulin secretagogues use. In the case of frequent hypoglycaemic episodes with exercise, the dose of such drugs should be reduced and adjusted before and possibly after exercise.7
Due to complications associated with diabetes, a variety of other drugs are prescribed on a regular basis and that can interfere with normal physiological response to exercise, leading to fatigue and making exercise an unpleasant experience for patients.40
β-Blockers can decrease heart rate response to exercise and limit maximal exercise capacity through negative inotropic and chronotropic effects. They can also block adrenergic symptoms of hypoglycaemia, increasing the risk of undetected hypoglycaemic episodes during exercise.7 Prescription and monitoring of exercise intensity through heart rate should be thereby adjusted, and the use of heart rate reserve method is recommended.
Diuretics can decrease the overall volume of blood and fluids, increasing the risk of dehydration and electrolyte imbalance, especially when performing exercising at high temperatures.40
The use of statins is associated with an increased risk of muscle side effects such as myositis and myalgia, which may be exacerbated by exercise.41 There is now also compelling evidence that statin therapy impairs pancreatic β-cell function and peripheral insulin sensitivity and results in hyperinsulinemia.42
Vasodilators, calcium channel blockers and α-blockers can cause hypotension with rapid cessation of exercise.40 A longer cool-down period is therefore recommended.
Pre-exercise clinical evaluation
The need for a detailed clinical evaluation before initiating exercise training appears to depend mainly on the patient characteristics and on the exercise intensity. To perform exercise at light to moderate intensity such as brisk walking, initial clinical evaluation does not appear to be necessary in asymptomatic individuals with diabetes since this type of activity does not represent an increased risk of aggravating complications possibly present.7 ,8 A detailed medical evaluation is recommended for elderly or sedentary patients with diabetes who intend to do more vigorous exercise than brisk walking or exercise that exceeds the requirements of daily life.7 ,8
Patients with symptoms suggesting coronary artery disease should always be properly assessed, regardless of diabetes status or exercise intensity.8 The evaluation is also important in severe forms of diabetic retinopathy (proliferative diabetic retinopathy or macular degeneration), diabetic foot, diabetic nephropathy and cardiovascular autonomic neuropathy, as well as in individuals who initiate exercise training after several years of sedentary lifestyle or diabetes.7
Conditions that may increase risk of cardiovascular events and that may contraindicate any type or mode of exercise or predispose to injury, such as uncontrolled hypertension, severe autonomic neuropathy, severe peripheral neuropathy or history of foot injuries and unstable proliferative retinopathy, should be searched and evaluated.2 ,7 Patients’ age, level of habitual physical activity, prescribed medication, glycemic control, possible physical limitations, smoking and other cardiovascular risk factors should also be considered.
Detailed medical evaluation may also include a stress test, although its recommendation is a debatable topic.2 ,7 ,8 ,17 Stress tests for screening coronary artery disease in cardiovascular asymptomatic individuals with diabetes are not currently recommended.2 However, sedentary or elderly individuals with diabetes who have moderate or high risk of cardiovascular disease and intend to perform vigorous exercise can benefit from a stress test.7 ,8 Patients with symptoms suggestive of coronary artery disease should be always submitted to a stress test before the beginning of exercise training.8 Individuals with cardiovascular autonomic neuropathy or advanced nephropathy with renal failure also appear to benefit from a stress test.7 Health professionals should use their clinical judgement in recommending the detailed initial medical evaluation, with or without a stress test.2 ,7 In this decision, other cardiovascular risk factors such as smoking, hypercholesterolaemia, hypertension or family history of premature coronary artery disease must also be weighed.43
One of the most unfavourable aspects of the initial medical evaluation and stress tests is that they represent an additional barrier to exercising in a population group where such barriers need to be reduced.7 ,8 In addition, stress tests are financially and logistically expensive.13
Programming exercise sessions
Exercise programmes for people with type 2 diabetes should include combined aerobic and resistance exercise complemented by flexibility exercises.44 Recommendations for aerobic and resistance exercise intensity range between moderate to vigorous.7
Moderate-intensity aerobic exercise represents a target training zone between 40% and 59% of heart rate reserve, 64%–76% of the maximum heart rate or 12–13 points in a rate of perceived exertion scale of 6–20 points, whereas vigorous-intensity aerobic exercise ranges between 60% and 89% of heart rate reserve, 77–95% of maximum heart rate or 14–17 points in a rate of perceived exertion scale of 6–20 points.45 For most people with type 2 diabetes, brisk walking is a moderate-intensity aerobic exercise and jogging is a vigorous-intensity aerobic exercise.7 The risk of cardiovascular autonomic neuropathy, the possible use of drugs with influence on heart rate and the heterogeneity of physical fitness of these individuals make the use of heart rate reserve method in the prescription of aerobic exercise intensity advisable. However, when equipment for measuring heart rate is not available, manual heart rate monitoring is challenging and is not always accurate or successful. The rates of perceived exertion scales are valid and important alternative tools in controlling aerobic exercise intensity (figure 3).46
Moderate-intensity resistance exercise involves the completion of 12–15 repetitions to near fatigue per set (the number of sets per exercise should range between 2 and 4), whereas vigorous-intensity resistance exercise involves the completion of only 7–11 repetitions to near fatigue.47 The rates of perceived exertion scales are also valid to monitor resistance exercise intensity.48
Participation in vigorous-intensity exercise represents an increased risk and is contraindicated in several complications of diabetes. The realisation of a stress test appears to be important before engaging in activities with this degree of intensity. Stress testing should be performed preferably on a treadmill so that the patient's results can be extrapolated to prescription of brisk walking and jogging. The results can be useful to determine the maximum heart rate, exercise tolerance and threshold of myocardial ischaemia or a hypertensive response.
Exercise intensity and duration should be inversely proportional within each exercise session, and the progression of intensity, duration and frequency of exercise sessions over a regular exercise programme should occur slowly.45 Warm-up and cool-down stages are essential for adequate prevention of adverse events associated with exercise, such as sudden increases in blood pressure during exercise or hypotensive episodes after the end of exercise. Exercise sessions should include regular monitoring of blood glucose and blood pressure, foot examination before and after exercise, and pauses for hydration.
Exercise sessions monitoring by trained and qualified exercise professionals is crucial to ensure safety and to minimise the risk of injury.44 These professionals should be adequately prepared to adapt exercises to the contraindications, complications and limitations of each individual.23
People with type 2 diabetes can exercise safely if certain preventative measures are adopted and if exercise is adapted to the complications and contraindications of each individual. Exercise prescription for patients with diabetes should include recommendations for the prevention and control of situations such as diabetic foot, diabetic retinopathy, diabetic nephropathy, diabetic autonomic neuropathy, cardiovascular risk factors, musculoskeletal disorders, hypoglycaemia, hyperglycaemia, dehydration and the interactions between medication and exercise. It is also important to consider age, habitual physical activity, anthropometric profile and other cardiovascular risk factors.
Complications of diabetes, individual characteristics and the intended intensity of exercise may determine the need for an initial medical evaluation that may include a stress test. Proper planning of exercise sessions and their monitoring by exercise professionals are crucial aspects to ensure the safety of participants and prevent exercise-related injuries.
People with type 2 diabetes may be exposed to an increased risk of injury and acute adverse events during exercise.
Exercise prescription for this population should include recommendations for the prevention and control of situations such as diabetic foot, diabetic retinopathy, diabetic nephropathy, diabetic autonomic neuropathy, cardiovascular risk, musculoskeletal disorders, hypoglycaemia, hyperglycaemia, dehydration and the interactions between medication and exercise.
Proper planning of exercise sessions and their monitoring by exercise professionals are crucial aspects to guarantee the safety of participants and prevent exercise-related injuries.
Current research questions
What is the incidence of exercise-related injuries and adverse events in people with type 2 diabetes?
What type of exercise-related adverse events are more prevalent in this population?
What is the impact of these events in exercise adherence?
Colberg SR, Sigal RJ, Fernhall B, et al. Exercise and type 2 diabetes: the American College of Sports Medicine and the American Diabetes Association: joint position statement. Diabetes Care 2010;33:e147–67.
Burr JF, Shephard RJ, Riddell MC. Prediabetes and type 2 diabetes mellitus: assessing risks for physical activity clearance and prescription. Can Fam Physician 2012;58: 280–4.
Colberg SR, Sigal RJ. Prescribing exercise for individuals with type 2 diabetes: recommendations and precautions. Phys Sportsmed 2011;39:13–26.
Cryer PE. Exercise-related hypoglycaemia-associated autonomic failure in diabetes. Diabetes 2009;58:1951–2.
Mendes R, Sousa N, Reis VM, et al. Diabetes em Movimento—community-based exercise program for patients with type 2 diabetes. Br J Sports Med 2013;47:e3.
Self assessment questions
Answer true (T) or false (F) for the below,
Which type of exercise is recommended for people with type 2 diabetes?
Only aerobic exercise
Only resistance exercise
Only aerobic and resistance exercise
Aerobic, resistance and flexibility exercise
Which medication can potentiate hypoglycaemia associated with exercise?
Insulin, metformin and sulfonylureas
Insulin, sulfonylureas and α-glucosidase inhibitors
Insulin, sulfonylureas and meglitinides
Insulin, meglitinides and thiazolidinediones
Monitoring capillary blood glucose before exercise is particularly important. Patients at risk of hypoglycaemia should ingest carbohydrates before exercise if capillary glycaemia is
Equal to or less than 130 mg/dL
Equal to or less than 120 mg/dL
Equal to or less than 110 mg/dL
Equal to or less than 100 mg/dL
Moderate-intensity aerobic exercise like brisk walking represents
11–12 points in a rate of perceived exertion scale of 6–20 points
12–13 points in a rate of perceived exertion scale of 6–20 points
13–14 points in a rate of perceived exertion scale of 6–20 points
14–15 points in a rate of perceived exertion scale of 6–20 points
Choose the true sentence:
Individuals with peripheral neuropathy and without active ulcers in the feet can engage in weight-bearing exercises of moderate intensity, such as brisk walking.
Vigorous-intensity aerobic or resistance exercise, high-impact activities with jumps and physical contact are recommended activities to individuals with diabetic retinopathy.
Patients with nephropathy and microalbuminuria require important exercise restrictions.
Hypotension and hypertension after vigorous exercise are less likely to develop in patients with autonomic neuropathy.
F, F, F, T
F, F, T, F
F, F, F, T
F, T, F, F
T, F, F, F
The authors acknowledge the support received from all participants and researchers of Diabetes em Movimento (ISRCTN09240628).
Contributors All authors were equally involved in the conceptualisation, writing and editing of the manuscript, and provided substantial contributions to the conception and design, as well as drafting the article and revising it critically for important intellectual content. All authors approved the final version to be published.
Funding This work was supported by the Portuguese Foundation for Science and Technology (reference no. SFRH/BD/47733/2008).
Competing interests None.
Patient consent Obtained.
Provenance and peer review Not commissioned; externally peer reviewed.
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