Exercise for the Management of Diabetes Mellitus : A Review of the Evidence

Diabetes mellitus is a public health problem in both developed and developing countries and has increased alarmingly, giving the disease the dimension of an epidemic. The aetiology of diabetes is multifactorial involving genetic, environmental, and behavioural origins. Exercise is an important part for the management of diabetes mellitus. Regularly planned exercise reduces insulin resistance, improves glucose tolerance, improves lipid profile and increases cardiovascular and cardiopulmonary function. This article critically reviews the more relevant evidence on the interrelationships between exercise and diabetes mellitus. This study included bibliography research from both the review and the research literatures on exercise in diabetes mellitus. From this review it appears that the effects of aerobic exercise are well established, and interventions with more vigorous aerobic exercise programmes resulted in greater reductions in HbA1c, greater increase in oxygen consumption and greater increase in insulin sensitivity. Considering the available evidence, it appears that resistance training could be an effective intervention to help glycaemic control, especially considering that the effects of this form of intervention are comparable with what is reported with aerobic exercise. It is well established that physical activity produces general and specific health benefits for diabetic patients. The basic principles of an effective exercise programme are the intensity, duration and frequency of exercise in an appropriate environment. Usually, moderate-intensity and long-duration exercise programmes are considered most suitable for diabetic patients. As it is supported by published evidence, encouragement to adopt increased physical activity and reduction of sedentary behaviour is a successful public health approach for diabetes mellitus prevention and management.

Although exercise and adequate physical activity are considered to be very useful in the treatment of diabetes mellitus (DM) 1 , actual translation of this knowledge into practice in daily life has been neglected by both the patients and treating physicians.Before the discovery of insulin, patients with diabetes, particularly those with type 1 diabetes were very limited in their ability to exercise, because it was almost impossible for them to avoid ketosis and dehydration.After insulin therapy was established as a mainstay treatment, exercise was no longer an elusive activity.Properly planned exercise is equivalent to one antidiabetic pill, but patients always attempt to replace exercise by another pill.Exercise also plays a critical role in patients with type 2 DM.The benefit offered by exercise exists from the very initial stages of diabetes till the terminal stage.It can help improve insulin sensitivity and assist with reduction and maintenance of body weight in obese patients.Exercise together with diet and pharmacological therapies, is important as part of the overall approach to improve glycaemic control

B. Metabolic effects of exercise in healthy individual
Exercise induces muscle glucose uptake in several ways. 7 Exercise-induced increased blood flow enhances insulin delivery to muscle and opens up previously nonperfused capillaries, thus increasing both surface area and effect of insulin for glucose transport.
• Muscle contraction can stimulate glucose transport from extracellular space to the cell.Even then, blood glucose is virtually maintained in a static state by hepatic glucose production which may even exceed the rate of glucose utilization.But hepatic glucose production may no longer keep pace with glucose utilization in case of prolonged exercise and glycaemia may begin to decline.

C. Metabolic effects of exercise in diabetic people
Type 1 DM: Higher amounts of habitual physical activity are associated with decreased incidence of diabetes related complications and reduced mortality in individuals with type 1 DM. 8The intensity and duration of exercise, the patient' s level of blood glucose control, the type, dose and site of preexercise insulin injections and the timing of the previous insulin injection and meals relative to the exercise can affect the response of an individual with diabetes to physical activity.Accordingly, blood glucose concentrations can decline (the most common response in moderate aerobic exercise), increase (particularly in very intense exercise) or remain unchanged.Type 2 DM: Hepatic and peripheral insulin resistance and hyperinsulinaemia in the fasting state are the characteristic feature of type 2 DM.During moderate intensity exercise, peripheral glucose uptake usually raises more than hepatic glucose production and the blood glucose concentration tends to decline. 9At the same time, plasma insulin level falls, and the risk of exercise induced hypoglycaemia in individuals with type 2 DM not taking exogenous insulin is relatively small, even during prolonged exercise. 10Chronic exercise improves insulin sensitivity in type 2 DM patients.The effects of moderate exercise on glucose tolerance and insulin sensitivity are similar whether the activity is performed in single or multiple bouts of the same total duration.

C. Flexibility exercise
Flexibility or stretching exercise is aimed at increasing or maintaining range of motion at joints and hopefully reducing risk of injury.

Benefits of exercise
A. Aerobic exercise 12 • Improves glucose tolerance • Helps to reduce risk of injury Structured exercise interventions of at least 8-week duration have been shown to lower HbA1c by an average of 0.66% in people with type 2 diabetes, even with no significant change in body mass index (BMI). 12Higher levels of exercise intensity are associated with greater improvements in A1c and in fitness. 16A joint position statement of the American Diabetic Association (ADA) and the American College of Sports Medicine (ACSM) summarises the evidence for the benefits of exercise in people with type 2 diabetes. 17

Preexercise evaluation
Exercise programmes need to be taken with expectation that potential benefits of exercise outweigh potential risks.So before advocating exercise to a diabetic person, particularly for moderate and strong exercises, a preexercise evaluation should be performed.This preexercise evaluation includes complete medical history, physical examination and laboratory evaluation to determine whether the patient has any long term diabetic complications, particularly coronary artery disease (CAD), neuropathy, nephropathy, retinopathy etc. Till date, debate remains how far and how invasive this screening is logical and acceptable to the patients.
The unavoidable area of controversy is that when a graded exercise ECG stress test should be done as for medical indication to avoid cardiac complications out of initiation of exercise.At present, no randomized large trials or cohort studies are available to dictate the indications and advantage of stress ECG in diabetics.Current ADA guidelines dictate that before initiating any moderate or intense exercise beyond brisk walking, stress ECG should be done in all diabetic individuals aged >35 and >25 years in the presence of even one additional CVD risk factor (Diabetes duration >10 years for type 2 DM and >15 years for type 1 DM, hypertension, dyslipidaemia, smoking, proliferative retinopathy, nephropathy, microalbuminuria, peripheral vascular disease, or autonomic neuropathy).But if this recommendation is strictly followed, great number of diabetics including large number of young diabetics with low risk of CAD should be screened before going above brisk walking.This involves a huge cost and a negative panic reaction among the patients.Moreover, exercise tests are highly false positive for low CAD risk than severe degree CAD, where positive stress test ECG will force the patient to go for costly invasive and noninvasive tests for CAD, which are nonrewarding in majority of cases.On the basis of this fact, US Preventive Service Task Force 18 recommends that stress test should usually not be done to detect ischaemia in asymptomatic individuals at low CAD risk.It should also be remembered that if stress ECG is possible, it also gives an idea about maximal heart rate and blood pressure responses to different exercise levels, initial performance status, and prognosis.These data finally help to plan a suitable exercise regimen for a diabetic.
In the absence of any specific definitive recommendation based on large trials, Gibbons et al has proposed a modified recommendation in ACC/AHA guideline. 19This suggests that all the diabetics with sedentarism, before practising aerobic physical activity with an intensity more than brisk walking and whose 10-year risk of coronary event is >10%, should be investigated.This risk can be directly estimated from United Kingdom Prospective Diabetes Study (UKPDS) Risk Engine and correspond to meeting any of the following criteria.Resistance exercise improves insulin sensitivity to about the same extent as aerobic exercise. 23Clinical trials have provided strong evidence for the A1c lowering value of resistance training in older adults with type 2 diabetes 24,25 and for an additive benefit of combined aerobic and resistance exercise in adults with type 2 diabetes. 26,27CSM now recommends 28 resistance training in adults with type 2 DM also.Resistance exercise also improves bone density, functional capacity, resting BMR, adiposity and insulin resistance appreciably.
In last 20 years, several trials have established the efficacy and safety of resistance exercise.ACSM recommends a minimum of 8--10 exercises involving major muscles with a minimum of 10--15 repetitions, at least three times a week including all major muscle groups initially under supervision and periodically reassessed by qualified exercise trainer.

C. Stretching exercise:
There is no sufficient evidence to recommend for or against stretching exercise as part of routine exercise programme.

Exercise protocol
The standard recommendation regarding exercise in DM patients includes 4 stages.

Timing of exercise
Ideally, physical activity should be done at the most convenient time of the day for the participant.In a diabetic patient, exercise however needs to be coordinated with meals, medication and glucose testing regimens.Exercise should be timed so that it does not coincide with periods of peak action of antidiabetic agent.It is initially preferable to exercise at the same time each day.

Exercise recommendation in special situation
A. Uncontrolled glycaemia: When people with type 1 diabetes are deprived of insulin for 12--48 hours and are ketotic, exercise can worsen hyperglycaemia and ketosis; 29  12. Exercise in the presence of chronic complications No definite trial is available, opinion is based on expert's experience.
A. Retinopathy: Exercise including both vigorous aerobic or resistant exercise is totally safe in the presence of background and nonproliferative retinopathy.But these can cause vitreous haemorrhage or retinal detachment in proliferative or advanced nonproliferative retinopathy. 31After laser photocoagulation, one should wait for 6 months for vigorous exercises.

B. Peripheral neuropathy:
Diminished pain sensation predisposes to damage to the skin and Charcot joint.Therefore, prior recommendations have advised only non-weight bearing exercises like swimming, cycling, and arm exercises for patients in the presence of severe peripheral neuropathy. 32owever, studies have shown that moderate intensity walking may not lead to increased risk of foot ulcers or reulcerations in those with peripheral neuropathy.Anyone with a foot injury or open sore should be restricted to non-weight bearing activities.

C. Autonomic neuropathy:
Very often, several problems, mentioned below, are seen with autonomic neuropathy which can be a bar to moderate to heavy exercises.
• Silent or overt CVD 33,34 • Gastroparesis with unpredictable food delivery leading to hypoglycaemia

Exercise and type 2 DM prevention
The role of exercise in type 2 DM prevention has been well established in multiple large number of trials such as Finish Diabetes Prevention Study, US Diabetes Prevention Program (USDPP) 37 , Malmo Study 38 , Da-Quing Study 5,39 , Indian Diabetes Prevention Program etc.There is strong and significant evidence that increasing physical activity and weight loss programme reduce the incidence of T2DM in individuals with impaired glucose tolerance (IGT).But relative contribution of diet and exercise is not yet substantiated even in larger studies like Finish Diabetes Prevention Study and USDPP.Till now, the effect of exercise in prevention of diabetes in persons with IFG is not well substantiated.In people with IGT standard recommendation for exercise is at least 150 min/week of moderate to vigorous physical activity with energy restriction.

Insulin and oral hypoglycaemic agent adjustments for exercise
In individuals with T1DM or T2DM treated with multiple insulin injections, the dosage of short acting insulin taken before exercise can be reduced instead of using dietary adjustment.The amount of such reduction, if required, should be tailored to each individual, based on blood glucose results before, during and after exercise, at least until the pattern of glucose response to exercise for that individual is known.Depending on the intensity and duration of exercise, the reduction required can be as much as 75% of the usual dose 40 , although dose reductions by 20-50% are more typical.The insulin formulation (short or intermediate acting) to be reduced is that which has its maximal action at the time of exercise.
In very intense exercise such as competitive hockey, weightlifting or sprinting, there may be no need to reduce insulin dose.If the blood glucose concentration increases during exercise, the insulin dosage may need to be slightly increased or the injection schedule is changed in order to achieve higher plasma insulin concentrations during exercise.
Use of an insulin pump may be advantageous for many physically active individuals, as circulating insulin levels can be more easily adjusted to accommodate meals, snacks and exercise. 41The variability of glucose absorption is also generally decreased, lowering the risk of hypoglycaemia. 41ecreases in insulin for pump users may or may not need to be accompanied by carbohydrate supplementation. 41 individuals with T2DM, exercise does not usually cause hypoglycaemia, and in obese individuals it can be a valuable tool to improve glycaemic control and assist with weight maintenance.For these reasons, carbohydrate supplementation is usually unnecessary with exercise.If blood glucose declines rapidly during exercise, as may occur in individuals taking oral hypoglycaemic agents or insulin, the dosage of the drug should be reduced or the drug should be withheld on exercise days.

Guidelines for exercise in diabetes mellitus
• Exercise used to reduce weight should be combined with dietary measures.
• Moderate intensity aerobic exercise should be part of the daily schedule if possible, accumulating 150 minutes each week.More vigorousexercise(>70%ofVO2max) undertaken 3-5 times per week will provide additional health benefit.Previously sedentary patients may have to build up exercise volume gradually, starting with as little as 5-10 min/day.
• Multiple shorter exercise sessions lasting at least 10 minutes each in the course of a day are probably as useful as a single longer session of equivalent length and intensity.
• Include low intensity warm up and cool down periods, especially if vigorous exercise is undertaken.
• Exercise should be appropriate to the person's general physical condition and lifestyle.
• Resistance exercise performed 2-3 times per week will provide benefits over those of aerobic training.The studies reporting greatest impact of resistance exercise on HbA1c have had subjects who progressed to 3 sets of approximately 8 resistance type exercises at relatively high intensity (8 repetitions performed at the maximum weight that can be lifted 8 times).
• Use proper footwear and, if appropriate, other protective equipments.
• Avoid exercise in extreme heat or cold.
• Inspect feet before and after exercise.

Specific considerations for exercise in type 1 diabetes
Hypoglycaemia during exercise is to be avoided by • Avoiding heavy exercise during peak insulin action.
• Using nonexercising sites for insulin injection.
• Reducing preexercise insulin doses by 20-50% or more if necessary when multiple daily injections are used.If using an insulin pump, decrease basal rate and/or amount of last bolus before exercise.These reductions be individualised and based on blood glucose monitoring; not all individuals will require an insulin dose reduction.
• Monitoring glycaemia before, during and after exercise as necessary.
• Taking extra carbohydrate before and hourly during exercise.This amount should be individualised and based on blood glucose monitoring.
• Monitoring glycaemia and taking extra carbohydrate after prolonged exercise to avoid delayed hypoglycaemia.The quantity required can be estimated using the semiquantitative technique (1 g carbohydrate/kg body weight/hour of activity) or by consulting tables of energy requirements for particular activities.
• Using extra caution in monitoring glycaemia if exercise is being performed within 24 hours of a hypoglycaemic episode.

Specific considerations for exercise in type 2 diabetes
• Hypoglycaemia is less common during exercise than in type 1 diabetes, and extra carbohydrate is therefore usually unnecessary.
• Patients taking insulin or sulfonylureas may need to reduce the doses of these medications during days when they exercise.Such adjustments should be guided by glucose monitoring.

Conclusion
It has long been known that exercise has beneficial effects for people with diabetes.In the past, it was often difficult to avoid the hazards of exercise, particularly in patients with type 1 diabetes.Now-adays a greater understanding of energy metabolism and fuel homeostasis has made it possible to include exercise as a realistic goal for almost all patients with diabetes.Improvements in glucose monitoring technology have further contributed to the feasibility of active physical exercise programmes for people with diabetes.It is important to address strategies for avoiding hypoglycaemia (both during and after exercise), as well as hyperglycaemia and ketosis, with all patients before they embark on routine exercise.
Patients with type 2 diabetes clearly benefit from frequent exercise.Physical activity plays an important part in the treatment strategy in these patients, as it decreases obesity, lowers blood pressure while improving insulin sensitivity, long term glycaemic control, and blood lipid profiles.Because of the risk of exercise unmasking ischaemia as well as causing soft tissue and joint injury or retinal haemorrhage, it is critical that all patients have a complete history and physical examination before they engage in moderate or vigorous activity.
For all patients with diabetes, physician-patient interaction is key to establishing a successful exercise programme.A team approach that involves coordination among exercise physiologists, nutritionists, diabetes educators, the physician, and the patient is usually the most effective way to create an individualised exercise regimen that provides benefits to the patient while avoiding potential harm.

6 .
Potential risks of exercise in DM patients

Stage 1 :
Warm up period of 5--10 minutes of aerobic activity at a low intensity level Stage 2 : Muscle stretching for 5--10 minutes will follow the warm up period Stage 3 : Exercise proper Stage 4 : Cool down period for another 5--10 minutes which helps to bring the HR gradually to pre exercise level

1. Introduction 99 Exercise for the Management of Diabetes Mellitus: A Review of the Evidence and
[2][3][4][5]diovascular risk factors.Prevention of type 2 DM is also possible by exercise, if practised in the stage of prediabetes and effects are stronger than drugs as shown in different large clinical trials.[2][3][4][5] Aerobic exercises, though safe, cannot be practised in the presence of severe peripheral neuropathy and gross obesity.Resistance exercises are not only acceptable in these cases but also cause more rapid changes in functional status and body composition, and it is also not monotonous like aerobic exercise as it involves different exercises at a time.It also involves muscle mass, muscle strength, and balance, which is particularly beneficial in older persons where sarcopenia is a problem.
21) than if combined with diet restriction and behaviour therapy (9--13 kg) after 20 weeks.21A.Aerobic exercise: The combination of intensity, frequency and duration is used to describe recommended volume of exercise.B.Resistance exercise:

Table I :
6dverse effects of drugs on exercise6 35