There is very good evidence that increasing physical activity and exercise, as part of a lifestyle change programme, can play a vital part in preventing the development of type 2 diabetes in people at increased risk. In these prevention trials it has not been possible to easily separate out the effects of the dietary measures as against the exercise measures in achieving the overall reduction in diabetes. Lifestyle change is advocated as the cornerstone of the management of type 2 diabetes. Most people newly diagnosed with type 2 diabetes are overweight and do not engage in regular physical activity, so weight reduction through eating less and increased physical activity is a vital part of management. Guidelines in the UK recommend that people newly diagnosed with diabetes should be referred to a group education programme (E.g. DESMOND or X-Pert). Such education programmes include the encouragement of increasing levels of activity as important parts of their curriculum. The precise definitions of physical activity and exercise vary but many articles and papers define physical activity as regular movement such as walking and define exercise as structured activities such as jogging or cycling.
In people living with type 2 diabetes there is good evidence that increased physical activity and exercise can reduce risk factors such as HBA1c and blood pressure.
People living with type 1 diabetes should be encouraged to increase physical activity and exercise as this improves insulin sensitivity. Living with diabetes does not mean that you cannot take part in extreme sports nor does it mean that you cannot be a world class sportsperson. There are specific websites that provide sources of information and advice about how people living with diabetes can achieve their maximum performance in sport.
An overview of the evidence from randomised controlled trials and observational studies
1. EXERCISE TO PREVENT TYPE 2 DIABETES
There is good evidence from a good number of randomised controlled trials, and a systematic review and meta-analysis of these trials, that lifestyle change can prevent or delay the development of type 2 diabetes in people with impaired glucose tolerance, a group at very high risk. The exercise component of the lifestyle change recommendation in the RCT’s was usually 30—40 minutes of moderate physical activity per day on all or most days of the week with variable emphasis on high intensity and resistance training exercise. However the approach used to promote physical activity in the interventions ranged from simply providing exercise goals and tips on how to increase daily exercise, to providing weekly supervised exercise training.
The lifestyle intervention also included dietary measures, and it is not possible to easily separate out the effects of the dietary measures and the exercise measures in achieving the overall outcome of reduction in developing diabetes. In the Finnish diabetes prevention study people who walked 2.5 hours or more per week were 63% to 69% less likely to develop diabetes than were those who walked less than 1 hour per week.
The lifestyle intervention in the prevention trials usually involved intensive one to one sessions. Researchers have adapted these findings into real-world settings by offering programmes that have a reduced number of sessions of intervention and making them group based, rather than one to one. These changes have been made to make diabetes prevention programmes more feasible in routine practice in community settings. A review paper providing a narrative synthesis of 17 such translational studies that reported on the outcome of weight loss concluded that there is potential for less intensive interventions both to be feasible and to have impact on future progression to diabetes in at-risk individuals .
There is good evidence from observational studies that physical activity, combining occupational physical activity and leisure time physical activity, measured by a validated self-report questionnaire, is associated with a reduction in the risk of developing type 2 diabetes across Body Mass Index (BMI) categories in men and women, as well as in abdominally lean and obese men and women. (InterAct consortium). Weight Training was also associated with a significant lower risk of type 2 diabetes, independent of aerobic exercise, but combining weight training and aerobic exercise confers an even greater benefit.
2. EXERCISE TO IMPROVE CONTROL IN PEOPLE WITH TYPE 2 DIABETES
In a systematic review and meta-analysis of 34 trials evaluating the effects of exercise on cardiovascular risk factors in people with established type 2 diabetes it was found that aerobic exercise alone or combined with resistance training significantly reduced HBA1c by 7 mmoles/mol (0.6%) and systolic blood pressure by -6mmHg. Combined aerobic and resistance exercise reduced waist circumference by – 3.1cms .
In an RCT comparing a dietary intervention with diet plus physical activity, compared with usual care, in people with newly diagnosed type 2 diabetes reported that HBA1c was 0.28% lower in the diet only group than in the usual care group compared with a 0.33% difference between the diet plus physical activity group and the usual care group. The difference between the two interventions was not statistically significant. The benefits were slightly attenuated but remained significant at 12 months. Compared with usual care people in both the intervention groups had significant improvements in weight, waist circumference and insulin resistance at both 6 and 12 months.  As the study did not include a group assigned only to physical exercise the results do not necessarily mean that an increase in physical activity is ineffective for diabetes management
DOES EXERCISE WORK DIRECTLY OR VIA WEIGHT CONTROL ?
Physical activity has a series of direct effects that can improve metabolic control independently of weight reduction. A single bout of exercise lowers blood glucose concentrations and reduces the prevalence of hyperglycaemic episodes throughout the next day in people with type 2 diabetes. These glucoregulatory properties of exercise are attributable to an increase in whole body insulin sensitivity, which has been reported to last 48hours and which may be lost 6-8 days after the cessation of training. Exercise may also lower hepatic glucose production. Improvements in insulin sensitivity with exercise have also been demonstrated in people with type 1 diabetes. Exercise is also a factor in weight reduction and weight maintenance so the simple answer to the question is that exercise has direct benefits and also helps weight control.
WHAT TYPES OF EXERCISE ARE MOST EFFECTIVE ?
Many studies of exercise have relied on self-reported measures of activity which have inherent biases and imprecision, and cannot therefore be used to give a precise answer to this question. In studies where there has been objective measures of activity there is the suggestion that increasing overall energy expenditure has beneficial effects on reducing glucose levels and increasing insulin sensitivity, independent of the degree of obesity and cardiorespiratory fitness, and independent of the type of exercise. Both increasing physical activity and doing aerobic and anaerobic exercise is beneficial. Activity intensity can be described in MET’s Metabolic Equivalents where 1 MET = at rest, 3-5.9 METS = moderate intensity activity and at or above 6 = vigorous intensity activity. The following table gives examples of MET’s for different activities
|Activity||Intensity||Intensity (METS)||Energy expenditure (Kcal equivalent, for a person of 60kg doing the activity for 30 minutes|
|Cleaning and dusting||Light||2.5||75|
|Walking - strolling, 2mph||Light||2.5||75|
|Walking - 3mph||Moderate||3.3||99|
|Golf - walking, pulling clubs||Moderate||4.3||129|
|Badminton - social||Moderate||4.5||135|
|Tennis - doubles||Moderate||5.0||150|
|Walking - brisk, 4mph||Moderate||5.0||150|
|Mowing lawn - walking using power mower||Moderate||5.5||165|
|Swimming - slow crawl, 50 yards per minute||Vigorous||8.0||240|
|Tennis - singles||Vigorous||8.0||240|
|Running 6mph(10 minutes/mile)||Vigorous||10.0||300|
|Running 7mph(8.5 minutes/mile)||Vigorous||11.5||345|
|Running 8mph(7.5 minutes/mile)||Vigorous||13.5||405|
HOW CAN INCREASES IN EXERCISE BE BEST ACHIEVED
A recent systematic review and meta-analysis of behavioural interventions to change physical activity behaviours found 17 RCT’s that fulfilled the inclusion criteria.  The authors stated that behavioural interventions showed statistically significant increases in objective and self - reported physical activity and exercise. Physical activity was defined as regular movement such as walking and exercise was defined as structured activities such as jogging or cycling. There were also clinically significant improvements in HBA1C of - 0.32% (-0.44 to -0.21%) and BMI. Intervention features (e.g. specific behaviour change techniques, interventions underpinned by behaviour change theories and models, and use of 10 or more behaviour change techniques) moderated effectiveness of behavioural change interventions. The behaviour change techniques that were associated with potentially significant improvements in HBA1c were (a) prompting generalization of a target behaviour (eg once physical activity is performed in one situation the individual is encouraged to try it in another (b) use of follow up prompts (e.g. telephone calls) (c) prompt review of behavioural goals (d) providing information on where and when to be active (e) plan social support and social change (f) goal setting (g) time management (h) prompting focus on past success (i) barrier identification and problem solving (j) providing information about the consequences of physical activity specific to the individual. Five studies reported that individuals delivering the interventions had been trained for that purpose but only two studies provided information on the mode, content and utilisation of strategies for monitoring and improving the delivery of training. Professional training is a crucial component of behavioural interventions because it improves treatment fidelity and enhances reproduceability in routine care.
Pedometers, which monitor the number of steps a person takes per day, have been shown, in a systematic review, to be an effective method of motivation for people with diabetes to make necessary lifestyle changes and increase their daily step rates. 
WHAT DO GUIDELINES RECOMMEND FOR EXERCISE
UK recommendations on activity for health for the general public recommend for adults: a total of at least 30 minutes a day (in bouts of at least 10 minutes) of at least moderate intensity physical activity on 5 or more days of the week.
Guidelines from the American College of Sports Medicine and the American Diabetes Association recommend that exercise should be performed at least 3 days per week with no more than two consecutive days between exercise bouts. 
NICE guidelines in England recommend that people newly diagnosed with diabetes be referred to a group education programme such as DESMOND. Such programmes encourage participants to identify their present levels of activity and how they can take small regular steps to increase activity by, for example, using stairs rather than lifts or escalators, getting off the bus one stop before your destination, and using a pedometer to record the number of steps taken per day.
Papers on the use of Pedometers recommend aiming for 10,000 steps per day
EXERCISE FOR THE SUPERFIT
Living with diabetes does not prevent taking part in extreme sports, such as cycling, swimming, long distance running and weight training. Specific information and guidance is available on the diabetes UK website www.diabetes.org.uk/MyLife-YoungAdults/Sport-and-physical-activity on, amongst other things, getting stated, injury prevention and treatment, foods and fluids. Insulin dose adjustments, blood glucose monitoring and warming up and cooling down.
The website www.Runsweet.com is dedicated to helping athletes with diabetes to achieve their maximum performance in sport and contains a wealth of helpful information and advice.
WHAT ARE THE GAPS IN THE EVIDENCE AND WHAT RESEARCH NEEDS TO BE DONE?
More evidence on how to translate research findings of the benefits of exercise on diabetes prevention and diabetes management into real-life community settings is needed. It is also important to understand how those delivering programmes of lifestyle change are trained and kept up to date.
We also need long term studies to understand the benefits of increasing physical activity/exercise and its impact on reducing long term microvascular and macrovascular complications and mortality in people with diabetes.
^ Alberti KGMM, Zimmet P, Shaw J International Diabetes Federation: a consensus on type 2 diabetes prevention Diabetic Medicine 2007 24: 451-463
^ Laaksonen DE, Lindstrom J, Lakka T 2005 Physical activity in the prevention of type 2 diabetes: The Finnish prevention study Diabetes 2005 54:158-165
^ Johnson M, Jones R, Freeman C et al Can diabetes prevention programmes be translated effectively into real-world settings and still deliver improved outcomes? A synthesis of evidence Diabetic Medicine 2012 30: 3-15
^ Grontved A, Rimm EB, Willett WC et al A Prospective Study of Weight Training and Risk of Type 2 Diabetes in Men Arch Intern Med 2012 172: 1306-1312
^ Chudyk A Petrella RJ Effects of exercise on cardiovascular risk factors in type 2 diabetes a meta-analysis Diabetes Care 2011 34: 1228-1237
^ Andrews RC, Cooper AR, Montgomery AA, et al Diet or diet plus physical activity versus usual care in patients with newly diagnosed type 2 diabetes: the Early ACTID randomised controlled trial Lancet 2011 378: 129-139
^ Jan-Willem VD, Hartgens F, Tummers K et al Exercise Therapy in Type 2 Diabetes Diabetes Care 2012 35:948-954
^ Avery L, Flynn D, Sniehotta FF et al Changing Physical Activity Behaviour in Type 2 Diabetes. A systematic review and meta-analysis Diabetes Care 2012 35: 2681-2689
^ Russell-Minda E, Jutai J, Speechley M et al Health Tecnologies for Monitoring and Managing Diabetes: A systematic Review J of Science and Technology 2009 3:1460-1471
^ Colberg SR, Sigal RJ, Fernhall B et al American College of Sports Medicine; American Diabetes Association Exercise and Type 2 Diabetes: joint position statement Diabetes Care 2010 33:el147-e167