University of Toronto - Faculty of Medicine

 

Author
The revision of this chapter was prepared by Rene Wong, MD, FRCPC

It is well established that regular physical activity is an important therapeutic option for people with type 2 diabetes. It improves risk factors, cardiovascular fitness, insulin resistance and glycemic control. Over 15-20 years of follow-up, it has been associated with 39-70% reductions in cardiovascular and all-cause mortality.

 

• Beneficial effects of exercise on blood glucose are due to 3 separate effects of contractile activity on skeletal muscle:
  1. Acute, insulin-independent stimulation of muscle glucose transport.
  2. Acute enhancement of insulin action during the post-exercise period.
  3. Long term upregulation of the insulin signalling pathway resulting from regular exercise training.
• Well controlled insulin-treated patients with adequate serum insulin levels will usually have a fall in blood glucose concentrations much larger than in normal subjects.
• Acute strenuous exercise can lead to an increase in blood glucose levels in patients with poor glycemic control and hypoinsulinemia. The lack of insulin can not prevent the increase in hepatic glucose output mediated by counterregulatory hormones (particularly epinephrine) and can lead to hyperglycemia and ketosis.
• Insulin sensitivity can be enhanced for close to 24 hours following a single bout of vigorous exercise
• Sustained glycogen depletion post-exercise prolongs the enhanced effectiveness of insulin, and can result in delayed hypoglycaemia (i.e. 4-8 hours after the termination of exercise).
• Cessation of regular exercise by trained individuals results in a deterioration of glucose disposal and glucose tolerance.
• The effects of exercise training occur independently of any changes in adiposity.

 

• Small studies on the effects of long-term exercise training programs on glucose control have produced conflicting results. A significant effect on lowering A1C has been shown despite the absence of weight loss.
• Resistance exercise may be equally effective at reducing A1C, and the combined aerobic and resistance training may have additive effects.

 

• Clinical trials evaluating exercise interventions in people with type 1 diabetes have not demonstrated a beneficial effect on glycemic control.
• Increased physical activity will necessitate a reduction in insulin dose in order to avoid hypoglycemia in the post-exercise period (e.g. reduction of 25% of the normal pre-meal dose).
• Strenuous exercise can result in hyperglycemia in patients with type 1 diabetes with poor glycemic control
• Long term exercise training reduces insulin requirements but does not appear to improve chronic glycemic control.

 

• In high risk individuals with impaired glucose tolerance, lifestyle intervention (weight loss and an exercise program equivalent to at least 150 minutes per week similar in intensity to brisk walking) was significantly more effective than metformin in reducing the rate of progression to type 2 diabetes over the average follow-up period of 2.8 years.
• The reduction in the incidence of type 2 diabetes with exercise intervention appears to be similar to that seen with dietary intervention, and both interventions results in an even greater reduction.

 

• Beneficial effects have been hard to maintain for intervention programs requiring extra visits for special classes.
• The effect of simple behavioural counselling by physicians during routine clinic visits is unclear.
• To increase compliance, health professionals should help the patient choose a type of exercise he or she will enjoy and/or be most able to perform. Regular encouragement and suggestions for overcoming barriers to exercise should be offered.
• Patients with proliferative retinopathy should avoid intense isometric exercise (e.g. weight lifting) which can cause a marked increase in blood pressure that could precipitate intraocular bleeding.
• Patients with neuropathy should avoid traumatic weight-bearing exercise which could precipitate stress fractures and pressure ulcers.
• Those with significant cardiovascular disease should not attempt unsupervised vigorous exercise.

 

Prior to starting an exercise program, all patients should undergo pre-exercise assessment:

• Screen for vascular and neurologic complications
• Review metabolic markers (e.g. fasting blood glucose, A1C)
• Identify potential limitations (e.g. arthritis)
• Cardiac stress test should be considered for previously sedentary people at high risk of cardiovascular disease who wish to undertake exercise more vigorous than brisk walking

Aerobic exercise:

• 150 minutes of moderate to vigorous exercise per week spread over at least 3 days
• Moderate (achieving 50-70% of maximum heart rate) examples: biking, brisk walking, continuous swimming, dancing, raking leaves, water aerobics
• Vigorous (achieving > 70% of maximum heart rate) examples: brisk walking up an incline, jogging, aerobics, hockey, basketball, fast swimming, fast dancing

Resistance exercise:

• 3 times a week in addition to aerobic exercise
• Start with 1 set of 10-15 repetitions at moderate weight. Progress to 2 sets of 10-15 repetitions, then 3 sets of 8 repetitions at a heavier weight.

 

• Measure blood glucose before, during and after exercise. If > 14 mmol/L, exercise should be delayed until a lower level is achieved. Postpone exercise if ketosis is present.
• Decrease the insulin dose that affects that time of the day by 25-30%
• The increase temperature and blood flow associated with exercise may speed insulin absorption from subcutaneous depots. Insulin should be injected in a site other than the muscles to be exercised to prevent increased insulin absorption, administered 60-90 min before exercise
• Inadequate replacement of carbohydrate before, during and after exercise is the most common cause of exercise-associated hypoglycemia. 15-30 g of quickly absorbed carbohydrates (e.g. glucose tablets, hard candies, juice) should be taken 15-30 min before exercise and approximately 30 min during exercise. Ingesting slowly absorbed carbohydrates (dried fruit, granola bars, trail mix) immediately after exercise can help prevent late hypoglycemia.

References

1. Boule NG, Haddad E, Kenny GP, et al. Effects of exercise on glycemic control and body mass in type 2 diabetes mellitus: a meta-analysis of controlled clinical trials. JAMA 2001; 286:1218-1227
2. Canadian Diabetes Association Clinical Practice Guidelines Expert Committee. Canadian Diabetes Association 2008 clinical practice guidelines for the prevention and management of diabetes in Canada. Can J Diabetes. 2008;32(suppl 1): S1-201
3. Church TS, LaMonte MJ, Barlow CE, et al. Cardiorespiratory fitness and body mass index as predictors of cardiovascular disease mortality among men with diabetes. Arch Intern Med 2005; 165:2114-20.
4. Harris SB, Petrella RJ, Leadbetter W. Lifestyle interventions for type 2 diabetes. Relevance for clinical practice. Can Fam Physician 2003; 49:1618-25
5. Hu FB, Stampfer MJ, Solomon C, et al. Physical activity and risk for cardiovascular events in diabetic women. Ann Intern Med 2001: 134:96-105
6. Hu G, Jousilahdi P, Barengo NC, et al. Physical activity, cardiovascular risk factors, and mortality among Finnish adults with diabetes. Diabetes Care 2005; 28:799-805
7. Knowler WC, Barrett-Connor E, Fowler SE, et al. Reduction in the incidence of type 2 diabetes with lifestyle intervention or metformin. N Engl J Med 2002; 346:393-403
8. Laaksonen DE, Atalay M, Niskanen LK, et al. Aerobic exercise and the lipid profile in type 1 diabetic men: a randomized controlled trial. Med Sci Sports Exerc. 2000; 32:1541-1548
9. Li G, Hu U, Yang W, et al. Effects of insulin resistance and insulin secretion on the efficacy of interventions to retard development of type 2 diabetes: the DA Qing IGT and Diabetes Study. Diabetes Res Clin Pract 2002; 58:193-200
10. Sigal RJ, Kenny GP, Boule NG et al. Effects of aerobic exercise training, resistance exercise, or both on glycemic control in type 2 diabetes: a randomized trial. Ann Intern Med. 2007; 147: 357-369
11. Tuomilehto J, Lindstrom J, Eriksson GJ, et al. Prevention of type 2 diabetes mellitus by changes in lifestyle among subjects with impaired glucose tolerance. N Engl J Med 2001; 344: 1343-1350