In the past, the American Diabetes Association recommended routine screening of asymptomatic diabetics with risk of coronary artery disease (CAD) prior to beginning an exercise program. As of 2009 routine screening is no longer recommended for every diabetic with risk of CAD. Instead, they suggest that providers counsel high risk patients to start with short periods of low intensity exercise and increase duration slowly. "Providers should assess patients for conditions that might contraindicate certain types of exercise or predispose to injury, such as uncontrolled hypertension, severe autonomic neuropathy, severe peripheral neuropathy or history of foot lesions, and advanced retinopathy." A patient's age and level physical activity should also be considered.
Too little insulin exaggerates the effects of glucagon. Glucagon increases hepatic glucose, fatty acid and ketone production . At rest, insulin deficient type 1 diabetics can become ketotic in 12-48 hours. Vigorous activity can exacerbate ketosis and should be avoided when blood or urine are positive for ketones. Hyperglycemia alone, is not a contraindication to exercise, provided that the patient feels well and remains well hydrated.
A mismatch of carbohydrate intake, physical activity and insulin or antidiabetes medications can cause severe hypoglycemia. Diabetics that require these medications should:
Insulin or antidiabetes medication dependent persons who exercise vigorously should be counseled to carry an emergency carbohydrate supplement. The recommended treatment for hypoglycemia (glucose <70 mg/dl) in the conscious adult is 15-20 g of glucose. Pure glucose is preferred because it produces the best glycemic response. Self-monitoring blood glucose should be done after glucose treatment. If hypoglycemia continues 15 minutes after treatment, the treatment should be repeated. Glucagon should be prescribed for individuals at significant risk of severe hypoglycemia. Significant others should be instructed in its administration.
Pre-diabetics and type 2 diabetics who don't use insulin or anti-diabetes medication rarely become hypoglycemic from exercise and therefore don't usually need to preload with carbohydrates.
Nonproliferation diabetic retinopathy or proliferative diabetic retinopathy may be a contraindication to vigorous exercise. These conditions can increase the risk of vitreous hemorrhage or retinal detachment. In a random sample of Diabetes Prevention Program participants, fundus photographs from 302 subjects with pre-diabetes (blood glucose 100–125 mg/dl) showed 7.6% had lesions that indicated early diabetic retinopathy, the leading cause of blindness in adults. Photos from 588 people who developed diabetes (blood glucose >126 mg/dl) showed 13% had retinopathy. The mean age of the subjects was about 54 years.
Non-weight bearing exercise is recommended for patients with severe peripheral neuropathy. Peripheral neuropathy increases the risk of skin breakdown, infection and joint disease. Peripheral neuropathy may cause muscle weakness and loss of reflexes, especially at the ankle, leading to changes in the way a person walks. Foot deformities, such as hammertoes and the collapse of the midfoot (Charcot), may occur. Blisters and sores may appear on numb areas of the foot because pressure or injury goes unnoticed. If foot injuries are not treated promptly, the infection may spread to the bone, and the foot may then have to be amputated. Some experts estimate that half of all such amputations are preventable if minor problems are caught and treated in time. Treatment first involves bringing blood glucose levels within the normal range. Good blood glucose control may help prevent or delay the onset of further problems.
Autonomic neuropathy is associated with cardiovascular disease, decreased cardiac responsiveness to exercise, postural hypotension, impaired thermoregulation, impaired night vision due to impaired papillary reaction and hypoglycemia resulting from gastroparesis. Persons with autonomic neuropathy should undergo cardiac assessment prior to undertaking increased physical activity. Diabetics should avoid vigorous exercise if the environment is extremely hot, humid, smoggy, or unusually cold.