Exercise in Diabetes

For type 2 diabetes, the aim is at least 150 minutes a week of moderate activity plus muscle strengthening on at least 2 days, and a combination of aerobic and resistance training improves glucose control more than either alone. Regular activity lowers glycated haemoglobin (HbA1c) on average by around 0.5 to 0.7 percentage points, roughly 5 to 8 mmol/mol, with considerable individual variation, and improves insulin sensitivity, though the effect on insulin sensitivity fades within a couple of days, so it is best not to go more than two days without activity. Reducing and breaking up sedentary time matters too, with a short burst of light activity every 30 minutes of prolonged sitting. Hypoglycaemia during exercise is mainly a risk for those treated with insulin or a sulfonylurea such as gliclazide, rather than metformin alone, and doses may need adjusting. For people using weight-management medication or aiming to lose weight, resistance work helps preserve muscle, and attention to foot care is important where there is peripheral neuropathy.

In type 1 diabetes, exercise causes large swings in glucose, and the direction depends on the activity: aerobic exercise such as running or cycling tends to lower glucose, whereas short, intense efforts, resistance training and high-intensity intervals can raise it. A practical starting point is an individualised pre-exercise glucose range, commonly around 7 to 10 mmol/L for aerobic exercise of up to an hour. If glucose is below 5 mmol/L, taking 10 to 20 grams of carbohydrate and delaying until it rises above 5 mmol/L is sensible; if it is high, above roughly 14 mmol/L, blood ketones should be checked, and exercise avoided if ketones are 1.5 mmol/L or more or the person feels unwell. Insulin usually needs reducing for planned aerobic exercise. On a pump, a temporary basal rate reduction of 50 to 80 percent started up to 90 minutes beforehand is commonly used. If exercising within about 90 minutes of a meal, the meal bolus is reduced instead, by an amount that depends on the timing, duration and intensity of the activity. On multiple daily injections, a basal reduction of around 20 percent is one approach, though adjustments are individualised to insulin on board and personal response. Supplemental carbohydrate of 10 to 20 grams for shorter sessions, and more for longer or higher-insulin situations, helps prevent hypoglycaemia. Injecting away from the exercising limb avoids speeding up insulin absorption, and continuous glucose monitoring (CGM) and automated insulin delivery systems make glucose much easier to manage around activity.

The risk of hypoglycaemia continues for 12 to 24 hours after exercise because insulin sensitivity is increased, so frequent glucose monitoring and extra carbohydrate afterwards are worthwhile, and overnight insulin may need reducing, with monitoring, carbohydrate and insulin adjustment individualised to the person. Continuous glucose monitoring helps, though readings can lag behind blood glucose during rapid change. Exercise is best avoided within 24 hours of a severe hypoglycaemic event. People should carry fast-acting carbohydrate such as glucose tablets or a sugary drink, and take care with high-risk activities like swimming alone after a recent hypo. A few complications shape the choice of activity: very high-intensity or straining efforts are approached cautiously where there is significant retinopathy, and good footwear and foot checks matter where there is neuropathy. Involving the diabetes team in planning, especially for those new to exercise or aiming for demanding goals, helps people stay safe and active.

Established microvascular and neuropathic complications each modify the prescription in a specific way, and this middle part of the ladder is easily skipped. Autonomic neuropathy blunts the heart rate response, so heart rate targets become unreliable and perceived exertion should be used instead; it also blunts the warning symptoms of hypoglycaemia and predisposes to orthostatic hypotension, so position changes should be gradual. Peripheral neuropathy calls for daily foot inspection and appropriate footwear, and non-weight-bearing options such as cycling or swimming where there is active ulceration. Proliferative retinopathy is a reason to avoid high-intensity effort, heavy straining with the Valsalva manoeuvre and head-down positions, because of the risk of vitreous haemorrhage or retinal detachment. Diabetic nephropathy is not a contraindication, and exercise is both safe and beneficial in chronic kidney disease.

One prescribing point is worth stating plainly. Insulin and sulfonylureas are the two classes that carry a meaningful risk of exercise-related hypoglycaemia and may need dose adjustment. Metformin, dipeptidyl peptidase-4 inhibitors, sodium-glucose cotransporter-2 inhibitors and glucagon-like peptide-1 agonists do not typically cause hypoglycaemia when used without insulin or a sulfonylurea, so a person on metformin alone does not usually need carbohydrate before exercising.

• •Regular activity substantially reduces the risk of developing type 2 diabetes.
• •Type 2 management is at least 150 minutes a week plus strengthening on 2 days, with combined aerobic and resistance work best.
• •In type 1 diabetes, aerobic activity lowers glucose while intense or resistance work can raise it.
• •Aim for a pre-exercise glucose around 7 to 10 mmol/L, and avoid exercise if ketones are 1.5 mmol/L or more.
• •On a pump, reduce basal by about 50 to 80 percent for planned aerobic exercise; bolus and injection adjustments are individualised.
• •Hypoglycaemia risk lasts up to 24 hours after exercise, so monitor and adjust overnight insulin.