Exercise With Diabetes: Sugar, Feet and Timing

How exercise affects blood sugar

• During and just after activity, muscles take up sugar, so blood sugar often falls. This is helpful for most people.
• For hours afterwards, muscles stay more sensitive to insulin, so sugar can fall later, even overnight, particularly after longer or unusual activity.
• With insulin or certain tablets (such as sulphonylureas), the fall can be too much, causing hypoglycaemia (low sugar). Metformin on its own rarely causes low sugar. Check which tablets you take.
• In some situations, sugar can rise with exercise, such as very hard exertion, or if the person is unwell, dehydrated or has very high sugar and insufficient insulin.
• Hot weather and dehydration can raise or destabilise readings.

Because responses vary, the best way to learn is to check blood sugar before and after exercise for the first few weeks, as the doctor advises, and note the patterns; see how to test blood sugar at home, glucometer buying guide and fasting and post-meal sugar targets.

Check with the doctor first

Ask your doctor or diabetes nurse before starting or changing exercise, especially if you have:

• insulin or tablets that can cause low sugar;
• heart disease, chest pain, high blood pressure or breathlessness; see exercise with heart disease;
• eye problems, such as diabetic retinopathy, where heavy straining or vigorous exercise may be unsafe, particularly if there is a risk of bleeding in the eye or after laser treatment or surgery; see diabetic eye care;
• kidney disease or protein in the urine;
• numb feet, foot sores or deformities; see diabetic foot care at home and neuropathy foot care;
• dizziness on standing, or a history of fainting (autonomic neuropathy);
• very high sugar (for example consistently above levels your doctor has given), ketones or feeling unwell;
• recent surgery or a fracture;
• frequent low sugars.

Timing exercise around meals and medicines

General principles (your own advice may differ):

• After meals is often a good time for gentle walking, 10 to 15 minutes after eating, which can reduce the post-meal sugar rise. Do not exercise vigorously immediately after a large meal.
• Avoid exercising at the peak of insulin or tablet action if you are prone to lows; ask when that is.
• Do not exercise on an empty stomach if you take insulin or sulphonylureas, unless your doctor agrees. Have a regular meal or a snack beforehand.
• Keep a consistent routine, with similar times and amounts of exercise each day, so that medicines can be matched.
• Late evening exercise can cause overnight lows; check sugar before bed, and have a snack if advised.
• Fasting days and festivals: do not do strenuous exercise while fasting, particularly on insulin or sulphonylureas; talk to your doctor before fasts; see fasting, festivals and older adults.
• Do not change your medicines yourself because you are exercising more. Tell your doctor, who may adjust doses.
• Carry a fast-acting sugar source if you take insulin or tablets that can cause low sugar: for example glucose tablets, sugar sachets, juice or a few sweets, and a snack.

Preventing and handling low sugar

Low blood sugar (generally below about 70 mg/dL, or as your doctor defines it) can come on quickly and is dangerous for older people, causing falls, confusion and, if severe, loss of consciousness. See hypoglycaemia in older adults and diabetes and low sugar emergencies.

Symptoms: shakiness, sweating, hunger, headache, fast heartbeat, blurred vision, irritability, confusion, weakness, drowsiness. In older people, symptoms may be subtle or masked by medicines such as beta-blockers.

If you feel any of these during exercise: stop, sit down, check your sugar if you can, and take a fast-acting sugar source as your doctor has advised, then rest and recheck in about 15 minutes, repeating if still low, and follow with a snack. Tell the doctor, who may adjust medicines.

Call 112 if a person is confused, cannot swallow safely, has a seizure or is unconscious. Do not put food or drink in the mouth of an unconscious person. Family members who live with a person on insulin should learn the plan, including any emergency glucagon, if prescribed.

Prevention: check sugar before exercise; eat a snack if it is lower than your doctor's threshold; carry sugar; avoid exercising with very low readings; do not skip meals; be extra careful with long walks, unusual activity and alcohol.

When not to exercise

Postpone exercise and contact the doctor if:

• sugar is very high (use the threshold your doctor has given, often around 250 mg/dL or higher, particularly with ketones or feeling unwell);
• sugar is very low or you have had a recent low;
• you have vomiting, diarrhoea, fever or feel unwell;
• you have chest pain, severe breathlessness or dizziness;
• you have a new foot sore, infection or injury;
• you have just had eye treatment.

Protect your feet

Feet need special care in diabetes, because reduced feeling and circulation make small injuries serious.

• Check your feet every day, and before and after exercise, for blisters, redness, cuts and swelling; use a mirror or ask for help.
• Wear well-fitting, supportive shoes with a wide toe box, cushioned soles and seamless socks. Never exercise barefoot. See choosing shoes for older feet and insoles and orthotics for foot and heel pain.
• Check inside shoes for stones and creases.
• Keep feet clean and dry, especially between the toes.
• Choose low-impact activity if feet are numb or have sores: swimming (only with healed skin and the doctor's advice), seated exercises, stationary cycling; see pedal exerciser guide and chair exercises for seniors.
• Avoid hot surfaces, hot sand and temple floors in summer.
• Do not use heat or electrical devices on numb feet.
• See a doctor or podiatrist promptly for any blister, sore, redness, swelling, warmth, or a change in foot shape.

Types of activity

The guidelines for older adults apply, with extra care:

• Aerobic activity: brisk walking, cycling, water exercise, chair routines; aim to build towards about 150 minutes a week, with no more than two consecutive days without activity if possible. See walking programme for older adults.
• Strength training on two or more days a week, with light to moderate loads, avoiding straining and breath-holding; see strength training after 60: how much is enough and resistance band routine for seniors.
• Balance and flexibility, particularly with neuropathy or dizziness; see balance exercises for seniors and stretching for stiff older bodies.
• Break up long sitting with a few minutes of light movement every half hour; see sitting for long hours.

Eyes, kidneys, heart and nerves

• Retinopathy: avoid heavy lifting, straining, head-down positions and high-impact activity unless cleared by the eye doctor.
• Kidney disease: moderate exercise is usually helpful, but ask about protein, fluid and effort; see chronic kidney disease home care.
• Heart disease: follow cardiac advice; diabetes can cause "silent" heart disease, so unusual breathlessness or fatigue needs attention.
• Autonomic neuropathy: dizziness on standing, abnormal heart rate or poor heat tolerance; exercise gently, avoid heat, and rise slowly; see dizziness and low blood pressure when standing.
• Peripheral neuropathy: balance training and foot protection; see neuropathy and balance.

Heat, humidity and the Indian context

• Exercise in the cool hours, with a fan, light clothing and plenty of water; see exercising indoors in Indian summer and monsoon.
• Dehydration affects sugar and kidneys; drink water, unless fluid is restricted.
• Do not exercise in the heat if feeling unwell.
• Keep insulin and glucose meters away from heat; check storage.
• Carry sugar and a snack on walks, and tell a companion where you are going.
• Wear ID stating that you have diabetes, with the medicines you take, in case of a low sugar episode; see emergency contact card and medical summary.
• In power cuts and fasting, plan the day.
• Include traditional activity such as walking after meals in family routine.

Monitoring and learning your pattern

For the first few weeks of a new routine, if you test at home, note: sugar before exercise, activity, sugar afterwards, and symptoms. Share with your doctor or diabetes educator. Over time you will learn how your body reacts, and your team can adjust medicines. CGM sensors, where used, show trends; see cgm sensors for older adults. Use meters and strips correctly; see glucose strips and lancets guide.

When to ask a professional

Ask your doctor, diabetes nurse or educator about exercise plans, medicine adjustments, targets and warning signs. A podiatrist can check feet. An eye doctor can advise on retinopathy. A physiotherapist can design safe programmes. A dietician can advise on snacks, meals and fasting; see nutrition for diabetes after 60. In an emergency, call 112.