FAQ: Activity, Exercise and Type 1 Diabetes

Activity versus exercise

What is the difference between activity and exercise?

Activity covers everyday movement — walking, cycling to the shops, gardening, playing with children. Exercise refers to structured training: running, lifting weights, team sports, endurance sessions. Thinking of activity as a glucose and health tool, and exercise as fitness and performance training, helps clarify when each approach applies.

Why does the distinction matter?

Activity carries lower hypoglycaemia risk, produces immediate glucose benefits, and is achievable for almost everyone in ordinary life. Exercise carries higher hypoglycaemia risk and needs planning across three phases — Before, During, and After — but brings meaningful fitness and performance gains. The skill is knowing which tool fits the situation, and not applying a full exercise protocol to every walk to the car.

See the Activity (Exercise Snacks) — Practical Guide for the activity system in full.

Activity FAQs

A Physical Activity and T1D FAQ (PDF) is available to download.

Why does a 10-minute walk after meals tend to be useful?

On average, a short walk after eating can lower the post-meal glucose peak and speed up insulin action, so the insulin already taken works more effectively. It also tends to build confidence that movement is safe and useful. The broader principle here is that small, repeatable movement doses can be more sustainable than ambitious exercise plans.

See the Activity (Exercise Snacks) — Practical Guide for more.

What happens when glucose is above 10 mmol/L (180 mg/dL)?

When glucose is elevated and there has been recent food and insulin, light activity can sometimes lower glucose without stacking a correction dose. On average, 20 minutes of light activity has been associated with a reduction of around 2 mmol/L (40 mg/dL) in some people — though this varies considerably. It is worth noting that exercise is generally avoided when ketones are elevated. Activity in this context is a tool, not a punishment, and not a replacement for insulin when insulin is genuinely needed. See Activity Snacking (20 by 2) and the downloadable guides 20 by 2 and 20 by 40.

How does CGM help with activity?

CGM provides real-time biofeedback that makes the effects of movement visible. Seeing a flatter post-meal peak after a short walk, or noticing a clearer cause-and-effect pattern, tends to build confidence — particularly for children and families who are new to thinking about activity and glucose. The immediate, observable feedback that movement changes glucose now (not “in theory”) is one of the most motivating aspects of CGM use. See the CGM series for more.

Exercise FAQs

What is the main risk with structured exercise?

Hypoglycaemia is the primary risk. For most people, large glucose drops during exercise are not random — they tend to be a predictable consequence of too much insulin on board for the session. If one principle is most worth understanding, it is this: insulin on board first, then starting glucose, then trend arrows. Exercise type comes after those three.

See the Exercise and Type 1 Diabetes — Practical Guide for the full system.

How can exercise be planned more safely?

A Before–During–After framework is widely used. The aim is not perfection — it is building safe starting plans and learning from outcomes over time.

Before exercise

The main variable to consider is insulin on board. The Three-Hour Rule — last significant bolus more than three hours before exercise — is a commonly used starting point. If eating within roughly two hours of exercise, eating closer to one hour before and reducing the bolus is a strategy many people explore. On AID systems, exercise mode or a temporary target set one to two hours before exercise tends to be useful. On pump therapy, a basal reduction of 50–80% one to two hours before is a common starting range — though the right amount varies individually.

During exercise

A commonly used working range is 7–10 mmol/L (126–180 mg/dL), though this is worth individualising with the care team. Checking glucose every 20–30 minutes and using both the value and trend arrows to inform decisions is a standard approach. Supplementing carbohydrate early and in small amounts — often 3–20 g depending on trends and intensity — tends to work better than reacting to a low. CGM is excellent, but if symptoms do not match the sensor, or if glucose is dropping rapidly, a fingerstick is useful because CGM can lag during exercise.

After exercise

The first one to two hours after exercise are a common risk window, particularly after longer sessions. For some people, a second risk window occurs overnight, particularly after evening exercise. On AID systems, leaving exercise mode or a temporary target on for one to two hours after finishing is a common approach. On pump therapy, continuing a basal reduction for approximately two hours after exercise and then reassessing is a frequently used strategy. On MDI, reducing the post-exercise meal bolus by 25–50% as a starting point and reviewing the outcome is worth exploring. Some people find a small protein-based snack before bed helps stability after evening sessions — this is best treated as an experiment rather than a fixed rule.

Benefits of activity

Why prioritise activity even when already doing structured exercise?

Activity brings benefits that formal training does not fully replicate: smoother post-meal peaks, reduced insulin requirements over time, cardiovascular protection, improved mental health, and better long-term health outcomes. Exercise is powerful. Activity is the tool available every day without needing ideal conditions.

See the Activity (Exercise Snacks) — Practical Guide.

Final word

The goal is not a perfect glucose trace during exercise. It is safe, repeatable plans that improve over time — with CGM as the feedback tool and the care team as the clinical guide.

Related GNL resources

• Exercise and Type 1 Diabetes — Practical Guide (hub)
• Activity (Exercise Snacks) — Practical Guide
• Aerobic and endurance exercise in T1D
• Anaerobic, sprinting and lifting exercise in T1D
• Mixed and team sports in T1D
• AID systems and exercise in T1D
• Podcast episode: Prof. Othmar Moser on exercise and type 1 diabetes