Managing Type 1 Diabetes During Exercise

Intro

Exercise is great for glucose control, heart health, mood, and sleep. With type 1 diabetes (T1D), the main challenge is avoiding hypoglycemia during and after activity while still getting the benefits of training.

Key Points

Aerobic activity (steady cardio) tends to lower glucose during/after.
Anaerobic/high-intensity or strength can raise glucose short-term, then sometimes drop later.
Plan ahead: check glucose, adjust insulin, and carry fast carbs.
Watch for late-onset hypos (up to 24 hours after long or intense sessions).

Pre-Exercise Checklist

Check glucose (and trend if using CGM).
Have 15–30 g fast carbs handy (glucose tabs/gel/juice).
Consider location of infusion sites/sensors—avoid pressure or direct hits.
Hydrate well; wear ID indicating T1D.

Insulin & Carb Strategies (general principles)

Always follow your clinician’s advice; individual responses vary.

If starting in target (≈5.6–10 mmol/L / 100–180 mg/dL):

Aerobic 30–60 min: reduce rapid-acting bolus 1–2 hours before by ~25–50% or take 10–20 g carbs at start; consider pump temp basal –20% to –50% starting 60–90 min before.
>60 min aerobic: plan 10–20 g carbs every 20–30 min; larger basal reductions may be needed.
Intervals/strength: may not need extra carbs up front; monitor for a later drop and correct if needed.

If starting low (<5.6 mmol/L / <100 mg/dL):

Take 15–20 g fast carbs, recheck in 15 minutes; delay exercise until ≥5.6 mmol/L (≥100 mg/dL).

If starting high (>13.9 mmol/L / >250 mg/dL):

Check for ketones. If positive, defer exercise and correct. If no ketones, light activity may be okay; avoid vigorous work until trending down.

During Exercise

Recheck every 30 minutes (or watch CGM trend arrows).
Take 10–20 g carbs if dropping or symptomatic.
For long sessions, mix fast carbs (to treat drops) with slower carbs (bars/banana) to sustain.

After Exercise (and Overnight)

Risk of delayed hypos is highest after long aerobic work or evening training.
Consider reduced basal (pump temp basal –10% to –30% for 6–12 h) or a bedtime snack with some protein/slow carbs if you trend low.
Set CGM alerts a bit higher overnight on hard-training days.

Site Management

Rotate infusion and sensor sites; avoid spots that get friction or heavy impact.
For swimmers/sweaty sports, use extra adhesive/overpatches.

Sick Days & Heat

Illness and heat can raise insulin needs; monitor more often and adjust with guidance.

Red Flags — Seek Medical Advice

Repeated severe hypos needing assistance.
Ketones that don’t clear with correction/fluids.
Unexplained high glucose during/after light activity.

FAQ

Do I need different targets for competition days?
Some athletes run slightly higher targets to reduce hypo risk—discuss a plan with your team.

Are sports drinks okay?
They can help during long intense sessions; otherwise prefer water and targeted carbs.

Pump vs. injections for sport?
Pumps allow temp basal tweaks; MDI can work well with planned bolus reductions and timed carbs.