Exercise: Different Types, Different Effects

Not all exercise affects blood sugar the same way. Understanding the differences lets you prepare specifically rather than generically.

Aerobic exercise (running, cycling, swimming): Consistently lowers blood sugar during and after activity. This is the category where basal reductions and pre-exercise fueling matter most. The glucose-lowering effect can last 12-24 hours.

Anaerobic exercise (weightlifting, sprinting, HIIT): May cause blood sugar to spike initially due to adrenaline and cortisol release. This spike is temporary — don't over-correct it. Then blood sugar may drop in the hours afterward as muscles recover. The tricky part: people see the spike during exercise and correct it, then crash hours later from the combined effect of insulin + delayed muscle uptake.

Mixed exercise (team sports, circuit training): Combines both effects. Blood sugar might spike during intense bursts, drop during sustained activity, and continue dropping for hours after. These are the hardest to predict. Start by tracking your individual response, and adjust from there.

Key takeaway for all exercise types: Monitor for 12-24 hours post-exercise. The delayed glucose-lowering effect is real regardless of exercise type — it just shows up differently.

Illness

Illness throws diabetes management into chaos. But here's what many people don't expect: while blood sugar often runs high during acute illness (stress hormones, inflammation, reduced activity), it can drop unexpectedly when you're recovering.

During Illness

• Blood sugar tends to run higher due to stress hormones (cortisol, adrenaline)
• You may need more insulin even if eating less
• Monitor every 2-4 hours — illness makes patterns unpredictable
• Stay hydrated — dehydration worsens highs and makes lows harder to treat

During Recovery

• As stress hormones normalize, insulin sensitivity rebounds
• Doses that were right during illness may now be too high
• Watch for lows as appetite returns but sensitivity is increased
• Gradually return to your pre-illness doses over 1-2 days

Sleep and Nighttime Lows

Nighttime hypoglycemia is particularly dangerous because you may not feel the symptoms while sleeping. The warning signs that wake you during the day — sweating, shaking, hunger — may not be enough to wake you at night.

Prevention Strategies for Night

• CGM alarms are essential. Set your low alert to 70-80 mg/dL and your urgent low to 55 mg/dL. Make sure the alarm volume is high enough to wake you. If you use a phone as your receiver, keep it close to your bed.
• Check your trend before bed. A BG of 110 mg/dL that's stable is very different from 110 mg/dL with a downward arrow. If you're below ~130 mg/dL and trending down, a small snack with slow-release carbs before sleep provides a safety margin (whole grain crackers, a small apple with peanut butter). Trending down from 200? That's probably fine — it depends on where you'll stabilize. With experience, you'll learn which bedtime readings need a snack and which don't.
• Review overnight basals regularly. If you're frequently going low between 2-4 AM, your overnight basal rate may be too high. Work with your endo to adjust.

Working with Your Healthcare Team

Prevention isn't a solo project. Your diabetes care team brings data analysis skills, pattern recognition experience, and treatment options that you might not have considered.

Bring data to appointments. Download your CGM reports, review your pump data, bring your trigger tracking log. The more data your team has, the better recommendations they can make.

Ask specific questions. Instead of "I keep going low," try: "I'm going low between 3-5 PM on days I exercise at lunch. My current bolus is X, my basal is Y, and I reduce by Z. What else should I try?"

Review your targets. Your correction factor, carb ratios, and basal rates should be reviewed every 3-6 months — or sooner if your patterns change. Weight changes, activity changes, stress levels, and seasonal shifts all affect insulin needs.

Building Sustainable Prevention Habits

Knowledge without habits is just information. Here are checklists to turn prevention strategies into automatic behaviors.

Daily Checklist

• Check CGM/BG before each meal and at bedtime
• Verify insulin-on-board before any correction
• Carry fast-acting glucose at all times (glucose tabs, juice, gel)
• Review CGM trend arrows before bolusing
• Eat within 15-30 min of rapid-acting bolus

Weekly Checklist

• Review past week's lows — look for time-of-day patterns
• Check glucose supply — are tabs/juice/gel stocked everywhere? (bag, desk, car, nightstand)
• Review upcoming week — any unusual activities, events, or schedule changes?
• Check if CGM/pump supplies are sufficient

Before-Activity Checklist

• Reduce basal (pump) or reduce pre-activity bolus (MDI) — 25-50% for moderate, 50-80% for intense
• Check starting BG — ideally 126-180 mg/dL (ISPAD target)
• Pack fast-acting carbs — accessible, not buried in a bag
• Set CGM low alert to 90 mg/dL
• Plan post-activity monitoring for 12-24 hours
• Have recovery snack ready

These checklists might seem like a lot at first. But after two weeks, most of them become second nature. The goal isn't perfection — it's building a system that catches the preventable lows before they happen.