Canadian Study: Exercise May Not Spike Blood Sugar in Active T1D Adults

Canadian Researchers Challenge Common Exercise Fears in Type 1 Diabetes

A study from Canada published in Diabetes Research and Clinical Practice (2021) offers reassuring news for active adults living with type 1 diabetes (T1D). Researchers at the University of Alberta's Faculty of Medicine and Dentistry found that both aerobic and resistance exercise in the afternoon had surprisingly limited effects on blood sugar variability over a full 24-hour period — and aerobic exercise may actually improve overnight glucose stability.

What Makes This Study Unique

Much of the exercise and T1D research cited in US clinical settings focuses on the risks of hypoglycemia (low blood sugar) during and after exercise. This Canadian study takes a broader view, tracking continuous glucose monitor (CGM) data across a full 24 hours — including overnight — to paint a more complete picture. Importantly, all 12 participants were habitually active individuals, which may distinguish their results from sedentary T1D populations more commonly studied in the US.

What the Researchers Did

Participants completed three randomized sessions at least 48 hours apart:

• Aerobic exercise (AE): 45-minute treadmill run at moderate intensity (60% of maximum oxygen capacity)
• Resistance exercise (RE): Three sets of eight reps across seven weight-lifting exercises
• No exercise control (CON): 45 minutes of rest

All participants wore a blinded CGM device, meaning neither the patient nor the researcher could see real-time readings during the sessions. Glucose variability was measured in three windows: 0–6 hours post-exercise, overnight (midnight to 6 a.m.), and across the full 24 hours.

Key Findings — In Plain English

The researchers measured blood sugar using mmol/L, the Canadian standard. Here's what they found, converted to US mg/dL-equivalent terms:

• Time in Range (TIR), average glucose, and time above or below range were similar whether participants exercised or not.
• Overnight after aerobic exercise, blood sugar was significantly less variable. The standard deviation dropped from roughly 25 mg/dL on rest days to about 14 mg/dL after a run — a meaningful difference for CGM users.
• Resistance exercise showed no significant impact on overnight or 24-hour glucose variability compared to rest.

Does This Align With US Guidelines?

Current American Diabetes Association (ADA) guidelines acknowledge that exercise can cause both hypoglycemia and hyperglycemia in T1D, and recommend individualized strategies. This Canadian study doesn't contradict those guidelines but adds nuance: for already-active individuals, the feared glucose swings may be less dramatic than expected. The ADA does support CGM use during exercise, which aligns with the monitoring approach used here.

Why This Matters for US Patients

Fear of blood sugar crashes or spikes keeps many Americans with T1D from exercising consistently — and that avoidance carries its own health risks. This study suggests that if you're already physically active, an afternoon workout may not destabilize your glucose as much as you think, especially overnight after aerobic activity. Tracking your patterns with a CGM remains the most reliable way to understand your individual response to exercise.

If you're managing T1D and want to better understand how your lifestyle choices affect your glucose trends, explore the diabetes management resources and support tools available at mdsdiabetes.com — including guidance on using CGM data to make smarter daily decisions.

Citation

Brockman, Sigal, Kenny (2021). Afternoon aerobic and resistance exercise have limited impact on 24-h CGM outcomes in adults with type 1 diabetes: A secondary analysis. Diabetes Research and Clinical Practice. PMID: 34052249. DOI: 10.1016/j.diabres.2021.108874. Country of Origin: Canada — University of Alberta, Faculty of Medicine and Dentistry, Edmonton, Alberta.