Exercise in type 2 diabetes: glucose, insulin, safety
Table of contents
- Why exercise is part of treatment
- What happens to glucose during and after exercise
- How much A1c falls with regular training
- When to train: after the meal and out of the chair
- Insulin and sulfonylurea: how to avoid hypoglycemia
- Retinopathy, neuropathy and the foot
- How to prescribe in practice
- How NEXO helps train this reasoning
- Frequently asked questions
- Take-home messages
- References
A 61-year-old teacher has had type 2 diabetes for eight years and takes metformin, a sulfonylurea and bedtime basal insulin. Her last A1c came back above target, and the team suggested exercise before adding another medication. She is afraid: the only time she walked briskly in the late afternoon, she woke up in the early hours sweating and shaking. She also has mild retinopathy and has lost some sensation in her feet.
The case brings together the three questions that come up most often in the office. Does exercise work for blood glucose? How do you avoid hypoglycemia in someone who uses insulin or a sulfonylurea? And what changes when there is already a complication in the eye or the foot?
This text goes through the acute and the chronic effect of exercise in type 2 diabetes, the best time to train, the precautions with glucose-lowering medications and the protection of the retina and the foot, ending with a practical prescription.
Key points
- Regular aerobic training lowers A1c by 0.5 to 0.7 percentage points in type 2 diabetes (Kanaley, 2022).
- Combined training, with aerobic and strength work, lowered A1c more than each modality alone in a network meta-analysis (Pan, 2018).
- Exercise done after the meal lowers the glucose peak more than exercise done before it (Engeroff, 2023).
- Insulin and sulfonylureas increase the risk of exercise-related hypoglycemia (Kanaley, 2022).
- Proliferative or severe nonproliferative retinopathy may contraindicate vigorous exertion (ADA, 2025).
- Walking in proper footwear appears safe for people with peripheral neuropathy (ADA, 2025).
Summary
- Why exercise is part of treatment
- What happens to glucose during and after exercise
- How much A1c falls with regular training
- When to train: after the meal and out of the chair
- Insulin and sulfonylurea: how to avoid hypoglycemia
- Retinopathy, neuropathy and the foot
- How to prescribe in practice
- How NEXO helps train this reasoning
- Frequently asked questions
- Take-home messages
Why exercise is part of treatment
Type 2 diabetes is, at its base, a problem of insulin resistance added to a secretion that does not keep up with demand. Skeletal muscle is the largest consumer of glucose after a meal, and exercise acts precisely on it. That is why physical activity appears in every guideline as part of treatment, alongside diet and medications (ADA, 2025).
The American College of Sports Medicine consensus summarizes that much of the benefit comes from improved insulin sensitivity, post-meal glucose and cardiovascular risk (Kanaley, 2022). In other words, exercise treats glucose and also what kills most in diabetes, which is cardiovascular disease.
The 2020 WHO guideline was the first to include specific recommendations for people with chronic diseases, with the same target of aerobic activity and strengthening as for adults in general (Bull, 2020). When the target is not possible, the guidance is to do what the conditions allow (Bull, 2020).
For the team, the practical question is rarely whether the patient should exercise. The question is how to start safely, what type of training to choose and how to adjust the medications so that exercise helps without causing hypoglycemia. This conversation works best when it starts from what the patient wants and fears, as the text on how to listen for change talk in motivational interviewing shows.
What happens to glucose during and after exercise
During the session
When the muscle contracts, it takes up glucose through a pathway that does not need insulin. That is why exercise lowers blood glucose even in someone with significant insulin resistance. The ADA position statement describes that glucose uptake stays raised for about 2 hours through insulin-independent mechanisms (Colberg, 2016).
In general, aerobic exercise lowers blood glucose when done in the period after the meal with that meal's usual insulin, and long sessions at that time can cause excessive drops (Colberg, 2016). Very intense exercise can have the opposite effect and raise glucose for a while, because of the catecholamine surge.
In the following hours
The effect does not end with the session. After prolonged exercise, insulin-dependent glucose uptake can stay raised for up to 48 hours, linked to muscle glycogen replenishment (Colberg, 2016). The ACSM consensus mentions improved insulin sensitivity lasting from 2 to 72 hours, with a glucose drop proportional to duration and intensity (Kanaley, 2022).
This window explains two clinical facts. The first is late hypoglycemia, like that of the teacher in the case, who walked briskly and had symptoms in the early hours. The second is the recommendation to spread exercise across the week: the gain in insulin sensitivity is temporary, and the ACSM recommends that no more than two consecutive days pass between sessions (Kanaley, 2022).
How much A1c falls with regular training
Aerobic
Meta-analyses and systematic reviews confirm that regular aerobic training improves glycemia in type 2 diabetes, with fewer daily hyperglycemia peaks and a drop of 0.5 to 0.7 percentage points in A1c (Kanaley, 2022). For comparison, this effect is in the range of some oral antidiabetic drugs, which helps show the patient that exercise is treatment, not just advice.
Strength
Strength training also lowers A1c. A meta-analysis found an average reduction of 0.39 percentage points with resistance training compared with controls (Jansson, 2022). The most useful finding for prescribing came from the moderator analysis: the greater the participants' strength gain, the greater the drop in A1c (Jansson, 2022).
The message is that strength needs to progress. Repeating the same light load for months tends to yield less than a program in which the load rises as the patient gets stronger.
Combined
The network meta-analysis by Pan and colleagues gathered 37 studies with 2208 patients with type 2 diabetes (Pan, 2018). Supervised aerobic and supervised resistance training each reduced A1c by 0.30 percentage points compared with not exercising, and combined training reduced it more than either one (Pan, 2018).
The ACSM consensus reaches the same conclusion, with an honest caveat: in some trials, the combined group did more exercise in total, which may explain part of the advantage (Kanaley, 2022). In practice, combining aerobic and strength training is the default choice, and total volume also counts.
When to train: after the meal and out of the chair
Exercise after the meal
The timing of exercise changes the effect on the glucose peak. A meta-analysis of randomized trials compared exercise before and after the meal, with the same intensity and duration, in people with and without type 2 diabetes (Engeroff, 2023). Exercise after the meal reduced glucose excursion compared with exercise before eating (standardized mean difference of 0.47) and with rest (0.55) (Engeroff, 2023).
In the subgroup with type 2 diabetes, exercise after the meal also reduced glucose compared with rest, with a standardized difference of 0.47 (Engeroff, 2023). Exercise before the meal, in turn, no longer showed a significant effect on postprandial glucose (Engeroff, 2023).
The ADA position cites trials in which 15 minutes of walking after meals improved glycemic control in type 2 diabetes (Colberg, 2016). It is a simple instruction to give and easy to fit into the routine, like a walk around the block after lunch and dinner.
Breaking up sitting time
Sitting time counts separately from exercise. In a study with overweight adults without diabetes, breaking up sitting time with short walks reduced the glucose response to a sugary drink by 24 to 30 percent (Dunstan, 2012). In type 2 diabetes, 3-minute breaks of light walking and simple bodyweight exercises every 30 minutes also improved glycemic control (Colberg, 2016).
That is why the ADA guideline recommends breaking up sitting time at least every 30 minutes (ADA, 2025). For those who work at a computer, the practical advice is to stand up, walk to the water or climb a flight of stairs, without needing to change clothes.
Insulin and sulfonylurea: how to avoid hypoglycemia
Who is at risk
People who manage diabetes only with lifestyle changes have minimal risk of hypoglycemia with exercise (Kanaley, 2022). The risk appears with medicines that increase circulating insulin: insulin itself and secretagogues, such as sulfonylureas and glinides (Kanaley, 2022). Metformin, DPP-4 inhibitors, GLP-1 agonists and SGLT2 inhibitors, used without insulin or a secretagogue, rarely cause hypoglycemia on their own.
The professor in the case uses both risk classes, and the early-morning episode is typical. Late hypoglycemia is more concerning when muscle and liver glycogen stores have been used up, and it tends to be rare in people who exercise for leisure without using insulin (Kanaley, 2022).
What to adjust
There are two strategies and they can be combined: eat carbohydrate and reduce insulin or the secretagogue. The ADA states that it is often necessary to add carbohydrate, reduce insulin or both to keep glucose balanced during and after activity (Colberg, 2016). Reducing basal insulin, meal insulin or both should be considered as an alternative or complement to carbohydrate (Colberg, 2016).
The size of the adjustment depends on the person, the time of day, the duration and the intensity of the session, and guidelines avoid fixed numbers. The safe way to calibrate is to measure: the ADA highlights that frequent blood glucose measurements are needed to apply carbohydrate and insulin adjustment strategies (Colberg, 2016). Timing also matters, because insulin given shortly before exercise increases the risk of hypoglycemia during the session (Kanaley, 2022).
In people who use a sulfonylurea and start exercising regularly, it is worth asking whether the medicine is still needed in the same amount. Sometimes the best decision is to reduce or switch the secretagogue to a class without hypoglycemia risk, a conversation that the text on how to talk about deprescribing with the patient helps to organize.
High glucose before training
The ADA suggests, as the ideal range before exercise, blood glucose between 90 and 250 mg/dL (Colberg, 2016). Between 250 and 350 mg/dL, the recommendation is to test for ketones, and moderate or large amounts of ketones contraindicate exercise (Colberg, 2016). Intense exercise should wait until glucose is below 250 mg/dL, because it can worsen hyperglycemia (Colberg, 2016).
There is a specific concern with SGLT2 inhibitors. In these patients, ketoacidosis can occur with normal or only moderately raised glucose (Kanaley, 2022). Malaise, nausea or abdominal pain after a long training session deserve ketone testing even with acceptable glucose. To review the recognition and correction of hypoglycemia in people who use insulin, see how to define and classify hypoglycemia and the case of how pilots with insulin fly today.
Retinopathy, neuropathy and the foot
Before starting
The ADA considers medical clearance before exercise unnecessary for asymptomatic people who are going to start light or moderate activity, no more strenuous than a brisk walk (Colberg, 2016). Assessment gains importance when the prescription includes vigorous effort or when a complication is already present.
The 2025 guideline lists the conditions that require attention before prescribing: uncontrolled hypertension, untreated proliferative retinopathy, autonomic neuropathy, orthostatic hypotension, peripheral neuropathy, balance impairment and a history of foot ulcer (ADA, 2025). In people with macrovascular disease or cardiac autonomic neuropathy, screening before exercise follows ACSM and ADA guidance (Kanaley, 2022).
Retina
In proliferative or severe nonproliferative retinopathy, vigorous aerobic or resistance exercise may be contraindicated because of the risk of vitreous hemorrhage or retinal detachment (ADA, 2025). The professor's mild retinopathy in the case allows moderate exercise, and an up-to-date ophthalmologic assessment defines the limit. Efforts involving breath-holding, head below the trunk and strong impact are the most concerning.
Foot with neuropathy
For a long time, people with peripheral neuropathy were advised to avoid walking. The view has changed: the ADA states that moderate-intensity walking may not increase the risk of ulcer or reulceration in those who wear appropriate footwear (ADA, 2025). All people with peripheral neuropathy should wear appropriate footwear and examine their feet daily to detect lesions early (ADA, 2025).
A randomized trial with 29 people with diabetes and neuropathy compared weight-bearing exercise, such as treadmill walking, with non-weight-bearing exercise, such as stationary cycling (Mueller, 2013). The weight-bearing group gained on average 1178 more steps per day than the non-weight-bearing group (Mueller, 2013). There were 4 ulcers in the study, and 3 of them occurred in the 5 participants who already had a previous ulcer (Mueller, 2013).
This finding separates two profiles. For those with neuropathy and no previous ulcer, walking with appropriate footwear and daily inspection is reasonable. For those who have already had an ulcer, non-weight-bearing exercises, such as cycling, swimming and seated strength training, are a safer option while the foot is monitored closely.
A 2025 umbrella review showed that exercise improves neuropathic symptoms, nerve conduction and balance in diabetic neuropathy (Gracia-Sánchez, 2025). The effect on falls and ulcer prevention remains inconclusive, with wide variation between studies (Gracia-Sánchez, 2025).
How to prescribe in practice
The weekly goal
The ADA position recommends 150 minutes or more of moderate to vigorous activity per week, spread over at least 3 days, without going more than 2 consecutive days without activity (Colberg, 2016). Strength training is included with 2 to 3 sessions per week on non-consecutive days (Colberg, 2016). The WHO recommends 150 to 300 minutes of moderate activity and muscle strengthening on 2 or more days per week for adults, including those with chronic disease (Bull, 2020).
The 2025 guideline suggests aerobic sessions of at least 10 minutes, with a goal of about 30 minutes per day on most days (ADA, 2025). Flexibility and balance exercises are probably important for older adults with diabetes (Colberg, 2016), and many strength exercises for legs and trunk already work as balance training (Kanaley, 2022).
A summary for the office
| Situation | What to advise | Basis |
|---|---|---|
| Lifestyle alone or metformin | Start walking and add strength training, without adjusting medication | Minimal risk of hypoglycemia (Kanaley, 2022) |
| Insulin or sulfonylurea | Measure glucose before, during and after; keep carbohydrate at hand; discuss reducing the medication on training days | Carbohydrate and insulin adjustment guided by measurements (Colberg, 2016) |
| Glucose between 250 and 350 mg/dL before training | Check ketones and postpone intense effort | ADA recommendation (Colberg, 2016) |
| SGLT2 inhibitor | Watch for ketoacidosis with normal glucose | ACSM consensus (Kanaley, 2022) |
| Proliferative or severe non-proliferative retinopathy | Avoid vigorous effort until ophthalmologic evaluation | ADA guideline (ADA, 2025) |
| Peripheral neuropathy without previous ulcer | Moderate walking with appropriate footwear and daily foot inspection | ADA guideline (ADA, 2025) |
| Previous ulcer | Prefer non-weight-bearing exercise and monitor the foot closely | Ulcers concentrated in those who already had an ulcer (Mueller, 2013) |
Applying it to the case
For the teacher, a reasonable prescription starts with 15-minute walks after lunch and dinner, a time that reduces the glucose peak (Engeroff, 2023). Twice a week, she adds strength training with elastic bands or light dumbbells, with load progression, since the gain in strength follows the drop in glycated hemoglobin (Jansson, 2022).
Because she uses insulin and a sulfonylurea, she measures glucose before and after sessions and before bed in the first days, carries fast-absorbing carbohydrate and agrees with the team on a reduction of the sulfonylurea if the measurements show a downward trend. With mild retinopathy and neuropathy without ulcer, walking is appropriate, with proper footwear and daily foot inspection (ADA, 2025).
The follow-up visit with a new A1c and a review of the glucose diary lets you decide whether exercise was enough or whether treatment still needs adjusting. Before adding a drug, it is worth recalling the lesson of quaternary prevention on cascades of care and of negotiating the agenda with the patient. For the context of targets and drug classes, see why the ADA replaced A1c with the organ and, in people who also have obesity, what to monitor with tirzepatide.
The limits of the evidence
Most trials measure A1c and glucose, and few have the size and duration to show an effect on heart attack, amputation or death. The A1c reduction figures come from heterogeneous populations, with supervised programs that are not always repeated outside the study (Pan, 2018). Part of the evidence on exercise timing and on breaks came from people without diabetes (Engeroff, 2023), and the effect of exercise on foot ulcer remains uncertain (Gracia-Sánchez, 2025).
How NEXO helps train this reasoning
In NEXO, the case of the day is fictional, with a real clinical presentation and up to six progressive clues, and you propose the diagnosis by looking for the ICD-10 code.
The limits of using the game are described on the NEXO economy page. If you research teaching of clinical reasoning, the page for researchers explains how to get in touch. Professionals who write or review cases find information on curation and on creators, and institutions can learn about the proposal on the partnerships page. For the most frequent reasons for consultation, see the most common codes in primary care.
Frequently asked questions
Which exercise is best for type 2 diabetes?
Combined training, with aerobic and strength work, lowered A1c more than either one alone (Pan, 2018). The best choice, however, is the combination the patient can keep up over the months.
How much can A1c fall with exercise?
Regular aerobic training lowers A1c by 0.5 to 0.7 percentage points (Kanaley, 2022). Strength training lowered it by an average of 0.39 points, with a larger drop in those who gained more strength (Jansson, 2022).
Is it better to train before or after eating?
After. Exercise after the meal lowered the glucose peak more than exercise before eating (Engeroff, 2023). A short walk after lunch and after dinner already takes advantage of this effect.
Do people who use insulin need to change the injection on training days?
Often, yes, and the adjustment is individual. The ADA recommends extra carbohydrate, reduced insulin or both, guided by frequent glucose measurements (Colberg, 2016). The adjustment should be agreed with the team that follows the diabetes.
Why can hypoglycemia appear hours later?
The muscle keeps taking up glucose to replenish glycogen, and insulin-dependent uptake can stay raised for up to 48 hours (Colberg, 2016). Measuring glucose before bed on training days helps detect this drop.
Can people with retinopathy exercise?
Yes, with adjustment of intensity. In proliferative or severe nonproliferative retinopathy, vigorous effort may be contraindicated (ADA, 2025), and the ophthalmologic assessment guides the limit.
Can people with neuropathy in the feet walk?
In general, yes. Moderate walking with proper footwear may not increase the risk of ulcer (ADA, 2025). People who have already had an ulcer tend to benefit from exercises without load on the feet while they are being followed.
Take-home messages
- Exercise is treatment in type 2 diabetes and lowers A1c by a magnitude comparable to that of some drugs.
- Combined training, with aerobic and progressive strength work, has the best evidence for A1c.
- Walking after meals and breaking up sitting time reduce glucose peaks.
- The effect on insulin sensitivity lasts hours to days, which explains late hypoglycemia.
- Insulin and sulfonylurea call for glucose measurements, carbohydrate at hand and individual adjustment, without fixed numbers.
- Severe retinopathy limits vigorous effort, and neuropathy calls for proper footwear and daily foot inspection.
- The best prescription is the one the patient can keep up.
Play the case of the day on NEXO.
References
- Colberg SR, Sigal RJ, Yardley JE, et al. Physical Activity/Exercise and Diabetes: A Position Statement of the American Diabetes Association. Diabetes Care. 2016. PMID 27926890. DOI 10.2337/dc16-1728.
- Kanaley JA, Colberg SR, Corcoran MH, et al. Exercise/Physical Activity in Individuals with Type 2 Diabetes: A Consensus Statement from the American College of Sports Medicine. Med Sci Sports Exerc. 2022. PMID 35029593. DOI 10.1249/MSS.0000000000002800.
- American Diabetes Association Professional Practice Committee. 5. Facilitating Positive Health Behaviors and Well-being to Improve Health Outcomes: Standards of Care in Diabetes-2025. Diabetes Care. 2025. PMID 39651983. DOI 10.2337/dc25-S005.
- Pan B, Ge L, Xun YQ, et al. Exercise training modalities in patients with type 2 diabetes mellitus: a systematic review and network meta-analysis. Int J Behav Nutr Phys Act. 2018. PMID 30045740. DOI 10.1186/s12966-018-0703-3.
- Jansson AK, Chan LX, Lubans DR, et al. Effect of resistance training on HbA1c in adults with type 2 diabetes mellitus and the moderating effect of changes in muscular strength: a systematic review and meta-analysis. BMJ Open Diabetes Res Care. 2022. PMID 35273011. DOI 10.1136/bmjdrc-2021-002595.
- Engeroff T, Groneberg DA, Wilke J. After Dinner Rest a While, After Supper Walk a Mile? A Systematic Review with Meta-analysis on the Acute Postprandial Glycemic Response to Exercise Before and After Meal Ingestion in Healthy Subjects and Patients with Impaired Glucose Tolerance. Sports Med. 2023. PMID 36715875. DOI 10.1007/s40279-022-01808-7.
- Dunstan DW, Kingwell BA, Larsen R, et al. Breaking up prolonged sitting reduces postprandial glucose and insulin responses. Diabetes Care. 2012. PMID 22374636. DOI 10.2337/dc11-1931.
- Mueller MJ, Tuttle LJ, Lemaster JW, et al. Weight-bearing versus nonweight-bearing exercise for persons with diabetes and peripheral neuropathy: a randomized controlled trial. Arch Phys Med Rehabil. 2013. PMID 23276801. DOI 10.1016/j.apmr.2012.12.015.
- Gracia-Sánchez A, López-Pineda A, Nouni-García R, et al. Impact of Exercise Training in Patients with Diabetic Peripheral Neuropathy: An Umbrella Review. Sports Med Open. 2025. PMID 40517337. DOI 10.1186/s40798-025-00863-4.
- Bull FC, Al-Ansari SS, Biddle S, et al. World Health Organization 2020 guidelines on physical activity and sedentary behaviour. Br J Sports Med. 2020. PMID 33239350. DOI 10.1136/bjsports-2020-102955.