Type 2 Diabetes and Endurance Exercise: A Complete Analysis of Blood Glucose Response Mechanisms and Pre-/Post-Exercise Precautions

Medical Disclaimer: This article is a compilation of health education information intended to help people with type 2 diabetes understand the general relationship between exercise and blood glucose. It does not constitute a medical diagnosis, treatment recommendation, or instruction for medication adjustment. The types of diabetes medications, dosages, and exercise prescriptions vary greatly between individuals. You must discuss these with an endocrinologist, metabolism specialist, or diabetes educator before acting on this information, and never adjust your medication or insulin dosage on your own. If you have complications such as retinopathy, nephropathy, peripheral neuropathy, or cardiovascular disease, your exercise plan must be individually assessed by a physician.

Why People with Diabetes Are Especially Concerned About Exercise

The popularity of road cycling and road running in Taiwan has continued to grow in recent years. Many middle-aged cyclists only start exercising seriously after their health check reports show “elevated HbA1c” or “abnormal fasting blood glucose.” This sequence is actually quite common: years of sedentary office work, frequent social engagements, lack of exercise habits, combined with family history, make type 2 diabetes one of the most common metabolic diseases among Taiwan’s middle-aged population. And exercise has long been regarded as one of the three pillars of diabetes care, alongside medication and diet.

But the statement “exercise helps diabetes” is simple to say, yet involves many details in practice. Blood glucose is not a steadily declining curve; it fluctuates based on exercise intensity, exercise duration, the type of medication currently in effect, meal timing, and even weather and mood. For people simply trying to maintain good health, these fluctuations may not matter much; but for patients on medication—especially those using insulin or sulfonylureas—hypoglycemia during or after exercise is a risk that must be taken seriously.

The purpose of this article is not to teach you how to “treat” diabetes, nor to tell you how much medication to take or how many units of insulin to inject—only your physician, who knows your complete medical history, kidney function, cardiac status, and medication history, can make safe judgments on these matters. What we will discuss are the general mechanisms of “why blood glucose responds the way it does” in exercise physiology, as well as the principles you can proactively observe and prepare for before, during, and after exercise, so that when you discuss exercise prescriptions with your medical team, you can ask better questions and better understand the advice your physician gives.

The General Mechanism of Blood Glucose and Exercise: Muscles Are the Largest Sink for Blood Glucose

To understand how exercise affects blood glucose, you first need to know where blood glucose comes from and where it goes. Glucose in the blood comes primarily from the digestion of carbohydrates in food, as well as from glycogen released by the liver. As for where blood glucose goes, besides being used as energy by various organs, skeletal muscle is one of the body’s largest glucose-utilizing tissues, and this characteristic is amplified during exercise.

During exercise, muscle cells increase glucose uptake through two pathways: one is the insulin-stimulated pathway, and the other is the pathway stimulated by muscle contraction itself, which is relatively less dependent on insulin. This is why exercise is considered particularly meaningful for type 2 diabetes—one of the core problems in type 2 diabetes is the body’s diminished response to insulin, known as “insulin resistance,” and regular exercise is believed to help improve peripheral tissue sensitivity to insulin, allowing the same amount of insulin to achieve a better blood-glucose-lowering effect.

This improvement at the mechanistic level is generally believed not to be achieved through a single exercise session for long-term effect, but rather requires adaptive changes accumulated through regular, sustained exercise. A single one-hour bike ride has an immediate effect on current blood glucose, but long-term improvements in insulin sensitivity take weeks to months of regular exercise habits to gradually appear, and the effect diminishes when the exercise habit is interrupted. This is why diabetes care typically emphasizes “regular” rather than “occasional” exercise patterns.

Aerobic Exercise and Blood Glucose: In Most Cases, Blood Glucose Decreases

For moderate-intensity, longer-duration aerobic exercise such as steady cycling, jogging, or brisk walking, blood glucose is generally observed to gradually decrease during the exercise session. This is because muscles continuously consume glucose, and increased insulin sensitivity allows glucose to be delivered into muscle cells more easily. For patients not using medications that readily cause hypoglycemia (such as insulin or sulfonylureas), this decrease is usually within a safe range; but for patients using such medications, if blood glucose is already low before exercise and they engage in prolonged aerobic exercise, the risk of hypoglycemia increases significantly.

High-Intensity Exercise and Blood Glucose: A “Paradoxical Rise” May Occur

One point worth special explanation is that not all exercise lowers blood glucose. High-intensity, explosive exercise (such as all-out sprints or high-intensity intervals in interval training) stimulates the body to release stress hormones such as adrenaline, which prompt the liver to release more glycogen into the bloodstream, potentially causing blood glucose to “rise rather than fall” in the short term. This phenomenon is relatively easy to observe in diabetic patients using continuous glucose monitoring (CGM): after high-intensity interval training, the glucose curve sometimes rises for a period before slowly coming back down.

The practical significance of understanding this mechanism is: if you originally assumed “exercise will definitely lower blood glucose,” and you see your glucose number actually rise after a high-intensity interval session, there is no need to panic excessively, nor does it mean the exercise was “ineffective” or “done wrong”—this is one of the normal physiological responses involving stress hormones. But it also reminds us that the choice of exercise intensity and monitoring methods should ideally be included in discussions with your medical team, rather than applying a single formula on your own.

Delayed Post-Exercise Hypoglycemia: A Frequently Overlooked Risk

Another concept particularly important for patients on medication is “delayed post-exercise hypoglycemia.” This refers to blood glucose potentially dropping to low levels several hours after exercise ends, or even the next day. The reason is related to muscles and the liver continuously replenishing glycogen stores after exercise—the body keeps “borrowing” glucose from the bloodstream to refill the glycogen depleted during exercise, and this process can continue for more than a dozen hours after exercise ends.

This means: after an evening long ride, the hypoglycemia risk does not end just because you finish riding and your glucose reading is fine. The middle of the night or early the next morning can also be risk periods. This is especially important for patients using insulin or sulfonylureas. Bedtime and early-morning glucose monitoring, as well as carbohydrate planning for dinner on exercise days, should all be discussed with your physician or diabetes educator to develop a personalized approach.

Before Exercise: It’s Not as Simple as “Eat Enough and Go”

General Principles of Blood Glucose Monitoring

If you monitor your blood glucose, most patient education materials recommend checking before exercise to confirm that your glucose is within a relatively safe range—both too low and too high are unsuitable for immediately starting exercise. However, the specific cutoff values will differ depending on the type of medication you use, your personal history of hypoglycemia, and how long you’ve had diabetes. Be sure to ask your medical team for a reference range specific to you, and do not blindly copy generic numbers you see online.

When blood glucose is too high (especially when ketones are also present—more common in type 1 diabetes, but patients with type 2 diabetes and chronically poor glucose control should also be cautious), exercising rashly may actually cause blood glucose and ketones to rise further. This is why the intuitive idea of “if my glucose is high, I’ll exercise more to bring it down” is not always a safe approach; you must first confirm whether you are at risk of ketoacidosis.

Coordinating Medication Timing with Exercise Timing Is Within the Physician’s Professional Judgment

Many diabetes patients’ medication schedules are designed around meals—for example, some medications are recommended to be taken before meals, and certain insulins have their peak effect at a specific time after injection. If you habitually exercise at a fixed time that happens to fall near the medication’s peak effect, the risk of hypoglycemia increases. Whether this requires adjusting medication timing, dosage, or shifting your exercise time falls within the physician’s professional judgment. This article makes no recommendations on this matter, and please do not change the timing or dosage of your prescribed medication on your own. What you can do is clearly tell your physician “what time you usually exercise, how long you typically exercise, and roughly what intensity,” so the physician can give you personalized advice based on that information.

Carry Enough Supplies to Handle Hypoglycemia at All Times

Regardless of your medication regimen, as long as you use medications that can potentially cause hypoglycemia, for prolonged outdoor exercise (such as long climbs like Wuling or Beiyi, or participating in half marathons or full marathons), it is recommended to carry sufficient, rapidly absorbable carbohydrate supplies—such as sports drinks, gels, or candy—and to let your riding or running companions know that you have diabetes and how they can assist you if hypoglycemia occurs. In Taiwan, the distance between aid stations on long climbing routes can be very long; if hypoglycemia strikes and no supplies are available, the risk is amplified. This is also a factor worth considering when planning your route.

During Exercise: Pay Attention to Your Body’s Signals, Don’t Push Through

Beyond the physical fatigue you feel during exercise, early signs of hypoglycemia include trembling hands, cold sweats, heart palpitations, dizziness, difficulty concentrating, sudden intense hunger, and mood changes (irritability or feeling dazed). During exercise, these symptoms can easily be mistaken for “the normal fatigue of high-intensity training,” especially for patients who are new to exercise and not yet familiar with their body’s responses.

There’s a common saying in the endurance sports community: “Better safe than sorry.” This means that if you suspect you might be experiencing hypoglycemia, treat it as hypoglycemia first—stop, consume fast-acting carbohydrates, rest and observe, rather than continuing to push through your training plan or race pace. If a diabetic patient experiences severe hypoglycemia during exercise, they may develop confusion, seizures, or even coma. This is an extremely dangerous situation on a downhill bike ride or on a remote road with few people around. Safety must always be the top priority.

If you use a continuous glucose monitoring (CGM) device, observing the glucose trend arrow (rising, steady, falling) during exercise is more informative than looking at a single number, because it reflects the rate of change and can help you detect a rapid drop in blood glucose earlier.

After Exercise: Don’t Overlook Delayed Hypoglycemia and Wound Care

As mentioned earlier, the risk of post-exercise hypoglycemia can persist for more than a dozen hours afterward. This is especially important for patients who plan evening workouts or participate in long-distance events that require an early start (such as marathons that begin at dawn or long cycling expeditions). For post-exercise meals and bedtime blood glucose monitoring arrangements, it is recommended to discuss with your medical team and develop a plan that works for you.

Additionally, diabetic patients often have peripheral neuropathy or poor peripheral circulation, which can dull the sensation of pain and friction in the feet. Blisters and abrasions caused by long hours of cycling or running, if not detected and properly cared for in time, may heal more slowly than in non-diabetics and are more prone to becoming infected. After exercise, check your feet (especially for runners). If you find any wounds, clean them promptly and seek medical attention as appropriate. Don’t dismiss them just because they “don’t hurt.”

Choosing the Type of Exercise: No Standard Answer, But There Are Principles to Follow

Aerobic exercises with low joint impact, such as cycling, walking, and swimming, are often considered suitable for diabetic patients who also have peripheral neuropathy, joint degeneration, or a higher body weight, because they can reduce the risk of injuries related to weight-bearing on the feet. Road running involves greater repeated impact on the feet. If combined with peripheral neuropathy that dulls foot sensation, running can more easily cause unnoticed foot injuries. Whether such patients are suitable for road running, and how to progressively arrange running volume, should be discussed with a physician and physical therapist.

Resistance training (weight training) has gradually come to be regarded as equally important as aerobic exercise in recent diabetes care concepts, because increasing muscle mass helps improve the body’s overall ability to utilize glucose. However, the common breath-holding with effort (Valsalva maneuver) during resistance training may increase risk for patients with retinopathy or hypertension. The choice of training methods and intensity should also be discussed with your physician before proceeding.

In These Situations, “Stop Exercising Immediately and Seek Medical Attention”

If any of the following occurs during or after exercise, stop immediately, and seek assistance or go to the hospital as needed. Do not push yourself to finish the workout or race:

• Altered consciousness: Sudden confusion, giving irrelevant answers, disorientation, or even coma.
• Severe hypoglycemia symptoms: Extreme cold sweats, severe hand tremors, blurred vision, inability to eat or swallow on your own.
• Chest pain, tightness, or pressure: Especially when accompanied by cold sweats, nausea, or radiating pain to the left arm or jaw.
• Significant difficulty breathing: Gasping for air, unable to speak in full sentences.
• Abnormal heart palpitations: Feeling a violent irregular heartbeat, accompanied by dizziness or a feeling of nearly fainting.
• Sudden vision changes: Black spots in front of the eyes, visual field defects, worsening blurred vision (possibly related to retinopathy).
• Severe pain in the foot or calf accompanied by pallor and coldness: May be related to peripheral vascular issues.
• Wounds with redness, swelling, heat, pain, pus, or fever: May be a sign of infection. Diabetic patients are at higher risk of infection because their wounds heal more slowly.
• Recurrent hypoglycemia: Even if symptoms are not severe, if they recur repeatedly within the same week, it is advisable to return to your doctor early to adjust your plan, rather than enduring it on your own or self-adjusting your medication dosage.

For any of the above, prioritize ensuring your own safety first (e.g., pull over to the side of the road, find a shaded place to rest), call 119 or ask a companion for help getting to the hospital as appropriate. Never force yourself to continue just because “the training plan isn’t finished” or “the race isn’t over.”

Why Different Types of Glucose-Lowering Medications Have Different Exercise Risks (Mechanism Only, Not Medication Advice)

Many diabetic patients who are new to exercise have a question: “My friend also has diabetes and also cycles. Why doesn’t he need to supplement sugar, but I often get trembling hands and cold sweats halfway through a workout?” The answer is often related to the different types of medications each person uses. This section only discusses general pharmacological mechanisms as common knowledge. It does not involve any recommendations on dosage or type selection. Actual medication use should follow your physician’s prescription.

Some diabetes medications work by stimulating the pancreas to secrete more insulin. These medications may continue to promote insulin release even when blood glucose is already low. Therefore, when combined with exercise, the risk of hypoglycemia is relatively higher, especially during fasted exercise or prolonged workouts. Insulin preparations follow a similar logic—insulin injected into the body does not automatically stop working when blood glucose drops, and exercise increases muscle glucose uptake. When these two factors combine, the risk of hypoglycemia is amplified.

In contrast, other diabetes medications work through mechanisms not directly related to insulin secretion, such as affecting the gut hormone pathway or altering how the kidneys process glucose. When used alone, these medications generally have a lower chance of causing hypoglycemia. However, when multiple medications are combined, the risk profile becomes more complex and difficult to generalize.

The table below summarizes the general mechanistic association between several common classes of diabetes medications and hypoglycemia risk. It is intended only for conceptual understanding and is not a basis for medication selection. Actual medication use should strictly follow your physician’s prescription:

Again, this table only illustrates the mechanistic concept of “why different people have different blood glucose responses during exercise.” It absolutely cannot be used as a basis for concluding “my medication is safer, so I don’t need to prepare supplies.” Everyone’s actual medication combination, dosage, and medical history are different. Please rely on your physician’s individual assessment and guidance.

This is also why “my friend’s experience with diabetes medication” cannot be directly applied to you—even if you both have the same diagnosis of type 2 diabetes, different people have different medication combinations, disease durations, and complication profiles, so blood glucose responses during exercise will naturally differ. Rather than comparing yourself to others, it is more practical to record your own blood glucose numbers after actual exercise and bring them to your follow-up visits to discuss with your physician. This is the most reliable way to build a safe exercise routine that works for you.

Additional Considerations for Diabetic Exercisers in Taiwan’s Climate and Terrain

The Double Burden of Summer Heat and Humidity

Taiwan’s common hot and humid summer environment places an additional physical burden on anyone exercising, and for people with diabetes, there are two further considerations. First, some people with diabetes also have autonomic neuropathy, which can affect sweat regulation and body temperature control, making them more prone to heatstroke or heat injury in high-temperature environments, and the warning signs may be less obvious than in the general population. Second, dehydration itself causes the glucose concentration in the blood to become relatively “concentrated,” meaning that even without consuming extra carbohydrates, blood glucose readings may run high in a dehydrated state. This means that during long summer rides or runs, hydration strategy and blood glucose monitoring need to be considered together—you cannot focus on only one.

It is recommended that during periods of extreme heat (for example, when the perceived temperature exceeds 35°C for extended periods) in the afternoon, you prioritize exercising in the cooler early morning or evening hours and increase the frequency of hydration. If you plan to tackle long climbing routes toward Wuling or the Hehuan Mountain area, temperatures will gradually drop as you gain elevation, and the diurnal temperature range and perceived changes are significant. These long-duration, high-intensity routes that cross multiple climate zones carry higher risk for people with diabetes who have unstable blood glucose control or cardiovascular risk than riding on flat terrain. It is recommended that you first discuss with your physician whether such routes are suitable and prepare thoroughly for hypoglycemia before taking on the challenge.

Plum Rain, Northeast Monsoon, and Flexibility in Training Schedules

Taiwan’s plum rain season at the turn of spring and summer, and the northeast monsoon in autumn and winter, frequently disrupt planned outdoor training schedules. For people with diabetes who have established a stable pattern between medication timing and exercise habits, weather-forced rescheduling (for example, moving an evening long ride to the next morning, or replacing an outdoor route with an indoor trainer session) can also affect the predictability of blood glucose responses. It is recommended that during seasons of unstable weather, you moderately increase the frequency of blood glucose monitoring, especially on days when your exercise timing changes, to observe whether your body’s response to “exercise at different times of day” remains consistent.

Common Misconceptions: These Statements Are Not Entirely Correct

Misconception 1: “The lower the blood glucose, the better—exercise is meant to push blood glucose down.”
This idea is dangerous. The goal of diabetes care is to keep blood glucose within a relatively stable range and avoid large fluctuations, not simply to chase the lowest possible number. Exercise-induced hypoglycemia, especially severe hypoglycemia, poses a risk of harm to the body (particularly the brain) no less than chronic hyperglycemia. Both must be avoided; you cannot focus on only one end of the spectrum.

Misconception 2: “As long as I exercise, I can reduce my medication on my own.”
Exercise can indeed improve insulin sensitivity, and over the long term, some patients’ medication needs may be adjusted—but this decision must be made by your physician based on your blood glucose monitoring data and HbA1c follow-up results. It is absolutely not something you decide on your own because “my blood glucose numbers have been good lately” and then reduce or stop your medication. Self-adjusting medication downward can lead to loss of glycemic control and increase the long-term risk of complications; improperly increasing medication on your own can trigger severe hypoglycemia.

Misconception 3: “Fasted exercise burns fat better, and this applies to people with diabetes too.”
Fasted aerobic exercise has both proponents and controversy among the generally healthy population, but for people with diabetes who are using medications that can cause hypoglycemia, fasted exercise significantly raises the risk of low blood glucose because there is no dietary source in the body to buffer the decline in blood sugar. Whether this type of exercise arrangement suits you must be discussed with your physician first.

Misconception 4: “If my blood glucose is normal right after exercise, that means there is no hypoglycemia risk today.”
As mentioned earlier, delayed hypoglycemia after exercise can occur several hours after the workout ends or even the next day. A normal blood glucose reading immediately after exercise does not mean the entire risk window has passed; evening and pre-bedtime monitoring remain important.

Building Your Own Exercise and Blood Glucose Recording Habit

For people with diabetes, rather than chasing some “standard exercise prescription,” a more practical approach is to build your own observation and recording habit. This can include: blood glucose before exercise, exercise type and intensity, exercise duration, whether any discomfort symptoms occurred during exercise, immediate and delayed (several hours later) blood glucose changes after exercise, and that day’s medication and food intake. These records do not need to be complicated; the key is consistent accumulation and bringing them to your follow-up appointments for your physician’s reference. Over time, you will gradually figure out “which intensity, which time of day, and what kind of fueling strategy is safest and feels best for me.” This answer often varies from person to person—others’ experiences are only for reference, not for copying.

For people with diabetes who are just starting cycling or road running, it is recommended to begin in environments where intensity is easier to control and you can stop at any time (such as riverside bike paths or running tracks). After accumulating sufficient self-observation experience, you can gradually challenge routes and activities of higher intensity or more demanding environments, progressing step by step and avoiding tackling long-duration, high-intensity segments with limited fueling options from the start.

Common Exercise Scenarios and Key Considerations

The table below summarizes common endurance exercise scenarios for people with diabetes in Taiwan as a reference framework for discussion with your medical team—it is not a prescription to be executed on your own:

Working with Your Medical Team, Not Going It Alone

Ideally, the exercise prescription for diabetes should be a collaborative process: your physician understands your overall condition and medications, the diabetes educator helps you understand blood glucose monitoring and dietary pairing, and you are responsible for honestly recording and reporting your exercise habits, blood glucose changes, and any discomfort symptoms. The closer this collaboration, the more stable and safer the benefits exercise can bring you.

In Taiwan, many medical centers and regional hospitals offer diabetes education clinics or integrated metabolic syndrome clinics. If you are seriously planning to commit to cycling or road running training, proactively tell your medical team about this plan so they can provide personalized exercise recommendations based on your complete medical history (including kidney function, cardiac function, retinal examination results, peripheral neuropathy assessment, etc.), rather than relying on general principles from an internet article and figuring things out on your own.

Key Takeaways

• The long-term benefits of exercise for type 2 diabetes are generally understood to come from regular exercise improving insulin sensitivity, which requires sustained accumulation rather than immediate results.
• Moderate-intensity aerobic exercise typically lowers blood glucose, but high-intensity exercise may cause a temporary rise due to stress hormones—this is a normal physiological response.
• The risk of post-exercise hypoglycemia can be delayed by several hours or even until the next day; be sure to discuss pre-bedtime and post-exercise monitoring arrangements with your medical team.
• The coordination of medication timing, dosage, and exercise schedules falls within the physician’s professional judgment—any medication adjustment should never be decided on your own.
• For prolonged outdoor activities, always carry an adequate supply of fast-absorbing carbohydrate fuel, and let those around you know your condition and emergency procedures.
• If warning signs such as altered consciousness, severe hypoglycemia symptoms, chest pain or tightness, difficulty breathing, or sudden vision changes occur, stop exercising immediately and seek medical attention.
• The choice of exercise type (cycling, road running, resistance training, etc.) should take into account whether you have coexisting complications such as peripheral neuropathy, retinopathy, or cardiovascular disease; it is recommended to plan this together with your physician and physical therapist.

Reminder: This article is for health education purposes only, intended to help readers understand the general physiological mechanisms between exercise and blood glucose. It cannot replace your physician’s professional evaluation and medical advice specific to your condition. For any medication adjustments or exercise prescription planning related to diabetes, be sure to discuss thoroughly with your physician and diabetes educator at your follow-up visits before proceeding. If any of the aforementioned warning signs occur during exercise, prioritize your personal safety above all—stop immediately and seek medical attention as soon as possible.

Related Reading

• Exercise and Blood Sugar Control: Exercise as Medicine for Diabetes — Coaches Turn “Movement” into a Prescription
• Nutrition Management for Diabetes and Exercise: A Coach’s Practical Notes on Blood Sugar, Carbohydrate Adjustments, and Hypoglycemia Prevention
• Cycling and Diabetes Management: The Science of Riding for Blood Sugar Control and Insulin Sensitivity
• Cycling Strategies for People with Diabetes: Stabilizing Your Blood Sugar Curve with Pedaling