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Physical Exercises & Hypoglycemia

author image Heather Hitchcock
Heather Hitchcock has been writing professionally since 2010. She has contributed material through various online publications. Hitchcock has worked as a personal trainer and a health screening specialist. She graduated from Indiana University with a Bachelor of Science in exercise science.
Physical Exercises & Hypoglycemia
Runner in a snowy field Photo Credit: Purestock/Purestock/Getty Images

Hypoglycemia, or low-blood sugar, occurs when blood glucose levels drop below normal, which is 70 mg/dL. When this occurs, you may become shaky, nervous, confused, dizzy or light-headed, weak or have trouble speaking. Hypoglycemia can occur in anyone and is often an issue in individuals performing long amounts of physical exercise that last more than one hour.

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Effects Of Hypoglycemia

In most cases, hypoglycemia is mild and can be treated quickly by eating or drinking a small amount of glucose-rich food such as fruit juice or honey. Hypoglycemia often occurs quickly and, if left untreated, it can result in confusion, clumsiness or fainting. Severe hypoglycemia can lead to seizures, coma and even death, according to the National Diabetes Information Clearinghouse. However, hypoglycemia can be prevented by planning the timing of your meals appropriately before, during and after exercise.

Muscle Glycogen

Muscle glycogen is the main energy source used during exercise, and depletion of these levels is often a leading cause of fatigue and exhaustion in exercise lasting more than an hour. Distance runners, cyclists and triathletes who exercise for several hours at a time often practice glycogen loading or carb loading. Glycogen loading is when the athlete consumes a carbohydrate-rich meal the days and hours prior to the event. This practice ensures that the muscles are full of glycogen and reduces the risk of developing hypoglycemia.


In endurance sports, performance can be enhanced and hypoglycemia prevented when carbohydrates are consumed within five minutes of when the exercise begins or more than two hours before exercise. An athlete should not ingest carbohydrate foods during the period 15 to 45 minutes before exercise, because it may cause hypoglycemia shortly after exercise begins, according to Jack H. Wilmore and David L. Costill, authors of "Physiology of Sport and Exercise." This occurs because glucose is absorbed into the muscles at a very high rate, resulting in low-blood sugar.

During Exercise

Individuals performing physical exercise lasting more than an hour can prevent hypoglycemia by ingesting carbohydrates during exercise, usually in a gel or liquid form. Several studies have shown that performance improves when individuals are given carbohydrate feedings in regular intervals during exercise lasting one to four hours, according Wilmore and Costill.


After a long bout of exercise, there is still a risk of developing hypoglycemia several hours after the workout. This occurs because your glycogen levels are low following exercise and need to be replenished. Muscle glycogen can be restored right after exercise with an adequate amount of carbohydrate intake to prevent low blood sugar. The period in the first 30 to 60 minutes after exercise is the critical time when your muscles can take up glucose without much need for insulin, according to Sheri Colberg, Ph.D., FACSM.

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