Optimal Blood Glucose Levels for Athletes: How to Fuel for Maximum Performance

Dec 16

As an athlete, managing your blood glucose levels is crucial to sustaining energy, optimizing performance, and ensuring quick recovery. Whether you're training for a race or pushing through a hard workout, understanding the ideal glucose levels for different types of exercise can help you avoid fatigue and enhance your performance.

The Role of Glucose in Performing

Glucose, the simplest form of sugar, is the primary fuel your body uses during exercise. It comes from the carbs you consume, which are broken down into glucose and stored as glycogen in your muscles and liver. During physical activity, especially intense or prolonged efforts like running and cycling, your body relies on these glycogen stores for energy.

Ideal Glucose Levels for Training

For most types of exercise, a blood glucose level between 90 and 120 mg/dL is considered optimal. This range suggests that your body is effectively processing and utilizing glucose for energy without the risk of a blood sugar crash. However, the ideal glucose level can vary depending on the intensity and duration of your workout.

For low-intensity exercise (such as light cycling or a recovery run), your body will primarily use fat for energy, with minimal reliance on glucose. Keeping your glucose level in the 90-120 mg/dL range ensures a steady supply of fuel without overloading the system.

During moderate-intensity exercise (like a zone 3 ride or longer run), your body will rely on a mix of glycogen and fat for fuel. Glucose levels in the 90-110 mg/dL range are ideal for maintaining energy throughout the session.

When engaging in high-intensity exercise, such as threshold work, sprinting or intervals, your muscles burn through glycogen quickly. In these situations, a higher blood glucose level is often required to support peak performance. Athletes aiming for maximum power output may target glucose levels between 130 and 180 mg/dL during hard efforts, especially during extended or intense training sessions. This elevated glucose ensures that your body has a readily available energy source to sustain high-intensity work.

Why Athletes Target Higher Glucose Levels for Harder Efforts

Higher glucose levels during intense efforts allow athletes to delay fatigue and maintain performance for longer. As glucose is the body’s preferred energy source for high-intensity activities, having an ample supply can help prevent glycogen depletion, which would otherwise lead to "hitting the wall" or muscle fatigue.

For elite athletes and those engaging in long races or challenging intervals, fueling with carbs during the workout—such as through energy gels, drinks, or snacks—can help maintain glucose levels in the 130-180 mg/dL range. This is especially important for efforts lasting more than an hour, where energy demands are high.

The Balance Between Too Much and Too Little

While higher glucose levels can be beneficial for intense efforts, it's essential to find a balance. Consuming too many carbs during a workout can lead to a rapid blood sugar spike and/or unused glucose. On the other hand, insufficient glucose levels may result in premature fatigue and suboptimal performance.

To optimize your glucose, aim to adjust your carb intake according to your effort and training goals. If you're planning an intense ride or interval session, aim for higher glucose levels to fuel performance. For lighter efforts, focus on a more moderate glucose level to maintain steady energy without overloading your system.

Fueling Your Workouts

The amount of carbohydrates an athlete should consume per hour during exercise depends on the intensity, duration, and the individual’s energy needs. However, general guidelines for carbohydrate intake during endurance exercise (such as cycling, running, or other aerobic activities) suggest the following:

General Carb Intake Guidelines:

For moderate to high-intensity exercise lasting 1-2 hours:
Athletes should aim for 30–60 grams of carbohydrates per hour to maintain glycogen stores and sustain energy levels during exercise.
For prolonged endurance efforts lasting 2-3 hours:
If exercise lasts longer than two hours, athletes should aim for 60–90 grams of carbohydrates per hour to continue fueling the body. This can be a combination of different types of carbohydrates, including glucose, fructose, and sucrose, to maximize absorption and energy availability.
For extreme or ultra-endurance events (over 3 hours):
Athletes may need to consume 90 grams of carbohydrates per hour or more, often in a mixed form (glucose and fructose, for example) to avoid gastrointestinal distress and optimize absorption. This level of carbohydrate intake helps to prevent glycogen depletion and maintain blood glucose levels during long events like marathons, ultra-races, or multi-hour bike rides.

Why Carb Intake is Important:

Glycogen Stores: During prolonged or intense exercise, glycogen (stored carbohydrate) is the primary fuel source for muscles. When glycogen stores begin to deplete, performance can drop significantly, leading to fatigue and reduced endurance. Consuming carbs during exercise helps replenish these stores and provides sustained energy.
Blood Sugar Maintenance: Consuming carbs also helps maintain blood glucose levels, preventing a dip that could lead to hypoglycemia (low blood sugar), which can cause dizziness, weakness, and a lack of energy.
Absorption Rates: The body can only absorb about 60-90 grams of carbohydrates per hour during exercise. This is why it’s recommended to consume carbs in smaller doses throughout the activity, rather than all at once. Some athletes use a mix of different carb types (such as glucose and fructose) to enhance absorption and minimize digestive discomfort.

Types of Carbs:

To optimize carbohydrate intake during exercise:

Glucose (found in sports drinks, gels, and energy bars) is absorbed quickly and provides fast energy.
Fructose (found in fruits and some gels) is absorbed more slowly but can complement glucose for better overall absorption when combined.
Sucrose (table sugar) is a combination of glucose and fructose and can be used for sustained energy release.

Practical Tips:

Start early: Begin consuming carbohydrates early in your workout (within the first 30 minutes) to ensure you're topping off glycogen stores before they dip too low.
Use easily digestible forms: Simple carbs like sports drinks, gels, and chews are good options for quick digestion during intense activity.
Test during training: It’s important to experiment with carbohydrate intake during training to find the right amount and types that work for your body, as too much or too little can cause discomfort.

Jeukendrup, A. E. (2014). Carbohydrate intake during exercise and performance. Nutrition, 30(1), 9-14.
This study discusses the importance of carbohydrate intake during exercise, particularly for endurance sports like cycling, to maintain blood glucose levels and support energy needs during prolonged or intense activity.
Coyle, E. F. (2004). Fluid and fuel intake during exercise. Journal of Sports Science & Medicine, 3(1), 1-7.
Coyle’s research explains how glucose and glycogen are used as energy sources during endurance exercise and how proper fueling can prevent fatigue and optimize performance during high-intensity efforts.
Bishop, D., Jones, E., & Woods, D. R. (2004). Recovery from training: A brief review. Journal of Strength and Conditioning Research, 18(3), 331-336.
This paper highlights the significance of blood glucose levels in post-exercise recovery and how they contribute to glycogen resynthesis and recovery in athletes, particularly in endurance sports like cycling.

Joe Sulak