What is energy and why are carbohydrates unique?

In any biological process, energy is present in the form of ATP (adenosine triphosphate), the "energy currency" of our cells that powers muscle contractions and all bodily functions. When it comes to fuel choice, carbohydrates are unique for several reasons:

Anaerobic Metabolism: Unlike fats, carbohydrates can be processed to produce ATP without the need for oxygen. This is vital in high-intensity situations or when blood flow (and thus oxygen) is restricted.
Oxygen-Rich: Carbohydrates are oxygen-rich molecules (they contain six oxygen molecules per carbohydrate oxidized), making them more efficient in using available oxygen.
Speed of Reaction: They require fewer reactions to replenish ATP compared to fats when metabolized aerobically, meaning a faster energy supply.

Carbohydrates and the climber: a critical link

The intensity and duration of exercise determine the amount of ATP required. Climbing, with its explosive movements, isometric holds, and sustained efforts, demands a large amount of ATP. This is where carbohydrates shine, especially in the forearms.

During climbing, isometric contractions (like gripping a hold tightly or locking off a move) can cut off blood flow to the muscles by up to 40-60% of maximal voluntary contraction. Without blood, there’s no oxygen. In this scenario, carbohydrates allow muscles to keep functioning and generating energy anaerobically.

Additionally, carbohydrate oxidation provides about 10% more energy per liter of oxygen than fat oxidation. This means carbohydrates reduce the oxygen demand for a given power output—a critical factor when oxygen supply is limited, as in the forearms during a "pump."

The "anabolic window" and energy systems

It’s important to understand that energy systems don’t switch on and off sequentially. Rather, they work in overlap. Aerobic metabolism is always in use, but as intensity increases and ATP demand exceeds oxygen supply, anaerobic systems (like phosphocreatine and anaerobic glycolysis, which uses carbohydrates) increase their contribution. In high-intensity climbing, you may be using 100% of all systems at their maximum capacity for short periods.

The post-training "anabolic window" for glycogen replenishment is not as strict as once thought, though adequate total intake throughout the day is more important. Recovery from post-exercise oxygen debt (EPOC), which can take hours or days, is also accelerated by greater oxygen use efficiency, which carbohydrates facilitate.

Glycogen: your carbohydrate reserves

Carbohydrates are stored in the muscles and liver as glycogen, long chains of glucose molecules.

Muscle glycogen is used locally and cannot leave the cell where it’s stored.
Liver glycogen is crucial for maintaining blood glucose levels, especially during fasting.

An average person can store between 300 and 600 grams of glycogen in the body. Notably, each gram of glycogen is stored with about 3 grams of water. That’s why a low-carb diet can result in rapid initial "weight loss" (5-10 pounds in a week), which is mostly water, not fat. Losing this water weight can affect thermoregulation and muscle hydration.

An interesting point for climbers is that, although forearm glycogen is limited (perhaps 10-15 grams per arm), lactate produced anaerobically can be transported to other parts of the body to be converted back into glucose (Cori cycle) and reused by the muscles that need it, including the forearms during rest periods.

Common myths about carbohydrates

Carbohydrates are often the subject of fear and misinformation. Let’s clarify some of the most persistent myths:

They Cause Insulin Resistance: This is false. Insulin resistance develops mainly from weight gain and excess body fat, not from carbohydrate consumption itself. In fact, exercise improves insulin sensitivity, as muscle contractions can activate glucose transporters independently of insulin.
They Are More Fattening (De Novo Lipogenesis): The conversion of carbohydrates into body fat (de novo lipogenesis) is an energetically costly process for the body. It’s much easier to store fat directly from the diet. For the body to start converting carbohydrates into fat significantly, extreme caloric surpluses are needed (e.g., >1000g of carbs per day). It’s "almost impossible" for an active person to turn dietary carbs into fat.
They Are Inflammatory: There is no scientific evidence that carbohydrates are inherently inflammatory. Pro-inflammatory diets are usually those high in processed foods, refined sugars, and low in anti-inflammatory nutrients (unlike a Mediterranean diet). In fact, for athletes, adequate carbohydrate intake is anti-inflammatory, modulates the immune system, and aids recovery, especially in intense training.

Practical application for climbers

Adequate carbohydrate nutrition is fundamental for climbers. Here are some practical guidelines:

1. General daily intake:

For moderate to high-intensity training: 5 to 7 grams of carbohydrates per kilogram of body weight per day (about 300-500g for a 65 kg climber).
For low-intensity or technique/mobility-focused days: 3 to 5 grams per kilogram per day (about 200-300g).
It can also be expressed as 40-75% of total dietary calories, varying by climbing type (bouldering vs. sport vs. multi-pitch).

2. Carbohydrate periodization:

During very intense training blocks or overreaching, increasing intake to 7-10 grams per kilogram per day can reduce overtraining symptoms, increase training volume, and improve recovery.

3. Intake during exercise:

For training or climbing sessions longer than 1.5 hours, it’s recommended to consume 30-60 grams of carbohydrates per hour. This improves concentration, muscle excitability, and performance.
Even small amounts (e.g., 15g of carbs from a cookie) can improve work volume by reducing fatigue.
Rinsing the mouth with a sugary drink (without swallowing) has been shown to improve performance by sending signals to the brain—useful in specific situations like competitions or restrictive diets.

4. Event/competition days:

In the days prior, be sure to "load" your glycogen stores by consuming the upper end of your recommended daily intake (7-10 g/kg/day if needed). This is more effective than traditional "carb loading" for endurance athletes.
On event day: Consume 3-4 grams of carbohydrates per kilogram of body weight 3-4 hours before, and 1-2 grams per kilogram 1 hour before.
During competition, drink sports drinks providing 45-60 grams of carbohydrates per hour, especially if it’s a long or multi-round event. Caffeine can enhance glycogen recovery and performance.
Always experiment! Never try a new nutrition strategy on competition day. Practice your fueling strategies and carb types in advance to avoid GI issues and optimize performance.
It’s usually recommended to compete with an "almost empty" stomach, eating solid foods 2-4 hours before and then only simple liquids.

5. Carbohydrate quality:

Prioritize whole food carbohydrate sources like fruits, vegetables, legumes, potatoes, sweet potatoes, and rice. These provide fiber and other beneficial nutrients. Supplements (shakes, gels) are useful for convenience during long sessions but shouldn’t replace a diet rich in whole foods.

Additional considerations

Reactive Hypoglycemia: Some people may experience a sharp drop in energy after consuming simple sugars. This is highly individual and less likely to occur during exercise due to glucose release from muscle contraction.
Diabetics: For people with diabetes, it’s suggested to exercise in the mid-postprandial period (30-90 minutes after eating) to help manage blood glucose levels. (Warning: This is not medical advice. People with diabetes should consult a qualified health professional.)
Women and Menstrual Cycle: Women may use carbohydrates differently during their cycle. In the follicular phase (first two weeks, high estrogen), they may be more glycolytic and better utilize carbs for power. In the luteal phase (high progesterone), they may shift to greater fat use.
Chronic Caloric Deficit in Elite Climbers: A study found that 40% of elite climbers consumed less than 2500 kcal/day, very low for their training demands. Many climbers, even professionals, may be under-fueled, limiting performance and recovery. Increasing caloric and carbohydrate intake can lead to significant increases in training volume and intensity, better recovery, and greater adaptation.

Carbohydrates are much more than just an energy source; they are a strategic tool for recovery, performance, and immune health in climbers. Experiment with these guidelines and feel the difference in your climbing!

Carbohydrates: The Essential Energy Source for Climbers