Category: Exercise physiology

Approximately 80% of the body's total glycogen is stored in the skeletal muscles, making it a critical fuel during physical activity. This article explains how carbohydrates are used in exercise, empowering you to optimize your nutrition for peak performance, regardless of your sport or training goals.

Approximately 75% of your body's total glycogen is stored in the muscles, with the remainder primarily in the liver. When answering the question, 'Does glycogen replenish overnight?', it's crucial to understand that while some replenishment occurs, complete restoration of muscle glycogen after heavy depletion often requires more than just a single night's rest.

For most athletes, muscle glycogen can be fully restored within approximately 24 hours under optimal nutritional conditions. However, this timeline is highly variable depending on the intensity of exercise, individual metabolism, and, most importantly, dietary strategy. Understanding how long does it take to restore glycogen stores is essential for maximizing recovery and performance in subsequent training sessions or competitions.

Glycogen, often referred to as 'animal starch,' serves as the primary storage form of glucose in humans and other vertebrates, with the liver and skeletal muscles being its main depots. Its branched structure allows for rapid breakdown, providing a quick energy source when blood glucose levels drop or during periods of intense physical activity.

The human body is capable of recycling its entire body weight in ATP each day to support essential functions and muscle activity. When it comes to fueling exercise, our muscles rely on a complex and dynamic system that can quickly produce energy, but what do muscles use as the primary source of energy? The answer depends heavily on the intensity and duration of the physical activity.

Over 90% of the body's stored energy is in the form of triglycerides within adipose tissue, but a significant and readily accessible portion is also stored directly within muscle fibers. This fuel depot, known as intramuscular triglycerides (IMTGs), is a crucial energy source during prolonged exercise, with its usage varying based on exercise intensity, duration, and an individual's training status.

During high-intensity exercise, the body’s muscle glycogen stores are the primary fuel source, and for a well-trained individual, these reserves can be significantly reduced in as little as 90 to 120 minutes. The exact timeline, however, is a complex interplay of intensity, nutrition, and training status.

Over three-quarters of the body's total glycogen, the stored form of glucose, is found in the muscles, highlighting its importance as a local fuel source for physical activity. This storage is critical for meeting the high energy demands of muscle contraction.

During a fast, the body primarily relies on liver glycogen to maintain stable blood glucose levels for the first 24 hours, depleting those stores before looking elsewhere for fuel. So, does fasting deplete muscle glycogen, or is this energy reserved differently, particularly during a short-term fast?

While protein provides four calories per gram, the same as carbohydrates, it is typically not the body's preferred or primary energy source during exercise. The body relies on a strategic hierarchy of fuel, and the question, "Are proteins a major source of energy during exercise?" has a nuanced answer that depends heavily on the intensity and duration of the activity.