Related Experiment Video
Updated: Aug 5, 2026
08:40
An Optimized Protocol to Analyze Glycolysis and Mitochondrial Respiration in Lymphocytes
Published on: November 21, 2016
Glycogen breakdown and lactate accumulation during high-intensity cycling
1National Institute of Occupational Health, Oslo, Norway.
Acta Physiologica Scandinavica
|September 1, 1993
Summary
High-intensity exercise breaks down muscle glycogen into lactate and other intermediates. Most glycogen breakdown during intense cycling results in lactate within the working muscle, not released to blood.
Area of Science:
- Exercise Physiology
- Biochemistry
Background:
- High-intensity exercise causes significant muscle glycogen breakdown.
- The fate of glycogen metabolites (hexose phosphates, lactate, oxidation) is not fully understood.
- Limited data exists on the relative importance of glycogen breakdown pathways during intense exercise.
Purpose of the Study:
- To quantify the relative contribution of different metabolic pathways to glycogen breakdown during high-intensity cycling.
- To determine the fate of muscle glycogen during exhaustive exercise.
Main Methods:
- 16 healthy men performed maximal intensity cycling for 30 seconds to 3 minutes.
- Muscle biopsies (m. vastus lateralis) were analyzed for glycogen, glucose, glucose-6-phosphate, and lactate.
- Blood lactate concentration and oxygen uptake were measured.
- Glycogen oxidation was calculated based on oxygen uptake.
Main Results:
- Muscle glycogen decreased by 17-24 mmol kg-1 wet wt.
- Muscle lactate increased by 20-30 mmol kg-1.
- 60% of lost glycogen reappeared as muscle lactate, 20-25% as other glycolytic intermediates, and 4-13% was oxidized.
- Lactate released into the blood accounted for ~10% of total lactate produced.
Conclusions:
- During high-intensity cycling, the majority of broken-down muscle glycogen is converted to lactate within the muscle.
- A smaller proportion is oxidized or appears as other glycolytic intermediates.
- Minimal lactate produced during intense exercise is released into the bloodstream.
More Related Videos
Related Concept Videos
01:13Outcomes of Glycolysis
Nearly all the energy used by cells comes from the bonds that make up complex organic compounds. These organic compounds are broken down into simpler molecules, such as glucose. As a result, cells extract energy from glucose over many chemical reactions—a process called cellular respiration.
Cellular respiration can occur aerobically (with oxygen) or anaerobically (without oxygen). In the presence of oxygen, cellular respiration starts with glycolysis and continues with pyruvate oxidation, the...
Cellular respiration can occur aerobically (with oxygen) or anaerobically (without oxygen). In the presence of oxygen, cellular respiration starts with glycolysis and continues with pyruvate oxidation, the...
01:25Energy Supply for Muscle Contraction
Skeletal muscle fibers have the unique ability to switch between rest and contraction states, using different sources of ATP for energy. The contraction cycle and Ca2+ transport back into the sarcoplasmic reticulum for relaxation require significant ATP. However, the ATP reserves in muscle fibers are limited and can only sustain contractions for a few seconds. Additional ATP production becomes necessary for prolonged contractions. As a result, muscle fibers generate ATP through various sources,...
01:24Muscle Recovery and Fatigue
Muscle fatigue refers to the decline in a muscle's ability to maintain the force of contraction after prolonged activity. It primarily stems from changes within muscle fibers. Even before experiencing muscle fatigue, one may feel tired and have the urge to stop the activity. This response, known as central fatigue, occurs due to changes in the central nervous system, namely the brain and spinal cord. While there is no single mechanism that induces fatigue, it may serve as a protective response...
01:19Overview of Carbohydrate Metabolism
Carbohydrate metabolism is a fundamental biochemical process that ensures a constant supply of energy to living cells. The most important carbohydrate is glucose, which can be broken down via glycolysis to enter into the Krebs cycle and eventually lead to the production of ATP through oxidative phosphorylation.
Glucose transport into cells is facilitated by a family of transport proteins called GLUT (Glucose Transporters). GLUT4 is the primary glucose transporter for insulin-stimulated glucose...
Glucose transport into cells is facilitated by a family of transport proteins called GLUT (Glucose Transporters). GLUT4 is the primary glucose transporter for insulin-stimulated glucose...
01:18Metabolic States of the Body: The Postabsorptive State
The postabsorptive state usually starts about four hours after a meal and lasts until the next meal is eaten. During this time, the digestive system stops absorbing nutrients, and the body uses stored energy reserves to maintain stable blood glucose levels.
Initially, glycogen stored in the liver is broken down to release glucose into the bloodstream, while glycogen in the muscles is broken down to supply glucose for energy directly within the muscle cells. As glycogen stores diminish,...
Initially, glycogen stored in the liver is broken down to release glucose into the bloodstream, while glycogen in the muscles is broken down to supply glucose for energy directly within the muscle cells. As glycogen stores diminish,...
01:24Metabolic States of the Body: Fasting and Starvation
During the initial hours of fasting, the body uses up its glycogen stores as an energy source. Once these glycogen reserves are depleted, the body begins breaking down stored triglycerides and structural proteins. During this stage, glycerol becomes a key substrate for gluconeogenesis, while free fatty acids undergo beta-oxidation to provide energy for tissues, such as skeletal muscle. In the fasting state, the body spares protein breakdown as much as possible to conserve muscle and structural...