Muscle+Metabolism

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=Muscle Metabolism= Any time we move, some muscle in our body contracts. In order to contract, skeletal muscles need energy. But where do they get this energy? And what kind of energy do they use anyway? The answers to these questions and more await you as you explore MUSCLE METABOLISM!!!

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Muscles and Energy
Muscles need energy to work. In cross-bridge cycling, the energy source ATP, or Adenosine triphosphate, is used. But where does this energy come from? Muscles have stored ATP sufficient for 4-6 seconds of contraction. After this, they must turn to other processes to regenerate ATP. The three processes used are creatine phosphate, glycolysis, and aerobic respiration.

Creatine Phosphate
The first process is Creatine phosphate is a high-energy molecule stored in skeletal muscles. When combined with ADP, a by-product of ATP hyrdolization, it instantly generates ATP. This method is extremely fast but short-lived. The ATP produced through creatine phosphate can power contraction for 10-15 seconds, or about a 100 meter dash, before being exhausted. If contraction continues, muscle must turn to the next process, glycolysis.

Glycolysis
Glycolysis is an anaerobic pathway, meaning that it doens't use oxygen. It is also known as anaerobic glycolysis. In glycolysis, the molecule glycogen is broken down into two molecules of pyruvic acid. This breakdown releases 2 molecules of ATP. In the absence of oxygen, pyruvic acid becomes lactic acid. Lactic acid is partly responsible for muscle fatigue and muscle soreness.

Glycolysis is very good for short periods of activity that require large amounts of ATP quickly. When combined with creatine phosphate, contraction can be sustained for at least a minute. However, if contraction continues, muscles must bring oxygen into the equation and begin aerobic respiration.

Aerobic Respiration
When exercise is prolonged, the muscle turns to the mitochondria. Glucose is broken down completely yielding water, carbon dioxide, and massive amounts of ATP. Glucose and pyruvic acid is broken down generating 38 molecules of ATP. This process is the most efficient of the three but also the slowest.