71. Metabolism in Muscle Tissue. Bioenergetics of Muscle Contraction in Various Types of Fibers and Various Types of Exercise. Metabolism of Creatine · Biochemistry · MU Pleven

71. Metabolism in Muscle Tissue. Bioenergetics of Muscle Contraction in Various Types of Fibers and Various Types of Exercise. Metabolism of Creatine.

Covers how muscle fuels itself at rest and during exercise, moving from creatine phosphate to anaerobic glycolysis and then aerobic metabolism as activity continues. It contrasts slow-twitch and fast-twitch fibres by mitochondria, myoglobin and fatigue resistance, then traces creatine synthesis, its conversion to creatinine, and the clinical relevance of creatine kinase in muscle damage. A closing section summarises the metabolic switches between high-intensity bursts, sustained activity and prolonged fasting.

Inside: 6 sections · 6 labelled pictures · 10 flashcards · 3 min

Topic 71 of 76 in the MU Pleven syllabus for Biochemistry (Medicine, Year 2). The free AceMed note covers it in 6 sections, about 405 words (3 min of reading), with 10 flashcards.

Metabolism in Muscle Tissue

Muscle metabolism changes depending on rest vs. activity, fiber type, and fuel availability.

Muscle stores glycogen, creatine phosphate, and small amounts of ATP.
It can use glucose, fatty acids, ketone bodies, and amino acids as fuels.
Unlike liver, muscle lacks glucose-6-phosphatase, so it cannot release glucose into blood.
Instead, glycogen breakdown (glycogenolysis) in muscle provides glucose-6-phosphate for its own use only.

During rest:

Muscle primarily uses fatty acid oxidation for ATP.
Aerobic metabolism dominates.

During intense exercise:

ATP demand spikes instantly.
Energy comes first from creatine phosphate, then anaerobic glycolysis, and later aerobic metabolism if activity continues.

Bioenergetics of Muscle Contraction

Immediate Energy Source

ATP stored in muscle supports only a few seconds of contraction.
Creatine phosphate (phosphocreatine) donates phosphate to ADP → ATP (via creatine kinase).
This system supplies energy for first 5–10 seconds of high-power activities (sprint, jump).

Short-Term Energy (Anaerobic Glycolysis)

When ATP and creatine phosphate begin to drop, muscle glycogen is rapidly mobilized.
Glycolysis converts glucose → lactate, producing ATP quickly without oxygen.
Supports intense exercise lasting up to ~2 minutes.
Leads to lactic acid accumulation → drop in pH → fatigue.

Long-Term Energy (Aerobic Metabolism)

For sustained exercise (running, cycling), muscle shifts to oxidative metabolism.
Uses glucose, fatty acids, and eventually amino acids.
Requires mitochondria and oxygen.
Produces high ATP yield, supports endurance.