Muscles as Metabolic Engines

The Story

When a fever hit, Stina’s muscles didn’t just ache — they screamed. A deepAway from the surface of the body., full-body myalgia would settle into her thighs, back, and shoulders for the duration of an attack, then fade once the fever broke and her strength returned to normal. Each episode earned the same shrug: a virus, take fluids, rest. No one lined up the attacks to notice they were identical, recurrent, and tied to fever rather than to any infection that ever grew on a test.

To see why fever wrecks muscle, start with how muscle is built and what it costs to run. Skeletal muscle is organized like nested cables: a whole muscle is bundled into fasciclesBundles of nerve fibers within a nerve.
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Bundles of nerve fibers within a muscle., each fascicle into muscle fibers (cellsThe basic structural and functional units of life.), each fiber packed with myofibrils, and each myofibrilCylindrical structures within muscle fibers that contain myofilaments. made of repeating sarcomeres — the contractile units of overlapping actin (thin) and myosin (thick) filaments. Every contraction burns ATPThe energy currency of cells used for muscle contraction., so muscle is a metabolic engine that must constantly make fuel. Here is the catch: fever itself raises the body’s metabolic rate, and the IL-1β/IL-6 that cause the fever also drive muscle breakdown and pain directly. So during an attack Stina’s muscles were aching engines forced to idle hot while their fuel was drained from two directions at once. Her “viral myalgia” was a metabolic engine running in the red.

From Stina’s chart: During attacks: severe, diffuse muscle pain (myalgia) with fever; between attacks, normal strength. Dx: “viral myalgia” each time. The recurrence was never questioned.