After 10 weeks of resistance training, acute exercise increases myofibrillar protein synthesis by 36%, while endurance training maintains elevated mitochondrial protein synthesis at 105% without increasing myofibrillar protein synthesis, demonstrating a training-specific adaptation in protein synthesis responses.

When you lift weights, your muscles sense heavy loads and turn on a molecular switch that tells the cell to build more contractile fibers. When you run for long periods, your muscles sense constant energy demand and turn on the same switch to build more energy-producing factories. After training, the muscle remembers which type of stress it faced and only builds the proteins it needs for that specific task.