section_path: Muscle fiber type evolution/Plasticity
section_name: Plasticity
paragraph_text: Plasticity
  
  In addition to having a genetic basis, the composition of muscle fiber types is flexible and can vary with a number of different environmental factors. This plasticity can, arguably, be the strongest evolutionary advantage among organisms with muscle.
  
  In fish, different fiber types are expressed at different water temperatures. Cold temperatures require more efficient metabolism within muscle and fatigue resistance is important. While in more tropical environments, fast powerful movements (from higher fast-twitch proportions) may prove more beneficial in the long run.
  
  In rodents such as rats, the transitory nature of their muscle is highly prevalent. They have high percentage of hybrid muscle fibers and have up to 60% in fast-to-slow transforming muscle.
  
  Environmental influences such as diet, exercise and lifestyle types have a pivotal role in proportions of fiber type in humans. Aerobic exercise will shift the proportions towards slow twitch fibers, while explosive powerlifting and sprinting will transition fibers towards fast twitch. In animals, "exercise training" will look more like the need for long durations of movement or short explosive movements to escape predators or catch prey.