Slow Twitch vs. Fast Twitch Muscle Fibers

EndurElite Chief Endurance Officer discusses the differences between Type 1 Slow Twitch Oxidative Fibers, Type IIa Fast Twitch Oxidative Glycolytic Fibers, and Type IIx Fast Twitch Glycolytic Fibers.

The Difference Between Type 1 And Type 2 Muscle Fibers

  • Ever wonder what the difference is between muscle fiber types?
  • Type I Slow Twitch Oxidative - small in size, great capacity for endurance, poor capacity for strength, lots of mitochondria, big blood supply.
  • Type IIA Fast Twitch Oxidative Glycolytic - medium in size, medium capacity for endurance and strength, average mitochondrial density and blood supply.
  • Type IIx Fast Twitch Glycolytic - large in size, great capacity for strength/power, poor capacity for endurance, poor mitochondrial density and blood supply.
  • Slow twitch type muscle fibers are the primary type of muscle fiber for endurance type exercise. However, that doesn’t mean that fast twitch fibers are not used at all.
  • If during a long run, you run a little faster for a stretch to make a pass or you have to run uphill and try to maintain your pace, fast twitch fibers take over.

Here’s a nice summary table!

Slow Twitch Between Fast Twitch
Size Small Medium Large
Endurance Great Moderate Poor
Strength Poor Moderate Great
Blood Supply Great Average Poor
Mitochondria Great Moderate Poor