You're relaxing on the sofa when suddenly your eyelid starts twitching. Or perhaps it's a muscle in your arm, your leg, or ...

If your fitness goal is to up the ante on endurance, pack more power into your sprint, or supercharge your strength gains in the gym, it’s worth exploring – what are the different muscle fiber types?

There's a lot of talk about lean muscle compared to bulk muscle, but experts say it's not worth differentiating the two. Learn why.