Exercise Science Review 1-1, Flexors and Extensors

Posted by on Jan 9, 2013 in Exercise Science, Review Topics | 0 comments

There are a lot of categories for muscles.  Primary movers & Secondary movers, Flexors & Extensors, Skeletal muscles and Smooth muscles, Type I and Type II (and type IIx, more on this later).  In this article I will attempt to differentiate between Flexors and Extensors in own words.  Keep in mind I’m not an expert at this point, but I do make a point of double checking my work.  Please let me know if you find anything inaccurate.

  • Flexor is a muscle that actively shortens the angle of a joint when it contracts in concentric action.
  • An Extensor is a muscle that actively widens the angle of a joint when it contracts in concentric action.

The easiest example is made with the elbow joint, and the biceps & triceps.  Take every bro’s favorite exercise, the curl.

At the start of the movement the angle of your elbow joint is roughly 180 degrees.  As your biceps contract the angle of your elbow decreases, and thus by definition your biceps are flexors.

Biceps are flexors

Flexors Example

On the other hand, take the triceps extension exercise.  At the bottom of the movement when your triceps are relaxed, the angle of your elbow is small.  Assuming you don’t have massive biceps to get in the way, probably somewhere around 45 degrees or less.  As your triceps contract the angle of your elbow increases and thus your triceps are extensors.

Pretty simple concept, and a good one to kick off this review with.

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