Common Misnomers and Mix-ups: Muscle Actions, Balance, Stability, Single Legs and Straight Back

Posted on 21 Feb 2009 20:52

1. Concentric, eccentric and isometric contractions

All muscle contractions involve the muscle shortening or attempting to shorten against resistance. There are not different types of contractions only different types of actions (movement or lack thereof) depending on the circumstances. A muscle is producing force by contraction but this may lead to shortening (concentric action), lengthening (eccentric action), or maintaining length (isometric action). So the concept of muscle actions specifically describe the type of length changes that skeletal muscle may undergo after it has been activated by the nervous system.

This is a very common misnomer and is used even in many textbooks. Muscle contracts by forming cross bridges betweenmyosin heads and actin filaments. These cross bridges happen whether the action is concentric, eccentric or isometric. So, there are not different types of contractions but only different results depending on the resistance. When resistance is overcome and the muscle shortens it is a concentric muscle action. When resistance is not overcome and the muscle lengthens it is an eccentric action.

Mel Siff made a big point of the fact that the muscle is not really "lengthening" but simply returning to its resting length:

"…we see that no muscle can voluntarily lengthen relative to its RESTING length. Of course, if a joint has not quite reached its greatest possible angle in any given plane (such as the elbow joint at rest), the maximum length of a muscle may be reached by means of passive loading or the action of antagonistic muscles. This will cause slight lengthening, but no further lengthening is possible under eccentric action.

It is a common misconception that a muscle lengthens under conditions of eccentric action. What actually happens is that the relevant muscle is still contracting while the joint angle is increasing, so it appears as if the muscle is contracting and lengthening at the same time. The muscle is simply returning actively to its original resting length under eccentric conditions, and when the tension developed in the muscle is equal to the resistance and the muscle length remains constant, it is an isometric action."

While this is all true it is one of those examples of a whole lot of analysis that doesn't really change anything. It is a bit semantic to say the least. "Length" is a relative term and it really doesn't matter how a physiologist would measure the length of a muscle. When we say a muscle is "lengthening" in an eccentric action we mean it is lengthening relative to its previously "shortened" (contracted) state and indeed having to use the word "eccentric" in a definition of eccentric action is very confusing as in "muscle is simply returning actively to its original resting length under eccentric conditions"

Lesson, don't over-complicate and over-think. The idea is to use analysis to SIMPLIFY not to COMPLICATE.

2. Balance and Stability


Don't blame the bosu ball;
blame the trainer.

These tend to be used interchangeably by many people but are two different things. Balance is simply the ability to control body position in equilibrium as required by the specific situation. Stability is how easy or difficult it is for this equilibrium to be disturbed.

It is important to understand that equilibrium does not automatically denote high stability since stability implies RESISTANCE to a disturbance in equilibrium. Both these factors work together to control and maintain body position and this control is SPECIFIC. Misunderstandings of this have lead to such ludicrous ‘innovations’ as doing squats on unstable surfaces.

The primary goal of a strength trainee, in regards to stability is to learn to PREVENT unwanted motion. If you cannot prevent unwanted motion then you cannot hope to produce wanted movement under stress.

3. Single leg squats, split squats, and lunges

Not the same thing! A single leg squat is exactly that..a squat on one leg. This does not ivolve any type of support from the other leg. Split squats and lunges are sometimes referred to as single leg squats but don’t kid yourself…these are not squatting on one leg as support is provided by the other leg.

Single leg squats, when performed with full range of motion are sometimes referred to as pistols (the free leg sticks out like the barrel of a pistol). Keep in mind that there is another version of this exercise in which the free leg is allowed to drift backward instead of to the front, which is not nearly as effective.


This is a single leg squat.

4. Straight Back

We are often told to deadlift or squat with a straight back. This really means a back with its natural lumbar curve maintained. That’s ok. The problem is many people seem to think that straight back means a “straight up and down back”. OR, a back that is parallel to the floor. Many people attempt to squat while maintaining their torso straight up and down, for instance. Or they think that a deadlift is a squat with the bar in the hands and deadlift with the butt down and the back vertical.


This is a bulgarian "split squat".

5. Ballistic and dynamic stretching or movement

Often interchanged and easily confused. Probably because both methods are dynamic in nature. Basically though, dynamic stretching involves the movement of limbs where the movement is controlled and momentum is NOT allowed to carry the limb to excessive ranges of motion. Ballistic stretching is where the limb’s movement is not checked and momentum is allowed to carry the limb as far as the initial input of force will take it. Both these methods easily overlap but it is important to note the difference. Dynamic stretching can be done safely by most trainees if proper guidelines are followed.

This page created 21 Feb 2009 20:52
Last updated 19 Jul 2016 20:42

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