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P&P #41 Maximum Muscle Tension May Not Generally Occur under Eccentric Conditions.

It is well known that the heaviest controlled loading of a limb occurs under eccentric conditions, when the muscle complex appears to be lengthening. Concentric action permits the lowest controlled loading, with isometric action somewhere between the concentric and eccentric extremes. Before we go any further, we have to note that isometric force may be generated slowly or very rapidly as 'explosive isometrics, a situation which occurs when a partially flexed limb is subjected to impulsive loading (e.g. during 'plyometric training') - so, it could be that the greatest controlled force production (albeit reflexive) occurs during explosive isometrics.

Can you quote any research which proves or disproves this proposition?

Now to the proposition concerning eccentric action. Does the fact that the heaviest loads can be controlled during eccentric action necessarily mean that the greatest muscle tension is produced during eccentric muscle 'contraction'?

Remember that the process of yielding eccentrically to the applied load intentionally may be decreasing the muscle tension so as to prevent one from exceeding the tensile strength of the muscle complex.

Are we justified in assuming that the tension in a muscle is directly proportional to the external load applied? Are we justified in assuming that EMG potentials provide a direct measure of functional muscle tension in a given muscle group?

Then again, how do we define maximal eccentric strength? Is this the maximum load which a subject can lower at a given controlled slow rate? (Probably this should be regarded as another PUZZLE - what exactly is meant by MAXIMAL ECCENTRIC STRENGTH?).

How do submaximal assessments of eccentric strength compare with submaximal measures of concentric or isometric strength? Can you recall any research which has examined the differences in muscle tension and EMG during the concentric, eccentric and isometric (slow vs explosive) loading of a given joint by the same mass?

You will note that this P&P probably constitutes several related, though related issues, so it should suffice as a substantial enough proposition for discusssion this week. I look forward to your comments.


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