MTU

A.V Hill was one of the great sports performance pioneers, whether he knew it or not. One of his many contributions included the 3 element model of the musculoskeletal-tendinous unit (MTU).

In short, it is broken up into 3 regions.

1. Contractile element (CE). These are your actively producing contractile structures (myosin and actin).
2. Parallel elastic component (PEC). Just kind of a fancy way to say the stuff that surrounds the contractile element, but isn’t actively contracting, making it passive. (The PEC and CE kind of work together. Because the PEC surrounds the CE, when the muscle tightens up, so does the PEC).
3. Series elastic component (SEC). This is just the tendon, which if you laid a muscle out on a table, it would be “in series” or basically just an extension of the CE and PEC.

Why does this matter?

Depending on the speeds and types of movement performed, either the PEC/CE or the SEC will deform (not as black and white as it may seem; it’s more of a spectrum, but the idea holds).

It is why plyometrics are demanding on tendons to store elastic energy. The SEC deforms as the PEC/CE remains stiff and rigid (due to a bunch of added strength it gets from higher speeds and stretch rates).

On the other hand, during slow movements, we put a greater demand on the PEC/CE to deform and while the SEC does not. This can be seen in traditional weight lifting and in the most extreme example, passive stretching.

Based on the above examples, it is easy to see that demands and contraction types are quite different during the two movements. This is not to say one is superior to the other, but instead to point out the specific differences.

Food for thought, one might use strengthening of the CE/PEC through weight training to increase its rigidity during higher speed movements to allow for greater elastic stored energy in the SEC…Go Science.

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