Research Round-Up: Eccentric Utilization Ratios and Lower Body Stiffness

carter

I’ve been digging through some research and starting to look at Eccentric Utilization Ratios (EUR) with some of my student-athletes (Women’s Basketball) this summer. We’ve been collecting data for a few weeks, coaching the procedures, and waiting out the “learning” part of the testing. We do verts all the time using a standard Countermovement Jump (CMJ) on the Just Jump mat, so this was pretty easy to get started on. Basically, in accordance with this McGuigan study,

EUREOS

I’ve been using a PVC across the shoulders during our EUR testing in order to test the lower body in a quasi-isolated manner. We still do our power output testing with 3 maximal efforts using the entire body.

My hypothesis however, seemed to betray me. I have two particular athletes who display many similar qualities. They have incredible quickness, great sprinting ability and visibly superior agility. However, these same athletes would consistently score lower (<1.0) on our EUR Testing (CMJ/SJ.) I needed to find out (if the EUR is so descriptive) what’s going on here.

What is an Eccentric Utilization Ratio?

Basically, an EUR is descriptive of the difference in jump height between a standard Countermovement (CMJ, Load & Explode) jump, and a Squat Jump (SJ, concentric only) jump. I let the athlete (with PVC across the shoulders – as in a back squat) perform their best CMJ, followed by a concentric only jump from a full squat with a 3-count amortization. The average of three trials is taken, and expressed as a ratio (CMJ/SJ.) In the case of the study below, the EUR is calculated this way: (CMJ-SJ / SJ) x 100.

What’s the point?

In athletic performance, a common goal is to improve/enhance the function of the SSC (stretch-shortening cycle.) The pre-stretch/loading of a muscle (or muscle-tendon unit) during the eccentric phase of coupled contractions can increase the subsequent force and speed it is capable of producing during the subsequent concentric contraction. Of course this is only possible when the eccentric is immediately followed (coupled) with the concentric action. In other words, there is no visible amortization phase. The EUR therefore, seems like a good idea in terms of figuring out whether or not our athletes are improving their capacity to take advantage of this mechanism.

Stiffness

I wanted to share a great paper from 2014 that I came across recently, which detailed some of the limitations of the EUR in women’s team court sports. Specifically in this case, they were looking at eighteen netball players ranging in age from ~20-26 years old with ~12-18 years of training age.

They were concerned primarily with determining the difference in performance measures based on comparisons with both EUR and lower body stiffness.

So how do you measure stiffness?

In the case of this study, a vertical hop test was used to determine functional stiffness barefoot, on a force platform. Additionally, myometry was used at 4 sites (medial and lateral gastroc, achilles aponeurosis, and soleus.) Basically a probe which delivers a 15ms impact to the tissue causes brief deformation. Naturally occuring oscillations are measured by an accelerometer sampling at high frequency (3200 Hz.)

OK Great, what are the performance implications?

Obviously, performance implications of the EUR seem very easy to understand. A more elastic athlete should be jumping higher, running faster, and generally more explosive. Additionally, stiffness should have that athlete appear to possess that heralded twitch quality, and have great reactive quickness.

This study looked specifically at a few different measures:

  1. 5m acceleration
  2. 10m acceleration
  3. Agility (5-0-5)
  4. 5BT (5-contact bounding)
  5. CMJ
  6. SJ
  7. EUR
  8. DJ (Drop Jump from 50cm w. minimal contact time)

SGvsCG

Interestingly, the SG (Stiffness Group) showed greater performance in:

  1. 10m Acceleration
  2. 5BT (5-contact bounding)
  3. SJ (Squat Jump – Static overcome by dynamic)
  4. DJ (Drop Jump – 50cm drop)

Whereas the CG (Compliant Group) showed greater performance in:

  1. Eccentric Utilization Ratio

Takeaway Thoughts and Discussion Points:

So, based on this paper (and netball being a court sport – like my WBB subjects) I was able to at least sleep a little bit better. Now I knew that it was normal for my more “explosive” or “twitchy” athletes to not have EUR’s off the wall. But, why the discrepancy between a measurable which is descriptive of SSC function, and seemingly related performance tests?

****The following includes paraphrasing of the results/discussions and my own personal understanding or interpretation****

Well it seems it wasn’t all as simple as I’d figured it was.

The SSC functions in two ways. Firstly, the muscular SSC is involved in large, compound, multi-joint movements. Things like squats, CMJ’s, bench presses etc. all make use of SLOW-SSC function. This is elastic energy stored primarily in the muscle tissue during coupled eccentric-concentric contractions. The multi-joint nature of these movements involve the use of larger biarticular muscles. SLOW(ER), HIGH RESISTANCE, LARGE R.O.M. movements are the ones which make use of this mechanism. Athletes with higher EUR’s will experience greater performance scores on measures which have these characteristic requirements. This mechanism requires greater R.O.M. to make use of eccentric loading and pre-stretch.

The second way in which the SSC functions is in the muscle-tendon unit. The classic example here is the lower leg ability to return stored elastic energy to the environment via the gastroc/foot. We all know that “stiffer” athletes possess greater acceleration and sprinting abilities. The mechanism at work here is deemed FAST-SSC Function. In this case, there is much shorter range of motion and more elastic energy is stored and recycled via a less compliant (closer to isometric) muscular component, which causes a greater amount of elastic energy to be stored and recycled by the tendinous continuations of these muscles. Commonly acting across only one joint, very quickly, and with less “resistance.” This mechanism requires far less R.O.M. to be effective, and relies more on concentric strength. This may also provide insight as to why these athletes may be more prone to certain types of injuries given their reduced tendency to use more typically “eccentric-focused” deceleration strategies.

Final Thought/Consideration:

It should also be noted that the most significant marker in this study in terms of lower leg stiffness was the medial gastroc. In performance measures requiring the use of Fast-SSC function, the medial gastroc was the greatest and ONLY contributor in the SG (Stiffness Group.) The reason for this is that when these measurables are executed, the ground contact time is simply not long enough for the foot to supinate to the point that the lateral compartment experiences any more than a stabilization role.

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