Wednesday, October 22, 2014

Stretch-Shortening Cycle Exercise Superior to Eccentric Exercises in the Elderly - Identical Size & Strength Gains, With a Functional Advantage for Stretch Shortening Ex.

A stretch-shortening cycle (SSC) is an active stretch (eccentric contraction) of a muscle followed by an immediate shortening (concentric contraction) of that same muscle - e.g. jump squats.
Sacropenia, i.e. the age-related loss of muscle mass is a huge problem in our society. A problem the consequences of which start to surface way before older men and women suffer from serious limitations in their mobility and their ability to master (no longer) ordinary everyday-life tasks.

The loss of muscle mass is after all associated with an ever-increasing risk of metabolic syndrome, i.e. obesity, diabetes, high blood lipids, etc. (Baumgartner. 2004; Kim. 2011) - in both, young and old individuals, as well.

In contrast to many pharma-funded which spends millions of dollar on "promising new drugs" (that's what they say) to solve the problem.
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Researchers like Márk Váczi and his colleagues from the University of Pécs have long recognized that the development "promising new drugs" holds much less promise that the optimization of exercise regimen that are targeted to prevent sacropenia. In their latest paper in Experimental Gerontology the researchers describe the results of an experiment that was conducted to compare the effects of exercise training using stretch-shortening (SSC) and eccentric contractions (ECC) on the mechanical function and size of the quadriceps muscle and hormonal adaptations in healthy old males (N=16; age: 60-70 year old).
Figure 1: The torque–time curves of a stretch-shortening cycle and an eccentric exercise training contraction highlight the main difference between SSC (short, ultra-intense) and ECC (long, medium intensity) knee extensions (Váczi. 2014)
In that, Vávzi et al used an experimental approach in which the total mechanical work was identical in the two training groups and hypothesized that mechanical, hormonal, and muscular adaptations would differ in response to SSC vs. ECC exercise (note: plyometric training harnesses the beneficial effects of SSC | learn more).

The exercise of choice was, as so often, the single-lateral knee extension. The subjects trained 2-3 times per week with 48h rest between two sessions (each between 9-11 am in the morning).
Benefit from SSC irrespective of your age after you've read the following SuppVersity Classic: "Building the Jack-of-All-Traits Legs Workout With Squats, Jump Squats and Body Weight Plyometrics? At Least for Physical Education Students that Seems to Work." | read more
"Subjects performed 4 sets of 8 to 14 repetitions of unilateral knee extensions with both legs, with 2 min of rest between sets. The exercising legs were alternated across sets. The training contractions in SSC and ECC groups were similar to the SSC and ECC test contractions. [...A] unique element of the training program was that the average mechanical work for a session was still similar in the two groups. This was achieved by manipulating the stretch-load in the SSC group. For example, if a subject in the ECC group improved mechanical work production due to adaptation to the training, the stretch-load was adjusted to match subject-pair's mechanical work in the SSC group." (Váczi. 2014)
If we take a look at the outcome of the work and volume matched training with stretch-shortening and eccentric leg extensions, we see the following differences and similarities, when comparing the two exercise regimen:
  • Figure 2: The hormonal response to the exercise regimen was more or less identical (Váczi. 2014)
    There was a significant group by period interaction for RTD30 [rate of torque development after 30ms] and RTD50 (p < 0.05), suggesting that the two groups responded differently to the training. 
  • There was no group by period by time interaction in any of the hormonal variables, suggesting similar re sponses to the two training regimens. There was a significant time main effect in testosterone (p = 0.010), suggesting that the two exercise bouts (before and after 10 weeks training) uniformly increased testosterone 15% from pre to IP, and then decreased 10% from IP to 5 min post-exercise. 
  • There was a time main effect for cortisol (p = 0.018), suggesting that the two exercise bouts uniformly increased cortisol 21% from pre to IP, and then further increased 6% to 5 min post-exercise. 
  • There was a time main effect for testosterone/cortisol ratio (p = 0.002), suggesting that the two exercise bouts uniformly decreased the ratio 17% from pre to 5 min post-exercise. 
Now, in view of the fact that the overall strength (MCV) and size gains (CSA) were identical, as well. It would seem as if both types of exercise were equally beneficial.
Figure 3: Changes in maximum voluntary contraction (MVC), rate of torque development after 30ms and 50ms and cross sectional area of the quadriceps muscle (CSA) after 10 weeks of training (Váczi. 2014)
If we look at the most important functional deficits in aging muscle, however, it becomes obvious that the ostensibly negligible increase in the rate of torque development at the beginning of the exercise could determine whether an older individual falls and breaks a bone or whether he or she manages to "catch him-/herself" in time.
Bottom line: Overall the study at hand underlines there is more than just one way to skin the cat. In that, small allegedly practically non-significant differences like the increased rate of torque development in the study at hand can - from time to time - have important real-world relevance.

Figure 4: Strength & size gains in young men in response to 8 wk of SSC exercise training
And even if you are not 60 years and older, you can benefits. In 2005, Malisoux et al. evaluated the contractile properties of chemically skinned single muscle fibers from the leg muscle of eight young men before and after 8 wk of maximal effort stretch-shortening cycle (SSC) exercise training and found that their maximal leg extensor muscle force, vertical jump performance and peak force were improved 12%, 13% and 15-19% (depending on muscle fiber type), respectively; and the single-fiber crosssectional area increased 23% in type I, 22% in type IIa, and 30% in the most growth prone type IIa/IIx fibers. Needless to say that this makes SSC exercises "an effective training approach to improve fiber force, contraction velocity, and therefore power." (Malisoux. 2005) | Comment on Facebook!
References:
  • Baumgartner, Richard N., et al. "Sarcopenic obesity predicts instrumental activities of daily living disability in the elderly." Obesity research 12.12 (2004): 1995-2004.
  • Kim, Tae Nyun, et al. "Skeletal muscle mass to visceral fat area ratio is associated with metabolic syndrome and arterial stiffness: the Korean Sarcopenic Obesity Study (KSOS)." Diabetes research and clinical practice 93.2 (2011): 285-291.
  • Malisoux, Laurent, et al. "Stretch-shortening cycle exercises: an effective training paradigm to enhance power output of human single muscle fibers." Journal of Applied Physiology 100.3 (2006): 771-779.