The Stretch Reflex

Posted by Louie Simmons on

Dave Yarnell wrote a great tribute to the Culver City Westside Barbell club and its connections with the Columbus, Ohio, Westside club. There is, of course, a lot about box squatting. We feel there is only one method to box squat, but many have these less effective methods. On the subject of the stretch reflex, however, someone said that the stretch reflex does not last four seconds as a study by Wilson (1990) states.

I wrote a study with the use of a tendo unit on both eccentric and concentric phases. With all top ten lifters including two world-record holders. Two groups, one for speed strength where the velocity is about 0.8 m/s and near-maximal where the bar velocity was 0.4-0.5 m/s. I stated that I could sit on the box for eight seconds and concentrically rise at close to the speed of the eccentric phase. Dave Tate could do the same for five seconds.

A Pete said the stretch reflex lasts only 0.025 seconds and I was incorrect due to the study by Siff and Verkhoshansky (1998).

First, I believe Pete is referring to an amortization phase for a plyometric action. The box squat is not an example of a plyometric action. The length of the amortization phase when lowering very heavy weights will not be immediate as in a plyometric action, where the delay can be as short as 0.15 seconds between the eccentric and a subsequent concentric contraction. A study by Wilson (1990) concluded that while bench pressing, the stretch would last up to four seconds. At that point all started elastic energy is lost.

Other studies by Chapman and Caldwell (1985) found it to be the same as Pete—0.25 seconds and the plyometric action is lost. But, in 1982 Bosco found how both could be correct. He found that those with a very high rate of fast-twitch fiber would lose the rebound. This would explain why Tate could only hold the position for five seconds while I held it for eight seconds. A second factor could be joint mobility and the maximum delays for each joint action.

While Chapman and Caldwell tested the forearm, the box squat done the Westside way is a multi-joint activity, where there is stored elastic energy in all three simultaneously. As you can imagine, the mass of knees, hips, and back would hold many times the amount of forearm action.

I don’t know whose forearm was tested, but our study was with several world record holders. The age of our participants was 22 to 50 years. The author was 50 at the time of the study and had the second highest squat on the top 10. This means the group was very talented, not merely students or novices. This could explain the results. 

When depth jumps are performed, the reversible muscular action is limited to the feet.

But, when box squatting, according to physical principles, the amount of stored energy is proportional to the applied force and the induced deformation. Deformation is the stretch shortening cycle during the support phase while running.

The same stretch-shortening cycle happens during the support while sitting on the box. There are many reasons to box squat, but think about why Westside releases the hip muscles after coming into contact. Let's compare the mass of your foot while running, then the mass of your body sitting on a box. Wait, there is no comparison.

We know that the stiffness of a tendon is constant, but the stiffness of a muscle can vary depending on the forces exerted. Elite athletes like the ones in the Westside study, have found ways to use this stored elastic energy for overcoming a large load while sitting on the box.

Most of our training is a combination of bar weight plus elastic bands, which sometimes are greater than the amount of weight on the barbell. The bands are pulling the barbell down at a faster rate than lowering just barbell weight. This produces a greater stretch reflex due to causing a faster eccentric phase.

Now let's look at elasticity and Hooke’s law. Hooke’s law states that the amount of deformation produced by a force is proportional to the amount of force. Now, clear your mind and think about Hooke’s law and box squatting concerning deformation.

If the amount of deformation produced by a force is proportional to the amount of force, what if you have a very strong man producing great force downward on a basketball causing great deformation, caused by the flattening on the bottom of the ball. Then suddenly, sliding his hands off the ball, it would rebound upward due to its elasticity properties.

A similar action happens when one slowly releases muscle while sitting on the box. Both will switch from an eccentric or lowering to concentric rising. The box squat uses a combination of the two greatest methods of strength training: Relaxed overcome by a dynamic action and static overcome by a dynamic action. While the muscles are relaxing, the tendons are maximally loaded. This is a skill and it must be learned correctly.

This is also why Westside achieves great results by sitting on a box. Just like box squatting, but when rocking back, pick the feet up and slam them down while rocking forward during the jump phase while box jumping.

I hope this explains how one can sit on a box for a long time period and concentrically raise at the same rate of speed as touching and going method.

There is much information in super-training about reversible strength. On page 219 there is a training device that lets a barbell fall. The athlete must first stop it from falling and immediately throw it upward. The idea is that the muscular force developed at the instant of going from eccentric to concentric work will be greater for a shorter amortization phase and a shorter braking time.

But if you constantly add weight to the falling bar, the amortization phase will be longer and longer. To build kinetic energy in the body it is best to add velocity, not mass. But one truly amazing method is the static overcome by dynamic method. Westside had developed a training device that's purpose is to build maximal muscle tension on a non-moveable bar.

The bar can be loaded to any weight but for explosive strength use 30 to 40 percent of a 1RM at any position from the bottom to near the top. To perform a rep, pull or push on the bar while it is locked in place for two to six seconds as powerfully as possible. Now by releasing a brake, the light load will explode upwardly at high velocity. It can be held for a longer period if breath is not held. There is no eccentric phase to this method, yet one can overcome the load on the barbell at great velocity.

When box squatting, the eccentric concentric phase is broken. This can explain why even after sitting on the box for sometime, a rapid concentric action is possible.

I hope the examples I have shown will explain how we could maintain the same concentric speed after a long pause up to eight seconds compared to a one second pause.



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