Fatigue (Central vs Peripheral)

Thanks to my current job, I have been lucky enough to mess around with a bunch of cool, sports science training tools. One of the recent devices I have been playing with is called a Moxy Monitor. In short, it allows me to see the local metabolic demands of the muscle via anaylsis of muscle oxygen saturation levels “SmO2%” (amount of oxygen my muscles are using) and the changes in local blood flow.

Without diving too far into the science, the SmO2% can tell you how much oxygen is being released from the blood stream (capillary level) to the local tissue. The rate at which SmO2% is reduced (desaturated) and the rate at which it returns (resaturates) to baseline during exercise can provide some interesting insights.

As some may know, I am a velocity nerd. I think it is one of the most unique measuring tools available. So naturally, I wanted to use the Moxy Monitor in conjunction with a Tendo Unit to get an understand of how fatigue was manifesting itself during a velocity drop off squat session.

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Free Radicals

I am going to preface this post by saying “I am not a Nutritionist”. The following content provided is to be considered thought provoking and not a definitive guide to management of free radicals.

What are free radicals?

 

Free radicals are developed in your body through many different means and reactions. To avoid diving too far in to the molecular biology, lets keep it short. Free radicals are bad. They are highly unstable, reactive oxygen molecules that are present in your body. Due to their instability, they are always looking for stability, which means they are looking to bind to other molecules and cause havoc.

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General Adaptation and Specific Adaptation

The process of the “general adaptive response” is conceptually a very simple process. Without going into great molecular detail, the following stress response occurs in the body

  1. Recognizes a stressor
  2. Hormones are released
  3. Mobilizes energies to deal with the stressor
  4. Structures may be destroyed while dealing with the stressor (myosin heads during a muscular contraction)
  5. Magnitude and duration of the stressor determines the amount of destruction and mobilization of energy
  6. Once stressor is removed or defeated (like a cold), the body can begin the repair process
  7. Energies that were used and structures were broken are rebuilt in a stronger fashion to allow the body to deal with future stressors of the same nature

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Internal versus External Loading

It is common for coaches to calculate external load to guide the training process. It is an easy to use tool that helps one get a better understanding of the total physical work being imposed on the athlete. To calculate external load, a coach may use one of many different metrics (tonnage, raw volume, relative volume, acute to chronic etc…).

 

At the end of the day, the goal of using external load is to help coaches better understand the internal loading/adaptive process. Ultimately, all we care about as coaches are the internal adaptations that occur. The accumulation and systematic application of the cellular stress-adaptation process is what eventually manifests itself in the form of improved athletic form. In other words, what happens inside of our body determines how we move in the external environment.

“accumulated cellular adaptations lead to systemic change”

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Explosive Strength Development

Figure 1: (Left Graph) relationship between load and percentage of 1rm. (Right Graph) An example of a force-time curve depicting how different elementary qualities are expressed with different external loads. Graphs are modified from “supertraining”

 

Explosive strength is not an independent quality, meaning there is no specific exercise that directly trains all of the components involved in its production. Instead, it is comprised up of four “elementary qualities” (listed below and in figure 1). These elementary qualities are independent of each other and must be developed through separate means. Together, they form the expression of explosive strength.

 

  1. Maximal Velocity (Vo)
  2. Starting Strength (early stage rate of force development) (SS)
  3. Acceleration Strength (late stage rate of force development) (AS)
  4. Maximal Strength (So)

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General Physical Qualities And Their Role As “Dimmers”

This post idea stems form Tim Gabbett’s research. For those interested in reading more about Tim Gabbett’s work, feel free to check out the link at the bottom of the post.

 

The roles of general fitness qualities are often debated. To what extent is enough of a general quality is heavily dependent on the specifics of the sport, athlete, and position. For example, it is hard to pinpoint what the exact demands of aerobic capacity are for a football player. Depending on the team the athlete plays for, the position they are, and the amount of workload they handle, it can differ quite a bit. However, this does not diminish from the fact that in a perfect world, assuming no conflicting demands on adaptation and time more is typically better. But, this is never the case. Regardless, the purpose of this post is not to give specific details, instead to highlight the role general qualities work in the grander scheme of development.

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Rate of Force Development (Early versus Late)

Rate of force development (RFD) can be broken down into two stages. There is an early stage rate of force development and a late stage rate of force development.  Early stage RFD is typically measured from 0-100 ms while late stage RFD is anything after.

Importance of Early Stage RFD

Sporting movements are often required to be fast, reactive movements that occur over a small amplitude. For example a large countermovement jump can take between 500-1000ms, while a squat jump with no countermovement may take around 300 to 430ms (1). In sport, movement amplitude is going to be much more similar to that of a squat jump (zero to minimal countermovement) than to that of a large CMJ. At the same time, sprinting ground contact times can last as short as 100ms. With this in mind, it is easy to see how early RFD may play an important role in sporting movement, especially those covering a small amplitude over a short period of time (ranging from 100-430ms).

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Muscle Slack

 

Frans Bosch has popularized the concept of muscle slack (Van Hooren has publications on it). It is hinges on early stage rate of force development and the speed at which the muscle, tendon, and series elastic element can go from “slack” to “tense”. When a muscle is not activated, it is relaxed and there is slack in the muscle, tendon, and series elastic element as it hangs from its origin and insertion. Bosch uses the analogy of a rope to help describe how muscle slack works. You are holding one end of the rope and the other end is tied to a car, you are the origin and the car is the insertion. Before you can pull the car with the rope, the rope first has to become tense. This is the point where the rope goes from lying slack on the ground, to now in a straight line from your hands to the car. This is synonymous with the process of the muscle fibers aligning from the origin and insertion. The second part of the slack is that the rope now needs to become tense enough so that force can be applied to the truck. At this point, the rope goes from being in a straight line from your hand to the car, to now taut, from you producing a force on the rope. This is synonymous with the muscle co-contracting to produce enough force on the tendon so the muscle can become tense. Muscle slack uptake occurs during start of where the contractile element receives the chemical signal to align all the way to the point where both the musculotendon unit and the series elastic element are tense.


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Muscle Slack and High Velocity Training: An Integrative Approach

Velocity Deficient

 

The idea of measuring and training for velocity deficiencies has become popular since the recent studies of JB Morin and colleagues. In one of their studies, they examined several different subjects and based on their profiling methods, determined whether or not the individuals had a force-velocity profile that was either velocity deficient or force deficient. Once the deficiency was determined, the subjects were trained using specific methods emphasizing the velocity component of the movement (slow velocity for max force and fast velocity for speed of movement). After the study’s training cycle, J.B Morin and colleagues were able to show that the specific training methods, either slow or fast, improved vertical jump performance and overall balance of the subjects’ force velocity profiles.

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