An advanced understanding of the muscle contraction process is as follows.

There are two nervous systems that work together to help create muscle contraction.

The two nervous systems are…

CNS (Central Nervous System) and the PNS (Peripheral Nervous System).

The following steps will walk you through an overview of the process that creates a muscle contraction by working from the CNS to the PNS…

CNS

The CNS includes the brain and the start of the nerves that innervate (connect) the muscles. The CNS affects the following in order as a communication system.

• First Step- The fatigue that is associated with CNS is the excitatory input to high motor centers (high motor centers = the brain). - This means the brain is sending a signal to the required muscles to contract.
• Second Step- The excitatory drives to the lower motor neurons (pathway to the muscle). - This is simply connecting the electrical signal sent from the brain to the muscle.
• Third Step- Motor neuron excitability (the amount of stimulation a muscle requires to contract). - This simply represents the amount of needed electrical signal required to allow step 4 to occur.
• Fourth Step- Neuromuscular transmission (transmission of the electrical signal to the muscle). - This is where the actual connection between the CNS and PNS occurs. This means that the signal goes from being electrical (action potential) to chemical (the release of acetylcholine which is needed for a muscular contraction to occur.)

 

PNS

PNS is all the nerves outside of the spinal cord. The PNS affects the following in a specific order providing the actual muscle contraction.

• Fifth Step- The Sarcolemma excitability (transmits action potential to the t-tubule).This is the pathway from neuron to t-tubule’s and sarcoplasmic reticulum. T-tubule’s (a pathway) connect the signal from sarcolemma to the sarcoplasmic reticulum. The sarcoplasmic reticulum is where calcium is stored.
• Sixth Step- Excitation contraction coupling (when the electrical signal converts to a mechanical response). - This is simply a length of time needed to convert the electrical signal (action potential) to mechanical response. Fatigue would increase the needed time to convert from electrical to mechanical causing a delay in contraction.
• Seventh Step- Contractile mechanisms (shortening of the muscle). - This is simply the shortening (contracting) of the muscle.
• Eighth Step- Metabolic energy supply (energy required to perform the task). - This is the amount of usable energy stored in the muscle. This energy plays a part in allowing the muscle to continually contract at a high rate.
• Ninth- Metabolite accumulation (the waste of muscle contraction) - This means waste products (hydrogen ions and inorganic phosphate) affect future muscle contractions. If there is an increase in these waste products the muscle will not continue to contact as effectively.

Now that we have established a basic understanding of fatigue it is clear to see the importance of why athletes must mitigate fatigue to compete at their highest level.

VBT accounts for daily fluctuations in fatigue.

Fatigue in the weight room will have the biggest factor on the athletes ability to produce force and progress in development. Due to many factors, the athletes’ fatigue level will change from day to day and throughout the season. Monitoring these fatigue level shifts and adjusting the training on a day to day basis to progress the athlete properly in a safe manner. VBT does with thorough objective data.

 

The graph above shows theoretical data of an athlete’s fatigue level over multiple days.

 

The biggest factor when it comes to causing fatigue in the weight room is volume. A common misconception of volume is that it is simply a change in total reps. Volume by definition though is the combination of load multiplied by total repetitions done by an athlete.

Other types of training use subjective data or no data to help athletes. Due to VBT being objective it allows for many added benefits that other forms of training can not.

VBT takes into account daily fatigue fluctuations, multiple ways to track progression, provides more specific training, and identifies weakness of the athlete.

In our next units we will continue to detail why VBT is simply the most advanced method of developing an athlete.

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We want to take a moment and thank Speed4Lifts for their sponsorship of this unit. Speed4Lifts has been an industry leader in VBT. Throughout this section we will highlight this technology to aid in the education of Velocity Based Training.

References

• Sanchez-Medina, L., & González-Badillo, J. J. (2011). Velocity loss as an indicator of neuromuscular fatigue during resistance training. Medicine & Science in Sports & Exercise, 43(9), 1725-1734.