Neural Mechanisms of Strength


    You may notice that every time you walk into a gym there is a cascade of involuntary physiological factors that take place in trained individuals. The nervous system is responsible for these adaptations.  When you are anticipating exercise, your palms begin to get a little sweaty, or suddenly you may feel your stomach “shift”. This reaction is anticipatory. Your mind knows that your body is about to work. The increase in perspiration and feeling in your stomach is your circulating blood being redirected from the visceral organs, to soon-to-be-working muscles. The aforementioned adaptations are only scratching the surface of your nervous system is capable in response to chronic controlled stress. 

 

     Maybe I am nerd, but this is a fascinating subject. Many classic schools of thought will attribute the first few weeks of strength gains due to similar mechanisms of the nervous system, but it seems to stop there. During the first few weeks of a structured resistance-training program radical strength increases can be witnessed. Such increases in strength are not structural adaptations, but neural. The nervous system becomes more efficient at recruiting the proper motor neurons, in the proper order (synchronistic), at the proper frequency and potentially recruiting neighboring motor neurons/ muscles. Little is said or attributed about training these mechanisms specifically after the first few weeks. We know that potentially over 100% increases in strength are possible. Leaving a major question unanswered. How much of strength increases is attributed to neural adaptations after several weeks, months or years?
    

     I have read a few articles covering such research in the past and the results were fascinating! The “gym bro’s” were not far off of the mark with the catch phrase “mind-body connection”. The power of the mind over musculature is evidenced in the responses of co-activation and internal inhibition, in response to a relatively heavy resistance. Co-activation, a contraction of the agonist muscle and the antagonist muscle simultaneously, reduces the amount of force we can produce voluntarily against a set resistance. This would be similar to trying to drive up an extremely steep hill in overdrive, with little momentum. We press the gas pedal but the resistance of the steep hill is decreasing the efficiency of the throttle response. Internal, or neural inhibition is a cancellation of a voluntary contraction against a resistance that is perceived, by the nervous system, as dangerous to the musculoskeletal system. These two factors of strength are partly responsible for early on drastic strength increases, but they can continuously be trained. Ideally with more experience under resistance or tension these mechanisms are reduced. Learning to efficiently recruit motor neurons is analogically expressed by using a dump truck equipped with a snow plow to clear your driveway after a snow flurry, as opposed to hiring neighborhood kids with shovels one at a time, until you had enough to finish the job. 
    

     Progressive overload is a primary principle of training. The specific adaptation to an imposed demand is created by chronic bouts of exercise training with a specific goal. The nervous system is no different in regards to response of training. The problem lies within trying to overload the same system that involuntarily shuts down a voluntary contraction, when the load detected is perceived as dangerous. This could be thought of as a parent teaching their kid to ride a bike. The kid wants to ride the bike but the parent knows it can be dangerous. So the child is given constraints, or limits. The child can ride the bike but only in the fenced in yard. Well Lance Armstrong didn’t get to where he was by riding his bike in his mom’s backyard. Neither will we become the strength freaks that we could potentially be, without challenging the nervous system. In regard to overloading the nervous system, we are often constrained by the amount of resistance we can overcome concentrically. Knowing that eccentric muscular contractions produce more force than concentrically, we are able to somewhat manipulate the ability to “super overload”.
  

     To investigate the benefits of neural adaptations I decided to leave my mom’s backyard, by field-testing this with the deadlift. One study I reviewed used the elbow flexors (biceps) and extensors (triceps) on accentuated eccentric resistance training versus traditional (same) resistance training, “The Effects of Accentuated Eccentric Loading on Strength, Muscle Hypertrophy, and Neural Adaptations in Trained Individuals.” The study found that there was a greater strength gain in accentuated eccentric resistance training than traditional on a single joint exercise. More interestingly, there were similar increases in cross sectional area (muscle contractile unit size). Suggesting that the added strength came from training the neural mechanisms. The chart below depicts a comparative chart of Dynamic Constant External Resistance (traditional) vs. Dynamic Accentuated Eccentric Resistance training of both elbow flexors and extensors.
 

Figure 1. Mean (6SD) values for concentric 1RM of the elbow flexors
over the duration of the study (* Indicates significant difference from week 0, p , 0.05).
 RM 5 repetition maximum.
 

Figure 2. Mean (6SD) values for concentric 1RM of the elbow extensors over
 the duration of the study (* Indicates significant difference from week 0,
 ** indicates significant difference from week 3, and *** indicates significant
difference from week 6 and from the DCER group at week 9, p , 0.05). 
RM 5 repetition maximum; DCER 5 dynamic constant external resistance.

 

    Body builders long ago adopted eccentric training for the increased muscular damage and therefore greater adaptation in response. What makes this different is the change in size was the same but more strength was gained in the research mentioned above. I wanted to test the same adaptation on an axial loading, multi-joint movement, such as the deadlift. It is vastly agreed upon that axial loading, multi joint exercises induce a greater stress on the whole body as an organism. Greater stress requires a greater response from the body for adaptation to the stressed system. 
  

     The subconscious mind is capable of much more involvement with strength than is often accounted for. Aside from making strength increases from neural overload, there are also increases of capable strength through involuntary measures, such as internal and external stimuli. Most of us have heard of “hysterical strength”, instances of people lifting cars off of loved ones in extreme scenarios. One study, “Some Factors Modifying the Expression of Human Strength”, investigated one’s ability under several different conditions, control, voluntary maximal scream, load surprise noise, hypnosis both with suggestions of weakness and strength. This study supported the researchers initial thesis that psychological, rather than physiological factors, determine overall performance when conducting a voluntary max effort movement. 

     One of the main reasons I wanted to become an exercise physiologists is to have a gym as a lab and performance optimization as a successful study! Now obviously, a scientific study would require a ton of resources and potentially years to complete, but a field test and a stronger deadlift will be pretty rewarding in my opinion. 
    

     For my field test I set a conservative training max concentric one-rep max (1RM) with no breakdown in technique. I added ~4% to the 1RM and started the program. Each week was an eccentric to concentric deadlift (un-racked the weight at lock out height). Week one, ~104% of concentric training max lowered to the ground, immediately a resistance band from the top of the rack was hooked on the end of the bar to assist in concentric contraction (band assisted deadlift). Once locked out bands were removed and action repeated for maximum reps, two sets were completed, 1x4 and 1x5, for 9 total repetitions.

Field Test Week 1:

     Week two was conducted in the exact same manner. During the second week there was better control over the resistance and posture with an added two repetitions, 1x5 and 1x6. 

Field Test Week 2:

     I have Just finished week three of the field-test yesterday with markedly better control and 15 total repetitions, 1x7 and 1x9!

Field Test Week 3:

 

     I am going to continue volume progression for one more week, then de-load (greatly reduced intensity) and on week 6 increase intensity to ~115% and start the volume progression all over. After week 9 there is another programmed de-load and a new 1RM test to measure efficiency, if any, of the program. 

 

                       

About the Author: Sean Mathis B.S., CSCS 

     Sean is a two-time Operation Iraqi Freedom veteran as an Infantry Squad leader/ Combat Medic. After completing active duty obligation, he earned his Bachelor's degree in Exercise Science from Montclair State University.
     Sean is a Strength and Conditioning coach at the Varsity House Gym in Orangeburg, New York http://www.varsityhousegym.com . Charged with writing the programs for the adult group classes and facility management, while enrolled as a full time graduate student at Montclair State University, in Exercise Science. Sean also competes in Strongman Competitions. 

Connect with Sean at: 
https://www.facebook.com/seancmathis 
http://seancmathis.wixsite.com/strengthconditioning
Instagram: @Sgt_Slaughter68


References:

  • “The Effects of Accentuated Eccentric Loading on Strength, Muscle Hypertrophy, and Neural Adaptations in Trained Individuals.”
  • “Some Factors Modifying the Expression of Human Strength”