Training For Optimal Motor Unit Recruitment
This is a relatively long article so I’ll keep the introduction brief and to the point:
My friends and colleagues Mike Boykin and Colin Griffin were generous enough to ask me to contribute in writing an article on training for optimal motor unit recruitment. It was a distinct pleasure to work with both of these coaches and I encourage you to keep your eyes out for each of them in the near future.
Without further adieu, here is Training For Optimal Motor Unit Recruitment:
Our duties as strength and conditioning coaches often fall into two categories: increasing general athleticism as it pertains to the sport at hand and decreasing the rate of injuries. What sounds simple is, of course, quite complicated; if it weren’t anyone would be successful at this job.
Still, the two objectives are more related than one might assume. It’s too easy to divide sessions into mobility and stability work “for injury prevention” and strength and speed work “for athleticism.” Instead, what we must remember is that “preventing injury” and “being athletic” often go hand in hand as both rely a great deal on overall strength.
Strength, and being able to optimally recruit muscle fibers, is one of the most important abilities required to survive and compete at high levels of sport. Without the ability to absorb large amounts of rapidly imposed force or to quickly and efficiently apply force injury will inevitably result.
Training for optimal recruitment of these fibers, however, is not a simple task. Throughout history, coaches have employed many different methods to try and elicit maximal muscle fiber recruitment with the fewest side effects. The CNS is particularly susceptible to fatigue and burnout which creates a challenge to train the fast-twitch muscle fibers with the least risk of injury or overtraining.
Since the 1950s, coaches in the Communist Bloc countries have been using Electronic Muscle Stimulation (EMS) to increase activity of the high threshold motor units. Dr. Y. Kots brought the idea to Western countries in 1973 and it was adapted by coaches such as Charlie Francis to aid in the development of their athletes. Yes, this is the same modality used in many rehabilitation settings today. However, the goals and protocols when applied in a training environment differ from those present in the typical athletic training room or physical therapy clinic.
So why does it work? When the EMS is attached to a patch of skin it sends an electric current directly into the periphery. While this seems obvious, it is a key concept. The signal does not originate in the CNS and because of this the size principle does not apply– in fact, what happens is the exact opposite. The EMS stimulates all motor neurons simultaneously in a predominantly isometric nature. Because motor neurons that innervate the Type II muscle fibers are larger in diameter and consequently have a lower resistance to current, the electrical signal reaches the Type II fibers more quickly and tension is produced by these white, fast twitch fibers before the Type I muscles. Thus an increase in muscular efficiency is developed without added cross sectional area (which improves the strength to weight ratio up).
Another important benefit of EMS is the addition of muscle adaptations without CNS fatigue. Because higher-level athletes reach a state of overtraining through exhaustion of the CNS before accumulated stress to the peripheral nervous system EMS may act as a useful training tool. In Supertraining, Dr. Siff and Dr. Verkhoshansky point out that muscle feedback to the CNS, CNS integration of this information, neuronal output, and perceived effort all increase rapidly before the “physiological endurance limit of skeletal muscle” (Supertraining, Page 15). It is thus critical to factor in various forms of fatigue when preparing an athlete or group of athletes.
The question then becomes: how do we integrate EMS training within a yearly periodization model? EMS use should coincide with one’s strength training block as the two qualities are fairly synergistic. Coach Francis’ strength training block took seven weeks- three weeks of loading followed by a deload week, followed by another three weeks of loading. In order to phase in the amount of work imposed upon the body EMS was not used until the second and third week of each three-week high intensity microcycle. During the week EMS was used on “high” days of loading. The following guidelines were also advised by Coach Francis:
• 10-15 EMS sessions are sufficient
• use on quads, hamstrings, glutes, erector spinae, and even the soles of feet
• use before bed and after a hot shower
• begin with gentle pulsing for 3-5 minutes (cool down the same way)
• limbs straight and unsecured
• no antagonists
• negative pad over largest bulk of muscle
• “rise-time” of .50-.75 seconds (as short as possible)
• 10 max contractions with 10 seconds on and 50 seconds off
• Crank it up! Coach Francis emphasizes this multiple times
While EMS can be useful for imposing additional demands upon the athlete without the negative drawbacks of CNS fatigue it’s imperative to note that in order to properly prepare for sport the nervous system must be trained. This can be accomplished through the use of a well researched and proven-in-the-trenches training method.
In The Science and Practice of Strength Training, Zatsiorsky recognizes three methods of strength training. These methods are:
• The Maximal Effort Method
• The Repeated Effort Method
• The Dynamic Effort Method
Each of these methods of strength training can be an effective means of recruiting high threshold MUs. However, the terms “effective” and “optimal” are not synonymous. The authors argue that the Maximal Effort Method, defined by Louie Simmons as “lifting a maximal load against maximal resistance” (Simmons, 2009), is the superior method for developing athletic development– Soviet sport scientist Vladimir Zatsiorsky determined that the ME method elicits recruitment of “the maximal number of motor units…” and is “considered superior for improving both intramuscular and intermuscular coordination” (Zatsiorsky, 1995).
To determine how to incorporate the ME method in the training of athletes one need only examine the methods employed by Louie Simmons at Westside Barbell.
Westside utilizes a version of the Conjugate Method developed by Louie Simmons in 1983: Since “the muscles and central nervous system (CNS) adapt only to the load placed on them,” Westside incorporates the Maximal Effort method twice per week- one session each for upper and lower body movements (Zatsiorsky, 1995). Specifically, on each Max Effort day, the athletes at Westside choose a variation of the Squat or Deadlift (on the lower-body day) and the Bench Press (on the upper-body day) to max-out with.
The two key aspects to recognize in Westside’s application of the ME method are the following:
- By maxing-out every week Westsiders are constantly challenging their body, muscles, and CNS to adapt and gain strength. We know in order to get stronger we must force our bodies to handle maximal loads. Westside’s method takes advantage of this knowledge by handling maximal loads each and every week.
- Westsiders choose a variation of the Squat or Deadlift and the Bench Press each and every week. The CNS is highly susceptible to fatigue especially as an athlete becomes more advanced; by maxing-out on different (albeit similar) movements each week, the athletes at Westside eliminate any harmful side effects of training with near maximal loads while continuing to gain strength.
To illustrate what a 4-week cycle of Max Effort work may look like, a sample table is provided below.
|Week||Lower Body Movement||Upper Body Movement|
|1||Close Stance Below Parallel Box Squat: 1RM||Close Grip Bench Press Against Chains: 1RM|
|2||Zercher Squat: 1RM||Floor Press: 1RM|
|3||Deficit Sumo Deadlift Against Bands: 1RM||3” Camber Bar Bench Press: 1RM|
|4||Concentric Good Morning Off Chains: 3RM||Football Bar Bench Press: 1RM|
To clarify, on Max Effort Day Westsiders will work up to a 1RM in a variation of the Squat or Deadlift and the Bench Press; occasionally they will use a 3RM for variations of Good Mornings.
Westside recognizes the fact that training with maximal loads too often will result in a de-training effect. For this reason they dedicate two sessions per week to the Dynamic Effort (DE) method which can be defined as “lifting a nonmaximal load with maximal speed,” (Simmons, 2009). The purpose of the DE method is to improve explosive strength and rate of force development (RFD).
Why is increasing RFD and explosive strength important? According to Newton’s 2nd Law, Force = Mass x Acceleration (F=ma). In the weightroom, when “m” is emphasized it serves as the basis for developing high levels of force which lead to maximal strength gains. On the field of play, “a” is the most transferable quality that increases the capacity to produce force in the smallest window of time. Acceleration, and consequently some aspect of speed, is a specific skill that must be taught and trained. While it may seem intuitive, for a given mass more force will be produced (into the bar or onto the playing surface) with a larger acceleration.
The Westside version of the Dynamic Effort method involves lifting sub-maximal weights (generally ranging from 50-60% of an athlete’s contest max) as quickly and explosively as possible (i.e. with maximum acceleration). Additionally, Westside incorporates the use of bands and chains in an attempt to increase accommodating resistance. The use of bands is especially important as it creates an overspeed eccentric portion of the lift. This is done specifically to optimize the use of the stretch reflex, develop incredible reversal strength, and increase kinetic energy (KE).
While “it is impossible to attain maximum maximorum force (Fmm) in fast movements against intermediate resistance,” (Zatsiorsky, 1999) the addition of bands increases potential energy (PE) during the lift, which in turn produces a greater amount of KE. By increasing KE and creating a larger collision (onto a box while squatting or onto the chest while benching) we can effectively “trick” our minds into believing the bar is heavier than it really is. In doing so, we can utilize the Dynamic Effort method to dramatically increase RFD, explosive strength, and speed.
Westside employs the Dynamic Effort method in 3-week waves. In each successive week they increase the load on the bar from 50%, to 55%, and 60% of the athletes contest 1RM while using the same variation of the lift. On the fourth week they change the variation of the lift and cycle back down to 50% of the athletes’ contest 1RM and start a new 3-week wave.
To illustrate the use of the DE day, provided below are two sample 3-week waves; one for the lower body and upper body respectively. It is important to note that on DE day Westsiders always squat onto a box.
|Week||Dynamic Effort Lower||Dynamic Effort Upper|
|1||SS Bar Box Squat Against Bands: 12 x 2 @ 50% 1RM||Football Bar Bench Press Against Bands: 9 x 3 @ 50% 1RM|
|2||SS Bar Box Squat Against Bands: 12 x 2 @ 55% 1RM||Football Bar Bench Press Against Bands: 9 x 3 @ 55% 1RM|
|3||SS Bar Box Squat Against Bands: 10 x 2 @ 60% 1RM||Football Bar Bench Press Against Bands: 9 x 3 @ 60% 1RM|
It should be noted that the Maximal Effort method is the superior method for recruiting the maximum number of motor units and for developing maximal strength. However, it is very easy to abuse the ME method and cause a de-training effect. By cycling the use of the ME method and the DE method you can prevent an athlete from suffering the Law of Accommodation, make incredible strength gains, increase explosive strength and RFD, and maximize the number of MUs recruited during training. In short, a combination of the Maximal Effort method and the Dynamic Effort method is optimal for increasing athletic performance.
While the Conjugate Method uses maximum strength and speed work on separate training days during the microcycle, Contrast Training places the two qualities together within the workout. This capitalizes on a powerful neurological priming effect often referred to as post-activation potentiation, in which the body becomes over-prepared for the second quality being trained. The increase in central drive for a specific neural pathway leads to a general overall increase in activity via neuromodulators- chemicals that aid in the long-term postsynaptic cell’s response to neurotransmitters, which can increase the likelihood that the large diameter motor neurons will reach threshold. This increase in activity can last anywhere from seconds to days. An example of a general response to an increase in neural drive can be seen in a knee jerk reflex. When the arm is flexed, there is an increase in force from the reflex compared to when the arm is relaxed.
However, Contrast Training relies on the specific increase in activity down a neural pathway generated by one biomotor quality that can further enhance the execution of a second. In its simplest form, this could mean doing a heavy set of squats followed by unweighted vertical jumps.
While true that the body will adapt over time when simply performing ballistic movements alone, improvements will come at a slower pace than when contrast training is used- in other words, we’re not training optimally.
Contrast training is based on the premise that our body develops a set of motor engrams- “instructions which tell the body how to perform a specific movement” (SSTM, page 110). Before an action is even initiated, the motor cortex must know the purpose of the action, and then have a method that accomplishes the movement. More experienced individuals — those that we also term efficient — have a much more clearly defined set of instructions that are less likely to be changed. These motor engrams also play a role in kinesthetic sensations- feedback given to the CNS from the periphery. The more often a specific task at a specific rate is relayed from the brain to the tissues, and then via proprioceptive feedback, back to the brain, the more this pattern becomes engrained. While this sounds good for many situations, it is not ideal unless the proper sequencing and speed of movements are employed. When trying to increase speed and/or power, if the body has engrained a pattern that is slower than desired, as a coach, you must rewire the neural pathway you wish to effect. Furthermore, while specificity for improving a quality is needed, too much of one thing can lead to a dampened training effect. The body adapts to what it is given and cannot improve linearly forever.
However, when we vary external conditions with the same movement, the body, at least in the short term, adapts a new kinesthetic feedback loop that feeds into a new motor engram. If the normal external conditions are then employed, the previous changes can allow for an increase in force and/or an increase in speed. In addition, with this new training stimulus, we decrease the adaptation to a specific movement.
Verkhoshansky divides this variation in loading parameters into two methods relevant to this article: the Stimulation Method and the Contrast Method (it should be noted that while this section of the article discusses contrast training, the combined method of training Verkhoshansky terms the “Contrast Method” deals specifically with patterns associated with sport).
The Stimulation Method pairs a tonic exercise (the stimulator) with a speed-strength exercise. As both exercises are of high stress to the CNS, adequate rest periods should be observed between sets and series. Verkhoshansky gives examples of pairings (in increasing order of intensity) that can aid in increasing the explosive strength of the take-off:
|First Exercise||Rest Between Exercises||Second Exercise||Number of Complex Reps||Rest Between Complex Reps|
|Kettlebell Squat Jumps6-24 Kg2 X 6-83-4 min between sets||3-4 minutes||Leg to Leg Bounce2 X 5-63-4 min between sets||2-3||6-8 minutes|
|Barbell Squat70-80%2 X 5-62-4 min between sets||4-6 minutes||Standing Triple Jump2-3 X 6-84-6 min between sets||2-3||6-8 minutes|
|Barbell Squat80-85%2 X 2-33-4 min between sets||3-5 minutes||Kettlebell Squat Jumps16-32 Kg2-3 X 4-63-4 min between sets||2-3||6-8 minutes|
|Barbell Squat90%2 X 2-33-4 min between sets||4-6 minutes||Vertical Jumps With Barbell30%3 X 6-83-4 min between sets||2-3||8-10 minutes|
|Barbell Squat90-95%2 X 22-4 min between sets||4-6 minutes||Depth JumpHeight= .75m2 X 6-84-6 min between sets||2-3||8-10 minutes|
Taken from Special Strength Training Manual for Coaches, Page 108
While the protocols outlined above are intended for athletes with a large training background and adequate preparation, the concepts can be applied to less advanced individuals. Research also supports the use of isometric exercises, with a six second contraction in the position needed in sport, as the stimulator to increase the power and decrease contact time of repeat vertical jumps. Variations of these protocols can be used when preparation for high-speed strength (in comparison to explosive strength) is needed. Lower percentages are employed in these instances.
The Contrast Method is the primary method for increasing high-speed strength in sport. The sporting action is replicated with an external load that increases the resistance as well as with one that decreases the resistance. This can be something as simple as a shot-putter using a heavier implement, or as complex as Russian biomechanics professor L. Ratov’s device that hooked an athlete up to a spring and essentially decreased the force of gravity exerted upon the individual. More commonly used today are belts with release clips that allow athletes to run against resistance for an allotted time period and smoothly transition into running in normal external conditions.
While protocols vary from between sports and coaches, it is important to end each training session with reps done in normal conditions. This ensures that athletes take advantage of the neurological priming effects and put this new motor engram into a context in which they will compete.
In summary, while a huge variety of training methodologies exists, the bottom line is that athletes need to recruit the high threshold motor units and gain strength.
Francis, Charlie. “The Truth About EMS.” T Nation. Web. <http://www.t- nation.com/free_online_article/sex_news_sports_funny/the_truth_about_ems>.
Dr. Kevin Strang, Professor of Physiology at UW-Madison, Personal Reference
Simmons, L. Westside Barbell Book of Methods
Simmons, 2004: Optimal Eccentrics
Simmons, 2005: Benefits of Box Squatting
Thibaudeau, C. Theory and Application of Modern Strength and Power Methods
Verkhoshansky, Y. & Siff, M. Supertraining, 6th Edition- Expanded Version
Verkhoshansky, Y. & Verkhoshansky, N. Special Strength Training Manual for Coaches, Page 105-113
Zatsiorsky, V. The Science and Practice of Strength Training
Mike Boykin is currently an undergraduate student at the University of Wisconsin-Madison where he is pursuing a degree in Kinesiology with a focus in Exercise and Movement Science. With an unending drive to further his education, Mike has interned under physical therapists, athletic trainers, and strength and conditioning coaches. Feel free to contact him at firstname.lastname@example.org
Colin Griffin is a certified personal trainer, physiology student, and intern assistant strength coach at the University of Wisconsin- Madison. He is also the strength and conditioning coach at Edgewood College. Colin competes in triathlons and is an Ironman finisher. He can be contacted at email@example.com
Jordan Syatt is an up and coming strength training and nutritional consultant. He is currently interning with Louie Simmons of Westside Barbell and studying Exercise Science and Nutrition at The University of Delaware. For more information visit his website at www.syattfitness.com or e-mail him at jsyattfitness.com