Stronger Athletes

Dear StrongerAthletes: Fiber Recruitment And Bias

May 6 "Truth is what stands the test of experience" -Albert Einstein

Mystery Guest

If you think you know the answer or simply want to chime in with a guess.. drop us an e-mail at our Mystery Guest Trivia Department. All correct answers will be recognized on Friday. "This week's mystery guest was named conditioning coach, [for the Steelers], in February 1992 following 10 years as strength and conditioning coach at Penn State.

A native of Harrisburg, Pa.,he is in his 10th season with the team and his 23rd year of strength training. He served as the assistant strength and conditioning coach at Penn State from 1979-80. He was named the first strength and conditioning coach ever at Weber State in Ogden, Utah, in 1981, before returning to Penn State to take charge of the strength and conditioning program in 1982. s

Our mystery guest, 48, graduated from Central State (Okla.) University in 1973 with a degree in physical education. He spent the next five years as strength coach and assistant coach in football and track at Harrisburg and Steelton-Highspire high schools. He also is a member of the National Strength and Conditioning Association."

**Note** Much of this bio was taken from

Dear StrongerAthletes: Fiber Recruitment and Bias

Coach Rusty Whitt, Sam Houston State University, writes expressing his concerns over various topics ranging from fiber recruitment to perceived bias. We use this forum to respond. It should be noted, even though we agree to disagree on many issues, that Coach Whitt is a wonderful representative of the Strength Coaching profession as he attempts to find the safest, most productive, and efficient training strategies for his athletes.

Coach Whitt's comments are in italics, our comments follow Coach Whitt's comments in bold. In addition we have Coach Tom Kelso from the University of Illinois-Chicago who also brings some facts to the table. Coach Kelso's words are in RED.

Dear Coach Rody,

You fellas have been standing behind Henneman's size principle of activation--and you state that this means that IIb fibers are recruited through slow, controlled motions--and that only the higher reps can reach these precious IIbs--

First of all, we never indicated that high reps must be used. We recommend 6 reps or maybe 5 reps would be the low end of the range because of safety concerns. Reps exceeding 15 depending on the person does tend to tap into their cardiovascular capabilities.

I discussed this with a leader in exercise physiology-- A professor of Exercise Fizz at a certain enormous college in the Southwest, a fella who has authored the number one selling exercise physiology textbook in the U.S., who has researched every topic of human fizz out there for 30 + years. Dr. Wilmore states this about the Henneman principle--That the motor unit with the smallest motor neuron is recruited first, the motor unit with the next largest goes second, etc-all the way to maximal force production-but that this happens during EACH REP--not after a series of reps.

First, dr. Ralph carpinelli -- professor in the dept. Of exercise science, adelphi university -- would be a good "go-to" guy for all the technical aspects of this topic. That said, here's my "2-cents.".... Hang with me now, in the end this will all make good sense.

It does happen at the beginning of each rep and consequently over the entire set of reps. The brain senses what needs to be done based on the task (i.E., heavy demand or light demand) and recruits muscle fibers with respect to the henneman principle. In example, let's say your max on a dead lift is 450 lbs. And you use 75% of this -- or 337.5 lbs. -- and perform a set for maximum reps. Because it is a sub-maximal resistance, a smaller percentage of muscle fibers are recruited during the first rep as compared to a greater percentage required to lift the maximum of 450 lbs. This is a natural phenomenon, as one recruits only enough fibers necessary to perform the required task. Understand that 337.5 lbs. Is still a significant "weight" which requires effort and concentration, thus a significant number of fibers are activated even during the first rep, more than a relatively lesser-demanding activity that humans are accustomed to doing during normal, daily activities. An example of this would be lifting a 60 lb. Box of books or a 60 lb. Chair, both equivalent to 13% of the 450 lb. 1-rm....Typical non-strength training activities. This is why why non-strength training people do not experience hypertrophy and/or strength increases going about "normal" (low-intensity) daily activities.

Back to the main point: On repetition #1 of the dead lift, the nervous system recruits the necessary fibers (referred to as motor units from this point on) to lift the 337.5 lbs. Through the range of motion. According to henneman's principle, type i motor units are recruited, then type iia, and if necessary (and most likely in this example they are), the type iib units because it is a significant tension-producing resistance (75% of the 1-rm = 75% more than zero resistance and only 25% less than the 1-rm!). For the sake of simplicity, the first rep may recruit in the "all-or-none" manner 100 type i, 45 type iia, and 20 type iib motor units to complete the task. As the number of repetitions performed increase -- and considering the fact that previously recruited motor units eventually fatigue and are rendered useless - the options available to continue the exercise are as follows:

Therefore, as in the previous example:

A key point of this whole endeavor is the third option -- the "recruit the larger, more powerful motor unit types." on that first repetition with 337.5 lbs. -- 75% of the 1-rm of 450 lbs. -- as stated, it is a significant amount of resistance as compared zero resistance. Even on rep #1, a large percentage of type iia and quite possibly iib motor units may be required to assist in lifting the 337.5 lbs. The point is that even though only 75% of the 1-rm is used-- a resistance considered by many as "light" -- it has the potential to create significant tension in the muscles and thus enhance type iia & iib motor unit overload if taken to the point of momentary muscular fatigue.

Momentary muscular fatigue -- ridiculed by many -- is a pretty objective indication that a maximal number of fibers/motor units have been recruited. You have to laugh at those who down-play it because it begs the question: Which rep before fatigue occurs should one stop at?!?!.

The bottom line is even a "light" resistance such as 75% of a 1-rm can recruit, fatigue, and consequently overload a significant number of type iia & iib motor units if worked to muscular fatigue -- somewhere in the range of 9 to 12+ repetitions depending on the exercise, person's fiber-type & nervous system, and lifting cadence (more on lifting cadence later).

A person using 85% of a 1-rm will naturally activate a larger percentage of motor units during the first repetition as compared to using 75%. It simply provides another option by which to create overload. It is the same with 72.5%, 80%, or any relatively "heavy" resistance. There are a lot of ways to create overload -- varied resistances and repetitions, exercises, exercise sequence, etc. This is good for program variety and individualism.

Again, the irony here is the heavier the resistance, the slower the movement speed due to the application of simple physics. If a resistance moves "fast" it has to be a light resistance relative to the strength of the person who is lifting it. Furthermore, the lighter the resistance, the more potential it has to move even faster. This is the point of confusion for those gung-ho for the "quick lifts." if one wants a quick/fast movement and minimal muscle activation, unload the bar/machine and throw the resistance. Simply use an unloaded 45 lb. Olympic bar and accelerate it like a mad-man. If one wants greater motor unit recruitment (read: More type iia & iib motor unit overload) then,

Another issue with lifting speed/cadence is the conscious effort exerted by the lifter to raise and lower the resistance. We actually conducted an informal experiment with some of our athletes to determine the effects on motor unit recruitment and speed of exercise movement.

Coach Kelso included the results of this test with the above information, however we want to give those results their own forum and will reserve those for another upcoming article.

Now, this is how I imply this: The amount of load dictates how many and what neurons are activated--not how many reps--so if an athlete makes an attempt at a triple of 315, and the second and third are extremely hard, then a great number of motor units are activated.

Yes, doing 3 reps at 315 lbs. -- provided it is demanding -- will recruit a lot of muscle, but over a smaller amount of time. This is an acceptable means of overloading at certain times and/or if used sparingly, but over the long run, constant use of super-heavy resistance can possibly limit the full-spectrum of motor unit recruitment due to the short length of time of the exercise. If one reaches muscular fatigue at 3 reps it is due to a high percentage of motor units initially recruited to perform the task (it's a very heavy weight for this person!). A high percentage of the larger, more powerful but more fatigable type iib motor units are recruited and fatigued, thus the exercise must cease. In such cases, there is usually a high percentage of the intermediate type iia motor units that never "get waxed" and consequently not overloaded....Another case for using higher reps to fully in-road the targeted muscle(s). In fact, zatsiorsky (a noted olympic-lift advocate) -- in his book, science and practice of strength training -- alluded to this fact and did a great job of explaining/depicting this issue.

More so than a set of 15 reps at say, 225--which may cause the athlete to lose muscle glycogen before all motor neurons are activated.


Now if an athlete does multiple sets at a weight, say 8x3 @ 70% of 1RM, the last few sets will touch on neuron recruitment-getting the desired training effect without handling a heavier load. This is a technique used with great success by the those of the Louie Simmons power lifting philosophy.


Your 8x3 being an effective way to train the Type IIb muscle fibers is certainly debatable and definitely not efficient. You had also mentioned that a set of 15 reps may cause the athlete to lose muscle glycogen before all motor neurons are activated is also debatable. The 8x3 and the 15 rep comments is a direct contradiction. If the 15 rep set did cause the athlete to lose muscle glycogen wouldn’t 8x3. You are performing 24 reps in those sets. Our example in the article is a set of 8. It could be a set of 3 or 5 as well but the Type IIb muscle fibers will be recruited if the force is there. Why would Type IIb muscle fibers be recruited when the weight is not heavy yet. Obviously if the weight is heavier Type IIb fibers will be recruited earlier in the set. As a set progresses with each rep more and more fiber will be recruited to perform the work. The force requirement is not that great at the beginning of the set (in the first few reps). Type II muscle fibers will be recruited if necessary as the set gets more difficult.

Dr. Wilmore believes that "great liberties have been taken with Henneman's Principle." Olympic lifting with multiple sets RULES.

In regards to Olympic lifting being the most productive way to train, if momentum is created on the bar the weight is too light to be very intense. How does this style of training recruit much of the Type II fibers?

As Ken Mannie stated in his article "Explosive Weight Training," "If the training goal is the recruitment and development of the fast twitch muscle fiber, fast weight training speeds at low intensity represent the *least* efficient approach."

How can momentum train Type IIb muscle fiber? Maximum continuous force is required and I’m sure Dr. Wilmore will agree with that as you have indicated. During each rep of a power clean, the tension on the muscle is taken off. Sure you will recruit fast twitch muscle fiber to a certain extent but it is a very unproductive way of going about it. Maximum force and full range of motion is the best way to train. Because of momentum, an athlete is providing minimal force and that lift is certainly not working any muscle to a full range of motion.

James R. Karp MS, in his article "Recruitment of Muscle Fibers" states, "Muscular strength is primarily developed when an 8 repetition maximum or less is used in a set. The body follows a certain order of recruitment beginning with the Type I fibers no matter what the load. However, if the Type I fibers (which do not have the potential for a whole lost of force production) cannot generate enough force to move the weight, the Type II fibers are called into play with Type IIa fibers being recruited before Type IIb. So, unless the load being lifted is sufficient to bring the Type IIb fivers into play, they will not be recruited and will not grow. However, sets in the 4-8 rep max range tend to be heavy enough to call the Type II fibers into play."

Keep in mind we are training athletes for their prospective sport. We are not training for Olympic lifting competition or Powerlifting competition. You keep bringing up Louie Simmons, we are not training powerlifters. If a coach trains for football players with singles, doubles, and triples, they are not thinking of the athletes' safety. Performing these low reps often is dangerous not to mention the Olympic lifts being extremely dangerous. These lifts are certainly not very efficient or very productive for our athletes.

Read some of Dr. Ralph Carpinelli’s publications. He is as highly a respected expert in neuromuscular physiology as there is in the world. He advocates slow repetitions as well as low volume training. He says that you can train with high intensity or train with volume, not both.

Coach Whitt responded to our first exchange.... "The 8 sets of 3 I mentioned is not contradictory, it is nothing like a single set of 15. With one minute rest between each set, muscle glycogen can be replenished--unlike the set of 15. As far as "efficiency" goes, this workout fits right in with the 1 hour slot that we have available for weight training our athletes."

Fair enough however, please see Coach Kelso's point above concerning multiple sets.

You keep calling Olympic lifts "momentum lifts"--and what generates the momentum? The legs, hips, and back. If an athlete is power- cleaning, say 286 lbs, they are performing an explosive deadlift, activating IIB fibers rather quickly--jumping with that kind of weight requires that type of recruitment. This "momentum" benefits the athletes--We had over 250 athletes power clean this semester, and we came out of it injury free--If these exercises are of such great danger, it would have gone another way. If their backs and hamstrings have been conditioned properly, the chances of back injury are minimal. I am 30, and have been power cleaning since I was 12-- (yes, and I used poor technique until I was taught correctly at 20) The back is fine.

We are as pleased as anyone that your athletes are safe. However, are you considering their long term health? If you dismiss that argument then we agree to disagree. You still haven't mentioned anything about the tension being taken off the muscle with each repetition. That minimizes recruitment of muscle. I recently presented a coach who was 100% power clean etc. He studied the research and realize

***No Liability is assumed for any information written on the website. No medical advice is given on exercise. This advice should be obtained from a licensed health-care practitioner. Before anyone begins any exercise program, always consult your doctor. The articles are written by coaches that are giving advice on a safe, productive, and efficient method of strength training.***

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