Apr 21, 2003

Muscle Fiber Recruitment-Again

April 21 "The sole advantage of power is that you can do more good." –Baltasar Gracian

With the help of several strength coaches we put together this comprehensive article on Muscle Fiber Recruitment.

We are very thankful for the help we received from a several of coaches across the country who helped us put this article together. Namely, Coach Tom Kelso and his staff at University of Illinois-Chicago. Some did not wish to receive credit for their help as they do not want to receive the "ranting" e-mail that come with taking a stand for safe, productive and efficient training. The topic of Muscle-Fiber Recruitment is an important element of why we train our athletes the way we do. However, this topic, like others in the strength training world can be confusing and misleading for many coaches. With the help of these coaches, who are considered experts in the field, we will make a further attempt to clear up this issue.

Coaches, please take the time to educate yourself on issues of strength development. If strength training is important enough to make your athletes do, then it is important enough for you to learn as much as you can about it. We know the time commitment coaches are under, we are coaches ourselves. This website serves to be an informal, yet informative resource for the busy strength coach. We are by no means experts! However, we rely on what we can read ourselves, and from coaches whom we have grown to respect who are on the front lines of athletic strength development.

If you are truly interested in learning more about safe, productive, and efficient strength training we recommend two books in particular: "Maximize Your Workout" which has various essays written by strength coaches from around the country who work with developing athletes in a variety of sports and "A Practical Approach to Strength Training" by Matt Brzycki. We are not trying to make a buck off of this endorsement, go check them out from the library for all we care. However, we feel that these books gave us a greater understanding of the topics discussed on this website and can help you as well.

Listed below are several responses to our question about muscle-fiber recruitment. They are listed in no particular order but are meant to clarify various issues concerning this topic. We begin with opening remarks from two collegiate strength coaches.
Many high school programs (and some smaller college programs) are sub-par (poor supervision, lack of qualified strength coaches, poor facilities, etc.) The information on StrongerAthletes.com is to provide practical suggestions to coaches who may have substandard "resources" to work with. Aside from this point, its difficult to argue against safe and time-efficient programs as they are proven to work at both the collegiate and professional levels, especially due to 1) limited time we all face and 2) the potential of legal issues in our increasingly lawsuit-happy society. From the outset, please understand this fact: one does NOT have to do Olympic lifts and/or variations of them in order to win championships or improve the physical qualities of athletes that will help them achieve in sport. Numerous teams/individuals have proven this – especially on the professional and collegiate levels. You are NOT at a disadvantage if you do not do them provided you are doing a progressive, total body-emphasized strength program, coupled with out-of-the-weight-room sport-related speed and skill training. End of that issue. -Tom Kelso
In my opinion, you must ask yourself three questions before you engage in a philosophical conversation regarding strength training.

  • 1. What is strength?

  • 2. What is strength training?

  • 3. Why strength train?

In my opinion, a major reason for the dissension within the profession is nebulous terminology. Forget HIT vs. periodization or one set vs. multiple sets, ask ten individuals their definition of strength and get ten different opinions. If you are going to develop something, it should be understood what it is that you are attempting to develop, in our profession, strength. -Coach B [This coach who, with the help of one of his university's faculty, were happy to help contribute to this article did not want us to use their name or school. They understand the problem associated with taking a stand for safe, productive and efficient training: angry e-mail's! While they support these issues they do not wish to spend their time receiving any e-mail from every power cleaning coach in the country.]

In regards to muscle fibers being recruited in an orderly fashion, some believe that by training fast in the weight room one can develop fast twitch fibers. If this were the case one would skip over the small motor units, A.K.A. slow twitch fibers, and begin to work the larger units or fast twitch fibers. Some coaches maintain that the muscle recruitment pattern is not the same from set to set.
Yes, each set would be "different" if 1) different loads were used, i.e. 70% would initially recruit "x" number of fibers and 85% would recruit "x" + "x" more, and/or 2) in consideration of fatigue, the fatigued fibers in set one would create a slightly different situation in set two due to some fibers being less than 100% fresh. However, a similar demand pattern is naturally elicited for each situation: clearly, the greater the demand, the greater number of fibers twitching and/or being recruited as opposed to a lesser demand where a lesser number of fibers are twitching and/or being recruited, independent of a person's genetic make up (i.e., fiber type, number and distribution through the body). That is why if you had ten people lift a 100 lb. barbell as many times possible you'd get varied results, but each would be governed by the aforementioned force demand/recruitment phenomenon. This is the essence of the Henneman's Principle of motor unit/muscle fiber recruitment. Henneman's Principle is the generally accepted recruitment process within the neuromuscular system. It is based on both science and common sense. Lower demand activities don't require a lot of force (relatively speaking), so the lower threshold (type I) fibers are called upon first. If more force is needed, 1) the working fibers (type I or even the higher threshold type II fibers, depending on how low the demand is) are stimulated more frequently then 2) more fibers are recruited to assist. Newly recruited fibers are then stimulated more frequently if more force is needed, then further recruitment of higher threshold fibers occurs to keep the activity going. This is the basis of the aforementioned scenario regardless of one's genetic make up (i.e., again, fiber type, number and distribution throughout the body).

Apply this to any situation you've encountered, athletic or not. For example, if I squat down to lift a two-pound rock, it requires very little fiber involvement. If I squat down to pick up a two hundred pound rock, I have to recruit a heck of a lot more fibers. I could rise and descend many times when repetitively lifting and lowering a two-pound rock before becoming fatigued, but the greater initial effort required to lift the two hundred pound rock would be more taxing when it is lifted repetitively. Consequently, I would have to halt the endeavor or take longer rest intervals between a series of lifts, long enough to replenish ATP-PC stores and remove accumulated lactic acid in order to continue. -Tom Kelso
Through personal research and in conversation with colleagues, the general principle of muscle fiber recruitment doesn't change per exercise. Those fibers that attach to lower electrical threshold motor units are activated first regardless of the activity. Granted, a second set of the same exercise may involve different fibers due to a change in repetition speed, angle of movement, etc. but that doesn't alter the general principle of muscle fiber recruitment. -Coach B

Some coaches believe that it is not possible to determine how muscle fibers are recruited during training.
It is true that increasing frequency of activation (twitching) and increasing the number of fibers being recruited lead to increased force production. However, the point that ".. it is not possible to determine how muscle fibers are recruited during training" contradicts the previous statement referring to increased force production by: 1) increasing frequency of activation (twitching) and 2) increasing the number of fibers being recruited. That IS how it is done: some combination of increasing firing rate and further recruitment of fibers. Specifically how it happens is not important, but what is important is we know it happens as the demand for force increases. This is simple common sense. -Tom Kelso

In an earlier article we wrote about muscle fiber recruitment we used an example of how one might go about tapping into their fast twitch muscle fibers. We labeled the various levels of motor unit groups into Type I (slow twitch), Type IIa (intermediate slow), Type IIb (intermediate fast), and Type II (fast twitch fibers). This example was a simplified breakdown of the various levels of motor units used. We have been criticized for limiting the body to these 4-types while there is a whole range of muscle types ranging from slow to fast twitch.
There are a number of classification systems, but for sake of simplicity, it is pragmatic to use the 4-class system as it represents a reasonable consensus on motor-unit (fiber) classification. The bottom line is that there are obviously different fiber types for different situations. How else could you explain the short-nature of lifting a heavy resistance for only a few number of repetitions, or the longer duration potential when lifting a lighter resistance? Likewise, muscle fiber characteristics do play a key role in running a marathon as opposed to sprinting 100 meters. I think we'd all agree to that. -Tom Kelso
I would agree that there is a continuum of muscle fiber types with Type 1 at one end and Type 2B at the opposite end. Along this continuum, there are intermediate fibers displaying characteristics that "bridge the gap" as the essay states. To simplify the obvious, approximately 10-180 slow twitch fibers attach per motor neuron. Approximately 300-800 fast twitch fibers attach per motor neuron. This explains why fast twitch can be defined as "strong" (capable of producing a large amount of force) and slow twitch are considered "weak". In regards to contraction speed, fast twitch fibers reach tetanus in approximately 10-50 milliseconds and slow twitch fibers can contract within 100-110 milliseconds. Therefore, the contractile difference is only 60-90 milliseconds. This fact becomes lost because of the term "slow" twitch fiber. "Slow" carries a negative connotation within the strength training field. -Coach B

Critiquing the same muscle fiber recruitment article some coaches argue that our example is misleading. We state that during the first 2 reps one trains the Type I fibers, the 3-4 reps train the Type IIa fibers, 5-6 train the Type IIab fibers and the 7-8 reps train the Type IIb fibers. That example can be misleading but the point we were making is that if a person were to reach the point on momentary muscular fatigue at the 8th rep they would be recruiting all of their muscle fibers, including the Type IIb. As the athlete was getting to rep 8 he would be depleting the slower twitch fibers and gradually acquiring the need for more motor units.
Tom Kelso gives another explanation: Maybe a better way to explain the schematic would be to say that on repetition number 1 "x' number of fibers are working. For sake of example, this could be 500 of one type, 200 of another and 125 of another. As each repetition is performed and fatigue begins to set in, the "x' fibers are stimulated more frequently (some of them being rendered useless due to fatigue) and more fibers ("y") are then recruited to assist. For example, one could then progressively recruit 150, 75 and 100 additional fibers of each of the previous types. As further repetitions are performed, the newly recruited "y" fibers are stimulated more frequently and the process continues (some combination of increasing frequency of stimulation and recruitment of more fibers) until it is impossible to due to fatigue. This is a hypothetical and simplistic overview of what happens, but a very good description of what is actually "going on" in muscle tissue/the neuromuscular system. Understand that there are numerous scenarios based on the force demand and time components of the situation. For example, a 2-RM resistance exercise would recruit a large number of fibers due to its nature, but would be a very short-duration endeavor due to the recruitment of the faster-to-fatigue, higher threshold type II fibers (B and C, for sake of example). When they are fatigued, the event is done as it is then impossible to continue on with the other "weaker" but un-fatigued fibers. A 20-RM resistance would actually work a greater "pool" of fibers due 1) a more prolonged frequency of stimulation and 2) the progressive recruitment of more and more fibers over a longer time period – that is, a greater percentage of overall fibers are recruited and a longer time they are under tension). This is why one feels more fatigued (lactic acid accumulation) following a higher repetition set as oppose to a lower repetition set (and one reason you can get "more bang for the buck" with sets of this nature). -Tom Kelso

Some coaches feel that Henneman's Size Principle does not apply to all situations, that there is a way to go around the slow twitch muscle fibers. They maintain that this can be done by using high speed movements that do not allow the slower type units to make their connections, or create tension.
Regarding "selective recruitment" (disregarding Henneman's Principle by suggesting lower threshold fibers are bypassed to go directly to higher threshold fibers), it depends on how you view this. Simply stated, if a huge demand is required (i.e., heavy resistance), then the dependence shifts to the higher threshold type II fibers (B and C, for sake of example). No question about this. However, it does not mean the lower threshold fibers are not recruited. They are. They would have to be, but their contribution is overshadowed by the higher threshold fibers. I state they "would have to be" because if the generally accepted Henneman's Principle is relevant, it would have to apply to ALL situations as it can't indiscriminately be applied. This would defy scientific law, similar to the law of gravity that applies everywhere and every time (on Earth). So, a high-demand activity does involve type I fibers, but the critical ones are the higher threshold type II fibers. This is analogous to going to war where a large-scale battle requires a large number of troops and progressively increased firepower. The first line of troops may be equipped with rifles, which gets part of the job done. As more power is needed, here come the tanks and Bradley Fighting Vehicles. To totally fortify the attack – building upon the continued effort and needed contribution of the rifles, tanks and BFV's – F-18 bombers are brought in to significantly impact the effort, making the greatest contribution of the four. -Tom Kelso
Is the fiber recruitment pattern set in stone? I would agree that it isn't. However, is it orderly? Yes. Is it possible for a movement to bypass slow twitch fibers. Yes. It is possible for a movement to bypass all fibers. Most biomechanics textbooks that I have read suggests that muscles respond to tension. Therefore, if no tension is placed upon a muscle there is no need for the cross bridges to attach because the muscle isn't performing mechanical work. Place a subject on a force plate connected to an oscilloscope and have the subject perform the jerk or push press. A sixty-pound barbell would exert as much as a few hundred pounds of force and as little as zero. With zero force, no mechanical interaction is present, because the muscles are not under tension (i.e. no need to perform work).

In regards to skipping over the slow twitch and developing the fast twitch fibers, one potential problem is how fast is fast enough to bypass the slow twitch fibers? At the speed needed to bypass the slow twitch fibers, do the forces exceed the structural integrity of the joints and connective tissue. If so, then doesn't an injury occur? As a health care professional, I'm under the Hippocratic oath, which states first, do no harm. -Coach B

Some coaches overly credit the use of quick lifts as the reason for their athletes' success on the field. These coaches down play the role genetics plays in determining fiber type make-ups. A reader recently wrote to us comparing weight lifters (athletes training for traditional sports) with bodybuilders noting the higher level of fast twitch to slow twitch fibers present in the weight lifter as compared with the body builder.
World-class weightlifters are undoubtedly genetically gifted. The amount of resistance they are lifting cannot solely be attributed to their work ethic and training program. They are blessed with an abundance of Type II fibers, good nervous systems and advantageous body leverages. Otherwise, you could take anyone (read: a "slow-twitcher" with lousy leverages) and put him/her on the same program as a world-class lifter and they'd lift similar poundage. It won't happen as the "raw material" (the aforementioned genetic advantages) must first be present. It has been proven that intermediate fibers (for example type IIA) can be influenced to "take on the look" of either type IIB or type I fibers if exposed to training that stresses them. In other words, if one does a lot of aerobic/low-intensity work, the intermediate fibers will adapt to that form of stress. Likewise, if high intensity exercise is undertaken on a regular basis, they will adapt to that. Therefore, if lifting very heavy resistance on a regular basis (i.e., weightlifters, bodybuilders or football linemen), a muscle biopsy may naturally reveal more type II fiber characteristics in these individuals.

Bodybuilders, however, do lift significant resistance in order to hypertrophy muscle. Even as low as 60% of a 1-RM is significant in that it is 60% greater than zero resistance. And taking a 60% resistance to the point of muscle fatigue does indeed overload a lot of fibers, many Type II included. And to end the issue on bodybuilding (we'd have to get into drug usage, extreme dieting and other nauseating issues which is beyond the scope of this point) I'm sure they use resistance equivalent to 75%, 80% and 85%+ of a 1-RM in their training, something weightlifters also do. And I doubt there are many championship-caliber bodybuilders out there who are muscularly weak. They do not practice the clean and jerk and snatch as there is no need for that. And I'm sure if they did they would become stronger in those lifts, so you can't really make a fair comparison on strength levels between weightlifters and bodybuilders (the old adage, comparing "apples to oranges" applies here).

Interestingly, in Zatiorsky's book, The Science and Practice of Strength Training, (Zatiorsky is widely noted by much of the quick lifting world -S.A.) he notes that the distribution of weights lifted by the former U.S.S.R. weightlifting team in preparation for the Seoul Olympics in 1988 was as follow:

  • (percentage are of a 1-RM)

  • <60% = 8% of all lifts (mainly warm ups/restoration)

  • 60% to 70% = 24% of all lifts

  • 70% to 80% = 35% of all lifts

  • 80% to 90% = 26% of all lifts

  • 90% to 100% = 7% of all lifts

Almost 60% of all lifts were in the rage of 60% to 80%, which is equivalent to a range of approximately 8 to 15 (give or take a few) repetitions when traditional set/rep schemes are applied (independent of such factors as lifting speed, cadence, R.O.M., level of muscular fatigue attained, etc.) Also, 26% of all lifts were in the 80% to 90% range, equal to a range of approximately 4 to 8 repetitions (give or take a few). Interestingly, in a sport where the goal is to lift as much resistance possible, only 7% of all lifts where in the "heavy" (90% to 100%) range. Time obviously had to be spent lifting competition-specific resistance, which the 7% would account for. It can be surmised that the relatively "lighter" resistance (60% to 90% resistance – totaling 85% of all lifts) where used to increase muscular strength somehow, which simply proves that these supposed "moderate loads" can indeed work in a strength-enhancing capacity.

It should also be noted that being "explosive" does not mean one has to be "fast" when moving a resistance. When we are discussing fast and slow – both relative terms – fast would naturally be on the continuum where the speed at which actual sport skills are performed (i.e., swinging a baseball bat, long jump take-off, tennis serve, soccer kick, etc.) In the weight room, to move a resistance fast the resistance MUST be relatively light as it is impossible (laws of gravity/physics) to move a heavy resistance fast compared to no resistance at all (i.e., sport skill). Even 40% of a 1-RM – considered "light" by most strength program standards -- cannot be moved at a speed that is exactly similar to the speed of an un-resisted sport skill.

The point here is simply as long as one is trying to be explosive against a resistance when strength training (significant tension-producing resistance), it does not have to move at the speed exhibited during an actual sport skill. In fact, it is impossible to exactly replicate the exact speed of ANY skill, even when only a few pounds of resistance are used. So, lifting meaningful resistance (i.e., 60%+ of a 1-RM) will naturally move "slow" but involve a greater amount of muscle fibers (force/demand relationship). The heavier it is the slower it becomes but with greater fiber involvement, all other factors equal. So, improving muscle force potential in the weight room (read: getting stronger!) will then better one's ability to exert force in an athletic situation, all other factors equal. This is really simple to understand, but many have hard time grasping it for some reason (ego? financial gain? Ignorance?). -Tom Kelso

Ultimately, the disagreement over this issue comes down to this. Some coaches will maintain that by moving a lighter load quickly an athlete can develop more power that moving a heavy load slowly.
This is a great point, and is essentially the crux of the matter: Part I If I stood on a force platform with 200 lbs. on my back and drove out of a squat position, the speed exhibited and amount of force registered would depend on two factors: 1) my maximum strength and 2) my conscious effort to move it. If my 1-RM was 200 lbs., it naturally would NOT move fast, but the force exerted would be high. If my 1-RM was 400 lbs., I could move the 200 lbs. consciously faster and thus with high force. If my 1-RM was 300 lbs. the 200 lbs. would not move as fast as compared to having a 400 lb. 1-RM, but it would still move faster than the first scenario (lifting a 200 lb. 1-RM).

If one becomes STRONGER, he/she can exert faster force with sub-maximal resistance. For example, if a person had a 1-RM of 300 lbs., he/she could consciously lift 200 lbs. faster than lifting the 300 lb. 1-RM. They could also consciously NOT lift 200 lbs. faster if they simply slowed it down. If the 1-RM was increased to 335 lbs., then they could consciously lift 200 lbs. even faster than when at a 300 lb. 1-RM because more muscle fibers can be recruited and/or their inherent capacities enhanced for greater force exertion.

In these examples, the exact amount of force registered on the force platform is unknown. Could the amount registered be higher when lifting 200 lbs. as fast as possible as compared to lifting 300 lbs. consciously slowly? Possibly. It all comes down to those two important factors: 1) strength and 2) conscious effort.

We all have the ability to regulate/control force within the confines of our neuromuscular systems: intra-muscular coordination (individual muscle firing rate/type of fibers recruited) and inter-muscular coordination (coordination of different muscle groups ). It is up to the individual how he/she wants to express force: 1) a quick burst/firing of fibers as in a vertical jump, 2) a sustained, maximal bearing-down fiber recruitment as in attempting to lift a 1-RM or 3) a sustained, but longer sub-maximal fiber recruitment as in a 15-RM set of an exercise.

In examples 2 and 3, "x' number of fibers are recruited to initiate the endeavor (1-RM = a maximal number and 15-RM = a sub-maximal number). Then, to keep it going:

  • 1. The initially recruited fibers increase their firing frequency (during a 1-RM it occurs immediately due to the extreme effort needed; during a 15-RM it occurs gradually over time).

  • 2. More (higher threshold) fibers are recruited to assist (during a 1-RM it occurs immediately due to the extreme effort needed; during a 15-RM it occurs gradually as the repetitions become more difficult due to the onset of fatigue).
Remember, depending on our individual genetics, we can express force in three primary ways as in the previous examples: 1) the quick burst (power) force application, 2) the maximal bearing-down (strength) application and 3) the sub-maximal extended (muscular endurance) force application. ALL OF THESE CONSCIOUS AND SELF-REGULATED EXPRESSIONS OF FORCE ARE GOVERNED BY ONE'S STRENGTH LEVEL AND INHERENT NERVOUS SYSTEM THEY ARE BORN WITH (AGAIN, FIBER TYPES, NUMBER AND DISTRIBUTION THROUGHOUT THE BODY). -Tom Kelso

Some coaches maintain that both moving a lighter load quickly and moving a heavy load slowly will both develop fast twitch muscle fibers.
The crux of the matter: PART 2. Yes, moving both consciously fast and slow with significant resistance – all other factors equal -- both work fast twitch (type II) muscle fibers, BUT THE FASTER MOVEMENTS UNDOUBTEDLY INCREASE THE RISK OF INJURY! (moving too fast can also create too much momentum and lessen muscular tension making it an inefficient means of overloading). I fully understand that many have trained for years doing high-momentum, ballistic lifting and have not incurred an injury. Similarly, one could drive his/her automobile for years without using a seat belt, but in that one moment when an accident does occur, it could be nasty. It's simply a matter of common sense and not worth the risk imparting excessive momentum in the weight room.

But a more significant point is this: if moving both slow and fast work fast twitch (type II) fibers, THERE OBVIOUSLY IS NO SUPERIOR ADVANTAGE IN MOVING FASTER (INJURY) AS COMPARED TO MOVING SLOWER. Likewise, there is no superior advantage in moving slower as compared to faster, other than less chance of injury (a no-brainer!) Rational conclusion: make it safer by slowing it down. You CANNOT argue that point when you are dealing with the health and well being of athletes. It would be quite awkward explaining to Mr. and Mrs. Smith that their son, athlete Johnny, fractured his wrist while performing an exercise and/or using a speed of movement that could have been avoided. -Tom Kelso
The term explosive is deceiving as you know. You can train explosively without a great deal of speed being produced on the bar. We have a student-athlete that participates in the sport of football. This student-athlete is non-traditional and was an alternate on the US Olympic weightlifting team for a few years. According to the preceding paragraph, this young man's percentage of fast twitch fiber to slow twitch fiber should be off the chart. It probably is. The bottom line is this athlete doesn't play in the fall due to limited football skills. All the fast twitch fiber in the world doesn't ensure success in specific sport skills. -Coach B

Many coaches are frustrated with our down play of using movements such as the power clean.
Regarding the power clean, I've heard many reasons why to do it:

  • 1) "It's a football lift" (so I assume basketball players have a "basketball lift"?).

  • 2) It develops power.

  • 3) It develops "explosion."

  • 4) It replicates jumping, which then would purportedly augment rebounding in basketball, spiking a volleyball, high jumping or blah, blah, blah).

  • 5) It develops overall coordination.

  • 6) It enhances "Hip Roll" (to purportedly augment football tackling).

  • 7) "It's a total body lift."

  • 8) It makes one mentally tough.
The power clean (or hang clean, snatch, push press, etc.) is unique as compared to other exercises because both the lower body and upper body musculature is involved. But that is simply the nature of the lift, and many have stretched the facts behind it elevating it to magical proportions. If you want to do it, fine, but you don't have to for a number of reasons (beyond the scope of this discussion, but mainly safety, time spent teaching, it's ineffectiveness on lower body musculature overload and that it's not "sport-specific"…if you want more, I suggest reading Dr. Ken Leistner's The Steel Tip discussions on it or Jim Kielbaso's chapter in Matt Brzycki's text, Maximize Your Training, or even Matt's other writings as there is a lot of truthful information on it "out there").

In reality it is simply a test of strength and skill. One can power clean (or snatch) more resistance than another if 1) they are stronger and/or 2) they are skilled at doing it. Likewise, an individual can power clean more resistance over time if he/she 1) becomes stronger in the muscles involved with the lift and/or 2) improves their skill at doing it. World-class weightlifters back squat, front squat and perform overhead presses in order to get STRONGER. They also practice the skills of their sport (clean and jerk, snatch) to perfect them. Yes, one could improve his/her muscular strength by doing power cleans or snatches if progressive resistance is used (in as much as the muscles performing the work are overloaded).

Regarding muscular failure, I've seen it during a power clean. Usually, it's in an upper body muscle group such as the traps, deltoids or arm flexors – the limiting muscle groups that prevent heavy loads from being used (as compared to heavier dead lift resistance). Ironically, this is one reason why the power clean would be a better upper body exercise than a purported lower body exercise and a squat clean a better option (although not recommended) because heavier resistance can be used in squat cleaning.

Regarding the "strength quality of rate of force development," (RFD) the "strength quality" WOULD be related to the force aspect of rate of RFD, so increasing strength would be a desired option. Also, reaching "failure"(muscular fatigue) is an objective way to 1) increase strength [muscular fatigue = a maximum number of fibers recruited and overloaded] and 2) measure progress from workout to workout.

RFD is primarily a nervous system/conscious effort issue. That is, RFD is increased when a person consciously attempts to fire the greatest amount of fibers possible in a given instance. If subject A has been blessed with a high neurological ability and a majority of type II fibers, they can produce high force and do it quickly. If subject B has a low neurological ability and a low percentage of type II fibers, their speed of execution and amount of force will be less than subject A, all other factors equal. Of course, enhancing the STRENGTH of all muscle fibers will improve either subject, but subject B will always be at a disadvantage as compared to subject A, all other factors equal. This simply shows the significance of the genetic factor, why some have it and some don't regardless of how hard they try or train.

Again, because we all (healthy people) have the ability to consciously regulate force development – quick burst, maximal bearing-down force, low force/extended, slow, etc. – the highest RFD is obtained by the conscious effort to fire a large number of fibers instantaneously. If these fibers have been enhanced via progressive strength training, even greater force can be expressed because of this enhancement and the fact that more can be recruited. Therefore, RFD is enhanced in the weight room not by moving fast, but by using heavier resistance (strength training!) as they demand greater fiber recruitment (i.e., types IIA, IIB and IIC).

Heavier resistance do not and cannot move fast, but the conscious effort to try to move them fast is the key. If moving fast in the weight room was important for improving RFD, then the lightest possible resistance would be used as it would offer the fastest speed. However, a light resistance requires less overall muscle fiber involvement, rendering them ineffective. Outside the weight room in practice is where one can augment RFD by performing sport skills as fast as will be needed in competition. They can train the nervous system to activate specific muscles, do so in the proper sequence(s)/joint angle(s) and recruit individual motor units/muscle fibers to express the force requirements needed to complete the task(s) (i.e., maximal, sub-maximal or quick burst actions). -Tom Kelso

Some coaches disagree with our use of the term "Intensity". We use the term intensity to mean the increasing difficulty to move a resistance through a working set. For example while the first few reps of a set are performed with somewhat ease the intensity is low. However, as the set continues and the resistance becomes more difficult to move the intensity increases. Finally when the set reaches the point just before momentary muscular fatigue, the intensity it at its highest. Some quick lifting coaches follow the Russian definition of intensity which is measured by a percentage of an athlete's 1-RM.
Strength training properly done takes great effort. It would be very difficult to find anyone who became larger and stronger without working hard at some point along the way (unless they were genetically gifted and/or utilized an effective drug program, yet even then they would have to exude some level of "above average" effort to create an overload on their muscles). It makes perfect sense then to define intensity as it relates to strength training in terms of level of effort/exertion (as intensity is defined in any dictionary). The Russian definition if intensity is applicable to a point, but doesn't take into account the trainees' level of effort exerted, which makes it somewhat of a misnomer and thus confusing (also, any mention of the former Soviet methods should include their performance enhancing drug program that undoubtedly was a factor in their overall success in international competition). They suggest that the heavier the resistance, the more intense it is. Therefore, lifting 90% of a 1-RM is more intense than lifting 70%. This is true if only a few repetitions were performed. Three to four repetitions with 90% would result in, or come very close to, muscular fatigue. The same number of repetitions with 70% of 1-RM would not, thus it would not be intense relative to those who ascribe to intensity being related to level of effort/exertion exuded. On the other hand, it's ridiculous to label 70% of a 1-RM as "low intensity" (by Russian standards) if it is lifted to the point of muscular fatigue. Because muscular fatigue is an objective of most safe and efficient programs, the level of effort required to take 70% of a 1-RM to the point of fatigue would be very high, thus making it intense. In fact, 70% worked to muscular fatigue involves a greater "corridor" (as Zatsiorsky calls it) of motor units/muscle fibers as compared to 90% worked to muscular fatigue. -Tom Kelso

Some coaches feel that by not preparing an athlete for the demands of sports, such as using momentum to ones advantage and absorbing momentum we are doing our athletes a disservice.
Now we are getting into a totally different topic: sport-skill training. To better prepare athletes for the demands of competition the practice of competition-specific skills/situations must occur. Through repetitive practice of sports/sport skills, it does prepare athletes to play with the forces of momentum. If I am an offensive tackle, to better myself I'm surely going to practice coming out of my stance, foot work and pass blocking against a live opponent. Same for a wrestler or tennis player: practice wrestling maneuvers and hit/return tennis balls against a live opponent, replicating competition-specific situations. In the above examples, they will use and absorb momentum through the nature of the sport, which could lead to an injury even when practicing. As a result, having stronger muscles throughout the body will minimize this risk in both practice and competition as stronger muscles can contract to better support/stabilize joints and absorb forces during skill performance and when the body is placed in compromised positions (i.e., landing or falling awkwardly). Lifting weights fast to develop supposed similar momentum encountered in competition is borderline ludicrous as it 1) does not replicate exact sport skills in the first place, 2) could lead to an immediate injury due to increased strain/force placed on muscles and joints and 3) increases the number of "exposures" to high-momentum situations which over time could lead to an over-use, wear-and-tear injury. -Tom Kelso

Some readers we hear from down play the role of training to fatigue use the example of distance runners, who train for long periods of time but obviously do not make use of their fast twitch fibers.
This is a questionable and somewhat irrelevant point. Distance runners do fatigue fibers, but primarily the Type I fibers as the intensity of distance running is far from the intensity of work that recruits the higher threshold fibers (i.e., sprinting, weightlifting). And fatigue DOES play a role in muscle fiber recruitment (Henneman's Principle, fatigue/continued force output options = firing rate, then recruitment of new fibers as FATIGUE sets in). Low intensity training (marathoners) = call upon predominately type I fibers; High intensity training (sprinters) = call upon predominately type II fibers. -Tom Kelso
First we must define intensity and duration of exercise. You may work out at a high intensity or a long duration but not both. For example, is a 100 meter dash an all out activity or do you run a 100 meter dash at 90% capacity? If the former, how long could you maintain the pace? 300 meters? 400 meters? I don't know that distance running is a good example of what I would consider a high intensity activity. -Coach B

Some coaches question our use of training to failure as athletes, specifically, football players use short bursts of energy. Train in the weight room in the manner in which you play is their argument.
How much is enough to prepare an athlete for competition? Ken Mannie has a great quotation regarding this line of reasoning. "Using potentially dangerous movements in the weight room to prepare for potentially dangerous activities is like banging your head against the wall to prepare for a concussion." -Coach B
We are talking about two different things here: 1) strength training and 2) sport-related conditioning. In the weight room (strength training), "…stopping an exercise short of fatigue…" will undoubtedly mean some fibers were not recruited and overloaded. The closer to muscular fatigue one gets, the more productive the exercise is. If one stops an exercise at 10 repetitions when 15 could have been performed, those fibers that would allow for the performance of the additional 5 repetitions were not worked as hard as they could have been. If 14 repetitions were performed, it would be a better situation as those extra 4 repetitions worked more fibers, thus more were overloaded. (duh!) Regarding the fact that football calls for short bursts of energy followed by periods of rest: a sound conditioning program would take this into consideration and prescribe appropriate interval conditioning. For example, 15 to 25 x 30 to 40 yard sprints with a 1:4+ work-to-rest ratio (:05 to :06 sprints followed by :20 to :25 (or :35) recovery time. Another example would be performing short (:04 to :10) agility/change of direction drills at full speed with a minimal recovery time between each bout (i.e., :30). Either example would address the anaerobic nature of the game and lead to better conditioning provided it was done progressively (i.e., manipulation of intensity, frequency, duration, and bout recovery time variables).

Bottom line: the weight room is for getting stronger to 1) improve the force needed for conscious expressions of strength, power and muscular endurance and 2) minimize the risk of injury. Running/conditioning workouts predominantly prepare the athlete for the energy demands of their sport to prolong their ability to execute skills properly (i.e., delay the onset of fatigue that diminishes functional ability). -Tom Kelso
Do you need to train to failure for a training adaptation to occur? Research has not been able to prove the minimum level of intensity to stimulate muscular growth. Is it 85%? If so, how do you determine 85% intensity? Do not confuse intensity with a percentage of a 1 RM. On the intensity continuum, only two levels of effort can be accurately identified. Zero percent or total inactivity and 100%, characterized by the inability to perform another repetition, an all out effort. -Coach B

Some coaches refuse to see the logic in finding the most efficient manner in which to train athletes. By efficient we mean best return in terms of the time spent in the weight room.
Here is just one example of why we believe in efficiency: Here is the reality of strength training. We currently have 13 men's basketball players training in off-season workouts. Twice a week for one hour. Four of the 13 are from Puerto Rico and lack basic English speaking skills. We have enough problems communicating coaching points of basic compound and isolation movements without over complicating the issue. In fact, our staff would be better served to enroll in some Espanol classes as opposed to attending a strength seminar. These realities are not understood or swept under the rug during academic discussions regarding strength training. Another reality, you set up a time to train a student-athlete (i.e. 2:00). The student-athlete shows 20 minutes late because of a meeting with an advisor. You have 40 minutes to train this athlete because a team lift is schedule at 3:00. Do you spend time teaching the skill of certain exercises or do you prescribe a protocol that you know will provide musculature overload with minimal coaching points? For me, a no brainer, option two. -Coach B

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