Motor Unit Properties and Fiber Types:
Speculations on Exercise Prescription
By Gus Karageorgos
There is little doubt that genetics play a major role in one's predisposition
for muscular strength and hypertrophy. Almost all authors also recognize the
need for a sufficient level of training intensity (i.e. the degree to which a
muscle has been fatigued/inroaded per unit time) for optimizing muscle strength
and hypertrophic adaptations. Precise quantification of training intensity,
however, is relatively difficult to monitor; consequently, relatively uniform
training guidelines are often prescribed (i.e. train to concentric muscular
failure within a 45-90 sec. time interval). Many authors also acknowledge the
importance of individual recovery ability and/or fiber type as important factors
that need to be considered when implementing any exercise program. Precisely how
and to what degree these factors affect exercise intensity and prescription is
currently being debated and will be the focus of this paper.
There is also increasing awareness by many authors that individuals will need to
change some aspect of their training, if long-term progress is to continue. One
group of authors believe that, in order to ensure optimal and continued
progress, all trainees (regardless of fiber-type, recovery ability, etc.), will
need to continually down-regulate the volume and frequency of workouts as they
get progressively stronger. It is argued that increases in recovery ability
cannot keep pace with strength increases. Some of these same authors also
contend that as one gets progressively stronger, there will also be a need to
decrease the muscular time under load (TUL) or number of repetitions
performed/exercise. Another group of authors disagree with this view. They argue
for variety in training parameters as the key to long-term progress (21). They
contend that only by continually varying the frequency, intensity, repetition
speed, volume of workouts, etc., can one ensure optimal adaptation of all the
different muscle components, fibers, enzymes, etc. By looking at some of the
relevant exercise research/principles and their biological correlates (i.e. how
these entities may be realized in physical mechanisms at a more "fundamental"
cellular level), an attempt will be made to offer some speculative input on some
of these issues and controversies.
Histochemical Properties of MUs
A MU includes a motor neuron and all the muscle fibers it innervates. Properties
of MUs include the following:
1. The physiological and biochemical properties of MUs can be divided into
distinct subtypes that show a variation in maximal force, isometric
twitch-speed, and fatigue resistance (22, 26, 36, 58, 59). Furthermore, the
transient appearance of hybrid forms, simultaneously expressing multiple forms
suggests that there may exist a gradual transition between them. Based on
contraction strengths, firing thresholds and fatigue resistance, they are
usually divided into 3 or 4 types. These include:
a. S(slow-twitch or type I)-these fibers are generally innervated by smaller,
slower conducting neurons. They have a lower firing threshold (i.e. recruited at
lower force levels), produce less force but show greater fatigue resistance.
They are rich in oxidative enzymes. Although quite variable, many of the
postural muscles or muscles designed to support sustained periods of activation
(diaphragm, spinal extensors, some leg muscles, soleus, abdominals) are
particularly rich in these fibers. Such units can be found to be tonically or
phasically active, firing at fairly low rates for up to 20-35% of the day (15).
Endurance athletes often display a higher relative percentage of these fibers
(15, 35).
b. FR (fast-twitch, fatigue resistant, or type IIA)-these fibers are generally
innervated by medium diameter neurons, have medium firing threshold, produce
medium or high force and are also rich in oxidative enzymes. Fatigue resistance
tends to be moderate or high. Many bodybuilders seem to have high relative
amounts of these fibers (33). This has led some researchers to suggest that
these fibers are particularly adaptive to hypertrophic responses under
appropriate training stimuli (33).
c. FInt and FF (fast-twitch, intermediate fatigue and fast-twitch, fatiguable or
type IIAB/IIX and IIB)-these fibers are generally innervated by the larger,
fastest conducting neurons, have the highest firing thresholds (i.e. last to be
recruited) and produce the greatest force. They fatigue quite rapidly and are
poor in oxidative enzymes and rich in glycolytic enzymes. Major antigravity
antagonists and/or muscles implicated in powerful phasic movements (biceps,
hamstrings, etc.) are often rich in these fibers. These units typically fire in
short, scarce, high frequency bursts. Sprinters and Olympic lifters often have a
higher relative percentage of these fibers (2, 63). Surprisingly, a few studies
show that bodybuilders often "possess significantly less type IIB Myosin Heavy
Chain (MHC) isoforms than untrained controls or even
endurance-trained...subjects." (33)
2. All fibers innervated by a given motor neuron have the same physiological and
histochemical properties. This is not surprising, since it is known that the
type of motor neuron and pattern of nerve impulses transmitted, plays a
significant role in determining the mechanical and histochemical properties of
the muscle fibers of a MU. In fact, cross-innervation of fast-twitch (FT) muscle
fibers by a nerve that previously supplied slow-twitch (ST) fibers has been
shown to transform those muscles to take on ST characteristics (3,4). Some
studies show complete myosin isoform transformations (3, 8). In cross-reinnervation
of ST fibers by FT nerves, there also appears to be changes in properties of
muscle myosin towards those of FT, but the transformation is less complete. It
has been suggested that "sensitivity to motor innervation increases from the
glycolytic to the oxidative types of fibers, in the order IIB>IIX/D>IIA>I (3)".
Transformations, however, are not complete with respect to all parameters. For
example, muscle satellite cells appear to maintain their original properties in
cross-reinnervation studies (4).
3. There is experimental evidence to suggest that chronic long-term stimulation
can transform type IIB fibers into IIA and even to type I (8, 15). In fact,
"chronic stimulation of a FT muscle at a frequency resembling that in a nerve to
a ST muscle causes as complete a transformation of the muscle fibers as cross-innervation."
(8) This includes not only complete isozymic transformation but also "a marked
increase in the time-to-peak and half-relaxation time of the isometric twitch,
decrease in tetanus-to-twitch ratio, and a decrease in the rate of development
of tetanic tension" (15). Thus, "indirect stimulation of a FT muscle with an
impulse pattern similar to that normally delivered to a slow muscle results in
an orderly sequence of changes affecting all functional elements of the muscle
fibers: the contractile and regulatory proteins of the thick and thin filaments,
the proteins of the Ca+-regulatory system, as well as enzyme activity and
isozyme patterns of energy metabolism" (51).
It has also been suggested that the use of particular training protocols
(endurance, sprint or strength) can similarly result in fiber conversion via
training-induced altered gene expression. In particular, resistance training has
been shown to alter the MHC toward the FR or type IIA fibers (2, 33, 51).
Likewise, sprint training has been shown to increase the ratio of type II/type I
cross-sectional area with some studies demonstrating greater hypertrophy of the
type IIB fibers (1, 39, 40).
Alternatively, many endurance training studies done in both animals and humans
"have demonstrated by mATPase histochemistry, increases in the fraction of type
IIA fibers with concomitant decreases in type IIB fibers" (51). Of course, the
changes that occur with exercise, are nowhere as dramatic as those seen with
stimulation or cross-reinnervation experiments; consequently, many authors
dispute the concept of exercise-induced fiber conversion (30, 55). They are
quick to point to twin studies which demonstrate that MZ and not DZ twins show
identical fiber distribution (15). Thus, they argue, fibers cannot be altered by
training and any "apparent" fiber conversion is the result of selective
hypertrophy of one fiber-type combined with selective atrophy of different fiber
type (due to disuse or overuse atrophy) (30). For example, while strength
training will induce hypertrophic adaptation of the larger FT fibers
(particularly, the type IIA), it will have a smaller effect on ST fibers. In
fact, depending on the previous level of endurance training, there may even be a
relative atrophy of ST fibers (52). Conversely, while endurance training and/or
high volume, low intensity, resistance training may induce hypertrophy of the S
units and some of the more fatigue-resistant FR units, it may result in atrophy
of the larger fatiguable units. In fact, "a decrease in muscle fiber size has
been demonstrated in the gastrocnemius muscle of marathon runners and a reduced
fiber size after endurance training has also been demonstrated in rats and
horses" (15). At this time, no conclusive proof exists for exercise-induced ST
to FT conversion, although there are many studies suggesting FT sub-type
interconversions (1, 2, 33, 40).
4. Statistical histological analysis also reveals that muscle fibers display a
distinct tendency to be surrounded by fibers of a different type. Similar fiber
subtypes are often not associated in the immediate vicinity of each other. There
also appears to be a predominance of slower fibers in the deep layers of muscles
while superficial layers tend to have a greater concentration of faster fibers
(26, 36). It has been hypothesized that this layering allows for optimizing
mechanical advantage during dynamic movements. Finally, as one ages, there seems
to be a preferential atrophy of type II fibers (17, 58). Whether this is the
result of disuse atrophy or is part of the "normal" biological aging process, is
currently not known. There is, however, plenty of evidence demonstrating the
usefulness of resistance training in reversing age-related muscular atrophy.
5. In general (although there are many exceptions), fast-twitch (FT) fibers are
about 30-40% larger in cross-sectional area than the slow-twitch (ST) fibers.
Thus, even in a muscle composed of a 50/50 mix, the overall % FT contribution to
total cross-sectional area of the muscle can be up to 65% or more, depending on
the level of hypertrophy (52, 62). In FT subjects and/or muscle groups, this is
even higher.
Relevancy to Bodybuilding and Strength Training
With regard to optimizing hypertrophy, will individual and/or muscle fiber-type
distribution affect training prescription? Although there is some controversy,
some authorities believe that fiber-type distribution is indeed, relevant to
exercise prescription (30, 31, 52, 68). In particular, it has been argued that
all other factors being equal, FT subjects and/or muscle groups usually require
(for optimal strength progression):
1.Lower volume and/or frequency of exercise.
2.Lower repetition ranges and/or TUL.
3.Longer recovery periods.
ST subjects and/or muscles show completely opposite characteristics requiring:
1.Higher volume and/or frequency of exercise.
2.Higher repetition ranges and/or TUL.
3.Shorter recovery periods.
Intermediate fiber type individuals and/or muscle groups fall somewhere in
between these two groups. A. Jones, in particular, has argued that an
individual's muscle fiber recruitment and fatigue characteristics are largely
genetically determined, so that there may exist an optimal TUL for each
exercise, where one's musculature receives optimal growth stimulation (30). In
fact, MedX technicians often incorporate the use of a "Fatigue Response Test" as
a way of finding out one's particular fatigue and fiber-type characteristics.
More recently, this theme has been repeated by several other authors who contend
, "that (even) the concept of double progression (increasing weight and reps) is
actually mistaken. Instead one should find the signature TUL for a given person
in that movement and then carry out single progression. That is, progress weight
at a fixed TUL as is determined by a particular fiber type and MU recruitment
pattern. Once you know the ideal TUL, single progression (increasing resistance)
appears to be the way to rapid gains." (44)
There are, however, relatively few (if any) properly controlled, peer-reviewed
research studies looking at these parameters. Most studies involve the
simultaneous variation of multiple variables, including different intensities,
volumes and frequencies that make any conclusions highly questionable. There
are, however, a number of non-formal studies, by at least one equipment
manufacturer (A. Jones of MedX and Nautilus) and two other exercise researchers
(T.V. Pipes and W.L. Westcott) suggesting differences in exercise prescriptions
based on fiber type (30, 52, 68). Furthermore, one study looking at the relative
effectiveness of a 50% of 1-RM (20 repetitions) protocol versus 80% of 1-RM (12
repetitions), showed statistically significant strength increases with the 80%
protocol and not the 50% protocol (13). Somewhat similar (although, not
universal) findings have been reported elsewhere (21, 43, 48). Furthermore,
these researchers found that the increases in strength were positively
correlated to the FT fiber content in the muscle being exercised. What is
interesting, however (and not reported by authors), is that in Fig. 6 of their
article, there seems to be a tendency for ST subjects to have a somewhat better
response than FT subjects with the 50% protocol and some of the extremely high %
FT subjects seem to display even a strength decrement with the 50% of 1-RM
training protocol (13).
In the final analysis, we do know that FT subjects and/or muscles clearly
display different levels of muscular endurance or fatigue in comparison to ST
subjects and/or muscle groups. For example, many studies show that skeletal
muscles with a predominance of FT fibers possess shorter contraction times,
higher twitch and tetanic tensions, and greater susceptibility to fatigue than
muscles with predominantly ST fibers (47, 61, 62, 64). Many studies involving
human subjects have shown a positive correlation between % FT distribution and
the level of muscle fatiguability (10, 15, 16, 28, 29, 34, 61, 65). It is also
known that women (who often have significantly smaller FT fibers, and a lower
typeII/type I area ratio) display significantly longer muscular endurance times
than men (45, 67). In some studies, the type I fibers in women were found to be
larger than their type II fibers (23, 58). Whether this difference between the
sexes is biologically dictated or the result of disuse atrophy in women, is not
known; there is, however, one study suggesting the latter view since it was
found that sprint training had a greater increase of type II fiber area
(especially the type IIB fibers) in women than in the men. These authors
"suggested that the smaller area of type II fibers generally found in muscle of
women may in part be due to less frequent activation of their type II fibers,
especially type IIB. It could be expected that less well-trained subjects (the
women) would show a greater training response than subjects closer to their
upper limit of performance (the men)" (39).
It is also known that individuals with congenital myopathies (central core
disease and nemaline rod myopathy) who are characterized by type I fiber
predominance, show greater levels of muscular endurance (and lower levels of
strength) relative to controls (42). Likewise, "there is no decline in endurance
time for older muscles when an isometric contraction is performed at a relative
percentage of the maximum force. The absence of an increase in fatiguability
with age is probably related to the greater proportion of ST muscle fibers"
(17).
There are many reasons given for the greater fatiguability of FT fibers and/or
muscles but "the preponderance of evidence suggests that the primary sites of
fatigue lie within the muscle itself." (20) In particular, it is known that FT
fibers have approximately a 50% lower lactate-H+ transport rate than ST fibers
(32). Differences are especially pronounced in the type IIB fibers. Thus, it has
been hypothesized that a greater level of exercised-induced acidosis (decrease
in pH) in FT fibers results in greater rates of fatigue. Recently, however, the
pH effects on muscle contractility have been shown to be less critical at normal
(above 25 degrees C) physiological temperatures (54, 69). Even more recently,
increases in the products of ATP hydrolysis (Pi, ADP, AMP) have been implicated
in muscle fatigue (54, 69). High intensity exercise is known to induce a greater
increase in Pi levels in FT fibers (20). Regardless, most researchers do not see
muscular fatigue as the result of neuromuscular transmission failure since
"fatigue (is) not associated with a substantial decline in the MU action
potential (either between-or within train)" (16, see also 7, 12, 20, 49, 70 ).
Finally, some studies have demonstrated fiber-type differences with respect to
decompensation/atrophy and length of detraining. For example, while "the muscle
oxidative potential was shown already to be significantly reduced as early as
after 1 week of detraining...the glycolytic enzyme activity remained stable even
after 12 weeks of interruption in training...(Furthermore)...even after 7 weeks
of detraining, the sprint training-induced hypertrophy in both extensor muscles
and fibers was maintained or even increased" (41). With all the known
differences in properties between the different classes of fiber types, it
would, therefore, not be surprising to also find differences in adaptive
training ranges among the different classes of fiber types. Whether the
simultaneous optimal hypertrophy of all the different fibers is physiologically
possible, is debatable. There are however, some data to suggest incompatibility
and compromise between different modes of training. In fact, Stone et al. (1996)
have argued that, "the function of the transforming myonuclei pool that is
maintained in adapting fibers in response to overload may be limited such that
they can adequately support the expression of proteins that enable a high
endurance capability, i.e. mitochondria, at the expense of a high
force-generating potential (contractile machinery) and vice versa" (14, 60).
MU Recruitment Properties
During graded voluntary muscular contractions, MUs are recruited in order of
increasing size, increasing contraction strength and diminishing fatigue
resistance. Thus, the smaller, less powerful, fatigue-resistant fibers are
almost always found to be recruited before the larger, more powerful, fatiguable
fibers, regardless of speed of contraction (Henneman's size principle).
Furthermore,"all MUs are recruited at successively lower force levels if the
contractions are performed at increasingly greater velocities. (In
fact)...during the fastest contraction of tested movements, the recruitment
threshold (becomes) so low for all units, including the largest, that the motor
neuron pool (is) virtually simultaneously activated." (22) Although, the
threshold force of fiber recruitment of all MUs decreases at increasingly faster
contractions of fiber recruitment (i.e. in brisk phasic or ballistic
contractions), the same general fiber recruitment pattern (from smaller to
larger) is still maintained. In some rare cases, however, if the movements are
carried with sufficient velocity and the conduction is occurring along a fairly
long axon (say 1 meter or so) even though the smaller motor neurons get
recruited earlier, there will be an "apparent" reversal of fiber recruitment
order, because of the slower conduction velocity of the smaller lower-threshold
motor neuron (22).
We also know that highly motivated subjects are quite capable of achieving full,
maximal voluntary contraction (MVC), since supramaximal electrical stimulations
superimposed upon a MVC have been shown not to increase muscular tension (5, 6,
15). Thus, when one is using a high % of maximum muscular tension (as is likely
to occur in most strength training protocols), there will come a point in any
set (and often quite early in the set) where you will have effectively recruited
all MUs available for that particular exercise movement. Subsequently, any
further increases in force are generated by increasing the firing rate (i.e.
pulse modulation) of all these recruited units. Since it is also recognized that
a fused muscle contraction is 5-10 times higher than an unfused contraction
then, it would seem reasonable to conclude that firing rate is the main
regulator of force during tonic contraction (15). In fact, in some of the
smaller muscles, only at relatively low levels of force, is the recruitment of
fibers, the major mechanism of increasing the force of voluntary contractions.
In these muscle groups, it was found that a large % of total MUs were already
recruited at relatively low force levels and increasing firing rate tended to be
the main mechanism at both intermediate and high force levels (15, 18, 22, 25,
46). Thus, pulse modulation "contributes the large majority of force if the
entire physiological range is considered." (46) In fact, Grillnar and Udo found
that about 90% of soleus MUs were already recruited at below 50% of maximal
tension and no MUs were recruited beyond 75% of maximal tension (25). In testing
the MU recruitment of hand muscles, Milner-Brown found that up to 50% of MUs
were already active at a 200g force level of a total maximal tension of about 4
kg (i.e. at only 5% of maximal tension)(46). Similar findings have also been
reported by others (15). It has been hypothesized that, "if recruitment were the
only (or even principle) means by which additional force was developed, the
muscle would be incapable of producing a smoothly increasing contraction. As
force increased, the orderly addition of large MUs would produce a 'staircase'
effect in the force output record" (11).
The tension at which new MUs are recruited, however, does seem to vary depending
on muscle group studied. There also seems to be some inconsistencies in the
research findings. While some studies report MU recruitment to play a major role
in up to 80% of MVC in the deltoid and brachial bicep muscles, others report no
new recruitment above 40% MVC for the same muscles (11, 18, 38). Whether these
differences are the result of differences in fiber-types and/or muscle use is
unclear. Many researchers have also suggested that during prolonged contractions
involving a relatively large % of MVC (as seen in most strength training
protocols), the larger, more fatiguable units, will inevitably be de-recruited
before the smaller units in the reverse order in which they were recruited (11,
18, 49). Thus, in most strength training protocols, which employ a relatively
high % of 1-RM, the majority of the fibers (including the largest, fatiguable,
high threshold types), will eventually be recruited (and often quite early in
the set,) especially if taken to concentric failure. In fact, even during
prolonged low levels contractions (employing a relatively low percent of a 1-RM)
"there was a successive recruitment of motor units to compensate for contractile
fatigue, so that all motor units finally were depleted of glycogen" (15).
Fallentin et al. (1993) contend that during prolonged low level contractions
(i.e. <20% of MVC or so), newly recruited MUs replace previously active and
fatiguing units so that "MU rotation" may be an important characteristic in such
prolonged submaximal contractions (18). Clearly such findings (if accurate) have
some bearing on current debates in training philosophies.
Thus, as R. Carpinelli points out, "as fatigue increases throughout a set of
repetitions, your brain recruits greater number of MUs and stimulates them more
frequently. When you achieve maximal recruitment, further increases in force are
generated by continuing to increase the frequency of stimulation of all the MUs.
At the point of momentary muscular fatigue (and probably much sooner)...you are
recruiting the maximal number of MUs available for that specific exercise." (9)
So the typical bodybuilding argument that multiple sets of the same exercise
will recruit more MUs or muscle fibers, is very likely erroneous. In fact, the
same level of fiber recruitment and a much greater level of fiber fatigue can be
induced by "drop-sets" (i.e. "descending pyramid" training protocol) (43) or
even single sets (carried to momentary failure) employing a longer set duration.
One may, however, argue that multiple sets of the same exercise (assuming
sufficient rest between sets) may provide greater hypertrophic stimulation by
recruiting the same fibers more times; whether this is more effective in
optimizing hypertrophic adaptations is currently being debated. The
preponderance of scientific evidence, however, does not support the superiority
of multiple sets (19, 50, 57). (For an extensive review see R. Carpinelli's
article in the February, 1997 issue of Master Trainer).
Speculations & Recommendations
1. All other factors being equal (i.e. recovery ability, training volume,
nutrition, etc.), those individuals and/or muscle groups that have a greater %
of FT, tend to fatigue more rapidly because a greater % of total muscular force
is generated by the more fatiguable and powerful FT fibers. As each of these
larger fibers fatigues (i.e. de-recruitment), one sees a fairly rapid drop in
strength (greater inroad/time under tension). This makes sense on two counts.
First, due to a greater level of fatiguability of the larger and more abundant
fibers in FT subjects, there will be a more rapid decline in strength in these
trainees’muscle groups. Secondly, each of these larger fibers contributes
greater increments of tension than smaller fibers. Thus, as these more abundant
and powerful fibers in FT subjects and/or muscle groups fatigue, a
correspondingly greater decrement in strength will result. With ST subjects
and/or muscle groups (where the majority of total muscular force is generated by
smaller, more fatigue-resistant fibers), one sees the opposite pattern. Since
these fibers are fatigue-resistant and contribute smaller increments to total
force, then, there will be a correspondingly shallower drop in muscular force
output and fatigue with each successive repetition or TUL. So, it's not
surprising to find great variability among these two contrasting fiber types. As
A. Jones has pointed out, "So far, out of several 100 subjects, the widest range
we have encountered involved one subject that could perform only 1 rep with 80%
of his positive strength...and another subject that performed 34 reps with more
than 80% of her positive strength." (31)
2. Since selective or greater hypertrophy of FT fibers is usually observed in
most strength training programs (27, 63), then, as an individual gets
progressively stronger, a greater % of total muscular tension will be generated
by the pool of FT fibers. It then follows that as one gets progressively
stronger, one's muscle fiber characteristics will take on more "FT-like"
characteristics. By this account, the recommendations put forth by some authors
to progressively down-regulate the volume and frequency of workouts as one gets
stronger, make sense (i.e. such long-term trainees are simply responding more
and more like FT subjects). Whether this fully explains the disproportionality
that exists between strength and recovery ability increases in long-term
trainees, is debatable. It does, however, offer a fairly simple explanation. The
need to decrease TUL as one grows stronger (a view put forth by some authors),
also makes sense by this account. As one gets progressively stronger, and the
adapting FT fibers hypertrophy (to a greater extent than the ST fibers), one
will see a greater level of fatiguability (increased inroad/time under tension).
Effectively, the level of intensity (inroad/time) tends to increase as one gets
stronger, since the FT contribution to total muscular force becomes greater.
Thus, if you want to continue maximizing hypertrophic adaptations of this newly
hypertrophied pool of fibers, you may also need to decrease TUL to match the new
intensity levels. Thus, for long-term strength and muscle growth, one may need
to continue adjusting training parameters such as recovery, volume, frequency,
TUL, etc. to allow for the best growth stimulus of one's largest and most
abundant fiber pool. Failure to do so, may result in less than optimal results.
3. Regardless of loads employed (at least, within reasonable limits), a set of
any exercise movement carried to momentary muscular failure (or close to
failure) will normally recruit the maximal number of MUs available for that
exercise. This includes the entire spectrum of muscle fibers, from the most
fatigue-resistant, slow-twitch (ST)-oxidative or type I muscle fibers, to the
moderately fatigue-resistant, fast-twitch (FT)-oxidative or type IIA fibers to
the most powerful, fatiguable, FT-glycolytic or type IIB fibers. In fact, in a
set taken to or close to momentary muscular failure, as the % of a 1-RM used
decreases (at least, within reasonable limits), one is effectively fatiguing a
greater percentage of available fibers (including the larger units). This
explains why one is momentarily weaker when training to failure with a set
involving a lower % of a 1-RM. It also explains the greater level of strength
decrement that occurs in successive sets carried to failure, when the initial
set employs higher repetitions or TULs. Effectively, you have exhausted a
greater % of total fibers (including the larger fibers) when employing a higher
set duration or TUL in the first set. Furthermore, if a set using a lower % of a
1-RM (taken to failure) recruits the same number of fibers (and fatigues a
greater number of them) than a set with a higher % of a 1-RM taken to failure
(as has been suggested in 15, 18) and yet, one finds a lower level of strength
and/or hypertrophic adaptations with the lower % of a 1-RM protocol (as has been
suggested in 13, 21, 43, 48), then, the concurrent maximal hypertrophy of all
fibers seems unlikely. Incompatibility of different modes of training is a
strong possibility (as has been proposed in 14, 60), so that attempts to
maximally stimulate all the different components of a muscle (as has been
suggested by some authors) is very likely not possible. One cycle or protocol
that may be optimal for stimulating certain fiber sub-types and/or enzymes may
compromise the development of other fiber sub-types and/or enzymes. In fact, one
may speculate that under conditions of competing exercise stimuli (where there
is fatigue of both glycolytic and oxidative fibers), one’s physiological
adaptive processes may shift optimal hypertrophic adaptation towards the
fatigue-resistant fiber spectrum. Fiber adaptation/transformation studies
already suggest this. If this scenario is accurate, then, if one is primarily
interested in maximizing muscle strength and hypertrophic adaptations, it may be
necessary to seek out a training protocol (through experimentation) that
optimizes adaptation of one's most abundant pool of fibers and adjust training
parameters accordingly as has been suggested in point 2. above.
Gus has his B.Sc. in Neuroscience from the University of Toronto. He also
pursued academics in dental surgery, law, and medical school. He is currently
attending some advanced part-time studies in physiology and physics, with some
independent research, which led to the writing of this article. While
incorporating a high volume routine for more than 5 years Gus was unable to get
past 155 lbs. (at a height of 5' 10.5"). Since employing abbreviated routines he
has been able to raise his bodyweight up to 190 lbs (with a 7-10% bodyfat). More
recently, Gus has been experimenting with various diets and have attained an
all-time low 4% bodyfat at a bodyweight of about 176lbs. We are informed that
Gus may be providing the Bulletin with a more critical discussion of the merits
of "periodization", believing there is sufficient scientific evidence (from
molecular biology) that seriously casts doubt on many of the arguments put forth
by the periodized camp (some of which were raised in this paper). Gus can be
reached via e-mail at shtud@accessv.com.
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