PP 98 : MUSCLE CLASSIFICATION PARADOX



Classification of muscles into tonic and phasic groups may be inaccurate and
misleading
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Muscles are very commonly divided into those which stabilise (tonic)
and those which mobilise or move (phasic).  Sometimes we also read
that the tonic muscles comprise predominantly slow twitch muscle
fibres, whereas phasic muscles are largely fast twitch.

If we consult research publications, however, we  note that some
postural or tonic muscles such as some of the trunk muscles are
predominantly fast twitch.

At the same time we appreciate that stabilisation is sometimes
dynamic, sometimes static and that some limbs undergo concurrent
stabilisation and movement by the same muscle groups.  For instance,
consider the actions of the lower extremity during running and
jumping - is it entirely appropriate to separate the actions of
certain muscles into stabilisation and mobilisation processes. What
about the actions which take place in cyclical movements such as
cycling and swimming?

Possibly we can talk about tonic and phasic functions, but to rigidly
define muscles as either one or the other may well be more confusing
and misleading than enlightening and accurate.  Is there any real
need to persist with this type of classification, particularly if
attempts are made to justify it on a simplistic basis of muscle fibre
types (which usually neglects to implicate the actions of the nervous
system in orchestrating the complex interactive processes of
stabilisation and mobilisation)?

Draw on appropriate references or your own powers of logical analysis
to resolve this issue.
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PP 99: BALLISTIC DANGER PARADOX

General condemnation of ballistic and other dynamic forms of stretching may
be misdirected and unnecessary.

The belief that ballistic stretches and any other forms of non-static
stretching are inherently dangerous is rife in the world of fitness and
rehabilitation.  Some forms of slow dynamic stretching borrowed from
physiotherapeutic PNF (Proprioceptive Neuromuscular Facilitation) such as
contract-relax are acceptable and often trendy in some fitness circles, but
any other ballistic or faster forms of moving during stretching generally are
regarded as taboo.

This blanket condemnation of any stretches which may rely on momentum or
strong muscular contraction is based on the seemingly logical reason that any
large or sudden increases in muscle tension can damage the muscles or their
associated soft tissues.  Moreover, rapid movements are known to elicit the
myotatic stretch reflex which rapidly promotes muscle contraction.  Since
stretching is presumed to be most effective when it is performed on relaxed
muscles, any muscular contraction during stretching exercises is strongly
discouraged.  After all, it is considered that short durations of ballistic
stretching are totally inadequate for producing permanent change in muscle
length, which usually is regarded as the basic purpose of all stretching.

The latter point already warrants comment, since some forms of stretching
(e.g. those borrowed from PNF) do not necessarily cause permanent change in
the resting length of the muscle complex (i.e. the contractile fibres and
their associated connective tissues).  Some changes may be transient or
short-term to allow the muscle complex to increase its range for a given
transitory purpose. 

Thus, we need to distinguish between structural and functional stretching,
where the former refers to long-term deformation of muscles and connective
tissue and the latter refers to stretches which temporarily increase ROM
(Range of Movement) largely by manipulation of reflexes and other
neuromuscular processes (as in PNF).  No doubt there is also a transient
stretching effect associated with short-duration mechanical elongation of the
muscle complex, though the neuromuscular effect probably dominates. 

In the case of ballistic stretches, these short-duration elongations no doubt
play a useful functional role in allowing any sudden increase in loading to
be dissipated less explosively, thereby protecting the tissues from rapid or
large RFDs (Rates of Force Development).  A great deal is said about the role
of the soft tissues (especially the tendons) in storing and releasing elastic
energy during so-called plyometric actions, but not enough is said about the
protective role played by the ability of the soft tissues to stretch whenever
changes in loading threaten to increase excessively the mechanical stress
(force/area) and strain (relative change in length) in these tissues.

We know that all systems of the body display great adaptive capabilities, so
that ballistic loading of any tissues should cause them to adapt to a greater
level of structural and functional performance. In fact, ballistic action is
so fundamental to all animal movement that its absence  tends to decrease
economy and efficiency in all high speed movement.  Ballistic and high speed
stretching action is implicated in all running, jumping and throwing, while
slower prestretching processes enhance the efficiency of many other less
rapid limb movements. 

We might, therefore, conclude that advice to avoid any ballistic stretches or
other forms of dynamic stretch training does not allow the body to adaptively
reconstruct itself to cope with the full range of movement types which it
might encounter in life.  Anyway, even if one excludes all ballistic
stretches or rebound actions as formal training methods, they will most
likely occur frequently during most physical activities.

Of course, one might argue that it is unnecessary to train ballistically
since ballistic, momentum assisted movements naturally occur all the time in
sport.  This is tantamount to stating that supplementary resistance training
is also totally unnecessary, because all sport involves some level of
resistance.  Research has shown that gradual increases in resistance
according to specific conditioning regimes definitely increase the ability of
the body to perform at a higher and safer level, so it would appear entirely
logical that progressive increase in ballistic and similar types of training
should similarly endow the body to cope more effectively with any actions
that are ballistic or rebound in nature.

In other words, avoidance of ballistic and other forms of active dynamic
stretching may be counterproductive and ill-advised.

Work by Russian scientists such as Iashvili (1982) is relevant in this
regard.  He has found that:

.  Static and passive flexibility enahnce passive flexibility, but only
moderately improve active joint mobility, which is by far the most important
flexibility quality needed in sport.

.  Active flexibility correlates more strongly (Correlation Coefficient R =
0.81) with sporting proficiency than passive flexibility (R = 0.69).

.  Combined full range strength and flexibility exercises are far more
effective in producing functional ROM than any static or non-ballistic
stretching

Comment on the above P&P.
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PP 100 : MUSCLE FIBRE TRAINING PARADOX

Physical training based on the relative proportions of slow and fast twitch
muscle fibres may be misleading and unnecessary.

BACKGROUND

Many sports scientists and coaches today consider that training is much more
effective if one devises exercise programs which most closely suit each
athlete's muscle fibre type, because science has discovered that human muscle
comprises different proportions of slow and fast twitch fibres. 

This research has recognised that human muscle fibres appear to lie on a
continuum which extends between slow contracting, slow fatiguing fibres at
one extreme and fast contracting, fast fatiguing fibres at the other.  Most 
classification schemes refer to the these extremes as Type I red, slow twitch
(ST) fibres and Type II white, fast twitch (FT) fibres, where the difference
in colour is due to the fact that red fibres have a higher content of
myoglobin.

ST fibres are efficient in maintaining posture and sustaining prolonged, low
intensity activity such as distance running.  FT (Type II) fibres are usually
subdivided into several sub-classes, the most frequently mentioned being FTa
(Type IIA) and FTb (Type IIB). 

Type IIA (FTa) fibres are also called fast twitch, oxidative-glycolytic
(FTOG), since they are able to draw on oxidative and glycolytic mechanisms
for energy.  They are apparently suited to fast, repetitive, low intensity
movement and are recruited next after Type I (ST) fibres.  They tend to be
reasonably resistant to fatigue and can recover fairly rapidly after
exercise.  Some authorities believe that they are Type II (FT) fibres which
are adapted for endurance activity.

Type IIB (FTb) fibres are fast contracting, whitish, low myoglobin fibres
with a large diameter, high glycolytic capacity, low oxidative capacity and
few mitochondria.  They are suited to high power output and are usually
recruited only where very rapid or very intense effort is required, as in
field athletics and weightlifting.  They fatigue rapidly and replenish their
energy supplies mainly after exercise has ceased. 

While the above classification is widely used in physiology as a matter of
convenience, much controversy still surrounds muscle fibre classification. 
For instance, the fast-twitch fibre population has been subdivided into types
IIA,  IIB, IIC and even types IIAB and IIAC.  The possible transformation
between fibre types or characteristics by specific types of exercise is
currently an area of prolific research. Another useful classification scheme
which may be remembered readily recognizes the following fibre types:

.  S   - slow contracting
.  FR - fast contracting, resistant to fatigue
.  FI  - fast contracting, intermediate fatiguability
.  FF - fast contracting, fast fatiguing

Every muscle group contains a different ratio between fast and slow twitch
fibres, depending on their function and training history.  For example,
muscles such as the soleus of the calf usually have a higher content of ST
fibres than gastrocnemius, whereas the arm triceps generally have a higher
proportion of  FT fibres.

FURTHER FINDINGS

All muscle fibres contract according to the same cross-bridging or sliding
filament action. The distinction between the different fibres lies in the
rate at which cross-bridging occurs and their ability to sustain a
cross-bridging cycle.  Goldspink (1992) has found that the rate at which
cross-bridging consumes the high-energy phosphate ATP varies considerably
with each type of muscle fibre.  Cross-bridging takes place far more rapidly
and consumes more ATP in fast twitch muscle fibres than in slow, postural
muscles.

Apparently, the difference in response between fibres lies in the diversity
of forms in which muscle fibre is synthesized.  Instead of occurring in one
identical form for all fibres, many of the protein building-blocks of muscle
exist in a variety of subtly different forms, known as protein isoforms. 

MYOSIN CHARACTERISTICS

Research reveals that a muscle will manifest itself as 'slow' or 'fast' on
the basis of precisely which protein isoforms it is manufacturing, in
particular which isoform of the heavy myosin filament is being formed
(Goldspink, 1992).  The role of the myosin is very important, not only
because of its size, but also of its diversity of function.  Besides
providing muscle fibres with cross-bridges, it also reacts with ATP to
harness the energy released by the mitochondria for contraction.

Is it not plausible then  that the current focus on prescribing training on
the basis of different muscle fibre types should be replaced by a greater
emphasis on differences in myosin isoforms?

Geneticists have discovered that different members of the myosin gene family
are activated at different stages of human development from embryo to adult. 
The reason for this is not yet known, but the fact that embryonic muscle
continues to grow in the absence of contraction or mechanical stimulation
suggests at least one hypothesis.  It is possible that the embryonic form of
the myosin heavy chain liberates muscle fibres from dependency on mechanical
stimulation for growth.  Evidence for this proposal comes from the
observation that the cells of damaged muscle fibres revert to synthesising
the embryonic form of the myosin protein in an apparent attempt to assist in
tissue repair.

The existence of numerous different forms of the myosin chain endows muscle
fibres with an inherent plasticity, thereby enabling them to modify their
myofibrils to produce muscles with different contractile properties.  Unlike
other genes, which are generally switched on and off by the indirect action
of signalling molecules such as hormones or growth factors, muscle genes are
regulated largely by mechanical stimulation.

 Although research indicates that fibre distribution is strongly determined
by genetic factors, it appears as if these differences may also be strongly
influenced by the type, intensity and duration of training, as well as the
pre-training status of the individual.  This becomes particularly evident if
the muscle fibre distribution is compared between weightlifters and
bodybuilders.  Weightlifters have a considerably higher proportion of FT
fibres, a fact which cannot be explained by the contention that specific
genetic types excel at specific sports.  Bodybuilders have about 10% fewer FT
fibres (or 10% more ST fibres) than untrained subjects, while weightlifters
have about 10% more FT fibres. 

It is apparent that even the specific type of strength training may influence
the relative proportions of FT and ST fibres and their sub-types.  The
difference between weightlifters and bodybuilders probably lies in the fact
that weightlifters usually execute considerably more low repetition, maximal
effort, explosive training than bodybuilders, who often use moderate loads
slowly to failure. 

Some researchers have suggested that there may be an optimal or maximum size
for individual muscle fibres undergoing training hypertrophy, since
efficiency of strength, power and work production decreases if muscle
cross-sectional area is too small or too large (MacDougall et al, 1982; Tesch
& Larsson, 1982).

ISSUES ARISING FROM THIS RESEARCH

Most of the applications of muscle fibre typing in prescribing training are
based on research into isolated muscle fibres without any focus on the
possible interaction between adjacent (parallel) fibre groups in a muscle or
on adjacent connective tissues such as epimysium, perimysium and fascia.  Is
it reasonable to omit the possible roles played by adjacent tissues?

Little mention is made of the density with which each different fibre type is
packed into a given muscle, nor of any possible series links between fast and
slow fibres.  Are we justified in assuming that a single fibre type runs the
entire length of a muscle or are there sequences of FT and ST fibres
attaching end-to-end along the length of a muscle?  If the latter case
occurs, what happens to our theories about classifying a muscle as
predominantly FT or ST?  This might force us to distinguish between
structural and functional fibre typing, where the former simply refers to the
volume or mass of a given fibre type per given muscle, and the latter refers
to the functional capability of a muscle to operate at a given velocity, as
revealed by electrical stimulation-response tests.

What is the effect of different cross-sectional densities of FT or ST fibres?
 What about any differences possibly introduced by higher concentrations of
FT or ST fibres near the exterior or interior of the muscle?  What about the
varying role played by viscoelastic connective tissue within and around the
muscle fibres at different rates of contraction during any changes in
contractile state - can we comfortably ignore any possible contributions of
elastic energy storage and release?  What is the effect of fibres that have
split and thereby created the impression that there may be more fibres of a
certain type than there really are?  Are we justified in classifying fibre
types in terms of their number alone rather than their volume or mass, their
cross-sectional area to length ratio or other ingenious measures?

Are we justified in assuming that every given type of fibre contracts with
the same force?  Can we ignore the possibility that faster ST fibres may
behave like slower FT fibres?  How do we make use of the finding that the
rate of contraction of a given muscle is determined by the characteristics of
the nerve fibre which excites the muscle?  Does this imply that it is a focus
on  neuromuscular excitation rather than muscle fibre type which determines
how a given muscle will operate?

Do all these questions suggest that it may be very misleading and
unproductive to place any major emphasis on applying our current knowledge of
muscle fibre typing to physical training?
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