Download TSCC 3 Physiology of the Throwing Events

Specialist Certification Program
The Throwing Events
Physiology of the Throwing
Events
Energy System Physiology

The Energy Systems. The energy systems are responsible for providing ATP, an energy rich
compound to fuel the work and recovery of cells. There are three such systems, the Alactic Acid
energy system, the Glycolytic energy system, and the Aerobic energy system.

ATP. ATP, or andenosine triphosphate, is the basic fuel of muscle contraction. The purpose of
all energy systems is to produce ATP from various substrates. ATP produces energy from the
breaking of a chemical bond, separating ATP into andenosine diphosphate (ADP) and inorganic
phosphate (Pi).

The Alactic Acid Energy System

o
Alactic Acid System Function. The alactic acid energy system uses ATP available in
muscle for immediate energy. It synthesizes additional ATP from ADP and Pi present in
the form of creatine phosphate. This system requires no fueling and creates no
byproducts that harm performance, but can provide energy for only 6-7 seconds.
o
Training Implications for the Alactic Acid System. The alactic acid system is the primary
system used in throws competition. Throw training programs employ great volumes of
training activities that use and challenge this system. For this reason, in spite of its
importance, concerted efforts to train this system are usually unnecessary.
The Glycolytic Energy System
o
Glycolytic Energy System Function. The glycolytic energy system makes ATP available
for muscle contraction and other purposes using glycogen as a substrate. The anaerobic
system can provide energy for very intense work for an extended period of time,
approximately 90 seconds. This system eventually produces lactic acid and an acidic
state that ceases performance. The glycolytic system enables us to produce energy at a
rate that surpasses our oxidative phosphorylation capabilities. Time is required at the
completion of work to buffer blood acidity, clear lactate and remove other byproducts.
o
Training Implications for the Glycolytic System. Glycolytic requirements for the throws
do exist, but are secondary to other performance factors. For this reason glycolytic
development in throws training programs should be addressed in a very specific
manner, with respect to these concerns.


Preparation for Specific Training. Many activities in throws training programs
have a high glycolytic component, so some glycolytic development work is
necessary to permit handling of certain volumes of specific training.

Fostering Recovery. There is evidence that moderate levels of lactic acid
produce blood chemistry and endocrine changes favorable to strength
development, speed development, and recovery. Achievement of moderate
lactate levels is a goal of most restorative training sessions and some
speed/power oriented sessions.

Lactate Shock. Severe acidic states associated with this type of training may
have temporary negative effects on efficiency of the neuromuscular system.
This fact, along with the limited need for this type of work, implies that care
should be taken in the scheduling of this work and the volumes undertaken.
The Aerobic Energy System
o
Aerobic Energy System Function. The Aerobic Energy System makes ATP available for
muscle contraction and other purposes using fat and/or glycogen as a substrate. The
aerobic system uses oxygen while producing ATP. The aerobic system is very efficient at
producing energy per molecule of oxygen and substrate, but it cannot keep up with the
demand for ATP at high work intensities.
o
Training Implications for the Aerobic System. Aerobic requirements for the throws
are practically nonexistent and secondary to other performance factors. Aerobic fitness
helps to withstand large training loads and permits easier recovery from exercise, but is
never the limiting factor in performance. The aerobic system is in use, even during
glycolytic activities, and recovery is an aerobic process. This provides sufficient
opportunity for aerobic development during training as a consequence of the total
training load. For these reasons, throw training programs should not contain units
devoted to aerobic development. In fact, excessive aerobic activity produces changes in
myosin isoforms that harm its speed and power production capabilities.
Neurophysiology

The Nervous System. The nervous system is one of the body’s two control systems. The
nervous system recruits and activates muscle tissue to meet force production needs. The
nervous system’s effectiveness at recruiting muscle tissue is critical, and the characteristics of
the nervous system dictate to some degree the characteristics of skeletal muscle tissue. For
these reasons, the effectiveness of the nervous system is possibly the greatest single factor in
performance, and training the nervous system may be the most important goal of training in
speed/power oriented sports.

Nervous System Anatomy. The nervous system is composed of a central nervous system (CNS)
and a peripheral nervous system. The CNS consists of the brain and the spinal cord. The
peripheral nervous system consists of the branch nerves and the neuromuscular junctions.
These branch nerves can be afferent or efferent. Efferent nerves effect action, while afferent
nerves are sensory in nature.

The Neuron. A neuron is a nerve cell. Its purpose is to conduct a neural impulse to muscle
tissue, or to another neuron. The nerve cell is composed of a soma (cell body), and axon, and a
dendrite. The axon conducts the neural impulse toward the cell body, while the dendrite
conducts the impulse away from the cell body.

Motor Neurons. Motor neurons are neurons that, when activated, stimulate skeletal muscle
tissue and produce muscle contraction.

The Neural Impulse. The neural impulse is basically composed of electrical pulses. If a neuron
receives these pulses, and the pulses are of sufficient magnitude, the affected neuron is
stimulated to conduct the impulse.

The All or None Principle. The all or none principle states that there are no varying degrees of
conduction, and neurons operate on an on or off basis. If the neural signal received is sufficient,
the neuron will conduct the received impulse. If a motor neuron is sufficiently stimulated, all
muscle fibers affected by that motor neuron will be stimulated into contraction. For these
reasons control of the force of muscular contraction is not possible at the cellular level.
Myophysiology

Skeletal Muscle. Muscles produce the force needed during performance. This force is produced
as the muscle contracts, applying force at its points of attachment to the skeleton. The muscles
and bones effectively operate as lever systems during force application.

Skeletal Muscle Anatomy. The sarcomere is the smallest unit of muscle tissue that is capable of
demonstrating contractile qualities. Many sarcomeres combine to form muscle fibers and entire
muscles. The sarcomere consists of noncontractile proteins (proteins not involved in the
contraction process) that provide structure to the muscle tissue, and contractile proteins
(proteins involved in the contraction process).

Sarcomere Anatomy. There are two types of contractile protein filaments, thick and thin. The
thin filaments are composed of the proteins actin, troponin, and tropomyosin. They are
attached to Z disks, which are noncontractile protein ends of the sarcomere, and extend toward
the middle of the sarcomere. Thick filaments are composed of the protein myosin, and are
found in the middle of the sarcomere and lie between the thin filaments. Also in the sarcomere
is a structure called the sarcoplasmic recticulum, which houses materials needed for the
contraction process.

The Sliding Filament Theory. Each thick fiber possesses many crossbridges, which extend
toward the thin filaments. There is a head at the end of each crossbridge, capable of carrying an
ATP molecule. Actin and myosin have a chemical affinity for each other, but in this situation, the
actin found in the thin filaments cannot bond with the thick filament. This is because actin
bonding sites are not available when the actin molecules are assembled in combination with the
other thin filament proteins. When sufficient neural stimulation contraction is applied at the
neuromuscular junction, filaments attach and slide against each other, producing movement.
Steps of this process are as follows.
1. Acetycholine Release. The neurotransmitter acetycholine is released at the
neuromuscular junction.
2. Calcium Release. Acetycholine triggers the release of calcium ions from the
sarcoplasmic recticulum into the sarcomere. If enough calcium is released, the
succeeding steps will occur. There are no degrees of contraction. This is referred to
as the threshold response principle.
3. Shape Changes. The calcium ions bond with the troponin molecules, causing a
cascade of shape changes in the thin filament. These changes make actin bonding
sites available to the myosin crossbridge heads.
4. Crossbridge Head Bonding. The crossbridge heads bind to the thin filaments at a 90
degree angle (if an ATP molecule is present), and ADP is released.
5. Crossbridge Head Swiveling. The crossbridge head swivels to a 45 degree angle,
causing movement, and Pi is released.
6. Bond Breaking. If ATP is present, the bond is then broken, and the process may
repeat, if calcium ions are still present in the sarcomere. ATP is required to form the
bond, and to break the bond.
7. The Calcium Pump. A calcium pump mechanism exists in the sarcomere, pumping
calcium out constantly, so that calcium ions do not linger in the sarcomere. This
prevents prolonged contractions. All contractions in their simplest form are
twitching type contractions. Prolonged contractions of a muscle are comprised of
many of these twitchlike contractions.
Motor Unit Physiology

Motor Unit Anatomy. A motor unit consists of a motor neuron (a nerve cell that activates
muscle fiber, effecting motor activity), and all the muscle fibers that cell innervates. The group
of fibers is normally scattered throughout a muscle, and is called a pool of fibers.


Motor Unit Function. Motor units may function in these two ways.
o
Volitional Function. In this type of operation, cognitive activity originates the
transmission of impulses to the motor neuron, activating it and producing contraction in
its pool of fibers. Movement is consciously originated.
o
The Reflex Arc. In this type of operation, a signal generated by some sensory organ or
proprioceptor is transmitted to the motor neuron, activating it and producing
contraction in its pool of fibers. The brain is left out of the loop, and movement is not
consciously originated. This type of movement is used in all reflex actions.
Types of Motor Units. There are three types of motor units that we will distinguish,
differentiated by motor neuron size, fueling enzyme activity, and fiber type.
o
Type I. These motor units have small motor neurons, are oxidatively fueled, and exhibit
low speeds of contraction.
o
Type IIa. These motor units have larger motor neurons, are fueled more glycolytically,
and exhibit higher speeds of contraction.
o
Type IIb. These motor units have the largest motor neurons, are fueled glycolytically,
and exhibit high speeds of contraction.
Physiology of Force and Velocity

Control of Force. As indicated in our discussion of the all or none principle, the body cannot
control force production by altering the magnitude of signal from the nervous system. Force
must then be controlled in these other ways.
o
Recruitment. More motor units are called into play as force production needs rise. Each
unit has a unique threshold of response, so those with lower thresholds are recruited
first, etc. The order of recruitment deserves examination. The size principle states that
size is the primary determinant of recruitment order; the smallest motor unit is
recruited first, then others are recruited in order of size until the largest is recruited last.
The advantage of the size principle is that the order of recruitment is predetermined,
saving time. The disadvantage is that the smaller units must first be recruited before the
large ones can be called into play. Also, training must occur at high intensities if the
largest motor units are to be trained. There may be exceptions to the size principle.
There is evidence that in reflexive actions smaller units may be bypassed and larger ones
recruited initially.

o
Rate Coding. Rate coding refers to the ability of the nervous system to increase the
frequency of the neural impulses. If these impulses occur sufficiently close together,
then the next impulse may begin before the previous subsides completely, allowing an
aggregate increase in the magnitude of the impulse. Tetanus results when these
individual impulses merge into one sustained impulse. Speed and power related
activities seem to have a positive effect on rate coding capabilities.
o
Temporal Patterning and Synchronization. Temporal Patterning and synchronization
refer to the ability of the body to call motor units into play in a particular sequence with
a particular timing. This unique pattern of timing of recruitment results in a greater total
force production. Speed and power related activities seem to have a positive effect on
temporal patterning and synchronization capabilities.
Force and Velocity. Force and velocity are the two characteristics of the muscle contraction
most important to performance.
o
Determining Force and Velocity Characteristics. Force is determined by the number of
crossbridges attached. Velocity is determined by the rate of crossbridge cycling, which is
determined by the myosin isoform (subtype) found in the sarcomere. Force and velocity
are generated independently.
o
The Force Velocity Curve. Force and velocity of contraction are inversely proportional
to each other. As one increases, the other must decrease. This is because at high
speeds, crossbridge cycling becomes less efficient, thus reducing the force produced.
We can train power by altering the rate of force or velocity loss, but we cannot change
the nature of this inverse relationship.

Motor Unit Type Determination. Research shows that usage patterns are the single most
important factor that determines the speed of contractions. Chronically used fibers tend to shift
toward slower contraction speeds and oxidative fueling to increase metabolic efficiency.
Inactivity produces faster contracting fibers, as does high speed training. This lends itself to a
philosophy of training for high speed movement that includes high speeds of movement in
training, lower volumes, and longer rest intervals.

Training Implications
o
Recruitment. The size principle dictates some training at maximal intensities is essential
to train the largest motor units.
o
Rate Coding and Temporal Synchronization. Achieving improvements in these force
control strategies dictate the necessity of training at high levels of power output.
o
Force and Velocity. The differing mechanisms of force and velocity production dictate
training along all points of the force-velocity curve.
o
Motor Unit Types. The documented effects upon mysosin isoform changes would
dictate that no chronic activity or aerobically based training regimes be used in speedpower training, and that all training must exhibit some significant level of power output,
punctuated with significant rest opportunities to minimize accumulative fatigue.
Physiology of Fatigue

Metabolic Fatigue. The contractile mechanisms may fatigue due to failure of the energy
systems or buildup of waste products. This type of fatigue is commonly classified as metabolic
fatigue, and recovery rates from this type of fatigue in humans are relatively quick. Most fatigue
encountered in throws training results from the accelerated buildup of ADP and inorganic
phosphate in the sarcomere.

Neural Fatigue. Fatigue may also occur in the nervous system, at the neuromuscular junction, in
the branch nerve, or in the CNS. This type of fatigue is quite different from metabolic fatigue,
and recovery from this type of fatigue occurs at a much slower rate. CNS fatigue commonly
observed is thought by some to be an inhibitory response, designed to prevent harm to other
fatigued tissues.
Types of Muscle Contractions

Concentric. In a concentric contraction, movement results as contraction takes place and the
muscle shortens. The contracting muscle performs work.

Eccentric. In an eccentric contraction, the muscle lengthens in spite of the engagement of the
contractile mechanisms. The contraction resists the lengthening of the muscle.

Isometric. In an isometric contraction, there is an absence of joint movement in in spite of the
engagement of the contractile mechanisms. In an isometric contraction, no movement takes
place and stabilization of a joint occurs.
Neuromechanics of the Stretch Shortening Cycle

The Elastic Response. Muscles contract more forcefully when they are stretched immediately
prior to the contraction. This prestretching, along with the enhanced subsequent contraction
and energy production is called the stretch shortening cycle (SSC). The muscles reaction to this
prestretch is called the elastic response. The stretch shortening cycle plays a crucial role in
performance.

Elastic Energy. The mechanical energy produced in this sequence of muscle activity, resulting in
increased force production is called elastic energy. This energy is created at no metabolic cost.
We must simply use techniques that elicit this reflex in order to gain this benefit.

Contraction Patterns in the Elastic Response. In the stretch shortening cycle, we see
contraction patterns that occur in the following sequence:
1. Isometric Preparation. Isometric contraction prior to impact, in order to stabilize the
joints and prepare them for impact.
2. Eccentric Activity. Eccentric contraction upon impact, as the muscles resists the
lengthening they are being forced to undergo. This phase is commonly called the
amortization phase.
3. Concentric Work. Concentric contraction, beginning when the lengthening phase ends,
resulting in concentric work.


Sources of the Elastic Response. The elastic energy produced in the stretch shortening cycle
come from several sources.
o
Noncontractile Proteins. These proteins stretch and rebound, contributing to the
elastic response.
o
Contractile Proteins. These filaments stretch and rebound provided crossbridges are
attached, contributing to the elastic response.
o
Proprioceptively Signaled Contraction. Proprioceptors in the muscle sense the
prestretch and transmit a signal that stimulates a motor neuron, producing contraction.
o
Connective Tissue. These tissues stretch and rebound, contributing to the elastic effect.
Tendons in particular are capable of storing great amounts of elastic energy so much so
that the tendon is considered to possess its own elastic reflex.
Quality of the Stretch Shortening Cycle. The quality of the initial isometric preparation
determines to a great degree the quality of the succeeding eccentric and concentric phases. For
this reason, teaching proper isometric preparation of the affected body part is a necessary
coaching practice.

Coupling Time. Coupling time is the time required for eccentric to concentric conversion. The
prestretch and the associated coupling times in SSC activities are to be optimized, not minimized
or maximized. Maximized coupling times are associated with excessive prestretch and collapse,
minimized coupling times are associated with insufficient prestretch and rigidity.

The Length – Tension Curve. The length of the muscle prior to contraction dictates the amount
of force it can produce upon contraction. As the muscle is stretched, force production
capabilities may greatly exceed 100% of its force production capabilities at normal resting
length. The intensities involved in competition regularly force skeletal muscle into eccentric
situations, so all training and rehabilitation activities must employ eccentric work.

Plyometrics. Plyometrics are exercises that train the SSC and elastic energy generation.
Normally we think of plyometrics as jumping exercises, but a plyometric effect can be created in
any body part with some creativity by the coach, and nearly all activities, such as sprinting and
throwing, are plyometric in nature.
Neuroendocrine Physiology

The Neuroendocrine System. The neuroendocrine system is one of the body’s two control
systems. It operates by releasing controlling substances called hormones into the bloodstream
in response to certain neural signals. The hormone acts as a chemical messenger that transports
a signal from one cell to another. In this section, we will examine various types of hormones,
their function, and the role of the neuroendocrine system in throws training and performance.

Hormone Types and Function. Hormones can be classified into two groups, anabolic and
catabolic. Anabolic hormones are associated with the enhancement of protein reactions, while
catabolic hormones are associated with the breakdown of molecules. There are many different
human hormones, but we will confine our discussion to these.
o
Anabolic Hormones

Testosterone. Testosterone is a male sex hormone. It is found in some degree in
males and females. Its presence normally indicates an anabolic state of the
organism. Elevated testosterone levels are nearly always associated with
improved athletic performance.

Growth Hormone. Growth Hormone is a hormone produced by the pituitary
gland. It regulates growth by stimulating the formation of bone and the uptake
of amino acids, molecules vital to building muscle and other tissue. Its presence
is important to foster recovery from exercise.

Insulin. Insulin is a hormone produced by the pancreas. Insulin causes cells in
the liver, muscle, and fat tissue to take up glucose from the blood, storing it as
glycogen in the liver and muscle. It also assists in regulating protein
metabolism.
o

Catabolic Hormones

Cortisol. Cortisol is a hormone that causes a breakdown of stored protein
molecules and an increase in the concentration of circulating amino acids. It also
promotes fatty acid release and stimulates formation of sugar from noncarbohydrate sources. Elevated cortisol levels are usually associated with heavy
training or overtraining.

Glucagon. Glucagon raises blood glucose levels. Its effect is opposite that of
insulin. Glucagon also stimulates the release of insulin, so glucose can be taken
up and used by insulin-dependent tissues. Thus, glucagon and insulin are part of
a feedback system that keeps blood glucose levels at a stable level.
Training Implications
o
Testosterone Levels. Research shows that high training intensity, and low volumes,
with long recovery times between exercise bouts, are associated with improved
endocrine profiles in men. Moderate intensities, with higher volumes are associated
with improved endocrine profiles in women. These increases generally improve the
organism’s anabolic state. While it is believed that these responses are primarily due to
testosterone increases, growth hormone level changes may be a part of this as well.
o
Growth Hormone Levels. Research shows that higher training volumes are associated
with growth hormone increases, especially for athletes with younger training ages.
These volumes normally take the form of high repetition/low resistance schemes.
Neuromechanics of the Proprioceptive System

Proprioceptors. Proprioceptors are sensory organs that obtain and transmit information about
body positions and movements. The proprioceptive system is responsible for body awareness,
control of movement, and kinesthetic sense. The proprioceptive system, via its sensory function,
is also a part of many of the body’s reflex actions.

Types of Proprioceptors. We will be concerned primarily with the four types of proprioceptors
listed below.
o
Muscle Spindles. Muscle spindles are small organs found in the fleshy part of the
muscles. They primarily sense the magnitude of stretch placed upon the muscle. When
stimulated, they reflexively signal muscle contraction.
o
Golgi Tendon Organs. Golgi tendon organs are small organs found in the area where
the muscle and tendon join. They primarily sense the rate of stretch placed upon the
muscle. When stimulated beyond their response threshold, they reflexively signal
muscle relaxation.
o
Pacinian Corpuscles. Pacinian corpuscles are small organs found in the joint capsule.
They convey a signal of long duration, relating static joint position information.
o
Ruffini Endings. Ruffini endings are sets of nerve endings found in the joint capsule.
They are stimulated by joint movements and send a signal of short duration. They are
involved in sensing joint movements.
o
Other Proprioceptors. The above is not by any means a complete list. There are
numerous other proprioceptors, most notably the vestibular equipment responsible for
stability and balance, and cutaneous receptors in the skin, and pain receptors.

Propriceptive Function. Proprioceptive ability is directly related to coordination abilities. The
ability to learn complex skills is greatly determined by the ability to obtain, receive, and process
proprioceptively gained information.

Implications for Training. Training proprioception is normally accomplished through activities
that demand and challenge coordination and balance. It is also possible to develop
improvements in proprioception by providing a variety of stimuli in the training environment.
This may include changing the training order of frequently used training activities from time to
time. This variety demands the body to coordinate movement under various states of
proprioceptive fatigue, thus forcing the body to rely more strongly on nonfatigued
proprioceptor types.
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