The Stretch Reflex
By Dr. Michael Yessis
For www.EliteFTS.com
Many people refer to the stretch reflex as the key to explosive training.
How it is applied, however, is frequently misunderstood. This article takes
an in-depth look at this action and how you can better utilize it in any or
all aspects of your training. The need for variety in the training program has been well established.
This includes not only the need to modify and change the exercises being used
but also how the exercises are executed and how the training regimes are
used. When you use different rates of speed in weight training exercises, you
can develop greater strength and muscle mass than when using only one rate. Because bodybuilders and athletes are using increasingly heavy weights
with high training volume, the speed of the movement is becoming slower. This
is effective in maintaining maximum tension on the muscle through the full
range of motion. However, using less resistance and increasing the speed of
execution is also effective for muscle mass and strength, especially for the
faster contracting (fast twitch) muscle fibers. Learning how to use the stretch reflex when doing certain exercises can
bring about even greater development of the fast twitch muscle fibers with a
quick, high intensity muscle contraction. Keep in mind that there are
basically four types of muscle fibers. This includes the slow twitch (ST)
fibers, which are slow contracting and slow to fatigue. They are efficient in
sustaining prolonged low intensity activity and are used extensively in
bodybuilding, powerlifting, and endurance sports. The fast twitch muscle fibers are sub-divided into several sub-classes and
include fibers that are fast contracting and resistant to fatigue (FRF), fast
contracting but more easily fatigued (FEF), and fast contracting fast
fatiguing white fibers (FFF). Near-maximal and explosive resistance training
produces greater hypertrophy of the fast twitch muscle fibers than the slow
twitch muscle fibers. At the same time, maximal muscle power output and the potential for
explosive movement is determined mainly by the proportion of fast twitch
fibers. For example, weightlifters and sprinters who must do more explosive
movements have a considerably higher proportion of fast twitch fibers than
bodybuilders, powerlifters, and endurance athletes. High intensity is not
necessarily dependent upon the use of near-maximal or maximal loads but more
to the degree to which the relevant muscle fibers are recruited during the
effort. The terms “fast twitch” and “slow twitch” do not necessarily mean
that fast movements recruit exclusively fast twitch fibers and slow movements
recruit exclusively slow twitch fibers. The fibers involved are determined by
the force that is produced. For example, the maximum force generated during rapid acceleration of a
220-pound bench press can easily exceed the maximum force produced during a
slowly accelerated 330-pound bench press. Small loads accelerated rapidly and
heavy loads accelerated slowly both involve fast twitch fibers. However, the
explosive movements rely heavily on the action of the fast twitch fibers.
Also, accelerated movements recruit the muscle stretch (myotatic) reflex,
which can elicit a faster and more powerful contraction. The pre-stretch
principle is well known in sports and in the plyometric method in explosive
training. Fast twitch fibers are the main contributors to force production in
ballistic motions while slow twitch fibers make their major contribution
during very slow movements. Fast twitch fiber action can be impaired by the
growth of slow twitch fibers because they appear to have a dampening effect
on fast twitch contractions during quick or fast movements. Thus, even though
heavy resistance training serves as a powerful stimulus for the development
and hypertrophy of both slow twitch and fast twitch fibers, fast twitch fiber
development requires special training. Training the fast twitch fibers also includes the storage and release of
elastic energy by the connective tissues in the muscle/tendon complex and
should not be ignored by bodybuilders, powerlifters, power athletes, and
endurance athletes. This is done by involving the stretch reflex, which entails
accumulation of energy in the muscle-tendon complex prior to a quick
explosive contraction and accelerates the weight or object held. After this,
the weight or object moves on its own momentum followed by some muscle
involvement until the movement stops. When using the stretch reflex, the muscles do not react in the same manner
as during a slow movement. During slow movements, the main muscles involved
in performing the movement as well as their antagonists undergo contraction
to control the movement via feedback over the full range of motion. To use
the stretch reflex to get a more explosive contraction, you must program it
in advance. This is needed so that the execution is safe and under control
throughout the entire range of motion. The bench press can be used to illustrate how the stretch reflex is used
to elicit a more powerful muscle contraction. Begin the exercise with the
arms straight, fully extended above the chest, and holding a barbell. Lower
the barbell at a normal rate of speed, and as you approach the bottom
position, before touching the chest, quickly change direction to accelerate
the barbell upward. In essence, you blast out of the bottom position and then
allow the barbell to continue the movement on its own inertia. Later, use the
muscles to completely extend the arms. Pause after completion and then repeat
for up to ten repetitions. During the exercise, it is important that you inhale and hold the breath
as you lower the barbell and execute the explosive change and acceleration
phase in the bottom position. Exhale after the barbell has passed the most
difficult portion of the lift or when the arms are extended. Holding the
breath is needed during the explosive movements to stabilize the trunk for
safety and assure effective execution. When the bench press is executed using the stretch reflex, there is much
greater force created in the initial pushing phase. The reason for this is
that you use the energy accumulated on the down movement to execute the
switch and upward acceleration of the barbell. Keep in mind that as you lower
the barbell, the triceps, pectorals, and anterior deltoids undergo an
eccentric contraction during which the muscles lengthen and become tenser.
This muscle tension is used to stop the downward movement, switch to a brief
isometric movement when the movement stops going down, and then change to the
concentric contraction with which you accelerate the barbell upward. The
eccentric contraction is most important for eliciting the stretch reflex and
for controlling the barbell on the down phase. The stretch reflex allows you to use the strength of the muscles involved
as well as the energy accumulated on the down phase to enable you to generate
even more power using mainly the fast twitch fibers. If you pause in the
bottom position, as often occurs in a slow movement, the energy gained in the
eccentric contraction will be dissipated in the form of heat. As a result,
you will have to generate additional concentric strength to push the barbell
back up. The quick switch from the eccentric to the isometric to the concentric
contraction is analogous to bouncing a super ball or other resilient ball.
When you toss the ball downward and it makes contact with the ground, the
ball undergoes deformation, which compresses the air or material on the
inside, creating greater pressure. This is analogous to the muscle developing
greater tension during the eccentric contraction as the weight is being
lowered. The built up pressure inside the ball then returns the ball to its
original or slightly elongated shape, and it leaves the ground (rebounds)
upward to almost the same height without additional force being added. This
equates to the release of energy stored in the eccentric contraction. When using the stretch reflex, the same muscles are involved in the down
phase as in the up phase. The ability of the muscles to undergo a stretch and
accumulate energy to produce a forceful and fast contraction in the
shortening phase is known as muscle resiliency. This is the key to all speed
and power movements (i.e. movements that involve acceleration). Phil Murphy, a former lineman for the then Los Angeles Rams football team
in the early 80s, is a great example of what can be accomplished with
explosive training using the stretch reflex. Phil, who was already extremely
strong, was brought to me for quickness and explosive training. He weighed
352 pounds and stood between 6’4” and 6’5”. After approximately seven weeks
of training, Phil lost 25 pounds of mostly fat and posted 255 pounds of lean
muscle mass at a weight of 325. This is more muscle than I have ever seen on
any other athlete. In testing done by the team, he was equal to, if not
superior, to all the other linemen (who weighed around 280) in the 10- and
20-yard dashes and in the agility test. He was so powerful that he was able
to leap up onto a three-foot table from a push-up position. Exercises that use the stretch reflex are ballistic in nature and are
perfectly safe and effective. However, they can’t be performed on exercise
machines because they do not allow you to begin the movement with a
pre-stretch. If you try speed or explosive movements on a typical exercise
machine, the weight stack, just as a free weight, develops momentum during
the lowering and raising phases. When you quickly change directions, the
momentum of the weights keeps them moving in sometimes the opposite direction
from which they should be going. This, in turn, may bind the cable and the
cable may leave the pulley or even break because of the great tension built
up on the quick switch. To ensure that the movements are done safely, it is important to have the
necessary eccentric strength to control the weights on the down phase and
generate the tension needed to make the quick switch and utilize the stretch
reflex. To provide safety, use about 50–75 percent of the usual training
weight used for a typical set. The lighter weight allows you to make a
quicker switch in directions. If the weights are extremely heavy, you will have co-contraction of the
agonist and antagonist muscles and you will not be able to make a quick
switch or quickly accelerate the weights. The key to utilizing the stretch
reflex is to generate maximum tension in the eccentric contraction with
relative relaxation of the opposing muscles, except as needed to keep the
joint stable. If the opposing muscles are strongly contracted, they will not
allow you to make a quick switch. However, the weights should not be too light in order to prevent excessive
momentum, which may keep the weights moving beyond the normal range of motion
of the joint. When the weight is light and moving fast, it may be difficult
for the muscles to stop the movement. Because of this, you can use medicine
balls with light weights so they can be released to dissipate the momentum.
However, with sufficient weight, the amount of momentum developed will allow
the barbell to stop before full extension of the limbs. In most cases, you
will have to contract the muscles to ensure reaching the end range of motion. The stretch reflex can be incorporated in many different exercises,
especially those that involve the extensor muscles, which usually contain a
greater proportion of fast twitch fibers. For example, it can be used in a
squat and overhead press (which, in many cases, becomes an overhead jerk or
push-press), triceps press, and others. In the squat, as in the other exercises, different down positions can be
used from which to execute the quick switch. For example, stop before
reaching the thigh level position and then leap upward. In this case, you may
do the squat to approximately a 135-degree knee joint angle and then quickly
change directions to return to the standing position. In some cases, you may
even leave the ground if there is sufficient power generated. In all cases,
however, the descent should be smooth and under control while the return is
executed quickly—as though you were shot out of a cannon. Understand that using the stretch reflex does not mean a bouncing rebound.
There is no bouncing as you approach the position for the quick reversal. You
merely make a quick change from the down movement to the up movement. You do
not give the muscles a chance to lose the tension generated as when you relax
or hold the down position even momentarily. When doing exercises involving the stretch reflex, stop after a complete
repetition. Doing this gives you a chance to mentally and physically prepare
for the next repetition. Keep in mind that you must think out the movements
in advance so that as you execute the exercise, you will be prepared for the
quick switch and will be able to execute it in a timely and explosive manner. Regardless of whether you use the stretch reflex, you should always think
in terms of starting an exercise with the muscles placed on stretch before
doing the overcoming work. For example, starting an exercise with the barbell
on the chest in the bench press or when using an exercise machine requires
considerably more energy and can overtax your joint stability. Use of the stretch reflex when executing exercises is used to a great
extent in the training of athletes. Almost all sports require greater speed
and explosive movements as opposed to slow movements, which involve maximum
strength or strength endurance. Bodybuilders, powerlifters, and endurance
athletes need this type of training for only a portion of the exercises done.
For example, do one or two sets using the stretch reflex with ample rest in
between the sets. Slower execution sets for strength endurance and muscle
mass can then complete the total sets used. To get the most out of the stretch reflex, the muscles and nervous system
should be fresh. Thus, speed and explosive exercises should always be done at
the beginning of training after you have undergone a vigorous warm up to
prepare the muscles for this work. When fatigue sets in, do not use the
stretch reflex. At this time, the eccentric contraction is not as strong as
needed, and you may not be able to control the weight either on the down or
up phases. The greater the levels of fatigue, the less the muscle resiliency
and the more prone you become to injury. When the stretch reflex is used, it can bring about additional gains in
strength and more muscle mass because of the greater development of the fast
twitch fibers. However, this is only one technique for training. It is not
meant to replace the other types of exercise execution. Keep in mind that
variety is most important in developing muscle strength and mass.
Incorporating the stretch reflex in some of the exercises is a very
effective, if not the most effective, method for maximally developing the
size of the fast twitch fibers. For more information, read Build a Better Athlete and Explosive Running. Dr. Michael Yessis is a professor emeritus in biomechanics and
kinesiology and president of Sports Training Inc., a diversified company that
does specialized work with athletes and develops specialized training
equipment. Dr. Yessis is the foremost U.S. expert on Russian training
methods. He has been to Russia multiple times, has worked with Russian
coaches such as Yuri Verkhoshansky, and has translated and published Russian
training articles in the Fitness and Sports Review International for over 29
years. He also wrote the number one article read in Muscle and Fitness
(Kinesiology, Training Notebook) for over 25 years. Visit his website at www.dryessis.com. Elite Fitness Systems strives to be a recognized leader in the strength
training industry by providing the highest quality strength training products
and services while providing the highest level of customer service in the
industry. For the best training equipment, information, and accessories,
visit us at www.EliteFTS.com. |
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