nsca cscs chapter 18 — program design for plyometric training

nsca cscs chapter 18 — program design for plyometric training

Plyometric exercise refers to those activities that enable
a muscle to reach maximal force in the shortest possible
time. Plyometric is a combination of Greek words that
literally means to increase measurement (plio = more;
metric = measure) (56). Practically defined, plyometric
exercise is a quick, powerful movement using a prestretch,
or countermovement, that involves the stretch–
shortening cycle (SSC) (53). The purpose of plyometric
exercise is to increase the power of subsequent movements
by using both the natural elastic components of
muscle and tendon and the stretch reflex. To effectively
use plyometrics as part of a training program, it is
important to understand (1) the mechanics and physiology
of plyometric exercise, (2) principles of plyometric
training program design, and (3) methods of safely and
effectively performing specific plyometric exercises.
Plyometric Mechanics
and Physiology
Functional movements and athletic success depend on
both the proper function of all active muscles and the
speed at which these muscular forces are used. The term
used to define this force–speed relationship is power.
When used correctly, plyometric training has consistently
been shown to improve the production of muscle
force and power (30, 50). This increased production
of power is best explained by two proposed models:
mechanical and neurophysiological (53).
Mechanical Model
of Plyometric Exercise
In the mechanical model, elastic energy in the musculotendinous
components is increased with a rapid stretch
and then stored (3, 14, 31). When this movement is
immediately followed by a concentric muscle action,
the stored elastic energy is released, increasing the
total force production (3, 14, 31). Hill (31) provides
an excellent description (illustrated in figure 18.1) that
helps with understanding the behavior of skeletal muscle.
Of the mechanical model’s many elements, it is the
series elastic component (SEC) that is the workhorse
of plyometric exercise. While the SEC includes some
muscular components, it is the tendons that constitute the
majority of the SEC. When the musculotendinous unit
is stretched, as in an eccentric muscle action, the SEC
acts as a spring and is lengthened; as it lengthens, elastic
energy is stored. If the muscle begins a concentric action
immediately after the eccentric action, the stored energy
is released, allowing the SEC to contribute to the total
force production by naturally returning the muscles and
tendons to their unstretched configuration. If a concentric
muscle action does not occur immediately following the
eccentric action, or if the eccentric phase is too long
or requires too great a motion about the given joint, the
stored energy dissipates and is lost as heat.
Neurophysiological Model
of Plyometric Exercise
The neurophysiological model involves the potentiation
(change in the force–velocity characteristics of the
muscle’s contractile components caused by stretch [21])
of the concentric muscle action by use of the stretch
reflex (figure 18.2) (8–11). The stretch reflex is the
body’s involuntary response to an external stimulus that
stretches the muscles (27, 42). This reflexive component
of plyometric exercise is primarily composed of muscle
spindle activity. Muscle spindles are proprioceptive
organs that are sensitive to the rate and magnitude of
a stretch; when a quick stretch is detected, muscular
activity reflexively increases (27, 42). During plyometric
exercises, the muscle spindles are stimulated by a rapid
stretch, causing a reflexive muscle action. This reflexive
response potentiates, or increases, the activity in the
agonist muscle, thereby increasing the force the muscle
produces (8–11, 35). As in the mechanical model, if a
concentric muscle action does not immediately follow a
stretch (i.e., if there is too long a time between stretch and
concentric action or movement over too large a range),
the potentiating ability of the stretch reflex is negated.
While it is likely that both the mechanical and
neurophysiological models contribute to the increased
production of force seen during plyometric exercise (3,
8–11, 14, 31, 35), the degree to which each model con-
tributes remains uncertain. Further research is needed
to improve our understanding of both models and their
respective roles in plyometric exercise.
Stretch–Shortening Cycle
The stretch–shortening cycle (SSC) employs the
energy storage capabilities of the SEC and stimulation
of the stretch reflex to facilitate a maximal increase in
muscle recruitment over a minimal amount of time. The
SSC involves three distinct phases as shown in table
18.1. While the table delineates the SSC’s individual
mechanical and neurophysiological events during each
phase, it is important to remember that all of the events
listed do not necessarily occur within the given phase.
That is, some of the events may last longer or may require
less time than allowed in the given phase. Phase I is the
eccentric phase, which involves preloading the agonist
muscle group(s). During this phase, the SEC stores
elastic energy, and the muscle spindles are stimulated.
As the muscle spindles are stretched, they send a signal
to the ventral root of the spinal cord via the Type Ia
afferent nerve fibers (see figure 18.2). To visualize the
eccentric phase, consider the long jump. The time from
touchdown of the foot to the bottom of the movement
is the eccentric phase (figure 18.3a).
Phase II is the time between the eccentric and concentric
phases and is termed the amortization (or transition)
phase. This is the time from the end of the eccentric
phase to the initiation of the concentric muscle action.
There is a delay between the eccentric and concentric
muscle actions during which Type Ia afferent nerves
synapse with the alpha motor neurons in the ventral root
of the spinal cord (see figure 18.2). The alpha motor
neurons then transmit signals to the agonist muscle
group. This phase of the SSC is perhaps the most crucial
in allowing greater power production; its duration must
be kept short. If the amortization phase lasts too long,
the energy stored during the eccentric phase dissipates as
heat, and the stretch reflex will not increase muscle activity
during the concentric phase (12). Consider the long
jumper mentioned earlier. Once the jumper has touched
down and movement has stopped, the amortization
phase has begun. As soon as movement begins again, the
amortization phase has ended (figure 18.3b).
The concentric phase, phase III, is the body’s response
to the eccentric and amortization phases. In this phase,
the energy stored in the SEC during the eccentric phase
either is used to increase the force of the subsequent
movement or is dissipated as heat. This stored elastic
energy increases the force produced during the concentric
phase movement beyond that of an isolated concentric
muscle action (13, 50). In addition, the alpha motor
neurons stimulate the agonist muscle group, resulting
in a reflexive concentric muscle action (i.e., the stretch
reflex). The efficiency of these subsystems is essential to
the proper performance of plyometric exercises. Again,
visualize the long jumper. As soon as movement begins
in an upward direction, the amortization phase has ended
and the concentric phase of the SSC has begun (figure
18.3c). In this example, one of the agonist muscles is
the gastrocnemius. Upon touchdown, the gastrocnemius
undergoes a rapid stretch (eccentric phase); there is a
delay in movement (amortization phase), and then the
muscle concentrically plantar flexes the ankle, allowing
the athlete to push off the ground (concentric phase).
The rate of musculotendinous stretch is vital to
plyometric exercise (35). A high stretch rate results in
greater muscle recruitment and activity during the SSC
concentric phase. The importance of the stretch rate
may be illustrated by three different vertical jump tests:
a static squat jump, a countermovement jump, and an
approach jump with several steps. As the rate of stretch
increases, an athlete’s absolute performance in these tests
improves; the static squat jump results in the lowest jump
height, and the approach jump results in the highest.
The static squat jump requires the athlete to get into a
squatting position (i.e., 90° hip flexion and 90° knee
flexion) followed by a jump up. This jump does not use
stored elastic energy and is too slow to allow potentiation
from the stretch reflex because there is essentially
no eccentric phase. The countermovement jump uses
a rapid eccentric element (i.e., partial squat) followed
immediately by rapid concentric muscle activity (i.e.,
jump up). The rapid eccentric phase allows the athlete to
store (and use) elastic energy in the stretched musculotendinous
unit and stimulates the stretch reflex, thereby
potentiating muscle activity (6, 29). The approach jump
uses an even quicker, more forceful eccentric phase than
?? The stretch–shortening cycle combines
mechanical and neurophysiological mechanisms
and is the basis of plyometric exercise.
A rapid eccentric muscle action stimulates
the stretch reflex and storage of elastic
energy, which increase the force produced
during the subsequent concentric action.
the countermovement jump; the increased rate of stretch
during the eccentric phase allows a further increase in
vertical jump height (4, 5, 7, 25).
Program Design
Plyometric exercise prescription is similar to resistance
and aerobic exercise prescriptions — mode, intensity, frequency,
duration, recovery, progression, and a warm-up
period must all be included in the design of a sound
plyometric training program. Unfortunately, there is little
research demarcating optimal program variables for the
design of plyometric exercise programs. Therefore, when
prescribing plyometric exercise, practitioners must rely
on the available research, practical experience, and the
methodology used for designing resistance and aerobic
training programs. The guidelines that follow are largely
based on Chu’s work (16, 18) and the National Strength
and Conditioning Association’s position statement (44).
Needs Analysis
To properly design a plyometric training program, the
strength and conditioning professional must analyze the
needs of the athlete by evaluating his or her sport, sport
position, and training status. Each sport and position
has its own unique requirements; some requirements are
unique because of the movements involved while others
have distinctive injury profiles and risks. Further, each
athlete possesses a unique training status. Some may be
new to training and have never performed plyometric
exercises; others may have been injured. Each of these
populations of athlete requires a different approach to
plyometric training. By understanding each sport’s individual
requirements, the positions within the sport, and
of the needs of each athlete, the strength and conditioning
professional is better able to design a safe, effective
plyometric training program.
Mode
The mode of plyometric training is determined by the
body region performing the given exercise. For example,
a single-leg hop is a lower body plyometric exercise,
while a two-hand medicine ball throw is an upper body
exercise. Modes of plyometric exercise are discussed in
the paragraphs that follow.
Lower Body Plyometrics
Lower body plyometrics are appropriate for virtually
any athlete and any sport, including track and field
throwing and sprinting, soccer, volleyball, basketball,
American football, baseball, and even endurance sports
such as distance running and triathlons. Many of these
sports require athletes to produce a maximal amount
of muscular force in a short amount of time. American
football, baseball, and sprinting generally require horizontal
or lateral movement during competition, while
volleyball involves primarily horizontal and vertical
movements. Soccer and basketball players must make
quick, powerful movements and changes of direction in
all planes to compete successfully. A basketball center is
an example of an athlete who would benefit greatly from
a plyometric training program, as the center is required
to jump repeatedly for rebounds. To be successful, the
center must be able to out-jump the opposing center in
order to rebound more loose balls. Lower body plyometric
training gives the player the ability to produce more
force in a shorter amount of time, thereby allowing a
higher jump. Further, participation in a plyometric training
program improves running and cycling performance
for endurance athletes by allowing muscles to produce
more force with less energy.
The various lower body plyometric drills have
differing intensity levels and directional movements.
Types of lower body plyometric drills include jumps
in place, standing jumps, multiple hops and jumps,
bounds, box drills, and depth jumps. See table 18.2
for descriptions of these drills.
Upper Body Plyometrics
Rapid, powerful upper body movements are requisites
for several sports and activities, including baseball,
softball, tennis, golf, and throws in track and field (i.e.,
the shot put, discus, and javelin). As an example, an elite
baseball pitcher routinely throws a baseball at 80 to 100
miles per hour (129–161 km/h). To reach velocities of
this magnitude, the pitcher’s shoulder joint must move at
more than 6,000°/s (19, 22, 23, 46). Plyometric training
of the shoulder joint would not only increase pitching
velocity; it may also prevent injury to the shoulder and
elbow joints, although further research is needed to
substantiate the role of plyometrics in injury prevention.
Plyometric drills for the upper body are not used as
often as those for the lower body and have been studied
less extensively, but they are nonetheless essential to
athletes who require upper body power (45). Plyometrics
for the upper body include medicine ball throws, catches,
and several types of push-ups.

Table 18.2 Lower Body Plyometric Drills
Type of drill Rationale
Jumps in place These drills involve jumping and landing in the same spot. Jumps in place emphasize the vertical
component of jumping and are performed repeatedly, without rest between jumps; the
time between jumps is the stretch–shortening cycle’s amortization phase. Examples of jumps
in place include the squat jump and tuck jump.
Standing jumps These emphasize either horizontal or vertical components. Standing jumps are maximal efforts
with recovery between repetitions. The vertical jump and jumps over barriers are examples of
standing jumps.
Multiple hops and
jumps
Multiple hops and jumps involve repeated movement and may be viewed as a combination of
jumps in place and standing jumps. One example of a multiple jump is the zigzag hop.
Bounds Bounding drills involve exaggerated movements with greater horizontal speed than other drills.
Volume for bounding is typically measured by distance but may be measured by the number of
repetitions performed. Bounding drills normally cover distances greater than 98 feet (30 m) and
may include single- and double-leg bounds in addition to the alternate-leg bounds illustrated in
this chapter.
Box drills These drills increase the intensity of multiple hops and jumps by using a box. The box may be
used to jump on or off. The height of the box depends on the size of the athlete, the landing
surface, and the goals of the program. Box drills may involve one, both, or alternating legs.
Depth jumps Depth jumps use gravity and the athlete’s weight to increase exercise intensity. The athlete
assumes a position on a box, steps off, lands, and immediately jumps vertically, horizontally, or
to another box. The height of the box depends on the size of the athlete, the landing surface,
and the goals of the program. Depth jumps may involve one or both legs.

Factors Affecting the Intensity of Lower Body Plyometric Drills
Factor Effect
Points of contact The ground reaction force during single-leg lower body plyometric drills places more stress on
an extremity’s muscles, connective tissues, and joints than during double-leg plyometric drills.
Speed Greater speed increases the intensity of the drill.
Height of the drill The higher the body’s center of gravity, the greater the force on landing.
Body weight The greater the athlete’s body weight, the more stress is placed on muscles, connective
tissues, and joints. External weight (in the form of weight vests, ankle weights, and wrist
weights) can be added to the body to increase a drill’s intensity.

Trunk Plyometrics
In general, it is difficult to perform true plyometric drills
that directly target trunk musculature, because all the
requisite plyometric elements may not be present. Plyometric
exercise uses stored elastic energy (mechanical
model) and potentiates muscle activity through stimulation
of the stretch reflex (neurophysiological model).
Following the eccentric phase of the SSC, there is likely
some storage of elastic energy during “plyometric” trunk
drills. However, research supports the notion that the
stretch reflex is not sufficiently involved during many
trunk exercises to potentiate muscle activity. Stretch
reflex latencies (time from reflex stimulation to the
beginning of agonist muscle activity) largely depend
on nerve conduction velocities and therefore increase
with greater distances from the spinal cord (i.e., longer
nerves) (34, 36, 38, 47). Quadriceps and gastrocnemius
stretch reflexes typically range from 20 to 30 ms and
from 30 to 45 ms, respectively (34, 47). Although no
research has addressed abdominal stretch reflexes, it may
be assumed that the latencies are shorter, as the muscles
are closer to the spinal cord.
Exercises for the trunk may be performed “plyometrically,”
provided that movement modifications are
made. Specifically, the exercise movements must be
shorter and quicker to allow stimulation and use of the
stretch reflex. The relatively large range of motion and
the time needed to complete the movement do not permit
reflexive potentiation of the abdominal muscles. The
exercise can be modified to decrease both the range of
motion and time, thereby allowing the agonist muscles
to be potentiated and making the exercise more like a
plyometric exercise.

Intensity
Plyometric intensity is the amount of stress placed on
involved muscles, connective tissues, and joints and
is controlled primarily by the type of drill performed.
The intensity of plyometric drills covers a large range;
skipping is relatively low in intensity, while depth jumps
place high stress on the muscles and joints. In addition
to the type of drill, several other factors also affect
plyometric intensity (table 18.3). Generally, as intensity
increases, volume should decrease (49). Because the
intensity of plyometric exercise can vary significantly,
careful consideration must be given to choosing proper
drills during a specific training cycle.
Frequency
Frequency is the number of plyometric training sessions
per week and typically ranges from one to three,
depending on the sport, the athlete’s experience with
plyometric training, and the time of year. As with other
program variables, research is limited on the optimal
frequency for training plyometrically. Because the literature
is sparse, strength and conditioning professionals
often rely on practical experience when determining the
frequency with which athletes train using plyometric
exercise. Rather than concentrating on the frequency,
many authors suggest relying more on the recovery time
between plyometric training sessions (16). Forty-eight
to 72 hours between plyometric sessions is a typical
recovery time guideline for prescribing plyometrics
(16); using these typical recovery times, athletes commonly
perform two to three plyometric sessions per
week. But the time of year, sport, and experience are
more commonly used determinants of the frequency of
plyometric training.
As previously mentioned, plyometric frequency
may vary depending on the demands of the given sport,
intensity and volume of daily workouts (e.g., practice,
resistance training, running, and plyometrics), athlete
experience with plyometric training, and time of the
training cycle. For example, during the season, one session
per week is appropriate for American football players,
while two or three sessions per week are common
for track and field athletes (2). During the off-season,
plyometric training frequency may increase to two or
three sessions per week for American football players
and to three or four sessions per week for track and field
athletes (2). Because research thus far is unfortunately
insufficient to provide appropriate guidelines for plyometric
training frequency, the use of proper recovery
times between sessions and practical experience may
be the best determinants of frequency.
Recovery
Because plyometric drills involve maximal efforts
to improve anaerobic power, complete and adequate
recovery (the time between repetitions, sets, and workouts)
is required (44). Recovery for depth jumps may
consist of 5 to 10 seconds of rest between repetitions
and 2 to 3 minutes between sets. The time between sets
is determined by a proper work-to-rest ratio (i.e., 1:5
to 1:10) and is specific to the volume and type of drill
being performed. Drills should not be thought of as
cardiorespiratory conditioning exercises but as power
training. As with resistance training, recovery between
workouts must be adequate to prevent overtraining (two
to four days of recovery, depending on the sport and
time of year). Furthermore, drills for a given body area
should not be performed two days in succession (44).
Although new research tangentially addresses recovery
and training frequency (47), manipulation of recovery
time between repetitions, exercises, and workouts has
yet to be adequately explored in plyometric research;
further work must be done in this area to provide more
concrete times for recovery.
Volume
Plyometric volume is typically expressed as the number
of repetitions and sets performed during a given training
session. Lower body plyometric volume is normally
given as the number of foot contacts (each time a foot,
or the feet together, contact the surface) per workout
(2, 16) but may also be expressed as distance, as with
plyometric bounding. For example, an athlete beginning
a plyometric training program may start with a double-
leg bound for 98 feet (30 m) per repetition but may
progress to 328 feet (100 m) per repetition for the same
drill. Recommended lower body plyometric volumes
vary for athletes of different levels of experience; suggested
volumes are provided in table 18.4. Upper body
plyometric volume is typically expressed as the number
of throws or catches per workout.
Program Length
Research has yet to determine an optimal plyometric
training program length. Currently, most programs
range from 6 to 10 weeks (2, 30); however, vertical
jump height improves as quickly as four weeks after the
start of a plyometric training program (47). In general,
plyometric training should be prescribed similarly to
both resistance and aerobic training. For those sports
requiring quick, powerful movements, it is beneficial
to perform plyometric exercise throughout the training
cycle (macrocycle). The intensity and volume of the
chosen drills should vary with the sport and the season
(i.e., off-season, preseason, or in-season).
Progression
Plyometrics is a form of resistance training and thus
must follow the principles of progressive overload.
Progressive overload is the systematic increase in
training frequency, volume, and intensity in various
combinations. Typically, as intensity increases, volume
decreases. The sport, training phase, and design of the
strength and conditioning program (resistance training,
running, plyometrics, and time of year) determine the
training schedule and method of progressive overload.
An off-season plyometric program for American football,
for example, may be performed twice a week. The
program should progress from low to moderate volumes
of low-intensity plyometrics, to low to moderate volumes
of moderate intensity, to low to moderate volumes of
moderate to high intensity.
Warm-Up
As in any training program, the plyometric exercise session
must begin with a general warm-up, stretching, and
a specific warm-up (refer to chapter 14 for a discussion
of warming up). The specific warm-up for plyometric
training should consist of low-intensity, dynamic movements.
Refer to table 18.5 for a list and explanation of
types of specific warm-up drills.
?? Effective plyometric programs include the
same variables that are essential to any
training program design: mode, intensity,
frequency, recovery, volume, program length,
progression, and warm-up.
Age Considerations
It is becoming more common for younger and older
individuals to want to augment the training programs
for their sport with plyometric exercise. When these
exercises are applied appropriately, these populations
can experience the same positive outcomes as other age
groups, with minimal risk of injury.
Adolescents
Although plyometrics have commonly been viewed as
appropriate only for conditioning elite adult athletes, pre-
training with plyometric and plyometric-like exercises.
Besides providing the well-documented muscular power
and bone strength adaptations, regular participation in
an appropriately designed plyometric training program
can better prepare young athletes for the demands of
sport practice and competition (17) by enhancing neuromuscular
control and performance. Research has yet to
determine a universal age at which people are physically
able to begin participating in a plyometric training program.
An analysis of the body’s development provides
some insight into the issue. Because the epiphyseal
plates of the bones of prepubescent children have yet
to close (33, 40), depth jumps and other high-intensity
lower body drills are contraindicated (2, 32, 39). While
the growth plates are open, highly intense activity and
injury may cause them to close prematurely, resulting
in limb length discrepancies (32). Further, and as with
all forms of exercise, boys and girls should have the
emotional maturity to accept and follow directions and
should be able to appreciate the benefits and concerns
associated with this method of training. Empirically,
7- and 8-year-olds have been trained in progressive
plyometric programs, and they continue to lead active
lives as teenagers and adults (17).
Plyometric exercise programs for children should
be used to develop the neuromuscular control and the
anaerobic skills that will carry over to safer participation
in sport and athletics, both during childhood and as they
advance to higher levels of competition. As an example,
several research studies cite the benefits of using proper
landing technique as a method of reducing an athlete’s
risk of lower extremity injury (figure 18.4). Excessive
inward (valgus) movement of the knees dramatically
increases an athlete’s risk of knee injury (see chapter 22
for a more detailed discussion on this topic).
It is extremely important that plyometric exercise
programs for children gradually progress from relatively
simple to more complex drills. It is important to focus on
the quality of the movements (e.g., proper body alignment
and speed of movement) to develop techniques that
will be essential for more advanced exercises.
As with adults, recovery between workouts must be
adequate to prevent overtraining. While the optimal
amount of recovery needed between plyometric workouts
is unknown, it should vary based on the intensity of
the training program and the athlete’s skills, abilities, and
tolerances as well as on the time of year (i.e., off-season,
preseason, or in-season). Therefore, a minimum of two or
three days between plyometric workouts should be considered
essential to optimize adaptations to the training
program and minimize the athlete’s risk of injury (17).
Figure 18.4 Proper plyometric landing position. (a) When viewed from the side, the shoulders are in line with
the knees, which helps to place the center of gravity over the body’s base of support. (b) When viewing from the
front, note that the athlete’s knees are over her toes; excessive inward (valgus) movement increases the athlete’s
risk of lower extremity injury.
a b
?? Under proper supervision and with an
appropriate program, prepubescent and
adolescent children may perform plyometric
exercises. Special attention to valgus positioning
must be given to reduce an athlete’s
risk of lower extremity injury. Depth jumps
and high-intensity lower body plyometrics
are contraindicated for this population.
Masters
Masters athletes find that they can maintain their physical
capabilities late into life and are looking for additional
training insights. When designing a plyometric
training program for a masters athlete, the strength and
conditioning professional needs to be specific in deciding
on the goal or goals of the program. Some primary
issues to consider are any preexisting orthopedic conditions
(such as osteoarthritis or any sort of surgical joint
intervention) or joint degeneration. These call for even
greater caution and a more careful use of plyometric
exercise. For example, a healthy masters athlete without
surgical history who wants to improve his or her running
performance should use depth jumps and single-leg
exercises cautiously, so alternate-leg bounding and the
double-leg hopping would be better choices. Similarly,
a masters runner with a history of knee surgery such
as partial meniscus removal, or with significant joint
degeneration, should regard depth jumps and single-leg
plyometric exercises as contraindicated and use other
forms of plyometrics cautiously.
After consideration of the predispositions related to
the masters athlete’s physical condition, a plyometric
program should be designed according to the same
guidelines as outlined for adult athletes, with the following
changes. The plyometric program should include no
more than five low- to moderate-intensity exercises; the
volume should be lower, that is, should include fewer
total foot contacts than a standard plyometric training
program; and the recovery time between plyometric
workouts should be three or four days. With these guidelines
in place — and as with all athletes — it is important
to note how the masters athlete feels after training and
recovery. Soreness may occur, but the program should
be modified if chronic or excessive pain or discomfort
is present.
Plyometrics and Other
Forms of Exercise
Plyometric exercise is only one part of an athlete’s
overall training program. Many sports and activities
use multiple energy systems or require other forms of
exercise to properly prepare athletes for competition.
Each energy system and sport-specific need must be
included in a well-designed training program.
Plyometric Exercise
and Resistance Training
A combination of plyometrics and resistance training
during a training cycle should be structured to allow
maximal efficiency and physical improvement. The
following list and table 18.6 provide guidelines for
developing a combined program.
• Combine lower body resistance training with
upper body plyometrics, and upper body resistance
training with lower body plyometrics.
• Performing heavy resistance training and plyometrics
on the same day is not usually recommended
(15, 20). However, some athletes may
benefit from complex training, a combination
of high-intensity resistance training followed
by plyometrics. If athletes perform this type of
training, adequate recovery is needed between
plyometrics and other high-intensity training.
• Traditional resistance training exercises may be
combined with plyometric movements to further
enhance gains in muscular power (54, 55). For
example, performing a squat jump with approximately
30% of one’s squat 1-repetition maximum
(1RM) as an external resistance further increases
performance (54, 55). This is an advanced form
of complex training that is appropriate only for
athletes who have previously participated in
high-intensity plyometric training programs.
Plyometric and Aerobic Exercise
Many sports — such as basketball and soccer — have both
an anaerobic (i.e., power) and an aerobic component.
Therefore, multiple types of training must be combined
to best prepare athletes for these types of sports.
Because aerobic exercise may have a negative effect on
power production (15), it is advisable to perform plyometric
exercise before aerobic endurance training. The
design variables do not change and should complement
each other to most effectively train these athletes for
competition.
Safety Considerations
Plyometric exercise is not inherently dangerous; however,
as with all modes of exercise, the risk of injury
exists. Injuries can occur simply due to an accident, but
they more typically occur when proper training procedures
are violated and may be the result of an insufficient
strength and conditioning base, inadequate warm-up,
improper progression of lead-up drills, inappropriate
volume or intensity for the phase of training, poor shoes
or surface, or a simple lack of skill. The following sections
identify and address these and other risk factors.
Knowledge of risk factors can improve the safety of
athletes performing plyometric exercise.
Pretraining Evaluation of the Athlete
To reduce the risk of injury and facilitate the performance
of plyometric exercises, the athlete must understand
proper plyometric technique and possess a sufficient
base of strength, speed, and balance. In addition, the
athlete must be sufficiently mature, both physically and
psychologically, to participate in a plyometric training
program. The following evaluative items can help determine
whether an athlete meets these conditions.
Technique
Before adding any drill to an athlete’s plyometric program,
the strength and conditioning professional must
demonstrate proper technique to the athlete in order to
maximize the drill’s effectiveness and minimize the risk
of injury. For lower body plyometrics, proper landing
technique is essential, particularly for depth jumps. If
the center of gravity is offset from the base of support,
performance is hindered and injury may occur. The
shoulders should be over the knees and the knees over
the toes during the landing, which the jumper accomplishes
through flexion of the ankles, knees, and hips. In
addition, when one views the frontal plane motion of the
athlete performing lower body plyometrics, it is essential
that the knees be positioned over the toes (figure 18.4).
Inward movement of the knees — also termed dynamic
valgus — is a significant risk factor for knee injuries of all
types, including patellofemoral pain and tears or ruptures
of the anterior cruciate ligament (ACL).
Strength
Consideration of the athlete’s level of strength is necessary
before he or she performs plyometrics. For lower
body plyometrics, previous recommendations held that
the athlete’s 1RM squat should be at least 1.5 times his
or her body weight (15, 20, 32, 44, 52). However, we
would suggest that a more important consideration is
technique. Many plyometric activities can be safely
taught to young athletes. It is our recommendation that
plyometrics be included for all athletes whose sports
require running, landing, jumping, or cutting. Teaching
proper alignment and movement mechanics through
the use of plyometric exercise has not been shown to
cause injuries; instead, this type of training has been
repeatedly shown to decrease the athlete’s risk of injury
during practices and games (43).
Balance
A less obvious lower body plyometric requirement
is balance. Balance is the maintenance of a position
without movement for a given period of time. Many
lower body plyometric drills require the athlete to move
in nontraditional patterns (e.g., double-leg zigzag hop
and backward skip) or on a single leg (e.g., single-leg
tuck jump and single-leg hop). These types of drills
necessitate a solid, stable base of support upon which the
athlete can safely and correctly perform the exercises.
Three balance tests are provided in table 18.7, listed
in order of difficulty; each test position must be held
for 30 seconds (51). For example, an athlete beginning
plyometric training for the first time would be required
to stand on one leg for 30 seconds without falling. An
experienced athlete beginning an advanced plyometric
training program must maintain a single-leg half squat
for 30 seconds without falling. The surface on which the
balance testing is performed must be the same as that
used in the plyometric drills.
Physical Characteristics
Athletes who weigh more than 220 pounds (100 kg)
may be at an increased risk for injury when performing
plyometric exercises (44, 52). Greater weight increases
the compressive force on joints during the exercises,
thereby predisposing these joints to injury. Therefore,
athletes weighing over 220 pounds (100 kg) should
avoid high-volume, high-intensity plyometric exercises
and depth jumps from heights greater than 18 inches (46
cm) (44, 52). As with other forms of exercise, an athlete’s
joint structure and previous injuries must also be
program. Previous injuries or abnormalities of the spine,
lower extremities, or upper extremities may increase
an athlete’s risk of injury during plyometric exercise.
Specifically, athletes with a history of muscle strains,
pathological joint laxity, or spinal dysfunction — including
vertebral disk dysfunction or compression — should
use caution when beginning a plyometric training program
(24, 25, 32, 48).
Equipment and Facilities
In addition to participants’ fitness and health, the area and
equipment used for plyometric drills may significantly
affect their safety.
Landing Surface
To prevent injuries, the landing surface used for lower
body plyometrics must possess adequate shock-absorbing
properties. A grass field, suspended floor, or rubber
mat is a good surface choice (32). Surfaces such as concrete,
tile, and hardwood are not recommended because
they lack effective shock-absorbing properties (32).
Excessively thick exercise mats (6 inches [15 cm] or
thicker) may extend the amortization phase and thus not
allow efficient use of the stretch reflex. Mini-trampolines
are commonly used for beginning plyometric and balance
training in rehabilitation (28). While these devices
may provide a necessary introduction to plyometrics,
especially for those recovering from musculoskeletal
injury, mini-trampolines, like thick exercise mats, are
not effective for plyometric training of uninjured athletes
because the amortization phase is extended while the
athlete is in contact with the elastic surface.
Training Area
The amount of space needed depends on the drill. Most
bounding and running drills require at least 30 m (33
yards) of straightaway, though some drills may require
a straightaway of 100 m (109 yards). For most standing,
box, and depth jumps, only a minimal surface area is
needed, but the ceiling height must be 3 to 4 m (9.8–13.1
feet) in order to be adequate.
Equipment
Boxes used for box jumps and depth jumps must be
sturdy and should have a nonslip top. Boxes should
range in height from 6 to 42 inches (15 to 107 cm) and
should have landing surfaces of at least 18 by 24 inches
(46 by 61 cm) (16). The box should be constructed
of sturdy wood (e.g., 3/4-inch [1.9 cm] plywood) or
heavy-gauge metal. To further reduce injury risk, there
are several ways of making the landing surface nonslip:
adding nonslip treads, mixing sand into the paint used
to cover the box, or affixing rubberized flooring to the
top (16).
Proper Footwear
Participants must use footwear with good ankle and foot
support, good lateral stability, and a wide, nonslip sole
(44). Shoes with a narrow sole and poor upper support
(e.g., running shoes) may invite ankle problems, especially
with lateral movements. Shoes with insufficient
foot support may lead to arch or lower leg injuries or
both, while footwear without enough cushioning might
lead to damage of more proximal joints (e.g., knee and
hip joints).
Supervision
In addition to the safety considerations already outlined,
close monitoring of athletes is necessary to ensure
proper technique. Plyometric exercise is not intrinsically
dangerous when performed correctly; but as with other
forms of training, poor technique may unnecessarily
predispose an athlete to injury.
Depth Jumping
There is a limit to the maximal height at which a depth
jump can be effectively and safely performed. A height
of 48 inches (1.2 m) would provide a significant overload
on the muscles, but the resistance may be too great for
many athletes to overcome while maintaining correct
technique (40). Jumping from such a height increases the
possibility of injury; furthermore, the amount of force
to be overcome is so great that the amortization phase is
extended and thus the purpose of the exercise defeated.
The recommended height for depth jumps ranges from
16 to 42 inches (41 to 107 cm), with 30 to 32 inches (76
to 81 cm) being the norm (4, 18, 26, 37, 38, 41). Depth
jump box height for athletes who weigh over 220 pounds
(100 kg) should be 18 inches (46 cm) or less.
Conclusion
The major goal of plyometric training is to rapidly apply
force to provide an overload to the agonist muscles.
Although it has been repeatedly shown that plyometric
exercise increases muscular power for participants in a
formal training program (30, 47, 54, 55), research has yet
to determine whether mechanical or neurophysiological
adaptations account for the improvement. Plyometrics
should be considered not an end in itself, but part of an
overall program that includes strength, speed, aerobic,
and flexibility training, and proper nutrition. After the
athlete has begun a proper strength and conditioning
program, plyometric training may be used to further
develop power.
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