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The Use of Contact Time
and the Reactive Strength
Index to Optimize Fast
Stretch-Shortening Cycle
Training
Eamonn P. Flanagan, PhD, CSCS
1
and Thomas M. Comyns, PhD
2
1
Biomechanics Research Unit, College of Science, University of Limerick, Ireland; and
2
Munster Rugby, c/o Irish Rugby Football Union, Dublin, Ireland
SUMMARY
THIS ARTICLE REVIEWS RE-
SEARCH RELATING TO THE
STRETCH-SHORTENING CYCLE
AND PLYOMETRICS. THE ARTICLE
INSTRUCTS STRENGTH AND
CONDITIONING PRACTITIONERS IN
THE USE OF GROUND CONTACT
TIMES AND THE REACTIVE
STRENGTH INDEX IN PLYOMETRIC
TRAINING. DOCUMENTATION ON
HOW THESE MEASUREMENTS
CAN BE USED TO OPTIMIZE
PLYOMETRICS AND TO IMPROVE
ATHLETES’ FAST STRETCH
SHORTENING CYCLE
PERFORMANCE IS PROVIDED.
RECOMMENDATIONS ARE MADE
REGARDING THE USE OF GROUND
CONTACT TIMES TO IMPROVE
TRAINING SPECIFICITY AND THE
USE OF THE REACTIVE STRENGTH
INDEX TO OPTIMIZE PLYOMET-
RICS, TO MONITOR TRAINING
PROGRESS, AND TO SERVE AS A
MOTIVATIONAL TOOL. A 4-STEP
PROGRESSION OF
IMPLEMENTATION IS DETAILED.
THE STRETCH-SHORTENING
CYCLE (SSC)
The SSC is a natural type of
muscle function in which mus-
cle is stretched immediately
before being contracted. This eccen-
tric/concentric coupling of muscular
contraction produces a more powerful
contraction than that which would
result from a purely concentric action
alone (14). When the force velocity
curve is measured during a complex
SSC movement involving a number of
joints and muscle groups, such as a
vertical jump, the use of a preceding
eccentric phase shifts the force–velocity
curve to the right. In comparison with
purely concentric movements, the SSC
allows greater forces to be produced
at any given velocity during the con-
centric phase (13).
The SSC is observed in a wide range of
activities. In real-life situations, exercise
seldom involves a pure form of iso-
metric, concentric, or eccentric actions
(15). The SSC appears to be the natural
form of muscle function, and it is
evident in everyday activities, such as
walking and running, as well as in more
challenging actions, including throw-
ing and jumping.
One view has been that the SSC causes
an enhancement during the concentric
phase attributable to the storage and
reutilization of elastic energy (7, 16).
During the eccentric phase, the active
muscles are prestretched and absorb
energy. Part of this energy is tempo-
rarily stored and then reused during
the concentric contraction phase of the
SSC (4). A short transition between the
eccentric and concentric phase is
necessary for this elastic energy to be
used optimally.
Additional mechanisms of action also
have been proposed. It has been
speculated that the prestretch in the
SSC may enhance the concentric
contraction through neural potentia-
tion of the muscle contractile machin-
ery during the eccentric phase,
allowing for a greater number of motor
units to be recruited during the con-
centric contraction (30). Walshe et al.
(32) observed an increase in work
output during the concentric phase of
squatting exercise when that concen-
tric phase was preceded by a prestretch
KEY WORDS:
stretch-shortening cycle; reactive
strength index; plyometrics; jumping;
ground contact time.
VOLUME 30 | NUMBER 5 | OCTOBER 2008 Copyright ÓNational Strength and Conditioning Association
32
Copyright © . N ational S trength and Conditioning A ssociation. Unauthorized reproduction of this article is prohibited
or by an isometric contraction, in
comparison with a purely concentric
squatting exercise. These authors sug-
gest that the performance enhancement
from the preceding stretch or from the
isometric contraction may result from
an attainment of a greater level of
neural excitation before the concentric
movement. This potentiation effect
increases with the speed of the eccen-
tric action and decreases with the
amount of transition time between the
eccentric and concentric phases (2).
Bobbert et al. (4) determined that in
tasks such as maximal effort vertical
jumps, in which eccentric-concentric
coupling is used compared with purely
concentric squat jumps, the perfor-
mance enhancement in the SSC is
likely caused by the eccentric phase,
allowing an increased time to develop
force. The slow eccentric phase allows
muscles to develop a high level of
active state (more attached cross-
bridges) before the start of concentric
motion. As a result, developed force
and joint moments are greater at the
beginning of the concentric phase and
more work is produced through the
first part of the concentric motion com-
pared to concentric only squat jumps.
Earlier work from Bobbert et al. (2)
supports this theory, showing that in
a countermovement jump, peak force is
already closely approached or even
reached at the transition point between
eccentric and concentric motion (before
the concentric phase has even begun).
The SSC causes an increased excitabil-
ity of proprioceptors for an optimal
reaction by the neuromuscular system.
Two proprioceptors are of most rele-
vance in the SSC. The first is the Golgi-
tendon organ (GTO), which is located
in the extrafusal fibers and innervated
by alpha motor neurons (24). The
second is the muscle spindle, which is
located in the intrafusal fibers and
innervated by g-motor neurons (19,24).
GTOs respond to changes in tension
(24) rather than of those in length.
They inhibit agonist muscles and
facilitate antagonist muscles (5). These
inhibitory effects function as
a protective mechanism (19). When
muscle contractile forces reach a point
at which damage to the muscle–
tendon complex may occur, GTOs
increase afferent activity, resulting in
inhibition of the motor neurons in-
nervating the stretched muscles while
simultaneously exciting the motor
neurons of the antagonistic muscles
(5,19,24). However, the inhibitory ac-
tion of GTOs can be minimized. Their
inhibitory action can be counteracted
by the contributions of muscle
spindles.
Reflex contributions of the muscle
spindle also can contribute to the
enhanced work output observed in
the SSC. The muscle spindle is a facil-
itatory mechanoreceptor, which reacts
to the rapid changes in a muscle’s
length to protect the muscle–tendon
complex. As eccentric stretching ap-
proaches a rate that could potentially
damage the muscle–tendon complex,
the muscle spindle activates and re-
flexively stimulates an opposite contrac-
tion of the agonist. Contributions from
the muscle spindle are one mechanism
that accounts for the performance
enhancement observed in SSC activities
such as depth jumps, which involve very
rapid eccentric phases (3).
The precise mechanisms that underpin
any given SSC activity may be de-
termined by the demands of the SSC
criterion task (10). Schmidtbleicher
(28) has suggested that the SSC can
be classified as either slow or fast. The
fast SSC is characterized by short
contraction times (,0.25 seconds)
and small angular displacements of
the hips, knees, and ankles. A typical
example would be depth jumps. The
slow SSC involves longer contraction
times, larger angular displacements and
is observed in maximal effort vertical
jumps.
For example, the muscle spindle reflex
is dependent on a fast rate of eccentric
stretching (2) and elastic energy con-
tribution may rely on a short transition
period between eccentric and concen-
tric phases (2). Decay in the magnitude
of potentiation has been observed as
the transition time between eccentric
and concentric contraction increases
(33). These mechanisms then are more
likely to contribute to the fast SSC
which has a faster eccentric velocity
and a shorter transition period than the
slow SSC (2).
Performance enhancement in slow
SSC activities may be primarily due
to the slow eccentric phase allowing an
increased time to develop force (4, 32).
The slower, longer eccentric phases
and the greater transition times be-
tween eccentric–concentric coupling
observed in slow SSC activities cast
doubt as to whether mechanisms such
as the muscle spindle reflex, elastic
energy contributions, and potentiation
could be as active in slow SSC tasks
compared with fast SSC activities (10).
As a result, it has been hypothesized
that the slow and fast SSC may
represent different muscle action pat-
terns that rely on differing biomechan-
ical mechanisms, which can affect
performance in different ways (10).
This hypothesis may have implications
for strength and conditioning practi-
tioners. Different exercises or the
manner in which exercises are per-
formed may elicit different mecha-
nisms of SSC action. Training slow
SSC activity may not by as beneficial
for athletes who primarily rely on the
fast SSC in their chosen sports and vice
versa. To adhere to the principle of
specificity, careful consideration must
be made to select modes of training
which incorporate the appropriate
SSC action for the athlete’s specific
needs.
PLYOMETRICS, GROUND
CONTACT TIMES, AND THE
REACTIVE STRENGTH INDEX
A common modality to enhance
athlete’s SSC capabilities is plyometric
training. ‘‘Plyometric training’’ is a col-
loquial term used to describe quick,
powerful movements using a pre-
stretch, or countermovement, that
involves the SSC (23). Plyometrics
have been commonly used in power
and speed training. Specific plyomet-
rics exercises can be used to train the
slow or fast SSC. Examples of slow
Strength and Conditioning Journal | www.nsca-lift.org 33
Copyright © . N ational S trength and Conditioning A ssociation. Unauthorized reproduction of this article is prohibited
SSC plyometrics include vertical jumps
and box jumps. Bounding, repeated
hurdle hops, and depth jumps typically
are regarded as fast SSC movements.
The primary focus of this article is the
optimization of fast SSC plyometrics,
particularly depth jumping. Appropri-
ate plyometric training programs have
been demonstrated in the literature to
increase power output (20), agility (22),
running velocity (17), and even running
economy (26,29).
Recently, the reactive strength index
(RSI) has been used in the practical
strength and conditioning setting as
well as in the exercise science literature
as a means to quantify plyometric or
SSC performance (11,21). The RSI was
developed as one component of the
Strength Qualities Assessment Test,
which originated at the Australian
Institute of Sport (33). Reactive
strength index is derived from the
height jumped in a depth jump, and
the time spent on the ground de-
veloping the forces required for that
jump (21). Using a contact mat during
a depth jump exercise, one calculates
the RSI by dividing the height jumped
by the time in contact with the ground
before take-off (Figure 1) (21).
Young (34) has described the RSI as an
individual’s ability to change quickly
from an eccentric to concentric con-
traction and can be considered as
a measure of ‘‘explosiveness.’’ Explo-
siveness is a coaching term that
describes an athlete’s ability to develop
maximal forces in minimal time (35).
The RSI also has been described as
a simple tool to monitor stress on the
muscle–tendon complex (21). Thus far,
RSI has been used primarily during
plyometric activities such as depth
jumps, which have a distinct, observ-
able ground contact phase. Depth
jumps are one of the most commonly
used and most commonly researched
plyometric exercises (31). In the depth
jump, the athlete drops from a fixed
height and immediately upon landing
performs an explosive vertical jump
(31). Because the RSI is a ratio between
ground contact time and height
jumped, both these variables need to
be considered in conjunction with the
overall RSI score.
The ground contact times in plyomet-
ric exercises are an important variable
for strength and conditioning coaches
to consider. By examining the ground
contact times during the performance
of a plyometric exercise, the attending
coach can assess precisely what type of
SSC (fast or slow) is being used. The
principle of specificity dictates that
the demands of an athlete’s sport, or
the demands of a task in which an
athlete wishes to improve his or her
performance will directly determine
the manner in which the plyometric
exercises should be performed (31).
Athletes whose training goal is simply
to increase maximum jump height,
such as line-out jumpers in rugby union,
can benefit from longer ground contact
times, allowing them to generate max-
imum force and maximum jump height
(31). Athletes wishing to improve their
maximum velocity sprinting speed,
which is primarily dependent on fast
SSC utilization, would require plyomet-
ric training with shorter contact times.
Examining the ground contact times of
his or her athletes during plyometric
training will give the strength and
conditioning coach an excellent indica-
tion of whether the exercise is being
performed in a beneficial manner to
their athletes’ specific sport. Contact
time can be measured in the practical
setting using contact mats or can be
analyzed in the laboratory setting by the
use of force plates.
Schmidtbleicher (28) has set a ground
contact threshold of 0.25 seconds and
shorter as the determinant of the fast
SSC. From working with elite rugby
players, we have observed this thresh-
old to be reflective of the fast SSC.
Indeed, contact times as low as 0.102
seconds have been recorded for jumps
over a series of hurdles. In training, we
use a long contact mat to measure time
on the ground for a depth jump
followed by 3 hurdle jumps where
the hurdle height is 60 cm. Commonly,
we have observed contact times short-
er than 0.150 seconds for such an
exercise.
If long ground contact phases are
observed, the attending coach must
emphasize to the athlete to be more
explosive and to get off the ground
quicker. If, after such instruction, too
great a ground contact time (.0.25
seconds) in a specific exercise is still
observed, then this suggests that the
intensity of that particular exercise is
too difficult for the athlete and needs to
be adapted or replaced. For example, if
an athlete is unable to exhibit ground
contact times representative of the fast
SSC in a depth jump from 40 cm, the
depth jump height will need to be
reduced. If an athlete cannot produce
short ground contact times when
executing repeated hurdle hops over
60 cm barriers, shorter barriers should
be used.
For coaches who may not have access
to such equipment as ground contact
mats, research has highlighted that
longer ground contact phases are
typified by the athlete being unable
to stay on the balls of the feet and
having their heels hit the ground
during the jumping action (3). If fast
SSC enhancement is the training goal,
coaches should observe that athletes
are minimizing ground contact times,
remaining on the balls of their feet
through their jumps, and using a stiff
lower-limb action with little flexion at
the hips and knees.
In addition to ground contact times,
the height to which athletes jump to
during plyometric exercises is also
Figure 1. Formula for calculating the RSI.
Reactive strength index can
be increased by increasing
jump height, decreasing
ground contact time, or
both.
VOLUME 30 | NUMBER 5 | OCTOBER 2008
34
RSI and the Fast SSC
Copyright © . N ational S trength and Conditioning A ssociation. Unauthorized reproduction of this article is prohibited
important. The height achieved in
a vertical jumping action is represen-
tative of the power production capa-
bilities of that athlete (6). Power output
capacity in vertical jumping tasks has
been correlated with performance in
a number of sports (6,9,27). Monitoring
the height jumped during plyometric
training will help the strength coach
ensure athletes are performing with
high effort and maximal power pro-
duction. In the training environment,
jump heights can be simply derived
from contact mat data indicating how
long the athlete has spent airborne in
the jump (flight time). However, many
modern ground contact mats automat-
ically calculate jump height for each
jump performed. The formula for
calculating jump height from flight
time is as follows:
Height ðmÞ¼ðgravity
ðFlight timeÞ2Þ=8;
where gravity ¼9:81 m=s
and flight time is in seconds
Alternatively, ‘‘jump-and-reach’’ equip-
ment could be used. In the research
setting, jump heights have been
commonly calculated using flight
times derived from force plate data
(6,8,10).
If the strength and conditioning coach
only examines contact times during
plyometric training, athletes may alter
their jumping strategies to reduce
ground contact times but at the
expense of power output. Similarly, if
jump height is the only examined
variable athletes may produce great
power outputs but accrue ground
contact times of long duration and
violate the specificity of training prin-
ciple. From our experience of working
with elite level rugby players, we have
found this to be the case. Conse-
quently, it can be of great benefit to
the athlete and the plyometric training
process for the coach to monitor the
training with a combination of these
two variables. The combination of
these two variables is the reactive
strength index.
OPTIMIZING AND MONITORING
PLYOMETRIC TRAINING
Although the monitoring of ground
contact times can provide a quick
reference to indicate plyometric exer-
cise specificity, the primary benefit of
measuring the RSI is its ability to
optimize the height from which plyo-
metric depth jumps can be performed
from both a performance perspective
and an injury risk perspective.
Anecdotally, in strength and condi-
tioning, the process of players perform-
ing 3 depth jumps from increasing
dropping heights (e.g., 15,30,45 cm)
with the RSI calculated for each jump
at each height has been described.
When the RSI is maintained or
improves with an increase in depth-
jump dropping height, and the ground
contact time is indicative of fast SSC
performance, it is assumed that an
individual’s reactive strength capabil-
ities are sufficient at that height of
depth jump. The dropping height at
which the RSI decreases, or ground
contact time goes above the fast SSC
threshold, indicates a height, which
may represent a heightened injury risk
for that individual or provide a sub-
optimal training stimulus.
Figure 2 illustrates 2 example datasets
for both a well-trained and an
untrained individual. In the case of
the well-trained individual, as the
depth jump height increases from 10
to 40 cm, performance as measured
through RSI also increases. The likely
reasons for this increase in perfor-
mance as depth jump height increases
are 2-fold. A higher depth jump height
will allow for a greater level of
preactivation to occur. Preactivation
involves the preparatory excitation of
motor units prior to an activity. A
degree of well-timed preactivation is
necessary for optimal utilization of the
SSC and appears to be a requirement
for the enhancement of muscular
activity during the eccentric phase
and for the timing of muscular action
during ground contacts (18). Preacti-
vation has been observed to increase as
the dropping height used in depth
jumps increases (12). The greater the
dropping height, the higher level of
neural excitation, which may be
achieved before the eccentric-concen-
tric coupling, begins which in turn
improves muscular action through the
ground contact phase.
Second, a greater depth jump height
will result in a higher level of velocity in
the eccentric phase. The greater the
level of eccentric velocity the greater
potentiation effect can be elicited from
Figure 2. A dataset of reactive strength index during an incremental jump test in a
trained and untrained athlete. The untrained individual generally scores
lower at all heights and reaches the critical threshold at which RSI
decreases at a lower dropping height. The drop-height training zone in
which each athlete would be recommended to perform the exercise is
circled.
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Copyright © . N ational S trength and Conditioning A ssociation. Unauthorized reproduction of this article is prohibited
mechanisms such as neural potentia-
tion of the muscle contractile machin-
ery and contributions from the muscle
spindle reflex provided the individual
possesses the requisite reactive
strength to transition quickly from
the eccentric to concentric phase.
The peak velocity of the eccentric
contraction during depth jumps de-
pends on the maximum downward
velocity of individual’s centre of mass.
In depth jumps, this is wholly de-
pendent on the height used in the
depth jump (3).
However, we hypothesize that a critical
threshold may be reached at which the
downward velocity becomes too great
and the athlete will lack the requisite
strength to overcome this eccentric
loading and transition effectively to
a powerful concentric phase. It could
be speculated that this reduction in
performance is due to GTOs exerting
their protective, inhibitory effects.
Therefore, as the muscle tension re-
quired to overcome the increased
downward velocity approaches a level
which could potentially damage the
muscle tendon complex, the GTOs
may be activated and might inhibit
contraction. From the same depth
jump height, a well trained individual
may have an increased muscular activity
during the eccentric-concentric cou-
pling when compared with an untrained
individual who has muscular recruit-
ment inhibited during depth jumping.
In this hypothetical well-trained athlete,
the critical threshold occurs at a depth
jump height of 50 cm. At this threshold,
typically, the athlete can no longer
remain on the balls of his or her feet
through the jumping action, the heels
hit the ground as he or she lands, and
a much longer ground contact period is
used in the transition to concentric
movement to absorb the great eccentric
loading. Ground contact times will
increase over 0.25 seconds, jump height
may decrease, and RSI decreases.
From the standpoint of specificity, this
is not optimal. The athlete is now
performing a slow SSC movement
rather than fast SSC and may be
activating and training very different
biomechanical mechanisms. The nota-
ble decrease in RSI indicates that depth
jump performance is not optimal at this
dropping height. The individual is not
expressing an appropriate jump height
relative to his or her ground contact
time. The jumping action is no longer
sufficiently ‘‘explosive.’’
A third point to note here is the effect
too great a dropping height can have on
the risk of injury. Plyometrics are known
to have a potentially increased risk of
injury because of the powerful forces
generated. Bobbert et al. (3) demon-
strated that when too great a height is
used in depth jumps, sharp peak forces
are generated, which can be potentially
dangerous to the athlete. These forces
were observed to be caused as a result of
the athlete’s heels hitting the ground,
producing sharp joint reaction forces at
the hips, knees, and ankles. Such joint
reaction forces can potentially cause
damage to passive structures of the
musculoskeletal system.
The dataset of the untrained individual
is also worth considering. Such an
athlete is likely to score lower in RSI at
all dropping heights and will reach the
critical threshold where RSI decreases
sooner than the well trained athlete.
Therefore, training becomes subopti-
mal, and this individual is exposed to
a potential dangerous training stimulus
at a lower dropping height. The
recommended ranges of dropping
height to be used for each athlete are
shown in Figure 2.
The use of too great a depth jump
height in plyometric training can re-
duce the specificity of the athletes
training, decrease performance, and
be deleterious to athlete safety. This
RSI procedure can assist coaches in
optimizing plyometric training from
a performance and safety perspective.
A team profile of plyometric ability can
be developed allowing athletes of
similar abilities to be grouped together
for training. Such a procedure may also
assist coaches in identifying athletes
whose reactive strength capabilities are
deficient.
THE RSI AS A MOTIVATIONAL
TOOL
Research has demonstrated that spe-
cific verbal instruction can positively
affect jumping performance. Arampatzis
et al. (1) found that instructing subjects
to ‘‘jump high and a little faster than
your previous jump’’ instead of instruct-
ing them simply to ‘‘jump as high as
possible’’ encouraged subjects to per-
form depth jumps with significantly
shorter ground contact times.
This research demonstrates the role
that knowledge of results can play in
motivating athletes through plyomet-
ric training sessions. Making the ath-
letes aware of their jump heights and
ground contact times or their reactive
strength index may motivate them to
perform their plyometric exercise at
a level closer to maximum effort.
However, it has been suggested that
when constant feedback in the form of
knowledge of results is given on every
single trial, participants can become
overly reliant on the feedback and fail
to process the information required to
improve performance (25). The attend-
ing coach may then be wise to only
provide knowledge of results intermit-
tently and might best be used when the
athlete’s performance is declining and
the individual is in need of motivational
support.
From our experience working with
elite rugby players, we have found that
the quality of the plyometric process is
enhanced by the use of contact mats
for performance feedback. To prevent
against a dependence on regular feed-
back, RSI is not used in every training
session. In addition, we question the
players after the plyometric exercise on
the quality of the jumps asking ‘‘which
was the quickest jump, and why?’’ This
questioning method is useful for mak-
ing the players think about what is
required for successful jump perfor-
mance and creates a more active
learning process.
It is recommended that strength and
conditioning coaches should provide
this augmented feedback in an enthu-
siastic manner indicating a personal
interest in the performance of the
VOLUME 30 | NUMBER 5 | OCTOBER 2008
36
RSI and the Fast SSC
Copyright © . N ational S trength and Conditioning A ssociation. Unauthorized reproduction of this article is prohibited
athlete and with encouragement to
make maximum effort (21). Intermit-
tently throughout the plyometric train-
ing session the coach should also
remind the athlete to ‘‘jump high’’
and ‘‘jump fast’’ when performing
depth jumps.
PRACTICAL APPLICATIONS: A
PROGRESSIVE PROGRAM FOR
USING THE RSI
The use of RSI during fast plyometric
exercises, such as repeated tuck jumps,
hurdle jumps, and depth jumps, is an
effective practical application of this
performance measure and can enhance
the quality of plyometric training.
From our experience with elite rugby
players, a 4-stage progression toward
the use of fast SSC exercises and the
RSI has been most effective (Figure 3).
A progressive plyometric program is
especially needed with athletes who
have limited plyometric training expe-
rience. This is done to ensure that
athletes perform fast plyometric exer-
cises with correct technique from
a performance and safety perspective.
Correct fast plyometric exercise tech-
nique involves the following coaching
points being adhered to (a) minimize
ground contact time, (b) maximize
jump height, (c) imagine the ground
is a hot surface, (d) imagine your leg is
a stiff spring that rebounds off the
ground on landing, and (e) pretense
your leg muscles before landing.
The first step of our 4-stage progres-
sion involves an eccentric jump phase.
Here, the focus is on landing
mechanics and the athlete concen-
trates on holding the landing of a low
intensity jump, such as an ankle hop,
with the center of gravity over the base
of support. The player is instructed to
focus on making a ‘‘quiet’’ landing and
is encouraged to exhibit minimal
flexion at the ankle, knee, and hip
joints during landing (imagining freez-
ing on ground contact). These exer-
cises are included to improve the
player’s ability to tolerate the down-
ward velocity of plyometric exercises
and the eccentric load associated with
the fast SSC.
After this step, the next stage focuses
on teaching the athlete to minimize
ground contact times. During any fast
plyometric exercises, the leg should act
like a stiff spring and rebound with
minimum delay off the ground on
contact. This is accomplished with
the institution of low-intensity, fast
plyometric exercises, such as ankle
jumps and skipping, where the focus
is on short ground contact times
(‘‘imagine that the ground is a hot
surface’’). The athlete can be instructed
to keep on the balls of his or her feet at
all times and pretense the lower leg
muscles before landing to assist with
this action.
Progression is continued by having the
player now jump over a series of low
hurdles where the focus is on mini-
mizing ground contact time and clear-
ing the hurdle. Contact time is given
here as the feedback score. Once the
player can clear the low hurdle with
a low ground contact time, then the
height of the hurdle may be increased
to provide an overload effect. In these
examples, the height is controlled by
the hurdle so that the focus is on
teaching the player to perform the
plyometric exercise with minimum
ground contact time.
Once the players have then learned to
perform these fast plyometric exercises
with short ground contact times, depth
jumps can be introduced where the
focus is on both minimizing short
ground contact times and maximizing
height jumped. In this case, the RSI can
be used as the feedback variable to the
athlete or as a coaching tool to optimize
plyometric exercises or to monitor
athletes’ plyometric performance.
Eamonn
Flanagan is a
strength and con-
ditioning coach
in Limerick,
Ireland.
Tom Comyns
is a strength and
conditioning
coach for the Irish
Rugby Football
Union based with
Munster Rugby.
Figure 3. A 4-step progression for developing fast stretch-shortening cycle (SSC) performance and introducing contact time (CT ) and
reactive strength index (RSI) as feedback tools.
Strength and Conditioning Journal | www.nsca-lift.org 37
Copyright © . N ational S trength and Conditioning A ssociation. Unauthorized reproduction of this article is prohibited
REFERENCES
1. Arampatzis A, Schade F, Walsh M, and
Bru
¨ggemann GP. Influence of leg stiffness
and its effect on myodynamic jumping
performance. J Electromyog Kinesiol 11:
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RSI and the Fast SSC
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