THE EFFECTS OF A 6-WEEK PLYOMETRIC TRAINING PROGRAM ON AGILITY
, Jeremy J. Herniman1, Mark D. Ricard2, Christopher
C. Cheatham1 and Timothy J. Michael1
of HPER, Western Michigan University, MI, USA
2University of Texas-Arlington, USA
21 June 2006
Journal of Sports Science and Medicine (2006) 5, 459 - 465
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|The purpose of the study was to determine if six weeks of plyometric
training can improve an athlete's agility. Subjects were divided into
two groups, a plyometric training and a control group. The plyometric
training group performed in a six week plyometric training program
and the control group did not perform any plyometric training techniques.
All subjects participated in two agility tests: T-test and Illinois
Agility Test, and a force plate test for ground reaction times both
pre and post testing. Univariate ANCOVAs were conducted to analyze
the change scores (post - pre) in the independent variables by group
(training or control) with pre scores as covariates. The Univariate
ANCOVA revealed a significant group effect F2,26 = 25.42, p=0.0000
for the T-test agility measure. For the Illinois Agility test, a significant
group effect F2,26 = 27.24, p = 0.000 was also found. The plyometric
training group had quicker posttest times compared to the control
group for the agility tests. A significant group effect F2,26 = 7.81,
p = 0.002 was found for the Force Plate test. The plyometric training
group reduced time on the ground on the posttest compared to the control
group. The results of this study show that plyometric training can
be an effective training technique to improve an athlete's agility.
WORDS: Jumping, training, performance variables, quickness.
are training techniques used by athletes in all types of sports
to increase strength and explosiveness (Chu, 1998).
Plyometrics consists of a rapid stretching of a muscle (eccentric
action) immediately followed by a concentric or shortening action
of the same muscle and connective tissue (Baechle and Earle, 2000).
The stored elastic energy within the muscle is used to produce more
force than can be provided by a concentric action alone (Asmussen
and Bonde-Peterson, 1974;
Miller, et al., 2002;
Researchers have shown that plyometric training, when used with
a periodized strength-training program, can contribute to improvements
in vertical jump performance, acceleration, leg strength, muscular
power, increased joint awareness, and overall proprioception (Adams,
et al., 1992; Anderst et al., 1994;
Bebi et al., 1987;
Brown et al., 1986;
Clutch et al., 1983;
Harrison and Gaffney, 2001;
Hennessy and Kilty, 2001;
Hewett et al., 1996;
Holcomb et al., 1996;
Miller et al., 2002;
Paasuke et al., 2001;
Potteiger et al., 1999;
Wilson et al., 1993).
Plyometric drills usually involve stopping, starting, and changing
directions in an explosive manner. These movements are components
that can assist in developing agility (Craig, 2004;
Miller et al., 2001;
Parsons et al., 1998; Yap et al., 2000; Young et al., 2001).
Agility is the ability to maintain or control body position while
quickly changing direction during a series of movements (Twist and
Benickly, 1995). Agility training is thought to be a re- enforcement
of motor programming through neuromuscular conditioning and neural
adaptation of muscle spindles, golgi-tendon organs, and joint proprioceptors
(Barnes and Attaway, 1996;
Potteiger et al., 1999).
By enhancing balance and control of body positions during movement,
agility theoretically should improve.
has been suggested that increases in power and efficiency due to
plyometrics may increase agility training objectives (Stone and
O'Bryant, 1984) and plyometric activities have been used in sports such
as football, tennis, soccer or other sporting events that agility
may be useful for their athletes (Parsons and Jones, 1998; Renfro, 1999; Robinson and Owens, 2004; Roper, 1998; Yap and Brown, 2000). Although plyometric training has been shown to increase
performance variables, little scientific information is available
to determine if plyometric training actually enhances agility. Therefore,
the purpose of this study was to determine the effects of a 6-week
plyometric training program on agility.
Twenty-eight subjects volunteered to participate. Subjects were
randomly assigned to two groups, a plyometric training group and
a control group (Table
Subjects were at least 18 years of age, free of lower extremity
injuries, and were not involved in any
type of plyometric training at the time of the study.
All subjects agreed not to change or increase their current exercise
habits during the course of the study. The plyometric training group
participated in a 6-week training program performing a variety of
plyometric exercises designed for the lower extremity (Table
2), while the control group did not participate in any plyometric
exercises. All subjects were instructed not to start any lower extremity
strengthening programs during the 6-week period and to only perform
activities of normal daily living. Prior to the study, procedures
and guidelines were presented orally and in written form. Subjects
agreeing to participate signed an institutionally approved consent
A 6-week plyometric training program was developed using two training
sessions per week. The training program was based on recommendations
of intensity and volume from Piper and Erdmann, 1998, using similar drills, sets, and repetitions. From a physiological
and psychological standpoint, four to six weeks of high intensity
power training is an optimal length of time for the CNS to be stressed
without excessive strain or fatigue (Adams et al., 1992). It is the belief of some sports physiologists that neuromuscular
adaptations contributing to explosive power occur early in the power
cycle of the periodization phase of training (Adams et al., 1992). Plyometrics were only performed twice per week to allow
for sufficient recovery between workouts as recommended by researchers
(Adams et al., 1992).
Training volume ranged from 90 foot contacts to 140 foot contacts
per session while the intensity of the exercises increased for five
weeks before tapering off during week six as recommended by Piper
and Erdmann, 1998 and used previously in another study (Miller et al., 2002). The intensity of training was tapered so that fatigue
would not be a factor during post-testing. The plyometric training
group trained at the same time of day, two days a week, throughout
the study. During the training, all subjects were under direct supervision
and were instructed on how to perform each exercise.
Three tests conducted both pre and post training were used to determine
agility outcomes. The T-test (Figure
1) was used to determine speed with directional changes such
as forward sprinting, left and right side shuffling, and backpedaling.
The Illinois agility test (Figure
2) was used to determine the ability to accelerate, decelerate,
turn in different directions, and run at different angles. These
tests were selected based upon established criteria data for males
and females and because of their reported validity and reproducibility
of the tests (Pauole et al., 2000; Roozen, 2004). Finally,
a force plate test (Figure 3)
was used to measure quickness and power (ground contact time while
hopping). This test was created to mimic the dot drill that requires
an athlete to stay balanced in order to shift their body weight
in several different directions.
Prior to training, all subjects had their baseline agility tested,
using the three tests previously mentioned. The total testing session
was approximately one hour for each subject which included warm-up,
ten minute rest times between tests and approximately three minutes
between reps. Each test was explained and demonstrated. Before testing,
subjects were given practice trials to become familiar with the
testing procedures. All tests were counterbalanced pre and post
testing to ensure that testing effects were minimized. Subjects
performed each test 3 times and the results were averaged.
Pre and post values for the dependent variables were analyzed to
determine if the distributions were normal using Kolmogorov-Smirnov
goodness-of-fit test and the Shapiro-Wilk Normality test. Change
scores (post - pre) were computed for each of the dependent variables:
T-Test agility, Illinois Agility Test and the force plate test.
Single factor ANCOVAs were used to test for differences between
groups (Control, Plyometric Training) for the dependent variable
change scores using the pre-test values as a covariate. Alpha was
established a priori at p < 0.05. The Statistical Package for
Social Science (version 11.0: Chicago, Ill) was used to calculate
means and standard deviations for times of the groups for all three
tests are provided in Table 3.
Tests of normality indicated that dependent variables were normally
distributed. The single factor ANCOVA revealed a significant group
effect F2,26 = 25.42, p = 0.000, power = 1.00 for the
T-test agility measure change score, when controlling for Pre-test
differences. As shown in Table
3, the plyometric group improved their T-Test agility times
by -0.62 ± 0.24 sec, while the control group times were virtually
unchanged 0.01 ± 0.14 sec. For the Illinois Agility test change
score, a significant group effect F2,26 = 27.24, p =
0.000, power = 1.00 was found, when controlling for Pre-test differences.
The plyometric training group improved their Illinois Agility Test
times by -0.50 ± 0.32 sec and the control group times changed by
-0.01 ± 0.05 sec. A significant group effect F2,26 =
7.83, p = 0.002, power = 0.923 was found for the force plate test
change score, when using the Pre-test values as a covariate. The
plyometric training group improved their force plate agility test
times by -26.37 ± 21.89 msec and the control changed their times
by -0.98 ± 6.33 msec, see Table
the T-test, times were improved by 4.86%, for the Illinois agility
test, 2.93%, and for the force plate, subjects improved by over
10%. By finding significant differences for all three tests, our
results indicate that the plyometric training improved times in
the agility test measures because of either better motor recruitment
or neural adaptations. In a previous study of plyometric training,
the authors speculated
that improvements were a result of enhanced motor unit recruitment
patters (Potteiger et al., 1999).
Neural adaptations usually occur when athletes respond or react
as a result of improved coordination between the CNS signal and
proprioceptive feedback (Craig, 2004).
However, we could not determine if neural adaptations occurred via
synchronous firing of the motor neurons or better facilitation of
neural impulses to the spinal cord which also supports the suggestions
of Potteiger et al., 1999.
Therefore, more studies are needed to determine neural adaptations
as a result of plyometric training and how it affects agility.
We chose to use a force plate test to determine ground contact time
when preparing to change direction, which is a major component of
agility and a benefit of plyometric training. Roper, 1998
used a four-point drill, which is very similar to the test we implemented
using the force plate, since the movement patterns require forward,
backward and lateral changes in direction in a rapid succession.
He stated that the relationship between plyometric exercise and
increased performance in agility tests may be high due to their
similar patterns of movement to facilitate power and movement efficiency
by the immediate change in direction upon landing. Our results using
the force plate test support Roper's claims that a plyometric training
program can decrease ground reaction test times because of increases
in muscular power and movement efficiently.
In our study, subjects who underwent plyometric training were able
to improve their times significantly on both the T-test and Illinois
agility test. Therefore, we found a positive relationship between
plyometric training and improvements of both agility tests. This
improvement in agility is beneficial for athletes who require quick
movements while performing their sport and support results form
other studies. In a study of tennis players, the authors used a
T-test and dot drill test to determine speed and agility (Parsons
and Jones, 1998).
They found that the players became quicker and more agile; enabling
them to get to more balls and be more effective tennis players.
measured agility using the T-test with plyometric training while
Robinson and Owens, 2004
used vertical, lateral and horizontal plyometric jumps and showed
improvements in agility.
results from our study are very encouraging and demonstrate the
benefits plyometric training can have on agility. Not only can athletes
use plyometrics to break the monotony of training, but they can
also improve their strength and explosiveness while working to become
more agile. In addition, our results support that improvements in
agility can occur in as little as 6 weeks of plyometric training
which can be useful during the last preparatory phase before in-season
competition for athletes.
Plyometric training can enhance agility of athletes.
weeks of plyometric training is sufficient to see agility results.
reaction times are decreased with plyometric training