268 Miller et al
Comparisons of Land-Based and
Aquatic-Based Plyometric Programs
During an 8-Week Training Period
Michael G. Miller, David C. Berry, Susan Bullard,
and Roger Gilders
Context: Land and aquatic plyometrics have clinical relevance for exercise, sport
performance, and rehabilitation, yet study is limited comparing both. Objective: To
compare the effects of land-based and aquatic-based plyometric-training programs on
performance variables, muscle soreness, and range of motion (ROM). Setting: Aquatic
facility and biomechanics laboratory. Subjects: Forty subjects randomly assigned to 3
groups: land (n = 13), water (n = 13), and control (n = 14). Main Outcome Measures:
Performance variables, muscle soreness, and ROM were measured before and after
an 8-week training period. An analysis of covariance (ANCOVA) and a Bonferroni
post hoc test determined significance. Results: ANCOVA revealed significant differences between groups with respect to plantar-flexion ROM (P < .05). Paired t test
determined that the aquatic group significantly increased muscle power pretest to
posttest (P < .05). Conclusions: Results indicate that aquatic plyometric training can
be an alternative approach to enhancing performance. Key Words: torque, soreness,
power, water, fitness
Comparisons of land-based and aquatic-based plyometric programs during an 8-week training period. Miller
MG, Berry DC, Bullard S, Gilders R. J Sport Rehabil. 2002;11:268-283. © 2002 Human Kinetics Publishers,
Inc.
Plyometrics is a training technique that was initially used by track-and-field
athletes but is currently used by athletes in all types of sports to increase
strength and explosiveness.1 Plyometrics can be described as a rapid prestretching of a muscle during an eccentric action, followed immediately
by a concentric action of the same muscle. This sequence of events, also
known as the stretch-shortening cycle, allows muscles to generate greater
forces than do muscles starting in a static position.2-4
Most plyometric programs include some type of jumps, hops, bounds,
or shock movements to develop power in the lower body. These types
of movements are crucial in sports such as basketball and volleyball, in
Miller is with the Graduate Athletic Training Program, Western Michigan University,
Kalamazoo, MI 49008. Berry is with the Athletic Training Program, Salem State College, Salem,
MA 01970. Bullard and Gilders are with the School of Recreation and Sport Sciences, Ohio
University, Athens, OH 45701.
268
Land- and Aquatic-Based Plyometric Programs
269
which vertical-jumping ability and power can increase one’s overall athletic performance. Research has shown that athletes who efficiently use
the stretch-shortening-cycle mechanism through plyometric exercises are
better able to increase acceleration and power.4-11 When used in conjunction
with a periodized strength-training program, plyometric training has been
shown to contribute to improvements in vertical-jump height, leg strength,
power, joint awareness, and overall proprioception.1,12-17
Although plyometric training has been shown to produce improvements in performance variables, a potential for injury exists, especially
when athletes are subjected to new exercise stimuli or greater intensity in
training. Exposure to a new exercise routine, in particular eccentric activities, increases force production in the musculoskeletal system and might
result in the occurrence of delayed-onset muscle soreness.18-20 Another factor related to the extent of injury or soreness when performing plyometric
training is the force associated with landing. Researchers have postulated
that plyometric exercises performed in the aquatic environment might potentially reduce the risk of muscle soreness and injury during plyometric
training21,22 while providing an ideal medium for athletes to begin training
before progressing to training on land.23
Exercising or training in an aquatic environment has several advantages.
First, the buoyancy provided by the water can be used to decrease an athlete’s weight status and joint loading, allowing for an earlier, safer, and more
comfortable return to land-based training.23 For example, the weight-bearing
status of an individual in chest-deep water is approximately 30% to 40% of
total body weight and 47% to 60% when submerged in waist-deep water.24,25
Second, the fluid dynamic properties of water, such as surface drag, profile
drag, and wave drag, provide resistance that can be incorporated into the
progression of the plyometric-training program. The level of resistance depends on the size and shape of the individual and the speed of movement
of the exercise in water.23,26 Thus, water enables an athlete to strengthen the
muscles by providing resistance on the segments that are submerged as each
is brought forward and upward through the water. The buoyant force of
the water, although decreasing the amount of force and joint compression
on landing, does not reduce the amount of force that must be produced to
control and stop the eccentric phase of the movement, nor does it reduce
the amount of force needed to overcome the resistance of the water during
the concentric phase of the movement.
Although the popularity and benefits of plyometrics and aquatic training have increased over the years, relatively few training programs have
explored the benefits of combining the two. Therefore, the purpose of this
study was to compare the effects of 8 weeks of land-based and aquatic-based
plyometric training on power, vertical jump, and peak torque. A secondary
purpose was to compare the effects of the 2 training programs on muscle
soreness and range of motion.
270 Miller et al
Methods
Design
An 8-week plyometric-training program was developed using 2 training
sessions per week. The training program was based on recommendations
of intensity and volume from Piper and Erdmann,27 using identical drills,
sets, repetitions, and volume for both the land and aquatic training groups.
Training volume ranged from a minimum of 80 foot contacts to 120 foot
contacts per session while the intensity of the exercises increased throughout
the course of the training program (Table 1). The subjects were instructed
to perform each exercise to their maximal ability.
The aquatic training was held at an aquatic center in approximately waistdeep water, and the land training was held in a biomechanics laboratory
on a cushioned surface that consisted of quarter-in industrial carpet with
quarter-in carpet padding below it. Both groups trained at the same time
of day, 2 days a week, throughout the study. The researchers and training-group leaders met once a week to discuss and demonstrate training
exercises and intensity levels. The training-group leaders were assigned
to supervise each training session.
Subjects
Forty subjects (21 women, 19 men), free of lower extremity musculoskeletal
injuries, volunteered to participate in this study. Treatment groups consisted
of control (n = 14, age = 23.0 ± 5.5 years, height = 177.8 ± 10.7 cm, mass =
79.8 ± 14.3 kg), aquatic (n = 13, age = 22 ± 2.5 years, height = 170.8 ± 9.3
cm, mass = 74.2 ± 20.2 kg), and land (n = 13, age = 21.5 ± 3.6 years, height =
171.1 ± 11.3 cm, mass = 72.2 ± 9.7 kg). In terms of activity level, the subjects
ranged from sedentary to recreationally active individuals, and they agreed
not to modify their current exercise regimens throughout the course of the
study. The study procedures and guidelines were orally presented to the
subjects before they signed an institutionally approved consent form.
Subjects were then randomized into 3 groups: 13 subjects in a traditional
land plyometric-training group, 13 in an aquatic plyometric-training group,
and 14 in a control group. The land and aquatic groups participated in an
identical plyometric-training program throughout the study. The 2 training groups were reminded at each training session not to begin a new
exercise program during the course of the study. The control group was
also instructed not to begin or alter their current exercise program during
the study. Baseline data were collected on performance variables before
the training program began and at the conclusion of the training period.
Intraclass correlations coefficients indicated a significant relationship (P
< .05) between pretraining and posttraining measurements, suggesting
relative reliability of the testing procedures.
Land- and Aquatic-Based Plyometric Programs
Table 1 Training Intensity and Plyometric Drills
During the 8-Week Session
Training
week
1
2
3
4
5
6
7
8
Plyometric drill
Training
intensity
Side-to-side ankle hops
Standing jump and reach
Front cone hops
Side-to-side ankle hops
Standing jump and reach
Front cone hops
Double-leg hops
Side-to-side ankle hops
Standing jump and reach
Front cone hops
Double-leg hops
Lateral cone hops
Side-to-side ankle hops
Standing jump and reach
Front cone hops
Lateral cone hops
Tuck jump with knees up
Side-to-side ankle hops
Standing jump and reach
Double-leg hops
Lateral cone hops
Tuck jump with knees up
Lateral jump over barrier
Standing jump and reach
Front cone hops
Double-leg hops
Lateral cone hops
Tuck jump with knees up
Lateral jump, single leg
Standing jump and reach
Double-leg hops
Lateral cone hops
Lateral jump over barrier
Lateral jump, single leg
Standing jump and reach
Lateral cone hops
Tuck jump with knees up
Lateral jump, single leg
Single-leg hops
low
low
low
low
low
low
medium
low
low
low
medium
medium
low
low
low
medium
medium
low
low
medium
medium
high
high
low
low
medium
medium
high
high
low
medium
medium
high
high
low
medium
medium
high
high
271
272 Miller et al
Testing Procedures
Subjects were tested on the following performance variables: vertical-jump
power, muscle power (Margaria-Kalamen), ankle and knee isokinetic peak
torque, and range of motion (ROM). Ankle- and knee-joint ROM and isokinetic testing were performed using each subject’s right leg. Subjects followed the same order of testing for pretest and posttest measurements. Total
testing time was approximately 1 hour for each subject. The same personnel
at each testing station measured all pretest and posttest variables.
Vertical-Jump Power. Vertical-jump height was measured using the VerTec jumping system (Sports Imports, Inc, Columbus, Ohio). The Ver-Tec
system consists of an adjustable upright pole with a 2-ft length of moveable plastic strips on the top. A base measurement for reach height was
determined by measuring the highest strip a subject could touch while
standing flat-footed with an outstretched arm. Each subject was allowed 2
practice jumps, followed by 5 stationary vertical 2-footed jumps. Vertical
jumps were recorded to the nearest half inch, and the difference between
the base reach height and the highest vertical jump was recorded. Vertical
jump height was calculated as
VJ = maximal jump height – initial reach height
Vertical-jump heights were converted to power outputs to account for
any improvements in vertical-jump ability that might have been masked
by increases in body mass or changes in body composition. Pretest and
posttest vertical-jump scores were then converted into power (in Watts)
using the Lewis Nomogram formula:
Power = 4.9.5 (mass in kg)(distance in m)
Muscle Power. The Margaria-Kalamen power test was used to measure
the subjects’ muscle-power output by having them run up a flight of steps
as quickly as possible. Electronic switch mats were placed on the third
and ninth steps to record the time. The subjects were placed 6 m in front
of the stairs and instructed to accelerate toward the steps and run up them
as rapidly as possible, taking 3 steps at a time. The electronic switch mat
started the timing when the subjects stepped on the third step (first switch
mat). Subjects then proceeded to the sixth step and then to the electronic
switch mat on the ninth step (second switch mat) to stop the clock. Times
were recorded using a performance-time analyzer (Lafayette Instrument
Co, Lafayette, Ind, clock model 54050) to the nearest thousandth of a second. After 2 practice trials, each subject performed 5 trials with complete
recovery between efforts. Power (in Watts) was calculated using the following formula:
Power = weight in N  vertical distance between first and last step in m
time in s
Land- and Aquatic-Based Plyometric Programs
273
Peak Torque. Peak torque generated across the ankle and knee joints was
measured using a Biodex Multi-Joint System 2 (Biodex Medical Systems,
Inc, Shirley, NY). Three speeds were used to measure peak torque, in the
following order: 1.57, 3.14, and 6.28 rad/s. Each subject was positioned
according to the Biodex system’s testing protocols. Subjects were provided
with 1-minute rest intervals between testing speeds. A practice session was
granted to the subjects before each testing speed.
To measure knee-flexion and -extension peak torque, subjects were placed
in a sitting position with the hip flexed to 85°, knee in 90° of flexion, and
the foot hanging in a resting position (slight plantar flexion). The femoral
condyles were aligned with the axis of the actuator arm in the sagittal plane.
The distal pad was aligned proximal to the malleoli and below the bulk of
the calf musculature. All subjects were securely fastened with thigh, pelvic,
and shoulder straps during testing procedures.
To measure ankle dorsiflexion and plantar-flexion peak torque, subjects
were placed in a sitting position with the hip flexed to 60° and the knee
flexed to 30° while the ankle was placed squarely on the footplate as indicated in the Biodex manual. The footplate was adjusted to ensure that the
ankle axis aligned with the input shaft. A multisupport pad was placed
distal to the knee and tilted to support the tibia in the horizontal position.
All subjects were securely fastened with pelvic, shoulder, and multisupport
straps during testing procedures.
Range of Motion
Maximal active ankle-joint dorsiflexion and plantar flexion and knee-joint
flexion were determined using a Baseline® 360° 12-in goniometer (Fabrication Enterprises Inc, White Plains, NY). All measurements were recorded
before isokinetic testing using the ROM guidelines recommended by Norkin
and White.28 Ankle-joint motion was determined by placing subjects in a
seated position with the knee flexed to 90°. The foot was passively placed
into 90° with the stationary arm of the goniometer aligned with the fibular
head and the moving arm following a line parallel to the lateral aspect of
the fifth metatarsal. The center of the goniometer axis was placed on the
axis of rotation, the lateral malleolus. Subjects then maximally dorsiflexed
and plantar flexed the foot while keeping the knee flexed at 90° and the
subtalar joint in neutral position.
Knee-joint flexion was measured by placing each subject in a supine
position. The goniometer was positioned with the stationary arm aligned
proximally with the greater trochanter and distally with the lateral malleolus. The axis of the goniometer was placed laterally at the tibiofemoral
joint. The examiner placed the hip into 90° of flexion and asked the subject to
flex the knee with the assistance of gravity. The supine position was chosen
over the prone position to eliminate active contraction of the hamstrings,
274 Miller et al
limiting the amount of knee flexion caused by soft-tissue approximation.
The supine position was also chosen to eliminate passive insufficiency of
the quadriceps, which can also restrict ROM in the prone position.
Muscle Soreness
Each week subjects in the land and aquatic training groups completed an
injury and visual analog scale (VAS) to report soreness. Using the VAS, subjects rated their perceived muscle soreness from 1 to 10 (1 = no soreness, 10
= extreme soreness) at 24, 48, and 72 hours posttraining. The injury and VAS
report forms were distributed on the first day of a training session when a
new intensity level was introduced. These forms were then collected at the
next training session. The VAS has been found to be both valid and reliable
in determining muscle soreness.29
Statistical Analysis
Maximum values for the variables of vertical-jump power, muscle power,
peak torque, and ROM for each group were calculated for pretest and posttest measurements. Mean values for muscle soreness at 24, 48, and 72 hours
posttraining were calculated weekly for the training groups.
Analyses of covariance (ANCOVAs) using posttest scores while controlling for pretest scores were conducted to analyze vertical-jump power,
muscle power, peak torque, and ROM with the group (land, aquatic, or
control) as the between-subjects factor. Post hoc comparisons of group
differences for each dependent variable were evaluated using a pairwise
comparison with a Bonferroni critical-value procedure. Paired t tests were
used to analyze any significant differences between the pretest and posttest
values within each training group.
Two-way repeated-measures ANOVAs were conducted to analyze
muscle soreness over the 8-week training period with the group (land or
aquatic) as the between-subjects factor and time (24, 48, or 72 hours) as the
within-subjects factor. Statistical significance of P < .05 was set a priori for
all statistical tests. The Statistical Package for Social Sciences (version 10.0,
SPSS, Inc, Chicago, Ill) was used to calculate the statistics.
Results
The means and standard deviations for vertical-jump and muscle power
are provided in Table 2. The ANCOVAs revealed no significant differences
among the 3 groups with respect to either power test. A paired t test determined that there was a significant increase in muscle power (pretraining
to posttraining) in the aquatic training group (P < .05).
Tables 3 and 4 provide results on the means and standard deviations
for peak torques measured during knee flexion and extension and ankle
Post
1247.9 ± 295.8
1460.9 ± 332.4
Post
89.7 ± 33.1
76.3 ± 27.8
63.4 ± 22.8
167.4 ± 53.3
124.0 ± 35.8
87.2 ± 26.6
Pre
78.6 ± 24.2
67.1 ± 20.7
56.7 ± 18.3
163.1 ± 55.8
123.4 ± 36.1
87.6 ± 25.1
Control
137.0 ± 46.5
102.5 ± 37.3
74.6 ± 25.0
71.4 ± 17.1
59.1 ± 16.4
47.3 ± 16.4
Pre
81.0 ± 26.4
66.0 ± 23.7
53.8 ± 19.0*
Post
140.7 ± 45.6
103.8 ± 37.4
75.9 ± 25.7
Aquatic
137.4 ± 35.6
100.3 ± 28.5
71.2 ± 19.7
71.6 ± 19.5
59.6 ± 16.9
46.3 ± 15.5
Pre
Land
139.0 ± 43.2
104.3 ± 34.5
73.3 ± 37.7
84.4 ± 19.5
69.4 ± 16.9
57.5 ± 16.9*
Post
Post
1062.2 ± 253.7
1248.4 ± 501.7
Land
Post
Pre
1092.7 ± 367.7 1046.5 ± 247.3
1304.1 ± 473.3* 1239.5 ± 338.6
Aquatic
Pre
1055.4 ± 337.9
1216.8 ± 425.0
Means ± Standard Deviations for Knee Peak Torque
*Significant increase from pretest.
rad/s
Flexion
1.57
3.14
6.28
Extension
1.57
3.14
6.28
Table 3
*Significant increase from pretest.
Pre
1229.8 ± 302.6
1434.9 ± 357.4
Control
Means ± Standard Deviations for Vertical Jump and Power (W)
Power
Vertical jump
Margaria-Kalamen
Table 2
Land- and Aquatic-Based Plyometric Programs
275
276 Miller et al
dorsiflexion and plantar flexion. The ANCOVAs revealed no significant
differences in peak torque between the 3 training groups at any speed or
joint (ankle or knee). Paired t tests revealed significant increases in pretestto-posttest knee-flexion peak torque at 6.28 rad/s in the aquatic training
group, as well as the land training group (P < .05). Paired t tests also revealed
a significant increase in ankle-dorsiflexion peak torques at 6.28 rad/s in the
land training group (P < .05). Knee and ankle ROM means and standard
deviations are presented in Table 5.
An ANCOVA revealed a significant difference between groups with respect to plantar-flexion ROM (P < .05; Table 6). Post hoc analysis revealed
significantly greater gains in plantar flexion in the aquatic training group (62
± 7.9) than in the land training group (57.3 ± 15.5). Paired t tests indicated
a significant increase in ankle plantar flexion in the aquatic group and in
ankle dorsiflexion in the land group.
A 2-way repeated-measures ANOVA revealed no significant differences
in the 24, 48, and 72-hour soreness scores for the subjects in the aquatic and
land training groups (pretraining and posttraining) during the course of
the 8-week training program.
Discussion
When comparing land-based and aquatic-based plyometric training, clinicians would expect to observe differences in the amount of force applied
during the landing phase and in the time interval of the amortization
phase of the activity. Because of the buoyant force of water, landing force
is decreased, thereby facilitating a more rapid amortization phase. By decreasing the amount of force applied during landing, clinicians might expect
to facilitate a more rapid transition from eccentric to concentric activity.
Therefore, the aquatic training group trains with a lower load but has a
faster transition time (shorter amortization phase), whereas the land training group trains with a heavier load (no buoyancy affect) and experiences
a longer amortization phase. According to speed specificity, a lower load
and faster amortization training stimulus would be expected to produce
improvements in power at higher velocities.30 This concept might help
explain why the aquatic training group showed improvements in musclepower output and supports the premise that aquatic plyometric training
might be useful in increasing power performance.
Research has found that extensor-muscle strength increases as a result
of plyometric training.31 In the current study, the only increase in muscle
strength (torque) used to generate vertical-jump force was in ankle plantar
flexion in the land training group. This increase in strength was found only
at the highest velocity (6.28 rad/s). This training effect is likely the result
of the heavier load applied while making contact with the ground for the
land training group compared with the low load applied by the aquatic
training group. It is interesting to note that both training groups showed
20.4 ± 6.0
15.2 ± 4.3
13.9 ± 10.1
51.2 ± 15.4
33.6 ± 10.6
20.1 ± 7.2
18.1 ± 5.3
12.6 ± 3.3
8.18 ± 5.1
44.8 ± 16.0
30.5 ± 9.1
17.3 ± 6.5
46.2 ± 12.8
30.1 ± 10.0
18.2 ± 8.5
15.3 ± 4.3
10.2 ± 2.1
6.1 ± 5.1
Pre
Aquatic
45.4 ± 9.9
30.2 ± 7.9
20.1 ± 5.2
17.5 ± 4.8
12.7 ± 2.5
10.6 ± 3.3*
Post
Post
137.0 ± 5.9
15.1 ± 4.7
56.7 ± 9.9
Pre
127.7 ± 7.7
13.6 ± 3.9
50.4 ± 10.6
Post
134.3 ± 4.9
15.7 ± 4.3
62.0 ± 7.9†‡
Aquatic (n = 13)
Pre
126.0 ± 8.7
15.0 ± 4.9
56.1 ± 10.4
Post
48.6 ± 13.2
31.4 ± 7.6
16.3 ± 8.8
17.3 ± 4.2
13.0 ± 3.9
9.9 ± 4.7*
Post
133.4 ± 5.7
17.8 ± 4.4†
57.3 ± 15.5
Land (n = 13)
43.7 ± 15.6
27.6 ± 10.2
15.8 ± 6.5
14.8 ± 4.2
9.6 ± 3.8
5.5 ± 5.5
Pre
Land
*Values for range of motion are measured in degrees. †Significant increase from pretest. ‡Significantly different from the land training group.
Pre
126.0 ± 7.6
12.8 ± 4.2
51.0 ± 10.3
Control (n = 14)
Means and Standard Deviations for Knee and Ankle Range of Motion*
rad/s
Knee flexion
Ankle dorsiflexion
Ankle plantar flexion
Table 5
*Significant increase from pretest.
Post
Pre
Control
Means ± Standard Deviations for Ankle Peak Torque
rad/s
Dorsiflexion
1.57
3.14
6.28
Plantar flexion
1.57
3.14
6.28
Table 4
Land- and Aquatic-Based Plyometric Programs
277
278 Miller et al
Table 6 Analysis of Covariance Summary for Vertical-Jump
and Margaria-Kalamen Power and Knee and Ankle Peak Torque and
Range of Motion*
Measurement
Power
vertical jump
Margaria-Kalamen
Peak torque at 6.28 rad/s
knee flexion
knee extension
ankle dorsiflexion
ankle plantar flexion
Range of motion
knee flexion
ankle dorsiflexion
F ratio
P
2‡
Power
0.51
0.75
.60
.48
.03
.04
.13
.17
1.09
0.28
0.71
0.86
.35
.76
.50
.43
.06
.02
.04
.05
.23
.10
.16
.19
2.89
0.46
.07
.64
.14
.03
.53
.12
ankle plantar flexion
3.41
.04†
.16
.60
*Source of variation for main effect was group (Control  Land  Aquatic). Degrees of freedom for all tests was 2. †Significant difference. ‡2 is a measure of strength of the relationship,
estimate of effect size.
some improvements in flexor-muscle strength as the result of plyometric
training. This might reflect an isometric-training effect in the preparation
for landing during plyometric training or the effects of eccentric actions
on 2-joint muscles.
The results of the study suggest that when a muscle is stressed at different points along the power–velocity relationship curve, different training
adaptations occur. The aquatic training group, training with lower loads
and higher velocities (theoretically), improved their muscle-power output.
The land training group, training with heavier loads and lower velocities,
improved their strength but not their power. These findings, again, are consistent with the concept of speed specificity of resistance training.30
This study did not measure landing forces and amortization times.
The results, however, suggest that future investigations comparing land
and aquatic training should evaluate landing forces and transition times.
Future investigations should also compare differences in specific gravity
of the subjects, effects of drag, and aquatic water depths and their impact
on performance variables.
Range of Motion
Active ROM, or dynamic flexibility, refers to the degree to which a joint
Land- and Aquatic-Based Plyometric Programs
279
can be moved by a muscle contraction.32 Many athletic injuries occur
because of a lack of or very poor flexibility.32 Results of this study demonstrated that dynamic stretching, which uses movements that might be
specific to sport or movement activities, can also increase joint ROM. The
aquatic training group increased their plantar-flexion ROM scores from
pretest to posttest, and the land training group increased dorsiflexion ROM
from pretest to posttest. An explanation for these changes is not obvious, but
it might be that different forces during eccentric stretch and amortization
can produce different kinds of ROM adaptations.
Proprioception
During the study, the aquatic plyometric group was observed to have
some difficulty maintaining balance and coordination during the first few
weeks of training. It has been recognized that proprioceptive input from
the articular and tenomuscular mechanoreceptors is necessary for dynamic
stability and muscle control.33 Research has shown that a loss in proprioception results in large systematic errors in multijoint movements.34 When
individuals begin a strength-training program, there is increased neural
input to the muscles that results in greater efficiency of proprioceptive
feedback and skill35-37 and leads to greater net force production, even in the
absence of morphologic changes in the muscles themselves.38 We believe
that the increase in vertical-jump height and power output in the aquatic
training group can be attributed to neural adaptations as a result of increased
need to maintain balance in the water.
Research has also shown that increases in strength with leg extensions
can be attributed to increases in muscle-fiber size and improved ability to
activate and coordinate the actions of these muscles.39 Because plyometric
training has not been reported as a factor in increasing the size of muscle
fibers, increases in this performance might also be attributed to adaptations
of the proprioceptive mechanisms. This theory is supported by the work
of Hakkinen and Komi,40 who attribute improvements in force production
from plyometric training to neuromuscular adaptation. Further research
should be conducted to validate the effects of balance, coordination, and
proprioception on plyometrics, especially in the aquatic environment.
Soreness
Because of the decreased force applied in landing in the aquatic group, it was
expected that muscle soreness would be reduced in this group. Repeatedmeasures testing of the training groups revealed no significant differences
in muscle soreness (pretest to posttest) throughout the training period. Both
groups increased the volume of work equally throughout each week, and
both performed the same plyometric exercises. The only difference was the
training environment.
280 Miller et al
Limitations
There were some limitations to this study that must be addressed. First,
after all the data had been collected, several of the subjects in the control
group admitted to having begun new weight-training and cardiovascular
exercises, even though they had agreed to refrain from all types of new
training during the course of the study. There were also differences in experiences with exercise between subjects. Many of the male participants
had previous experience in plyometric training, whereas the women had
relatively little formal training in plyometrics. These differences might
account for the outcome assessment for both training groups and be the
sole contributor to the differences in power production found pretraining
to posttraining in the aquatic group. In addition, these differences could
also explain the variation in perceived soreness, training adaptations, and
the time to become accustomed to the plyometric-training activities. It is
recommended in subsequent studies to have subjects with no previous plyometric-training experience and who do not train regularly. Future research
examining the differences between sexes and the training environments
might be warranted.
Conclusions
Results from this study are encouraging and demonstrate the benefits that
aquatic plyometric training might have in increasing performance variables
similar to land plyometric training when initiating or advancing a rehabilitation program. In addition, the buoyant properties of water can provide
a decreased load during the eccentric phase of the exercise, and the drag
properties can provide a resistance load for training during the concentric
phase. These findings might be beneficial for health-care professionals who
are looking for alternative programs to stimulate increases in performance
variables. Finally, most jumping or bounding activities on land can be conducted in water without requiring special equipment (except a pool) or
preparation time. Therefore, exercising in the water reduces the potential for
injury, increases strength and power, and can allow clinicians to initiate and
rehabilitate injured athletes more quickly. Plyometric activity in water also
changes the training environment and might motivate athletes and prevent
the monotony and repetitiveness of training and conditioning on land.
Acknowledgments
The authors would like to thank Andrew Darling for allowing us access to the
aquatic center during the course of the study and the graduate assistants for their
supervision of the subjects.
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