SEQUENCING EFFECTS OF BALANCE AND PLYOMETRIC
TRAINING ON PHYSICAL PERFORMANCE IN YOUTH
SOCCER ATHLETES
RAOUF HAMMAMI,1 URS GRANACHER,2 ISSAM MAKHLOUF,1 DAVID G. BEHM,3
AND
ANIS CHAOUACHI1
1
Tunisian Research Laboratory “Sports Performance Optimization,” National Center of Medicine and Science in Sports, Tunis,
Tunisia; 2Department of Training and Movement Sciences, Cluster of Excellency in Cognition Sciences, University of Potsdam,
Potsdam, Germany; and 3School of Human Kinetics and Recreation, Memorial University of Newfoundland, St. John’s,
Newfoundland, Canada
ABSTRACT
Hammami, R, Granacher, U, Makhlouf, I, Behm, DG, and
Chaouachi, A. Sequencing effects of balance and plyometric
training on physical performance in youth soccer athletes. J
Strength Cond Res 30(12): 3278–3289, 2016—Balance
training may have a preconditioning effect on subsequent
power training with youth. There are no studies examining
whether the sequencing of balance and plyometric training
has additional training benefits. The objective was to examine
the effect of sequencing balance and plyometric training on
the performance of 12- to 13-year-old athletes. Twenty-four
young elite soccer players trained twice per week for 8 weeks
either with an initial 4 weeks of balance training followed by 4
weeks of plyometric training (BPT) or 4 weeks of plyometric
training proceeded by 4 weeks of balance training (PBT).
Testing was conducted pre- and posttraining and included
medicine ball throw; horizontal and vertical jumps; reactive
strength; leg stiffness; agility; 10-, 20-, and 30-m sprints;
Standing Stork balance test; and Y-Balance test. Results
indicated that BPT provided significantly greater improvements with reactive strength index, absolute and relative leg
stiffness, triple hop test, and a trend for the Y-Balance test (p
= 0.054) compared with PBT. Although all other measures
had similar changes for both groups, the average relative
improvement for the BPT was 22.4% (d = 1.5) vs. 15.0%
(d = 1.1) for the PBT. BPT effect sizes were greater with 8
of 13 measures. In conclusion, although either sequence of
BPT or PBT improved jumping, hopping, sprint acceleration,
and Standing Stork and Y-Balance, BPT initiated greater
training improvements in reactive strength index, absolute
and relative leg stiffness, triple hop test, and the Y-Balance
Address correspondence to David G. Behm, [email protected].
30(12)/3278–3289
Journal of Strength and Conditioning Research
Ó 2016 National Strength and Conditioning Association
3278
the
test. BPT may provide either similar or superior performance
enhancements compared with PBT.
KEY WORDS children, adolescents, power, jumps, sprints
INTRODUCTION
V
arious scientific associations (2,17,36) and published research and reviews have recommended
advanced training concepts such as plyometrics
(4,30) and balance training (2,24) for children to
improve muscular strength and power while decreasing the
severity and the incidence of sport injuries (17,41). A metaanalysis by Johnson et al. (30) reported that youth plyometric
training had large positive effects on jumping, running, kicking
distance, balance, and agility. Furthermore, the Canadian
Society for Exercise Physiology position stand recommends
that plyometric training can be safe and effective for enhancing muscle power in children (2). Specifically, studies using
plyometric training programs for youth reported improvements in vertical jump height (18), rebound jump height
(42), running speed (35), agility (24), and balance (24).
A meta-analysis by Behringer et al. (4) on the transfer of
resistance training gains to motor performance in youth, reported the highest effect sizes with a combination of plyometric and traditional training programs. However, plyometric
exercises can involve high velocity, power, and impact forces
(9), which without adequate coordination and balance may
attenuate training effects or even lead to injuries.
Adult balance training studies have been documented to
enhance athletic performance (1,25,31) and contribute to the
prevention and rehabilitation of joint injury and postural
stabilization (7). Behm and Colado (1) in their review of
balance training studies (N = 85 adults) reported a mean
improvement of 105 and 31% with functional performance
(e.g., vertical jump, shuttle run time, squats) and balance
measures, respectively. Given that balance and coordination
are not fully developed in children (45), specific balance
activities should be incorporated into youth training programs because balance is essential for optimal performance
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and the prevention of athletic injuries (2,53). A 4-week balance training program integrated into high school physical
education lessons resulted in improved postural control,
jumping height, and enhanced rate of force development
of the leg extensors (22). Notably, Behm et al. (2) recommended that balance training should be incorporated before
plyometrics with children to allow more effective force
transmission during plyometric exercises because of better
postural alignment.
Although there are studies combining plyometric and
balance activities, there are no studies with youth examining
whether the sequencing of balance and plyometric training
has additional impact on the training outcomes. Chaouachi
et al. (10) trained 12- to 15-year-old boys for 8 weeks either
with plyometric only or a combination of balance and plyometric exercises and found that the combined training program was superior for sprint and shuttle run performance.
Similarly, a 6-week combined agility and balance training
program showed significantly better performance enhancements for dynamic balance, running speed, agility, and
ground contact time during a drop jump compared with
an agility-only training group (54). Bruhn et al. (8) had subjects either train first with 4 weeks of sensorimotor activities
(i.e., balance) followed by 4 weeks of high-intensity strength
training or in the opposite order. They suggested that sensorimotor training would be a useful preparation and provide
important preconditioning effects for subsequent strength
training. Bird and Stuart (5) suggested that balance and postural stabilization exercises would promote enhanced
dynamic core stability and postural control. Although there
seems to be an advantage to including balance exercises
within strength or power training programs, it is not known
whether the sequence of balance and alternative exercises is
a significant factor for youth.
Thus, the purpose of the present study was to consider the
sequencing effects of balance and plyometric training programs on muscle power, reactive strength, leg stiffness, sprint
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performance, agility, and static and dynamic balance in
12- to 13-year-old youth. Based on a similar study (balance
and strength) conducted with young adults (8), it was
hypothesized that balance training before plyometric training would provide greater gains in balance, power, sprint,
and agility performance.
METHODS
Experimental Approach to the Problem
Twenty-four young, elite, male soccer players trained twice
per week for 8 weeks either with an initial 4 weeks of balance
training followed by 4 weeks of plyometric training (BPT) or
4 weeks of plyometric training proceeded by 4 weeks of
balance training (PBT). Testing was conducted pre- and
posttraining and included assessment of upper- and lowerbody strength and power (medicine ball throw, horizontal
and vertical jumps, reactive strength, and leg stiffness), agility
(4 3 9-m shuttle run), speed acceleration (from a stationary
position: 10-m sprint), maximal speed (flying 20- and 30-m
sprints), and static (Standing Stork Test) and dynamic
balance (Y-Balance Test).
Subjects
Twenty-four young soccer players between 12 and 13 years
of age, recruited from a first-division Tunisian soccer club
(Esperance Club Tunis, Tunisia), volunteered to participate
in this study. All participants were from similar socioeconomic status and had the same daily school training
schedules. Because they lived in the same city, environmental conditions for testing and training were similar for all
individuals. None were involved in any after-school activities
or any formalized strength and conditioning training programs. To estimate the maturity status of participants,
a maturity index (i.e., timing of maturation) was calculated
(44). This assessment is a noninvasive and practical method of
predicting years from peak height velocity (PHV) as a measure
of maturity offset using height and age as variables (PHV =
27.999994 + [0.0036124 3 age 3
height]). Peak height velocity has
been shown to be a valid tool for
estimating physical maturation
TABLE 1. Characteristics of the study participants.*
(15,39,52) and has been used as
BPT (n = 12),
PBT (n = 12),
a reference landmark to reflect
Characteristic
mean 6 SD
mean 6 SD
p
the occurrence of other body
dimension velocities or measAge (y)
12.7 6 0.3
12.5 6 0.3
0.293
Standing body height (cm)
158.9 6 7.4
157.0 6 6.7
0.513
ures of physical performance
Sitting body height (cm)
77.9 6 4.3
76.1 6 3.2
0.250
(46). The equation has previBody mass (kg)
45.5 6 7.0
43.1 6 7.7
0.429
ously been validated with stan22
Body mass index (kg$m )
17.6 6 1.7
0.575
dard error of estimates reported
Body fat (%)
20.3 6 4.1
19.7 6 5.1
0.740
as 0.57 and 0.59 years, respecPredicted PHV (years from PHV)
20.7 6 0.3
20.9 6 0.4
0.285
Leg length right (cm)
81.0 6 3.5
80.9 6 4.3
0.959
tively (46) (Table 1).
Before participation in this
*BPT = sequence of balance and plyometric training; PBT = sequence of plyometric and
study,
the subjects were given
balance training; PHV = peak height velocity.
a letter that included written
information about the study
VOLUME 30 | NUMBER 12 | DECEMBER 2016 |
3279
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3280
1 3 10
3 3 15
Procedures
All procedures were carried out during the second half of the
competitive season (March–May 2015). Before the commencement of the study and before the initiation of testing,
all players completed a 2-week orientation period (3 sessions/
week) to become familiar with the general environment and
form and technique of each fitness test used to evaluate sprint,
power, agility, and balance technique for each training exercise,
equipment, and the experimental procedures. During this time,
the children received consistent instructions on proper technique for the balance exercises, plyometric exercises, and landing from Certified Strength and Conditioning Specialists. Each
player’s height and body mass were collected using a wallmounted stadiometer and electronic scale, respectively. Body
mass index was calculated as weight/height squared (kg$m22).
The sum of skinfolds was monitored with Harpenden skinfold
calipers (Baty International, West Sussex, England). Body
measurements were conducted according to Deurenberg
et al. (14), who reported similar prediction errors between
adults and young adolescents.
Performance testing occurred before and after the 8-week
training period. Similar to other previously published training
studies (24,27,40), a true control group could not be incorporated as the 2 experimental groups were national-level elite
athletes and there were no comparable athletes available who
would provide similar baseline values. As previous studies
have already demonstrated the effectiveness of plyometric
and balance training in youth (10,22,24,25), the objective of
the present study was to compare the effect of training
sequence order in 2 comparable groups of athletes.
The testing protocol included assessment of upper- and
lower-body strength and power (medicine ball throw, horizontal and vertical jumps, reactive strength, and leg stiffness),
agility (4 3 9-m shuttle run), speed acceleration (from a stationary position: 10-m sprint), maximal speed (flying 20- and 30-m
sprints), and static (Standing Stork Test) and dynamic balance
(Y-Balance Test). Testing was conducted pre- and posttraining
at the national team club: Esperance Club Tunis, Tunisia.
2 3 10
138
2 3 12
2 3 15
1 3 10
3 3 12
1 3 10/leg
1 3 10/leg
3 3 15/leg
3 3 15/leg
2 3 10/leg
2 3 10/leg
1 3 8/leg
1 3 8/leg
2 3 12/leg
2 3 12/leg
2 3 15/leg
2 3 15/leg
1 3 10/leg
1 3 10/leg
3 3 12/leg
3 3 12/leg
1 3 10/leg
3 3 15/leg
2 3 10/leg
1 3 8/leg
2 3 12/leg
2 3 15/leg
1 3 10/leg
3 3 12/leg
1 3 30
3 3 45
3 3 40
2 3 30
the
and a request for consent from the parents to allow their
children to participate in the study. Legal representatives and
subjects provided informed consent after thorough explanation of the objectives and scope of this project, the procedures,
risks, and benefits of the study. The study was conducted
according to the Declaration of Helsinki, and the protocol
was fully approved by the Ethics Committee of the National
Centre of Medicine and Science of Sports of Tunis before the
commencement of the assessments. No player had any
history of musculoskeletal, neurological, or orthopedic disorder that might impair their ability to execute plyometric or
balance training or to perform power or balance tests.
Kneeling on Swiss Ball progressing to
closed eyes execution
Single- and 2-leg standing on inflated
disk progressing to squat exercise
Supine straight leg bridge on Swiss Ball
Lunge on foam surface progressing to
BOSU ball or inflated disk with holding
dumbbells
Bilateral squat with elastic straps
attached to bar placed on the
shoulders on a foam surface
progressing to BOSU ball or
inflated disk
1 3 30
2 3 40
2 3 45
1 3 30
Workout 7
Workout 2
Workout 1
Exercise
TABLE 2. Description of the balance training program.
Workout 3
Workout 4
Workout 5
Workout 6
Workout 8
Sequencing of Balance and Plyometric Training
Dependent Variables
Vertical Jump Tests. Three vertical jumps were used in this
study: countermovement jump, maximal hopping, and
submaximal hopping. All these tests have been shown to
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Journal of Strength and Conditioning Research
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the
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Journal of Strength and Conditioning Research
be reliable and valid measures in pediatric populations
(10,38). For each test, participants were instructed to place
their hands on the hips to minimize lateral and horizontal
displacement during performance, to prevent any influence of
arm movements on the vertical jumps, and to avoid coordination as a confounding variable in the assessment of the leg
extensors’ neuromuscular performance (11). Participants also
had to leave the ground with the knees and ankles extended
and land in the same position and location to minimize horizontal displacement and influence on flight time. All vertical
jump tests were performed using an Ergojump system (ErgojumpP apparatus; Globus Italia, Codogne, Italy), which recorded jump height, contact time, and flight time. Each test
was separated by a passive recovery period of at least
5 minutes.
The countermovement jump involved the participants
lowering themselves as quickly as possible from an upright
standing position to a self-selected depth, followed immediately by a vertical jump. Three trials were performed with
approximately 2 minutes of recovery, and the best result was
used for analysis.
Maximal and submaximal hopping protocols were performed in the same manner as previously described (10,38).
The maximal hopping protocol involved participants performing 5 repeated bilateral maximal vertical hops in place
on the contact mat. Participants were instructed to maximize
jump height and minimize ground contact time (13). The
first jump in each trial was not included in the analysis. Jump
height and ground contact time were averaged across the 4
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remaining hops and used to calculate the reactive strength
index as follows:
RSI ¼ Jump height ðmetersÞ=ground contact time ðsecondsÞ:
Absolute leg stiffness was measured during submaximal
hopping by modeling the vertical ground reaction force, based
on the flight and contact time during hopping (10,13,38). Leg
stiffness was also normalized relative to leg length and body
mass. Participants were asked to hop bilaterally for 20 consecutive hops at 2.0 Hz. An electronic metronome helped the
subjects to maintain the required frequencies by means of an
auditory signal. The initial 5 and last 5 hops were discarded
and the subsequent 10 hops averaged to provide a measure of
leg stiffness. Leg stiffness (kilonewtons per meter) was calculated from the average contact time and flight time across the
10 hops, together with body mass (13).
Horizontal Jump. Each participant performed a series of
horizontal jumps including a bilateral standing horizontal
(long) jump and triple hop test (THT) with the dominant
leg. For the standing horizontal (long) jump test, participants
stood stationary with the toes aligned level with the start line
and were instructed to push off vigorously and jump forward
as far as possible. Participants were allowed the use of
a countermovement with arms and body swing. The
distance jumped from the start line at takeoff to the position
of the heel upon landing was measured in centimeters using
a metal tape measure.
TABLE 3. Description of the plyometric training program.
Exercise
Countermovement jump
Drop jump +1 step
Horizontal line jump
Lateral hops
Ankle jump
Single-leg cone jump:
front to back and side
to side
Single-leg maximal
rebounding: hops
+5 m acceleration
Hurdle jump
Drop from a low platform
and perform ballistictype push-ups or
clapping push-ups
Total foot/ground
contact
Workout
1
1
1
1
1
1
3
3
3
3
3
8
8
8
8
8
Workout
2
2
2
2
2
2
3
3
3
3
3
10
10
10
10
10
Workout Workout
3
4
2
2
2
2
2
3
3
3
3
3
12
12
12
12
12
2
2
2
2
2
3
3
3
3
3
15
15
15
15
15
Workout
5
1
1
1
1
1
3
3
3
3
3
10
10
10
10
10
Workout
6
Workout
7
Workout
8
3 3 12
3 3 15
1 3 10
3 3 12/leg 3 3 15/leg 1 3 10/leg
3 3 12/leg 3 3 15/leg 1 3 10/leg
40
50
60
75
40
3 3 12
3 3 12
3 3 15
3 3 15
1 3 10
1 3 10
60
75
40
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Journal of Strength and Conditioning Research
BPT (n = 12)
Variables
Pre,
mean 6 SD
Post,
mean 6 SD
PBT (n = 12)
D (%)
Pre,
mean 6 SD
TM
Strength, power
Countermovement jump (cm)
25.5 6 4.0
29.2 6 2.9
14.3 24.7
Reactive strength index (mm/ms)
1.1 6 0.1
1.4 6 0.3
21.5 0.89
Absolute leg stiffness (kN/m)
24.5 6 2.9
28.1 6 2.9
14.7 22.1
Relative leg stiffness (kN/m$kg)
42.3 6 4.9
48.4 6 3.7
14.5 39.5
Standing long jump (cm)
186.0 6 15.9 220.7 6 10.3 18.6 177.1
Triple hop test for distance (cm)
572.5 6 26.7 587.2 6 24.5
2.6 550.0
Speed
10-m sprint (s)
2.1 6 0.1
2.0 6 0.1
26.9
2.1
30-m sprint (s)
5.1 6 0.2
5.0 6 0.3
21.0
5.1
Flying time (s)
2.9 6 0.2
3.0 6 0.3
3.2
3.0
Agility
Shuttle run test (s)
10.0 6 0.4
9.7 6 0.3
22.2 10.0
Balance
Standing Stork test (s)
4.9 6 2.7
13.3 6 6.6 169.5
4.4
Y-Balance test CS score on right stance 110.5 6 5.7 143.1 6 6.4
29.5 106.3
leg (%)
6
6
6
6
6
6
Post,
mean 6 SD
2.4
26.8 6
0.15 0.94 6
2.7
23.0 6
3.6
40.9 6
11.6 206.8 6
24.2 543.3 6
1.8
0.07
3.4
3.6
13.9
15.4
p (Cohen’s d)
Interaction:
D (%) Main effect: time time 3 group
8.6
4.8
3.8
3.4
16.8
21.2
0.001
0.110
0.01
0.01
0.01
0.002
(1.71)
(0.73)
(2.26)
(2.19)
(3.49)
(1.52)
0.296
0.008
0.003
0.003
0.531
0.000
(0.46)
(1.28)
(1.40)
(1.40)
(0.27)
(2.15)
6 0.1
6 0.2
6 0.2
1.9 6 0.2
5.0 6 0.2
3.1 6 0.3
210.3
22.1
3.9
0.01 (1.81)
0.140 (0.65)
0.138 (0.66)
0.407 (0.36)
0.619 (0.21)
0.879 (0.06)
6 0.2
9.9 6 0.3
21.4
0.028 (1.00)
0.631 (0.21)
6 2.7
6 8.6
10.0 6 5.4
129.7 6 11.6
130.2
22.0
0.01 (2.38)
0.01 (5.29)
0.293 (0.46)
0.054 (0.87)
*BPT = balance followed by plyometric training; PBT = plyometric followed by balance training; CS = composite score.
†The CS for the Y-Balance test was calculated according to the following formula: CS = [(maximum anterior reach distance + maximum posterior medial reach distance +
maximum posterior lateral reach distance)/(leg length 3 3)] 3 100 (Filipa et al., 2010) (19).
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Sequencing of Balance and Plyometric Training
3282
TABLE 4. Sequencing effects of balance and plyometric on measures of physical fitness in youth athletes.*†
the
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Journal of Strength and Conditioning Research
TABLE 5. Intraclass correlation coefficients for all
measures.
Variables (measures)
Countermovement jump
Reactive strength
Absolute leg stiffness
Relative leg stiffness
Standing long jump
Triple hop test
10-m sprint (acceleration)
Flying 20-m sprint
30-m sprint
Shuttle run
Standing Stork test (static)
Y-Balance test
Intraclass correlation
coefficients (ICC)
0.997
0.926
0.743
0.856
0.973
0.998
0.981
0.739
0.999
0.999
0.749
0.920
With the THT test, the tape measure was fixed to the
ground, perpendicular to a starting line. Subjects were
instructed to stand behind the starting line with their
nondominant leg forward and the dominant leg off the
ground. The leg used to kick a soccer ball identified the
dominant leg. The subject performed 3 consecutive maximal
hops forward on the same leg to reach the maximal
horizontal distance. Arm swing was allowed. The investigator measured the distance hopped from the starting line to
the point where the heel hit on the completion of the third
and final hop. Both tests were repeated 3 times, and the
maximum distance achieved during the 3 trials was recorded
in centimeters and was used for analysis.
Sprints. Acceleration and maximal running speed were
evaluated using a stationary 10-m sprint, 30-m maximal
speed, and flying 20-m sprint test. Stationary 10-m sprint
involved sprinting 10-m as fast as possible from a stationary
standing start position just behind the first timing gate. Start
stance was consistent for each subject. Maximal speed 30-m
and the flying 20-m sprint involved sprinting 20-and 30-m,
respectively, as fast as possible from a maximal-speed start.
Players were located 20 cm behind the start line position and
were instructed to run as quickly as possible along the 30-m
distance. Time was automatically recorded using photocell
gates (Brower Timing Systems, Salt Lake City, UT, USA;
accuracy of 0.01 seconds) placed 0.4 m above the ground.
Subjects performed 2 trials with at least 2 minutes of rest
between trials. The run with the lowest 30-m time was
selected for analysis.
Agility. Agility was evaluated with the 4 3 9-m shuttle run
test (32). With subjects standing behind a starting line, they
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started the electronic clock by passing through the first timing gate. At the end of the 9-m section, subjects were asked
to step with one foot beyond a marker while reversing the
running direction and sprinting back to the start where the
same reversal of movement direction was required. After
the fourth 9-m section, the subject passed through the second timing gate to stop the electronic clock. The best time of
2 consecutive trials was recorded for the statistical analysis.
Static Balance. Static balance was assessed using the Stork
stand balance protocol. To perform the Stork stand test (48),
participants stood with their opposite foot against the inside
of the supporting knee and both hands on the hips. On the
command, the subject raised the heel of their foot from the
floor and attempted to maintain their balance as long as possible. The trial ended if the subject moved his hands from his
hips, the ball of the dominant foot moved from its original
position, or if the heel touched the floor. This test was carried
out on the dominant leg acting as the standing leg. The test
was timed (seconds) using a stopwatch. The recorded score
(duration in seconds) was the best of 3 attempts.
Y-Balance Test. The lower-quarter Y-Balance test is a dynamic
test that requires subjects to maintain single-leg stance while
reaching as far as possible with the contralateral leg in 3
different movement directions (i.e., anterior, posteromedial,
posterolateral) (47). For this purpose, a grid consisting of 3
lines was constructed on a gym floor using a mechanical
goniometer and adhesive tape measure. The 2 posterior lines
extended from the center of the grid and were positioned
1358 from the anterior line with 458 between the 2 posterior
lines. Each line was marked in 5-mm increments for measurement purposes. Before the test started, participants’
length of the right leg was assessed in supine lying position
by measuring the distance from the anterior superior iliac
spine to the most distal aspect of the medial malleolus. Further, subjects practiced 6 trials per reach direction to get
familiarized with the testing procedures. All trials were conducted barefooted. Subjects always started with the left foot
placed at the center of the grid and the right leg reaching in
anterior direction as far as possible, lightly touching the farthest point possible on the line with the most distal part of the
reach foot. Participants then returned to a bilateral stablestance position. After 3 reaches, the same test procedure
was conducted for the posteromedial and the posterolateral
reach. Between reaches, a rest of 15 seconds was allowed. The
examiner manually measured the distance from the center of
the grid to the touch point, and the results were documented
after each reach. Trials were discarded and repeated if the
participant (1) did not touch the line with the reach foot while
maintaining weight bearing on the stance leg, (2) lifted the
stance foot from the center grid, (3) lost balance at any point
during the trial, (4) did not maintain start and return positions
for 1 full second, or (5) touched down the reach foot to gain
considerable support. For further data analyses, the mean of 3
VOLUME 30 | NUMBER 12 | DECEMBER 2016 |
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Sequencing of Balance and Plyometric Training
Training Interventions. After the
initial baseline testing session,
players were randomly assigned to 2 groups. The BPT
group (n = 12) had to perform
4 weeks of balance training first
followed by 4 weeks of plyometric training. The PBT group
(n = 12) had to perform 4
weeks of plyometric training first
and then 4 weeks of balance
training. Groups were matched
for age, maturation status, and
physical characteristics. The
groups did not significantly differ
on all preexperimental measures
(p . 0.05) so that posttraining
differences could not be ascribed
to unequal group composition
or to preexperimental biases.
Both experimental groups followed a training program of 8
weeks with a frequency of 2 sessions per week performed in the
spring of 2015. All training
sessions were preceded by
a 15-minute warm-up, including
submaximal running; dynamic
stretching; low-intensity forward, sideways, and backward
running; several acceleration
runs; jumping at a progressively
increased intensity; and a range
of mobility exercises that provided appropriate activation of
the lower-limb musculature (18)
(Table 1).
According to its origin in
injury prevention and rehabilitation, the balance training
Figure 1. Individual and mean pre- and posttesting data for (A) reactive strength and (B) triple hop test
performance test by intervention group (BPT = sequenced balance and plyometric training; PBT = sequenced
program (BTP) consisted of
plyometric and balance training). Unfilled circles indicate individual data of the BPT group and filled circles indicate
special postural stabilization
mean data of the BPT group. Unfilled squares indicate individual data of the PBT group and filled squares indicate
tasks performed 45 minutes
mean data of the PBT group. Because of baseline differences between groups, adjustments were performed with
pretesting values as covariate.
for each training session. The
training session lasted about
60 minutes with warm-up and
cool-down phases. Each task was 30–40 seconds and was
successful reaches was used in each of the 3 directions. Acrepeated 1–3 times with 8–12 repetitions with 20-second rest
cording to Filipa et al. (19), a composite score (CS) was calbetween sets. The postural stabilization tasks consisted of 5
culated and considered as the dependent variable using the
exercises, including: (a) kneeling on a Ball progressing from
following formula: CS = ([maximum anterior reach distance
eyes opened to eyes closed, (b) unilateral and bilateral stand+ maximum posteromedial reach distance + maximum posing on an inflated disk progressing to a squat exercise,
terolateral reach distance]/[leg length 3 3]) 3 100. Excellent
(c) supine straight leg bridge on a Swiss Ball, (d) lunge pertest–retest reliability has been reported for the Y-Balance test
formed on a foam surface progressing to a BOSU ball or
in all 3 movement directions with ICC values ranging
inflated disk while holding dumbbells, and (e) performing
between 0.89 and 0.93 (47).
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risk of injury, all sessions progressed from low to moderate
high-intensity drills, thus gradually imposing a greater eccentric
stress on the musculotendinous
unit. The intensity of the program was increased in accordance with previous plyometric
training guidelines (37). Training
volume was defined by the
number of foot contacts made
during each session, starting
with 40 contacts in the first session, increasing to 75 contacts in
the prefinal session. Plyometric
drills lasted approximately 5–10
seconds, and at least 90 seconds
rest was allowed after each set
(42). Progressive overload principle was incorporated into the
program by increasing the number of foot contacts and varying
the complexity of the exercises.
For all rapid stretch shortening
cycle plyometric exercises, subjects were instructed to give
maximal efforts with minimal
ground contact times. Plyometric drills included standing vertical and horizontal jumps, lateral
jumps, ankle hops, skipping,
single-leg hopping, maximal
hopping, and low-level drop
jumps (20 cm) (Table 3).
Because of the relative lack of
plyometric experience, verbal
feedback in the initial stages
was focused on correcting takeoff and landing mechanics.
Additionally, and even in the
Figure 2. Individual and mean pre- and posttesting data for (A) absolute leg stiffness and (B) relative leg stiffness
early stages of the program, chilby intervention group (BPT = sequenced balance and plyometric training; PBT = sequenced plyometric and
balance training). Unfilled circles indicate individual data of the BPT group and filled circles indicate mean data of
dren were exposed to repeated
the BPT group. Unfilled squares indicate individual data of the PBT group and filled squares indicate mean data of
submaximal hopping in a bid to
the PBT group.
maximize the likelihood of
simultaneous development of
fast elastic recoil and stretch reflex use.
bilateral squat with elastic band straps (Theraband, Akron,
OH, USA) attached to a bar placed on the shoulders while
Statistical Analyses
standing on a foam surface progressing to a BOSU ball or
Data are presented as group mean values and SDs. After
inflated disk (Table 2). Each stabilization task was performed
normal distribution was examined, an independent-samples
with the objective to retain balance. The degree of difficulty
t-test was used to determine significant differences in pretestwas progressively increased according to the progress of the
ing values between groups. The sequencing effects of balance
subjects.
and plyometric training on variables of physical fitness were
According to the recommendation and the training guideanalyzed in separate 2 (Group: BPT, PBT) 3 2 (Time: pre,
lines for pediatric population (2,37), the plyometric training was
post) analysis of variance with repeated measures on “Time.”
performed with 1–3 sets of 8–15 repetitions. To minimize the
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Sequencing of Balance and Plyometric Training
significant differences in pretraining values between the 2
experimental groups. Table 5 illustrates the intraclass correlation coefficients of the measures.
Strength and Power
The statistical analysis indicated
significant main effects of
“Time” for all strength and
power variables (all p , 0.001),
except the reactive strength
index and the medicine ball
throw test (Table 4). Significant
“Group 3 Time” interactions
(all p , 0.01) were observed
for reactive strength, absolute
and relative leg stiffness, and
the THT (Table 4, Figures 1
and 2). Further, our statistical
calculations revealed no significant main effects of “Time” and
Figure 3. Individual and mean pre- and posttesting data for Y-Balance test performance by intervention group
no significant “Time 3 Group”
(BPT = sequenced balance and plyometric training; PBT = sequenced plyometric and balance training). Unfilled
interaction for the medicine ball
circles indicate individual data of the BPT group and filled circles indicate mean data of the BPT group. Unfilled
squares indicate individual data of the PBT group and filled squares indicate mean data of the PBT group.
throw test (Table 4). For those
“Time 3 Group” interactions
that reached the level of significance, post hoc analyses indicated significant improvements in
If baseline differences between groups were found, adjustreactive strength (Δ 21.5%, p = 0.002, d = 2.31), absolute (Δ
ments were performed with baseline measurements as cova14.7%, p , 0.001, d = 1.22) and relative leg stiffness (Δ 14.5%,
riate. Bonferroni corrections were not required because our
p , 0.001, d = 1.25), and THT (Δ 2.6%, p , 0.001, d = 0.55)
study design (2 3 2) did not entail multiple testing. When
from pre- to posttraining in the BPT group. For the PBT group,
“Time 3 Group” interactions reached the level of signifisignificant pre–post changes were found for absolute leg stiffcance, group-specific post hoc tests (i.e., paired t-tests) were
ness (Δ 3.8%, p = 0.036, d = 0.31) and a tendency toward
conducted to identify the comparisons that were statistically
significance for relative leg stiffness (Δ 3.4%, p = 0.063,
significant. Additionally, the classification of effect sizes was
d = 0.38) (Figures 1 and 2).
determined by converting partial h2 to Cohen’s d (12). The
effect size is a measure of the effectiveness of a treatment,
Speed
and it helps to determine whether a statistically significant
With regards to the 10-m sprint, the analyses showed
difference is a difference of practical concern. According to
significant main effects of “Time” but no “Time 3 Group”
Cohen (12), effect sizes can be classified as small (0.00 # d #
interaction. For all other sprint parameters, analyses failed to
0.49), medium (0.50 # d # 0.79), and large (d $ 0.80). The
indicate significant main effects of “Time” and significant
significance level was set at p # 0.05. Tendencies toward
“Time 3 Group” interactions (Table 4).
significance were denoted as 0.051 # p , 0.1. Intraclass corAgility
relation coefficients were analyzed to assess the intrasession
A significant main effect of “Time” was found for the 4 3 9reliability of the researchers and subjects (2 trials performed
m shuttle run test. The “Time 3 Group” interaction was
for each measure at pretest) (50). All analyses were performed
nonsignificant (Table 4).
using Statistical Package for Social Sciences version 22.0.
Balance
RESULTS
All subjects received treatment conditions as allocated.
Twenty-four participants completed the training program,
attended all training sessions and none reported any trainingor test-related injury. Table 4 describes pre- and postintervention results for all outcome variables. Except for 2 tests
(i.e., reactive strength index, THT), there were no statistically
3286
the
The statistical analysis indicated significant main effects of
“Time” (Table 4). A tendency toward a significant “Group 3
Time” interaction (p = 0.054) was found for the Y-Balance
test. Post hoc analyses indicated significant improvements in
Y-Balance test performance in the BPT group (Δ 29.5%,
p , 0.001, d = 5.25) and the PBT group (Δ 22.0%, p ,
0.001, d = 2.24) from pre- to posttraining (Figure 3; Table 4).
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DISCUSSION
The major finding of the present study was that sequencing4
weeks of BPT in 12- to 13-year-old male elite soccer players
resulted in either similar or superior performance enhancements
compared with plyometric before balance training (PBT).
Compared with PBT, BPT provided significantly greater
improvements in the reactive strength index, absolute and
relative leg stiffness, THT, and a trend for the Y-Balance test
(p = 0.054). Although all other measures had similar changes
for both groups, the average relative improvement for the BPT
was 22.4% (d = 1.5) vs. 15.0% (d = 1.1) for the PBT. The
magnitude of change (effect sizes: Cohen’s d) with BPT was
greater with 8 of the 13 performance measures. This is the first
study to examine and demonstrate the benefits of sequencing
balance before plyometric training in youth athletes.
Behm et al. (2) in their review/position stand on youth resistance training recommended that balance training should precede plyometric training because balance and coordination are
immature in children (45), and balance is essential for optimal
performance and the prevention of athletic injuries (2,53). Bruhn
et al. (8) suggested that in young adults, balance training could
have a preconditioning effect on subsequent resistance training.
Because the immaturity of balance and coordination are not
gender specific (45) and balance is a requisite for success in
almost every sport (1–3,10,14), the findings of the present study
should be applicable to all youth. The present study provides
experimental data corroborating this recommendation.
Although there are no studies examining the sequencing of
balance and plyometric training, there are only a few studies
that combine resistance and balance training in youth. Eight
weeks of training of 12- to 15-year-old boys either with
plyometric only or a combination of balance and plyometric
exercises (no sequencing; exercises performed in same sessions) showed that the balance–plyometric training program
was superior compared with the sprint and shuttle run performance (10). Youth soccer players (;15 year old) who trained
with plyometric exercises either on stable or unstable surfaces
generally had similar performance enhancements (drop jump
height, sprint, agility, and balance). However, countermovement jump height improvements were significantly greater
with stable plyometric training (24). However, a systematic
review and meta-analysis by Behm et al. (3) found only 4
controlled studies that met their criteria when comparing
unstable with stable resistance training programs in children
(0 studies) and adolescents (4 studies). They concluded that
providing balance challenges with unstable compared with
stable resistance training had limited additional benefits for
muscle strength, power, and balance in healthy adolescents
and thus the use of unstable as compared with stable surfaces
during strength training is only partially recommended. The
meta-analysis by Behringer et al. (4) reported the greatest
magnitude of change (effect sizes) with a combination of plyometric and traditional resistance training programs. In accordance with these studies, the present study found significant
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improvements with a combination of balance and plyometric
training regardless of the sequence. Although BPT had significantly or nearly significant superior results with 5 measures vs.
PBT, there were significant improvements in 8/13 and 6/13
measures with BPT and PBT, respectively.
If the literature recommends that plyometric training can be
safe and effective for youth (2,36), can improve muscular
strength and power (17,30), and vertical jump height (18,30),
rebound jump height (42), running speed (30,35), agility
(24,30), and balance (24,30), then why should balance training
be provided before plyometric training? The present study demonstrated an advantage for BPT because it provided comparable
(8/13 measures) or significantly greater (5/13 measures) training
benefits than PBT. Balance training may better prepare the
individual for subsequent plyometric training by improving landing and takeoff mechanics. Kean et al. (31) explained that the
;10% increase in vertical jump performance after 5 weeks of
balance training might be attributed to a decreased postural
sway allowing the individual to have a more stable landing
and then propel themselves at a more optimal vertical angle.
Increased postural sway either when stationary or with movement can project the center of mass beyond an individual’s base
of support, resulting in a loss of balance and an inability to
maintain an erect posture (33). Because precise control of postural sway is needed for static equilibrium conditions (e.g., handstand) and dynamic movement (e.g., shifting the center of
gravity from the rear foot to the forward foot when skating),
individuals with enhanced control of postural sway can better
control their body position or center of mass over their base of
support (34). Balance may be impossible if postural sway results
in the center of mass velocity to be directed outside the base of
support as with running (29). As some athletes (e.g., archer) seek
high stability and low mobility, and others (e.g., sprinters)
need low stability and high mobility, the skilled athlete learns
to control postural sway for the optimal task-specific mix of
stability and mobility (33).
Gandevia in their review (21) indicated that balance training could improve proprioceptive afferent feedback resulting
in a more rapid and greater neuromuscular activation during
plyometric exercises. Adult balance training studies have reported enhanced athletic performance (1,25,31) and improved
prevention (2,53) and rehabilitation of joint injuries and postural stabilization (7).
Although plyometric exercises are recommended as safe
when appropriate training volumes, intensities, and supervision
are provided (2), there is a possibility of injuries occurring with
these dynamic, more complex, high-velocity, and high–reaction
force plyometric activities (9). Because the adolescent growth
spurt can adversely affect balance, coordination, and movement
patterns (26), initially implementing balance training can
improve anticipatory postural adjustments (28) and motor coordination (2,51), possibly decreasing the likelihood of injuries
from awkward or unstable landings and positions.
A perceived limitation of the study might be the possibility of a detraining effect impacting the testing of the PBT
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Sequencing of Balance and Plyometric Training
group 4 weeks after the plyometric training. This detrain
effect is unlikely as the PBT group would not have
experienced a true detraining period. During the 8 weeks
of training, both groups continued to train with their soccer
teams. This training included sprinting, change of direction,
agility, and jumping among other power-related activities.
Additionally, during the subsequent 4 weeks of balance
training (PBT group), there were also strength training
activities performed upon unstable surfaces. It has been
reported that training gains can be maintained with 1–2
high-intensity sessions per week (6). Furthermore, youth
tend not to detrain at the same rate as adults. There are
a number of adolescent training studies that have reported
no loss of training gains after 8 weeks of detraining
(16,23,43,49). Faigenbaum et al. (16) indicated that the phenomenon of detraining is more complex in children and not
characteristic of the typical regressions found with adults.
Based on the previously published youth literature, adolescents do not typically detrain at the same rate as adults and
with the additional extracurricular activities common to
both groups; it is highly likely that detraining was not a significant factor in the results.
In conclusion, although either sequence of BPT or PBT
generally improved jumping, hopping, sprint acceleration
(10 meters), and balance, applying 4 weeks of balance
training before 4 weeks of plyometric training initiated
greater training improvements in reactive strength index,
absolute and relative leg stiffness, THT, and the Y-Balance
test. The superiority of the BPT over the PBT may be
attributed to improved anticipatory postural adjustments
and decreased postural sway (greater stability) among
other balance-related mechanisms that provided a higher
quality training foundation for the subsequent plyometric
regimen.
PRACTICAL APPLICATIONS
Based on the present findings, it would be more effective
for coaches and strength and conditioning professionals
who wish to implement plyometric training for their
youth athletes and fitness enthusiasts to institute at least
4 weeks of initial balance training. The balance training
should progress from less demanding stationary activities
to more complex dynamic balance activities. Such a program should enhance the subsequent plyometric training
adaptations.
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