Comparison of ground reaction forces and contact times between two lateral plyometric exercises

Abstract

There are no studies examining the differences in kinetics between lateral plyometric exercises and the selection of these exercises is largely based on the experience and observation of coaches. This study aimed to compare ground reaction forces (GRF) and contact times (GCT) between two lateral plyometric exercises: (lateral alternative leg hopping- (HOP), and speed lateral footwork- (SPEED). Sixteen professional male soccer players (age: 24.6 ± 5.5 years; and BMI: 21.7 ± 2.2 kg.m-2) participated in this within -participant repeated measures study. Three-dimensional GRF data were measured by force platform. Our study (statistical power = 0.93) revealed significant differences between the two lateral plyometric exercises in all kinetics parameters (F = 573.7, P < 0.01). HOP produced significantly longer GCT (0.45 s vs. 0.23 s, P < 0.01, large effect), significantly higher values (P < 0.05, large effect) in peak force (3.31 vs. 2.47 Body Weight- [BW]), peak rate of force development (0.94 vs. 0.29 BW/s), and impulse (0.76 vs. 0.31 BW.s) except for peak force in the medial-lateral (P < 0.05, medium effect) and impulse in the anterio-posterior direction (not significant, small effect). Therefore, SPEED is an exercise that aims to increase step frequency because of its short GCT (< 0.25 s), while HOP increases leg strength and power.

Full text

Page 1

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Training & Testing
Wong DP et al. Kinetics of lateral plyometric exercises … Int J Sports Med 2012; 33: 647–653

accepted after revision
January 16 , 2012

Bibliography
DOI http://dx.doi.org/
10.1055/s-0032-1304588
Published online:
April 17, 2012
Int J Sports Med 2012; 33:
647–653 © Georg Thieme
Verlag KG Stuttgart · New York
ISSN 0172-4622
Correspondence
Dr. Del P. Wong
Department of Health and
Physical Education
The Hong Kong Institute of
Education
Tai Po
Hong Kong
Tel.: +852/2948 64 21
Fax: +852/2948 78 48
delwong@alumni.cuhk.net
Key words
● ▶ strength
● ▶ football
● ▶ force
● ▶ agility
● ▶ training
Comparison of Ground Reaction Forces and Contact
Times Between 2 Lateral Plyometric Exercises in
Professional Soccer Players
planned lateral plyometric exercises targeting 2
types of improvements: explosive leg power (e. g.
lateral alternative leg hopping) and high step fre-
quency (e. g. speed lateral footwork), respectively
[ 3 , 12 , 19 ] . Specifi cally, explosive leg power exer-
cises employ the stretch-shortening cycle, which
improves movement initiation and acceleration
performance, whereas the high step frequency
exercises involve short ground contact time
(GCT) ( < 0.25 s), which improves changes of
direction and movement frequency [ 19 , 21 ] .
Intervention studies have shown positive train-
ing eff ects in agility performance. In this regard,
Bloomfi eld et al. [ 3 ] conducted speed, agility, and
quickness (SAQ) training in a variety of sports,
including soccer, tennis, hockey, basketball,
rugby, and netball. The participants received a
range of 10–18 h training over 6 weeks that
resulted in 50–73 % improvement in speed, agil-
ity, power, and dynamic balance after training.
Agility performance is not only infl uenced by
speed and quickness but also by muscular power
as demonstrated in a previous study [ 5 ] , which
found that agility T-test time was highly corre-
Introduction
▼
Agility is defi ned as a rapid whole-body move-
ment with changes in velocity and/or direction in
response to a stimulus [ 4 , 18 ] . Agility is one of the
important abilities in many athletic perform-
ances [ 18 , 19 ] and may be considered as a sepa-
rate fi tness factor [ 4 ] as there are only low to
moderate correlations between agility and
sprinting. Agility is one of the factors that dis-
criminates athletes with respect to competition
levels [ 9 , 14 ] and positional roles [ 7 ] , for instance,
elite soccer players have better agility perform-
ance than their sub-elite counterparts [ 16 ] and
better rugby tacklers tend to have better agility
[ 8 ] . To be agile, athletes must demonstrate a
combination of physical ability (movement speed
and strength), cognitive processing (perception
and decision making), and technical skills (foot-
work and movement technique) [ 18 ] . To opti-
mize physical ability and technical skills related
to agility, preplanned training exercises allowing
athletes to practice closed agility skills in a pre-
dictable or stable environment have been used
[ 3 , 19 ] . In this regard, coaches typically use pre-
Authors D. P. Wong 1 , A. Chaouachi 2 , A. Dellal 2 , 3 , A. W. Smith 1
Affi liations

1 Department of Health and Physical Education, The Hong Kong Institute of Education, Hong Kong
2 Tunisian Research Laboratory “Sport Performance Optimisation”, National Center of Medicine and Science in Sports, Tunis,
Tunisia
3 Department of Fitness Training and Research, Olympique Lyonnais FC (Soccer), Lyon, France

Abstract
▼
There are no studies which have examined the
diff erences in kinetics between lateral plyomet-
ric exercises and the selection of these exercises
is largely based on the experience and observa-
tion of coaches. This study aimed to compare
ground reaction forces (GRF) and contact times
(GCT) between 2 lateral plyometric exercises:
lateral alternative leg hopping (HOP), and speed
lateral footwork (SPEED). 16 professional male
soccer players (age: 24.6 ± 5.5 years; and BMI:
21.7 ± 2.2 kg.m − 2 ) participated in this within-par-
ticipant repeated measures study. 3-dimensional
GRF data were measured by force platform. Our
study revealed signifi cant diff erences between
the 2 lateral plyometric exercises in all kinetics
parameters (F = 573.7, P < 0.01). HOP produced
signifi cantly longer GCT (0.45 s vs. 0.23 s, P < 0.01,
large eff ect), signifi cantly higher values (P < 0.05,
large eff ect) in peak force (3.31 vs. 2.47 Body
Weight [BW]), peak rate of force development
(0.94 vs. 0.29 BW/s), and impulse (0.76 vs. 0.31
BW.s) except for peak force in the medial-lateral
(P < 0.05, medium eff ect) and impulse in the
anterio-posterior direction (not signifi cant, small
eff ect). Therefore, SPEED is an exercise that aims
to increase step frequency because of its short
GCT (< 0.25 s) while HOP increases leg strength
and power.

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Wong DP et al. Kinetics of lateral plyometric exercises … Int J Sports Med 2012; 33: 647–653
lated with horizontal jumping distance (the 5 jump test,
r = − 0.61, p < 0.05).
To date, there are no studies which have examined the diff er-
ences in kinetics between lateral plyometric exercises. The
choice of lateral plyometric exercises is largely based on the
experience and observation of coaches, with little empirical evi-
dence supporting their choices. Therefore, the purpose of our
study was to compare the diff erences in ground reaction force
(GRF) and GCT patterns between 2 commonly used lateral plyo-
metric exercises: lateral alternative leg hopping (HOP) and speed
lateral footwork (SPEED). The results of our study will be useful
for coaches in the selection of agility training exercises and will
facilitate sport scientists’ understanding of the mechanism of
agility performance in athletes. Taken together, this knowledge
will lead to an improvement in the quality of training programs
and will optimize athletic performance. From our practical
experience, we hypothesized that SPEED aims to increase step
frequency and therefore has short GCT ( < 0.25 s) while HOP aims
to improve leg strength and power and therefore has high peak
force, peak rate of force development, and impulse.
Methods
▼
Design
In this within-subject repeated measures study, all players vis-
ited the Human Performance Laboratory and performed 2 lat-
eral plyometric exercises (HOP and SPEED) on a force platform in
a counterbalanced order. To compare the 2 lateral plyometric
exercises, we recorded the 3-dimensional (3D) GRF, i. e., anterio-
posterior (AP), medio-lateral (ML) and vertical (V) forces. All
players were familiar with these exercises as they perform them
regularly during on-fi eld training. We scheduled the data collec-
tion sessions during the 5 th week of the 6-week pre-season prep-
aration period and we asked players to refrain from any vigorous
physical training 48 h prior to the test.
Participants
We recruited 16 male professional soccer players to participate
in our study (age: 24.6 ± 5.5 years; height: 1.79 ± 0.05 m; weight:
687.8 ± 58.2 N; and BMI: 21.7 ± 2.2 kg.m − 2 ). Prior to the start of
the league season, there were 6 weeks of pre-season training
during which the players had 6–8 soccer training sessions per
week each lasting for approximately 90 min. Each training ses-
sion generally consisted of a 10-min warm-up, 30-min technical
training, 30-min tactical training, 15-min simulated competi-
tion, and 5-min cool-down.
Our study was conducted according to the Declaration of Hel-
sinki and the protocol was fully approved by the Clinical Research
Ethics Committee before the commencement of the assess-
ments. Moreover, our study met the ethical standards of the
International Journal of Sports Medicine [ 10 ] . We received writ-
ten informed consent from all players following an explanation
of the general nature of our study to all players without giving
them its detailed aims so as to eliminate any biases during data
collection. We also explained the benefi ts and risks involved
with this investigation. We told players that they were free to
withdraw from our study at any time without penalty.
Warm-up
Before testing, we recorded each player’s age, height, and body
weight (BW). Players stood motionless on the force platform to
record their BW, which was used to normalize GRF data. Players
completed a standardized warm-up that consisted of 5-min of
jogging at 10 km.h − 1 on the motorized treadmill, followed by
5-min of static (quadriceps, hamstrings, and calf muscle groups)
and dynamic stretching (walking knee to chest, high knee, butt
kicks, hip adduction and abduction). Following this, players
were given a minimum of 5 practice trials to familiarise them-
selves with the testing procedure which required them to step
on the force platform ( ● ▶ Fig. 1 , 2 ) at approximately 75, 85, and
100 % of individual’s perceived maximal speed and power while
performing the 2 lateral plyometric exercises. Testing began
5 min after the familiarization session.
Lateral plyometric exercises
We instructed each player to perform HOP exercise such that
they achieved maximal diagonal distance in each step using
alternative legs in a smooth, continuous manner ( ● ▶ Fig. 1 ). In
addition, we instructed each player to perform the SPEED exer-
cise to achieve maximal movement speed ( ● ▶ Fig. 2 ). These
instructions were in accordance with the exercise guidelines
[ 15 ] . The movement of “1 foot out and 2 feet in” as described in
a previous study was used [ 21 ] . The force platform was located
in the middle of the pathway so that the GRF and GCT of 1 step
were recorded during each trial. For each exercise, we allowed
1-min passive recovery between trials and recorded 5 successful
trials on the dominant leg (determined by the ball kicking pref-
erence) where the player’s foot landed completely on the force
platform without any alteration in their movement and speed.
The mean values of each exercise were used in the analysis.
Kinetics measurement
GRF data were collected from a Kistler piezoelectric force plat-
form (Model: 9281C, 400 mm × 600 mm), which measured the
3D forces applied to the platform’s surface. It was mounted on
the fl oor and oriented such that the X, Y, and Z axes of the
platform corresponded to AP (positive = anterior), V (posi-
tive = upward) and ML (negative = lateral) forces applied by the
players, respectively. We sampled signals from the force plat-
form at 1 000 Hz and stored on disk using SMART Capture program
(BTS S.p.A, Milan, Italy). Force data were not fi ltered. The player’s
GCT was determined by examining the vertical ground reaction
force trace in each trial from landing to take-off ( ● ▶ Fig. 3a ). We
wrote a customized SMART Analyzer (BTS S.p.A, Milan, Italy)
protocol to identify GCT (s) from the force data and calculate
peak forces (N) and rate of force development (N/s). The latter
was calculated by determining the peak value of the fi rst deriva-
tive of the force with respect to time. The GRF data ( ● ▶ Fig. 3b )
were represented in the XYZ directions (components) and in
overall (resultant). Individual GRF data were then normalized
using the player’s BW, and subsequently we calculated individu-
alized peak forces (BW), peak rate of force development (BW/s)
and impulses (BW.s). Force data in each direction were diff eren-
tiated with respect to time using central diff erences formula and
the maximum value of the fi rst derivative was taken as the peak
rate of force development. During each step on the force plat-
form there were phases of braking and propulsive shear (hori-
zontal) forces. In our study, the propulsive phases were visually
identifi ed and used in the analysis.
Statistical analysis
Data are expressed as mean ± SD. The normal distribution of the
data was confi rmed using the Shapiro-Wilk test. Measurement

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Wong DP et al. Kinetics of lateral plyometric exercises … Int J Sports Med 2012; 33: 647–653
reliability and variance were indicated by calculating the intrac-
lass correlation coeffi cient (ICC) and coeffi cient of variance (CV),
respectively. Repeated-measure MANOVA was used to examine
the diff erences between the 2 lateral plyometric exercises by con-
sidering all kinetics parameters. We used paired-sample t-test to
compare the diff erence in each kinetics parameter between
SPEED and HOP exercises. Eff ect sizes (Coden’s d ) were calculated
to determine the practical diff erence between the 2 lateral plyo-
metric exercises. Eff ect size (ES) values of 0–0.19, 0.20–0.49, 0.50–
0.79 and 0.8 and above were considered to represent trivial, small,
medium and large diff erences, respectively [ 6 ] . Pearson product
moment correlation coeffi cient was used to assess the relation-
ship between the kinetics parameters. The magnitude of the cor-
relations was determined using the modifi ed scale by Hopkins
[ 11 ] : trivial: r < 0.1; low: 0.1–0.3; moderate: 0.3–0.5; high: 0.5–
0.7; very high: 0.7–0.9; nearly perfect > 0.9; and perfect: 1. Sig-
nifi cance level was defi ned as P < 0.05.
Results
▼
The reliability and variance of our kinetics measurement are
shown in ● ▶ Table 1 . GCT had high ICC ( > 0.90) and acceptable CV
( < 15 %). Overall, impulses had higher ICC and lower CV as com-
pared to peak force and peak rate of force development ( ● ▶ Table 1 ).
Repeated-measure MANOVA showed signifi cant diff erences
between the 2 lateral plyometric exercises in all kinetics param-
eters (F = 573.7, P < 0.01). Paired sample t-test showed that SPEED
exercise induced signifi cantly shorter GCT as compared to HOP
exercise (P < 0.01, large eff ect: 1.48, ● ▶ Table 2 ). Furthermore, as
compared to SPEED, HOP exercise induced signifi cantly higher
values (P < 0.05, large eff ect) in peak force (ES: 1.68–1.71), peak
rate of force development (ES: 1.46–1.87), and impulse (ES:
2.61–3.49) parameters except for the peak force in medial-lat-
eral (P < 0.05, medium eff ect: 0.54) and impulse in anterio-pos-
terior direction (not signifi cant, small eff ect: 0.43).
When the data of SPEED and HOP were pooled together, signifi -
cant correlations (P < 0.01, ● ▶ Table 3 ) were observed between
GCT and peak force (very high), peak rate of force development
(very high), and impulse (nearly perfect).
Discussion
▼
The purpose of our study was to compare the diff erences in GRF
and GCT between HOP and SPEED plyometric exercises. This is
the fi rst reported 3D GRF-based study of lateral plyometric exer-
cises. Specifi cally, we measured the GCT, peak force, peak rate of
force development, and impulse, and each of the kinetics param-
eters were normalized by BW. Furthermore, these values were
Fig. 1 Movement illustration a and experimental set up b of lateral alternative leg hopping-HOP.
F
b
a
Start: right leg lead

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Wong DP et al. Kinetics of lateral plyometric exercises … Int J Sports Med 2012; 33: 647–653
represented as overall resultant value, and respectively in 3D
components. The results support our hypotheses and therefore,
the SPEED exercise could be considered as an exercise that aims
to increase foot step frequency because of its short GCT ( < 0.25 s),
while the HOP exercise aims to increase leg power because it
induces higher peak force, peak rate of force development, and
impulse [ 19 ] . Likewise, SPEED is classifi ed as fast stretch-short-
ening cycle exercise whereas HOP is slow stretch-shortening
cycle exercise [ 4 ] . However, it was found that the reliability (ICC)
of impulse at the anterio-posterior direction during HOP was
moderate and the variance (CV) was quite high. This may be the
result of diff erent braking and propulsive techniques being used
in response to the landing and take-off impulse.
As compared to the SPEED exercise in our study, longer GCTs
(0.41 s) were reported in a previous study using a lateral cutting
movement during the custom agility test [ 2 ] . This can be attrib-
uted to the higher lateral movement speed and the associated
braking movement immediately before the change of direction
in the study of Barnes et al. [ 2 ] . Furthermore, GCT appears to be
relevant to agility performance in that Barnes et al. [ 2 ] demon-
strated that higher division volleyball players have shorter GCT
in drop jump test (0.42 s vs. 0.44 s) and simultaneously better
performance during agility test (5.93 s vs. 6.1 s) than those in the
lower division. Collectively, GCT should be minimized if the
training purpose is to increase step frequency (i. e. the SPEED
exercise in our study) and subsequently improve the agility per-
formance.
The GRF profi les of the SPEED and HOP trials showed some dif-
ferences ( ● ▶ Fig. 3b ). Specifi cally, the magnitudes of the peak
vertical GRF in the SPEED were greater than the HOP whereas
the anterio-posterior and medio-lateral GRF peaks were greater
in the HOP. Additionally, vertical and medio-lateral GRF of HOP
had plateaus from around 20 % to 80 % of the GCT. This may be
related to the fact that the subjects spent more time in contact
with the force platform in HOP as they were attempting to gen-
erate maximal impulse in contrast to the SPEED where they
were trying to maximize movement speed.
Agility performance is characterized by the ability to change
direction and therefore greater improvement has been shown
when training is specifi c to the movements in horizontal medial-
lateral and anterio-posterior directions [ 4 , 13 ] . Our results
provide empirical evidence supporting the fact that lateral plyo-
metric exercises have higher forces in the medial-lateral and
anterio-posterior directions as compared to vertical jump exer-
cise that involve lower horizontal forces [ 16 ] . Specifi cally, the
HOP exercise has ~1.1 times higher peak force in the medial-
lateral direction, and ~1.9 times higher in the anterio-posterior
direction, as compared to the SPEED.
The peak normalized vertical force of HOP in our study was
comparable to a drop jump from 0.6 m and in agreement with a
Fig. 2 Movement illustration a and experimental set up b of speed lateral footwork-SPEED.
F
Start: right leg lead
a
b

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Wong DP et al. Kinetics of lateral plyometric exercises … Int J Sports Med 2012; 33: 647–653
previous study of female basketball players performing similar
side step pivoting movement (ranged 2.34–2.68 BW) [ 1 , 21 ] . On
the other hand, SPEED has lower normalized peak vertical force
than drop jump from 0.2 m (2.2 vs. 2.6 BW) [ 1 ] .
In their review of agility literature, Sheppard and Young [ 18 ]
suggested that reactive strength is one of the factors in leg mus-
cle quality category that aff ect agility performance. Specifi cally,
reactive strength is the ability to change rapidly from an eccen-
tric to concentric action. It is considered to be high when con-
centric contractions can generate high power or long distance
jumping (either in vertical or horizontal direction) within the
shortest GCT. During agility movement and other plyometric
exercises, the active muscle is usually pre-stretched and imme-
diately followed by concentric contraction (i. e., the stretch-
shortening cycle). Our results showed that the HOP exercise
induced ~3.2 times higher resultant peak rate of force develop-
ment than the SPEED exercise. Therefore, HOP is an appropriate
training exercise to improve the reactive strength with an
emphasis on the power generation.
Impulse is defi ned as the change in momentum, the product of
mass and velocity, resulting from a force being applied to a body
over a period of time [ 19 ] . Thus, changes in impulse result
directly in changes in the player’s velocity since the player’s
mass does not change during the exercises. To increase impulse,
players can apply greater force over the same time; or apply the
same force for a longer period of time; or a combination of
increased force and application time. This information has prac-
tical training uses for coaches. For example, in cases where play-
ers are working against their own body weight, coaches can
design drills that will increase the GCT to produce higher
impulses. On the other hand, if additional external loads are
used, for example weight belts, pulled sleds and similar, coaches
can either increase the external load, increase the loading time
or do both to increase the training impulses.
Previous studies [ 2 , 21 ] only measured the peak force during lat-
eral plyometric exercises. However, our study showed larger
eff ects in peak rate of force development and impulse when
comparing the 2 lateral plyometric exercises. It is reasonable
because these parameters consider both the peak force and the
GCT. Therefore, it is suggested to use peak rate of force develop-
ment and impulse in future studies to diff erentiate among lat-
eral plyometric exercises. Specifi cally, using peak rate of force
development and impulse to analyze the plyometric exercises
provide higher sensitivity in the comparison, and these 2 param-
eters indicate the peak force and GCT at the same time point.
0
200
400
600
800
1000
1200
1400
1600
22.12.2 2.32.4 2.5
Force (N)
Time (s)
SPEED
0
200
400
600
800
1000
1200
1400
1600
22.12.22.32.42.5
Force (N)
Time (s)
HOP
Impulse = 350.1 Ns
–300
–200
–100
0
100
200
300
400
500
02040 60 80100
Force (N)
GCT (%)
X
SPEED:
0
200
400
600
800
1000
1200
1400
1600
0204060 80100
Force (N)
GCT (%)
Y
–700
–600
–500
–400
–300
–200
–100
0
020406080100
Force (N)
GCT (%)
Z
–300
–200
–100
0
100
200
300
400
500
020 406080100
Force (N)
GCT (%)
X
HOP:
0
200
400
600
800
1000
1200
1400
1600
020 40 6080 100
Force (N)
GCT (%)
Y
–700
–600
–500
–400
–300
–200
–100
0
0204060 80100
Force (N)
GCT (%)
Z
Peak force
Ground
contact time
ab
Fig. 3 a Vertical peak force and ground contact time (GCT); b Anterio-posterior (X), vertical (Y) and medio-lateral (Z) ground reaction force traces of the 2
plyometric exercises.
Table 1 Measurement reliability and variance in 2 lateral plyometric
exercises (N = 16).
ICC a CV b ( %)
SPEED c HOP d SPEED c HOP d
contact time (s)
peak force (BW)
– anterio-posterior (X)
– vertical (Y)
– medial-lateral (Z)
– resultant
peak rate of force development (BW/s)
– anterio-posterior
– vertical
– medial-lateral
– resultant
impulse (BW.s)
– anterio-posterior
– vertical
– medial-lateral
– resultant
a ICC: intraclass correlation coeffi cient; b CV: coeffi cient of variance; c SPEED: Speed
lateral footwork; d HOP: Lateral alternative leg hopping
0.91 0.93 10.20 14.46
0.71
0.57
0.85
0.55
0.83
0.53
0.82
0.60
44.24
15.11
11.64
12.96
22.66
21.37
15.20
19.05
0.69
0.67
0.53
0.69
0.91
0.87
0.90
0.89
36.42
33.09
31.00
30.59
24.09
31.08
27.60
26.37
0.62
0.94
0.95
0.94
0.44
0.92
0.89
0.92
73.92
10.74
10.84
10.02
67.92
11.59
8.53
10.61

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Wong DP et al. Kinetics of lateral plyometric exercises … Int J Sports Med 2012; 33: 647–653
Acknowledgements
▼
The authors thank Miss Lo Ka Kai for her assistance in statistical
calculation.
References
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Furthermore, there are many lateral plyometric exercises being
used in training that have not been quantifi ed [ 3 , 21 ] . Further
studies in this topic are necessary, including studies that quan-
tify the 3D kinematics and kinetics of the players performing
lateral plyometric exercises to assist coaches in selecting the
most appropriate sport-specifi c training exercises that eventu-
ally maximize specifi c training eff ect and improve the effi ciency
of the whole training program.
As mentioned, the lateral plyometric exercises used in our study
involved both physical abilities (movement speed and strength)
and technical skills (footwork and movement technique) but did
not address cognitive processing skills (perception and decision
making) [ 18 ] . Recent studies have developed agility exercises
and tests that take the cognitive processing into consideration
[ 10 , 20 ] , and further studies are required in regard to these com-
plex agility exercises [ 19 ] .
In conclusion, the present kinetics study found that HOP pro-
duced longer GCT, higher peak forces, peak rate of force develop-
ment and impulses, whereas SPEED produced shorter GCT,
lower peak forces, peak rate of force development and impulses.
Therefore, SPEED is considered an exercise that aims to increase
foot step frequency while the HOP exercise aims to increase leg
power, which both improve agility performance. With this
knowledge, quality of training programs and athletic perform-
ance could be improved.

Peak force
(resultant)
Peak rate of force
development (resultant)
Impulse
(resultant)
pooled
– contact time
– peak force (resultant)
– peak rate of force development (resultant)
SPEED
– contact time
– peak force (resultant)
– peak rate of force development (resultant)
HOP
– contact time
– peak force (resultant)
– peak rate of force development (resultant)
a represent a signifi cant correlation at P < 0.05; b represent a signifi cant correlation at P < 0.01
0.75 b 0.80 b
0.89 b

0.95 b
0.82 b
0.90 b


− 0.46


0.04
0.32

0.81 b
− 0.17
− 0.01
0.53 a 0.82 b
0.81 b

0.99 b
0.56 a
0.84 b


Table 3 Relationships between
kinetics parameters (pooled
data of the 2 lateral plyometric
exercises).

SPEED HOP Ratio (HOP/SPEED) c Eff ect size
contact time (s)
peak force (BW)
– anterio-posterior (X)
– vertical (Y)
– medial-lateral (Z)
– resultant
peak rate of force development (BW/s)
– anterio-posterior
– vertical
– medial-lateral
– resultant
impulse (BW.s)
– anterio-posterior
– vertical
– medial-lateral
– resultant
a represent a signifi cant diff erence between exercises at P < 0.05; b represent a signifi cant diff erence between exercises at P < 0.01;
c SPEED: Speed lateral footwork; HOP: Lateral alternative leg hopping
0.23 ± 0.03 b 0.45 ± 0.14 2.02 1.48
0.44 ± 0.16 b
2.19 ± 0.23 b
− 1.05 ± 0.15 a
2.47 ± 0.23 b
0.83 ± 0.20
2.98 ± 0.43
− 1.15 ± 0.14
3.31 ± 0.42
1.89
1.38
1.10
1.34
1.71
1.68
0.54
1.86
0.15 ± 0.05 b
0.23 ± 0.08 b
0.10 ± 0.03 b
0.29 ± 0.10 b
0.36 ± 0.16
0.81 ± 0.39
0.27 ± 0.11
0.94 ± 0.40
2.40
3.52
2.70
3.24
1.46
1.69
1.55
1.87
0.003 ± 0.008
0.28 ± 0.05 b
− 0.13 ± 0.03 b
0.31 ± 0.05 b
0.008 ± 0.010
0.70 ± 0.14
− 0.29 ± 0.03
0.76 ± 0.14
2.67
2.50
2.23
2.44
0.43
2.61
3.49
2.78
Table 2 Kinetics comparison
between 2 lateral plyometric
exercises (N = 16).

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Wong DP et al. Kinetics of lateral plyometric exercises … Int J Sports Med 2012; 33: 647–653
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