Two-Leg Squat Jumps in Water: An Effective Alternative to Dry Land Jumps

Abstract

The current study was designed to quantify and compare the kinetic parameters of two-leg squat jumps carried out on dry land, in water and in water using area devices that increase drag force. Twelve junior female handball players who had been competing at national level for the previous two years volunteered to participate in the study. Intensity of the two-leg squat jump was examined using a force plate (9 253-B11, Kistler Instrument AG, Winterthur, Switzerland) in three different conditions: on dry land, in water and in water using devices. An ANOVA with repeated measurements (condition) was applied to establish differences between the three jumps. The results show that peak impact force and impact force rate for the water jumps was lower than for the dry land jumps (p<0.05), while peak concentric force was higher for the water jumps than the dry land jumps (p<0.05). In addition, no statistically significant differences were found between water jumps for these variables (p>0.05). These results indicate that water provides an ideal environment for carrying out jumps, as the variables associated with the exercise intensity are boosted, while those related to the impact force are reduced and this fact could be less harmful.

Full text

Training & Testing118
Colado JC et al. Two-Leg Squat Jumps in Water: An Eff ective Alternative … Int J Sports Med 2010; 31: 118 – 122
accepted after revision
October 19, 2009
Bibliography
DOI http://dx.doi.org/
10.1055/s-0029-1242814
Published online:
December 17, 2009
Int J Sports Med 2010; 31 :
118 – 122 © Georg Thieme
Verlag KG Stuttgart · New York
ISSN 0172-4622
Correspondence
Dr. Luis-Mill á n Gonz á lez
University of Valencia
Physical Education
C / Gasc ó Oliag, 3
46010 Valencia
Spain
Tel.: 00 34 963 864 374
Fax: 00 34 963 864 353
luis.m.gonzalez@uv.es
Key words
● ▶ vertical jump
● ▶ strength training
● ▶ aquatic load plate
● ▶ unilateral
Two-Leg Squat Jumps in Water: An Eff ective
Alternative to Dry Land Jumps
speed [15, 21, 23] . These improvements in per-
formance may be due to the forces resisting for-
ward movement (e. g. increased load) that are
generated during jumps in water [5, 6, 23] .
This leads us to believe that jumps in water may
be an eff ective alternative to dry land jumps to
produce adaptations and improvements to motor
performance, with the additional advantage that
they reduce the risk of injury.
In addition, certain professionals have recently
used aquatic area devices that increase resistance
to forward progress so as to increase intensity,
thus counterbalancing the fact that apparent
weight is less in water than on dry land. It has
been shown that using said materials increases
maximum concentric force and reduces the
impact forces generated during one-leg jumps in
water [25] . Despite this evidence, we believe that
more research is necessary to corroborate the
eff ectiveness of the area devices.
This study was designed to quantify and compare
the kinetic parameter of two-leg squat jumps
carried out on dry land, in water and in water
using area devices.
Introduction
&
Traditionally, dry land jumps have been used in
sport to improve muscle force, strength, overall
mobility and joint stability, as well as to prevent
injuries [12, 15, 19] . In the therapeutic fi eld, these
exercises have been associated with diff erent
benefi ts, including an increase in bone mineral
density [2] , an improvement in motor and occu-
pational tasks [14] and facilitation of the fi nal
stages of recovery from injury [10] . However,
there are a number of risks associated with these
exercises that are linked to the impact forces pro-
duced during the landing stages, and which can
cause great stress to structures of the muscu-
loskeletal system [16, 23, 25] .
Carrying out jumps in water may be an alterna-
tive that helps to reduce articular compression
forces during the landing stages by reducing
impact forces [15, 17, 25] . This could be due to
the fact that there are thrust forces in water that
act on subjects to reduce their apparent weight
[24] . In addition, some studies have shown that a
programme of jumps in water increases power,
peak concentric torque, vertical jump height and
Authors J. C. Colado
1 , X. Garcia-Masso
1 , L.-M. Gonz á lez
1 , N. T. Triplett
2 , C. Mayo
1 , J. Merce
1
Affi liations 1 University of Valencia, Physical Education and Sports, Valencia, Spain
2 Appalachian State University, Health, Leisure and Exercise Science, Boone, United States
Abstract
&
The current study was designed to quantify and
compare the kinetic parameters of two-leg squat
jumps carried out on dry land, in water and in
water using area devices that increase drag force.
Twelve junior female handball players who had
been competing at national level for the previ-
ous two years volunteered to participate in the
study. Intensity of the two-leg squat jump was
examined using a force plate (9 253-B11, Kist-
ler Instrument AG, Winterthur, Switzerland)
in three diff erent conditions: on dry land, in
water and in water using devices. An ANOVA
with repeated measurements (condition) was
applied to establish diff erences between the
three jumps. The results show that peak impact
force and impact force rate for the water jumps
was lower than for the dry land jumps (p < 0.05),
while peak concentric force was higher for the
water jumps than the dry land jumps (p < 0.05).
In addition, no statistically signifi cant diff erences
were found between water jumps for these vari-
ables (p > 0.05). These results indicate that water
provides an ideal environment for carrying out
jumps, as the variables associated with the exer-
cise intensity are boosted, while those related to
the impact force are reduced and this fact could
be less harmful.

Training & Testing 119
Colado JC et al. Two-Leg Squat Jumps in Water: An Eff ective Alternative … Int J Sports Med 2010; 31: 118 – 122
Materials and methods
&
Subjects
Twelve junior female handball players who had been competing
at national level for the previous two years volunteered to par-
ticipate in this investigation. Subject characteristics were as fol-
lows – age: 16.0 ± 0.7 years; height: 170 ± 10 cm; weight:
64.4 ± 8.9 kg; and body fat percentage: 25.7 ± 5.7 % . The subjects
did not have any cardiovascular, neuromuscular, orthopaedic or
psychological disorders, and were used to performing two-leg
jumps during their normal sport training. The participants were
notifi ed about the potential risks involved and gave their volun-
tary informed consent, approved by a Research Commission
belonging to our institution.
Study design
A randomised, repeated measures experimental design was used
to examine the hypothesis that there were diff erences between
two-leg jumps on dry land and two-leg jumps in water with and
without devices. Subjects completed a familiarization session
and a testing session 24 – 48 h later. The intensity of the two-leg
squat jump was examined in three diff erent conditions: on dry
land, an aquatic jump and an aquatic jump using devices. The
dependent variables included were peak concentric force, con-
centric force development rate, total time, time to peak concen-
tric force, impact force, time to peak impact force, and impact
force development rate.
Test procedures
The subjects fi rst performed a session to familiarise themselves
with the correct technique for two-leg squat jumps on dry land
and in water with and without devices. After a 24 – 48 h break,
the subjects completed the testing session in which the depend-
ent variables were evaluated. Subjects had performed no
strength training in the 48 h prior to data collection. The mea-
surement protocols were always strictly controlled by the same
evaluators with the additional help of video recording and gonio-
metry. Subjects were always encouraged to make the maximum
eff ort during all measured jumps. Three attempts were made at
each type of jump, with the best attempt at each type of jump
(e. g. peak concentric force value) chosen for analysis, also con-
sidering the landing profi le of the same attempt (e. g. whether
the subjects landed solidly on the plate or landed partially off
the plate due to fl otation). Subjects performed a general warm-
up prior to both the familiarization and testing sessions, which
consisted of 5 min of range of motion movements for the main
joints with light jogging between exercises. Following the warm-
up, subjects were allowed a practice jump prior to each diff erent
type of measured jump. All jump conditions were randomised
within a jump environment to avoid fatigue eff ects and one
minute of rest was given between trials. Due to the logistics of
submerging the force plate, all dry land jumps were completed
fi rst, followed by the diff erent types of aquatic jumps. The plate
submersion and calibration required approximately 20 min, so
the warm-up was repeated just prior to measured jumps. The
aquatic jumps consisted of jumping with or without devices that
increased drag force (i. e. the subjects took up in each hand a rec-
tangular device through a handgrip placed in the middle of the
device). The sizes of the device were: 25 cm (height) × 17 cm
(width) × 1 cm (depth). The subjects were asked to keep their
hands on their hips during the whole test (push-off , fl ight and
landing) or, in the case of the aquatic jumps with the devices, to
keep their arms straight by their sides with the devices parallel
to the surface of the water. Subjects were instructed to jump as
normally as possible and land as they would during training,
bending the knees and avoiding violent impact with the ground.
The degree of knee fl exion for the starting position of the jump
was set at 90 ° with a manual goniometer and monitored through
the use of live video imaging sent to a computer.
Standing height in the water (prior to knee fl exion) was at the
xiphoid process ( ± 3 cm). However, the level of immersion at the
beginning of the jump was deeper since the subjects had to
squat down to 90 ° knee fl exion. Previous studies such as Miller
et al. [17] and Stemm and Jacobson [23] used an immersion
depth equal to the waist or less. It is known that the compressive
load on the spine that is generated when running at an immer-
sion depth equal to the waist is no diff erent to that generated
when running on dry land [8] . Since a clear mechanical diff er-
ence exists between running and jumping, it is important to
understand diff erences in impact force with diff erent immersion
depths during jumping. Although that concept was not the focus
of the present investigation, a standing immersion depth of the
xiphoid process ( ± 3 cm) was chosen because previous works
using walking activities at the same immersion depth found a
lower impact force compared to dry land activities [3, 22] . More-
over, previous studies that used general aquatic exercise pro-
grams at a similar immersion depth found positive results as
regards improving physical performance [15, 16, 21] .
Data collection and analysis procedures
Height, body mass, and body fat percentage (Tanita model BF-
350) were obtained according to the protocols used in previous
studies [5, 7] . A portable force plate (9253-B11, Kistler Instru-
ment AG, Winterthur, Switzerland) measuring 400 mm
(width) × 600 mm (length) × 45 mm (depth) was used to assess
ground reaction forces for all conditions tested. The force plate
contained four piezoelectric sensors and each recorded the force
produced in the three spatial directions. All the signals were
recorded at a frequency of 200 Hz, amplifi ed and converted A / D
using a 16-bit card. We used the manufacturer ’ s own software
(BioWare
® Type 2812A1-3, version 3.24) to calculate the three
absolute components of the force.
Prior to calculation of the statistics parameters, each signal was
corrected by the removal of the force that every subject pro-
voked as a result of their own weight, and it was also considered
that the subject ’ s weight decreased by the fl otation force. In
water, the measured vertical ground reaction force while stand-
ing still in water was a result of body weight minus buoyancy,
which was denominated “ apparent body weight ” . For example,
the measured vertical ground reaction force while standing still
(apparent body weight) with the water at the xiphoid process
was approximately 28 % (17.8 ± 6.1 kg) of the same position on
dry land (64.4 ± 8.9 kg). Apparent body weight was further
reduced when the subject reached the starting position (90 °
knee angle), as the body was submerged further [18] . This cor-
rection was performed with the purpose of analyzing only verti-
cal forces of taking off phase of the jump.
Dependent variables were defi ned as follows: (i) Impact force as
the highest ground reaction force during jump landing; (ii) Peak
concentric force as highest ground reaction force before fi nish-
ing the propulsive phase of the movement; (iii) Concentric rate
of force development as the fi rst peak of ground reaction force
divided by the time from the initiation of the concentric phase
to the fi rst peak of ground reaction force; (iv) Total time as the

Training & Testing120
Colado JC et al. Two-Leg Squat Jumps in Water: An Eff ective Alternative … Int J Sports Med 2010; 31: 118 – 122
time necessary to fi nish the propulsive phase of the movement,
that is, from beginning of the propulsive phase to take-off ;
(v) Time to peak concentric force as the time necessary to reach
peak concentric force from the beginning of the propulsive phase
of the movement; (vi) Time to peak impact force as the time nec-
essary to reach peak impact force from the beginning of the
landing phase of the movement; and (vii) Rate of force develop-
ment for impact force as the fi rst peak of impact force divided by
the time from the initiation of the landing phase to the fi rst peak
of impact force.
●
▶ Fig. 1 shows an example of a standard signal
and the analysis carried out. One previous research suggests that
the mechanical power is the variable that can predict the per-
formance [1] . We did not measure the mechanical power in the
three conditions. However, some vertical ground reaction forces
were considered an interesting form to quantify the intensity
[13] of the exercises and other ones indicate the stress to the
musculoskeletal system [11] . Test-retest reliabilities for the vari-
ables measured in the single-leg jumps (both dry-land and
aquatic) were previously established with an intraclass correla-
tion coeffi cient (ICC). They consistently ranged from 0.89 to
0.95.
Statistical analysis
Statistical analysis was carried out using SPSS software version
17 (SPSS Inc., Chicago, IL, USA). It was checked that all the varia-
bles complied with the assumption of normality (K-S normality
test). Standard statistical methods were used to obtain the mean
as a measurement of the central trend and the standard error of
the mean (SEM) as a measurement of dispersion. One ANOVA
with repeated measures (condition) was applied to establish dif-
ferences between the three jumps. Univariate contrast was uti-
lized to determine the main eff ects of the condition over the
dependent variables. Greenhouse-Geisser correction was used
when the assumption of sphericity (Mauchly ’ s test) was vio-
lated, and Bonferroni correction ( α / number of comparisons) was
applied to avoid increasing familywise error (e. g. increasing the
possibilities of having made one Type I error) because several
dependent variables were included in the analysis. Helmert
planned contrast was used to establish diff erences between the
dry jumps and the two aquatic jumps and between aquatic
jumps. This contrast was employed because it is more powerful
than post hoc analysis [9] . The level of statistical signifi cance
prior to applying Bonferroni correction was set at p < 0.05.
Results
&
The results show that the main eff ect on maximum concentric
force (F
2,22 = 10.52, p = 0.001), peak impact force (F 2,22 = 35.98,
p < 0.001), time to maximum concentric force (F 2,22 = 7.55,
p = 0.003), total time (F 2,22 = 11.77, p < 0.001) and impact force
development rate (F
1.17,12.89 = 22.31, p < 0.001) is the medium in
which the jump was performed.
Planned contrast revealed that maximum concentric force was
greater when the jumps were performed in water than on dry
land (F
1,11 = 15.7, p = 0.002, r = 0.77), but there were no diff er-
ences between aquatic jumps. In addition, peak impact force
was lower for the aquatic jumps than for dry jumps (F
1,11 = 44.21,
p < 0.001, r = 0.89), and no diff erences were observed between
aquatic jumps. Also, diff erences in impact force development
rate between dry land and aquatic jumps were found (F 1,11 = 24.16,
p < 0.001, r = 0.83), with the values for aquatic jumps being lower
than the values for dry land jumps (
●
▶ Fig. 2 ).
On the other hand, the time to maximum concentric force was
higher for aquatic jumps than for dry jumps (F
1,11 = 8.4, p = 0.015,
r = 0.65), and the contrast also showed that aquatic jumps with
devices showed greater times to maximum concentric forces
2000
1500
1000
Force (N)
500
0
2000
1500
1000
500
0
E
C
A
D
G
B
F
1 s 0.5 s
Fig. 1 Example of a standard signal and the
analysis performed during the aquatic jump. On
the left a typical signal of the forces generated
by a subject during the aquatic jump is shown.
The diff erent phases of the jump can be observed
through the dolls placed in the superior zone
separated by dotted lines. The shading shows the
fragment of the signal selected for the posterior
analysis. On the right side an example of the
statistical parameters calculated in the data
reduction section is shown. As can be checked
the signal force was corrected removing the force
exerted by the subjects body weight on the right
side signal compared to the left side signal. The
statistics mean: A . Peak Concentric Force; B . Peak
Impact Force; C . Rate of Concentric Force;
D . Rate Impact Force; E . Time Concentric Force;
F . Time Impact Force; G . Total Time. Although
the graphical representation of the rates is not
exact, it can provide a visual help to understand
the calculation of these parameters. The rate
impact force was calculated dividing the diff erence
between the force at the beginning of the braking
phase and the peak impact force by the time to
impact force. The rate of force development was
calculated dividing the peak concentric force by
the time to concentric force.

Training & Testing 121
Colado JC et al. Two-Leg Squat Jumps in Water: An Eff ective Alternative … Int J Sports Med 2010; 31: 118 – 122
(F
1,11 = 6.2, p = 0.03, r = 0.36) and total time (F 1,11 = 26.35, p < 0.001,
r = 0.84) than aquatic jumps without devices ( ● ▶ Table 1 ).
Discussion
&
The fi rst important question associated with our study deals
with the parameters used to characterise the signals acquired
during the jump attempts. Despite there being a signifi cant
number of calculations to summarise the data collected during
jumps, in line with other authors, we think that the impact force
and impact force development rate are two parameters that
indirectly indicate the stress level that the musculoskeletal sys-
tem receives [11] . In addition, the intensity of the jumps can be
expressed by peak concentric force and force development rate
[13] .
Research into jump characteristics is a well-consolidated fi eld in
scientifi c literature, but to date we only know of one study
describing jumps in the aquatic medium. Vicente-Rodriguez
et al. [27] quantifi ed the peak force in dry squat jumps per-
formed by female handball players and they did not show any
similar data to ours within this variable. The mean value of their
measure of the peak force during the dry squat jump was 519.36
N and our results indicated a value of 838.14 N when the jumps
were performed on dry land. This diff erence can be explained by
the fact that the females they studied were younger and their
body mass was lower (14.2 ± 0.4 years and 53.6 ± 1.8 kg respec-
tively) than the females in our study (16.0 ± 0.7 years and
64.4 ± 8.9 kg respectively). On the other hand, the experimental
data we gathered clearly coincides with a previous study carried
out by Triplett et al [25] . that measured the vertical ground reac-
tion forces in the same three conditions but using one-leg jumps
instead. Basically, our data supported the suitability of using the
aquatic medium as a way of increasing the intensity of the
jumps, although the diff erences with regard to certain parame-
ters measured in our laboratory and those mentioned in the
above study require additional explanation.
Triplett et al. [25] , observed that when one-leg squat jumps were
performed in water, the concentric force peaks were higher and
the impact forces were lower when compared with the same
jumps carried out on dry land. However, in his study the resist-
ance materials were signifi cantly eff ective, reducing impact
forces by 31.6 % and increasing maximum concentric forces by
12.7 % when compared with aquatic jumps performed without
using said materials.
Although our experiment also showed that both aquatic jumps
generated higher concentric forces and lower impact forces, we
were unable to demonstrate statistically that the use of area
devices was signifi cantly eff ective. The resistance off ered by the
material was quite possibly not high enough in our study, as the
jumps were performed with both legs and the devices used were
1150
AB
CD
3500
3000
2500
2000
1500
1000
35000
30000
25000
20000
15000
10000
5000
1100
1050
1000
950
900
850
800
750 DRY LAND JUMP
FORCE (N)RATE (N.S-1)
FORCE (N)RATE (N.S-1)
AQUATIC JUMP AQUATIC JUMP (DEVICES) DRY LAND JUMP AQUATIC JUMP AQUATIC JUMP (DEVICES)
DRY LAND JUMP AQUATIC JUMP AQUATIC JUMP (DEVICES) DRY LAND JUMP AQUATIC JUMP AQUATIC JUMP (DEVICES)
4250
4000
3750
3500
3250
3000
2750
Fig. 2 Forces and rates during dry land and
aquatic jumps. A . Peak Concentric Force; B .
Peak Impact Force; C . Rate of Concentric Force;
D . Rate Impact Force, in the three conditions.
Squares represent mean (n = 12) and error bars
represent standard error of the mean. * Signifi cant
diff erences (p < 0.05) related to both aquatic
jumps.
Table 1 D i ff erences between dry and aquatic jumps in time variables
(n = 12).
Dry Jump Aquatic Jump Aquatic Jump
with Devices
time
concentric force
0.26 (0.02) * 0.31 (0.03) 0.38 (0.02) †
time impact force 0.11 (0.01) 0.18 (0.02) 0.14 (0.03)
total time 0.36 (0.01) 0.35 (0.02) 0.45 (0.02) †
Data are expressed as mean (standard error of the mean). * Signifi cant diff erences
(p < 0.05) related to both aquatic jumps. † Signifi cant diff erences (p < 0.05) related to
aquatic jump

Training & Testing122
Colado JC et al. Two-Leg Squat Jumps in Water: An Eff ective Alternative … Int J Sports Med 2010; 31: 118 – 122
the same size as those used in the above-mentioned study. In
addition, we found no signifi cant reduction in the impact forces
as a result of using the aquatic devices, despite the fact that the
reduction was high (e. g. 12.7 % less impact for the aquatic jumps
with devices when compared with the aquatic jumps without
devices). It may be that no signifi cant diff erences appeared in
our study because the size of the eff ect to be detected was very
small (r = 0.28).
It should also be remembered that the maximum concentric
force was maintained and even increased in the aquatic jumps,
as we detected increases of 25.6 % over the fi gure for dry land
jumps for this variable when the jumps were performed in
aquatic conditions. These increases may be due to the increased
resistance to movement generated by the drag forces [4] , which
have a positive relationship with the speed of movement [5, 6] .
These results explain why previous studies have found a pro-
gramme of jumps in water designed to improve the vertical
jumps of athletes to be more eff ective than one carried out on
dry land [15, 17] . With regard to concentric force development
rate, no diff erences were found between the conditions tested.
This could be due to the fact that the time taken in water to reach
maximum concentric force is prolonged, with the force develop-
ment rate being reduced, despite the fact that the subjects gen-
erate higher maximum forces.
The main implications of our study centre on the use of jump
exercises in water. It is known that open kinetic chain exercises
in water are normally used because they can be performed eas-
ily and the drag force can be increased by using devices, all in
order to increase strength and muscle mass [20, 26] . The fi nd-
ings of the present study show that applying closed chain kinetic
exercises such as jumps in water is as effi cient as dry land jumps,
or even more. In the sporting performance fi eld, aquatic jumps
can be used to improve overall physical capacity in periods when
the workload is more important than focused training. In addi-
tion, these low impact activities can be used by obese individu-
als or athletes with large body masses (e. g. shot putters,
heavyweight judo competitors, etc.) to improve their explosive
force, as performing jumps on dry land greatly increases the risk
of joint injuries for these individuals, due to the high impact
forces generated when landing. They can also be very useful in
slowing the reduction in neuromuscular performance that
occurs with ageing [12] , as the use of exercises focusing on
improving explosive forces has been recommended for this pop-
ulation [20] , and water can off er a safe environment for the mus-
culoskeletal system.
To sum up, it seems to be clear that water is the optimum envi-
ronment for performing jumps, as the variables associated with
the exercise intensity are boosted, while those related to the
impact force are reduced and this fact could be less harmful.
However, the eff ectiveness of aquatic devices that increase drag
forces to augment the intensity and safety of these exercises has
not been proven. This information may be useful in fi elds associ-
ated with prevention, sporting performance, rehabilitation and
health-related recreational activities.
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