Advances in Physical Education
2012. Vol.2, No.3, 95-98
Published Online August 2012 in SciRes (http://www.SciRP.org/journal/ape) http://dx.doi.org/10.4236/ape.2012.23017
Relationship between Ball Kick Velocity and Leg Strength:
A Comparison between Soccer Players and Other Athletes
Takanori Noguchi1*, Shinichi Demura2, Yoshinori Nagasawa3
1Fukui University of Technology, Fukui, Japan
2Graduate School of Natural Science & Technology, Kanazawa University, Kanazawa, Japan
3Kyoto Pharmaceutical University, Kyoto, Japan
Received April 28th, 2012; revised May 29th, 2012; accepted June 9th, 2012
This study compared soccer players with non-soccer players, with respect to the relationship between ball
velocity due to an instep kick and various leg strengths. Ten young university soccer players and ten other
athletes (non-soccer players) had their instep kick ball velocity (BV) measured with respect to isokinetic
leg strength. The BVs from the soccer players were significantly greater than those from the non-soccer
group. However, this group also had significantly inferior dorsiflexion strength of the ankle joint (low:
low angular velocity), extension of the knee joint (low, middle, and the total value of the evaluation pa-
rameters of all angular velocities), and flexion of the hip joint (middle). Positive and significant correla-
tions between BV and flexion and dorsiflexion strengths of the ankle joint (low), extension (low, middle,
high, and total), and flexion of knee joint (low and total), extension (low, high, and total), and flexion
(high) of the hip joint were found in the soccer group, but a significant negative correlation was found
only between BV and hip joint flexion strength (middle) in the non-soccer group. In conclusion, soccer
players have similar or inferior isokinetic leg strength in comparison to other athletes, but their BV is faster.
Keywords: Soccer; Ball Kick Velocity; Leg Strength
Introduction
Recently, a device for training and evaluating the isokinetic
strength of the lower limbs, i.e., the isokinetic strength meas-
urement device, has been used not only by top players but also,
more broadly, by non-professional players. This device can evalu-
ate and increase the muscle strength of various body sites (Tsuy-
ama, Kobayashi, Saito, Kiyota, & Nakajima, 2007; Chan, Chan,
Fong, Wong, Lam, & Lo, 2011). In addition, it has the addi-
tional advantage that players and coaches can select body sites
and specific motions of interest, and examine competitive char-
acteristics in order to improve the strength of specific muscle
groups. To best understand conditioning and muscle strength, it
is important for athletes to be motivated to improve their com-
petition performances and to participate in a vigorous training
regime. In soccer games, players need to make quick, precise
movements. In particular, the instep kick is frequently used
when the ball needs to be kicked very hard.
In order to obtain a high leg swing velocity, the exertion of
knee extension and hip flexion strength is important (Levanon
& Depena, 1998). Hence, many studies have been performed
using the above-stated isokinetic strength measurement device.
Tsuyama et al. (2008) reported that the extension and flexion
strength of the knee joint and flexion strength of the hip joint in
soccer players were significantly greater than those of archery
athletes. In addition, they also reported that senior soccer play-
ers have greater isokinetic leg strength than junior soccer play-
ers (Rochcongar, Morvan, Jan, Dassonville, & Beillot, 1988; Gür,
Akova, Pündük, & Küçükoğlu, 1999; Hoshikawa, Iida, Muramatsu
& Nakajima, 2007). However, the above previous studies mainly
examined the magnitude of leg strength or morphological char-
acteristics of their legs as soccer players. In short, the relation-
ship between ball kick velocity and leg strength has not been
examined in detail. In the case of isokinetic muscle contraction,
contraction characteristics differ for each person and with re-
spect to angular velocity (Tsuyama, Kobayashi, Saito, Kiyota, &
Nakajima, 2007). In addition, the type and amount of necessary
leg strength differs among competitive sports. Because soccer
players need to make quick instep kicks, the ability to exert a
large amount of force over a very short time is necessary.
The peak velocity and right angle of the foot at the time
when the ball is kicked determines the resultant ball velocity
(Kellis & Katis, 2007). With regard to an instep kick in soccer,
it is important that the hip, knee and ankle joints all work to-
gether in a chain reaction, transferring the base energy to the
end area with an accelerating flail-like action. In this case, the
hip joint—which fulfills the base role—must move large mus-
cle groups and exert a large amount of power to begin the
swing action (Sports Medicine Committee of Japan Football
Association, 2005). Because muscles have the physiological
characteristic that their contraction speed decreases when put-
ting forth a large amount of power (Sports Medicine Committee
of Japan Football Association, 2005), it is considered that mus-
cle power exertion with not only high angular velocity but also
with low angular velocity at the early stage of the kicking is
important. In addition, the ankle joints must be maintained in a
fixed position in order for the power conveyed at the moment
of kicking the ball to not be dispersed. Therefore, training for
increasing swing speed, and the technical practice for keeping
the ankle joint in a fixed state (right angle) when the ball is
being kicked is indispensible for soccer players.
*Corresponding author.

T. NOGUCHI ET AL.
It is expected that existing products will be improved and
measuring devices will be developed in the future, and the
isokinetic strength measurements will be used in the teaching
fields of various types of sports. Taking this into account, it is
important for soccer players to isolate the characteristics of
isokinetic strength as well as its relationship with ball velocity
in order to adequately use the measuring device for training and
strength evaluation purposes.
This study compared soccer players with other athletes with
respect to the relationship between ball velocity and various leg
strengths.
Methods
Subjects
Subjects in this study included ten healthy young male soccer
players (age 20.0 ± 0.8 years, height 172.3 ± 5.0 cm, weight
64.4 ± 5.3 kg) and ten male athletes (age 21.1 ± 0.57 years,
height 173.2 ± 5.1 cm, weight 68.8 ± 5.9 kg) who were not
soccer players (the non-soccer group). All subjects have trained
for at least five years in their respective sports. The non-soccer
group consisted of four baseball players, two kendo competitors,
one softball player, one basketball player, one American foot-
ball player, and one track and field athlete, all of whom did not
receive special training in soccer. Before the measurements
were taken, the purpose and procedure were explained in detail
and informed consent was obtained from all participants. This
experimental protocol was approved by the ethics committee at
Kanazawa University.
Measurement Procedure
Matsuda et al. (2010) divided the legs into a kicking leg and
a supporting leg, defining the former leg as the dominant leg.
All measurements were performed on the dominant leg.
Ball kick velocity was measured by using the formula No. 5
ball officially recognized by FIFA with moderate air pressure
(Pelada, molten), using an ultrasound speed meter (2ZM-1300,
Mizuno). The distance from the ball to the speed meter was set
at 10 m, and a net (height 2.0 m × width 2.0 m) was placed a
distance of 1.0 m in front of the speed meter (height 1.5 m)
(Figure 1). The subjects were free to choose an approach dis-
tance and performed an instep kick at maximum effort twice.
Kilometers per hour (unit: km/h) was used for the evaluation
variable.
Isokinetic leg strength was measured using a CYBEX-NORM
(CN77, SIMIZU MEDICAL). This device is capable of meas-
uring isokinetic strength values by adjusting an attachment while
matching the range of motion in each joint. The measurement
10m
Theultrasound
speedmeter
Thenet
Theball
1m 1.5m
Figure 1.
Measurement of ball kick velocity
data obtained from this device was taken into a note-PC via a
USB cable and analyzed with specialty software (HUMAC2009,
SIMIZU MEDICAL). Isokinetic strengths of hip and knee joint
flexion/extension and ankle joint flexion/dorsiflexion were meas-
ured. Extension and flexion of hip and knee joints were meas-
ured for three specific angular velocities; low (30 deg/sec),
middle (120 deg/sec), and high (240 deg/sec).
In a preliminary experiment, it was confirmed that the sub-
jects’ flexion and dorsiflexion strength of their ankle joints at
middle and high angular velocities could not be measured.
Hence, their strengths were measured only at low angular ve-
locities. After one practice run, the test was performed twice in
between one-minute intervals to eliminate the effects of fatigue.
Isokinetic strength was evaluated with maximum torque (unit:
Nm) and the larger value was interpreted to have the larger
isometric leg strength (Kannus, 1994).
Of the two trials, the highest values of the ball kick velocity
and leg strength were used. In addition, flexion and extension
strengths of the knee and hip joints were used as the respective
values of low, middle, and high angular velocities and their
total value as evaluation parameters.
Statistical
Mean differences of physical characteristics (height and weight),
ball kick velocity, and isokinetic leg strengths between the soc-
cer group and the non-soccer group were examined by an un-
paired t-test. The mean difference was assessed by effect size
(ES). The relationships between ball kick velocity and isoki-
netic leg strengths were examined using Pearson’s correlation
coefficient. Statistical significance (α) was set at p < .05.
Results
Height and weight (height: t = 0.37, weight: t = 1.61, p >
0.05) showed no significant differences between the soccer group
and the non-soccer group. Table 1 shows the means and stan-
dard deviations of ball velocity and isokinetic strength of each
leg part, correlations between ball kick velocity and each strength
value, test results of the mean differences between both groups,
and effect size (ES). Significant correlations were found be-
tween ball kick velocity and ankle joint flexion and dorsiflexion
strengths (low angular velocity), knee joint extension (low, mid-
dle, and high angular velocities and total) and flexion (low angu-
lar velocity and total), and hip joint extension (low and high
angular velocities, and total) and flexion (high angular velocity)
(r = 0.70 over) in the soccer group, but only between ball kick
velocity and hip joint flexion strength (middle angular velocity)
and (r = –0.65) in the non-soccer group
Ball kick velocity of the soccer group was significantly greater
than that of the non-soccer group (t = 9.71, p < 0.05. Ankle
joint dorsiflexion strength (low angular velocity), knee joint
extension strength (low and middle angular velocities, and total)
and hip joint flexion strength (middle angular velocity and total)
were significantly larger in the non-soccer group. Insignificant
differences were found in knee joint flexion and hip joint ex-
tension strengths. Effect sizes of the mean difference in ball
kick velocity and ankle joint dorsiflexion strength (low angular
velocity) between both groups were 0.92 and 0.82, respectively.
Effect sizes of the mean differences in ball kick velocity and in
knee joint extension (middle angular velocity, total) and hip joint
flection strengths (middle angular velocity) were 0.53 - 0.60.
96

T. NOGUCHI ET AL.
Table 1.
The relationship between ball kick velocity and each isokinetic strength.
The soccer group (n = 10) The non-soccer group (n = 10) t-test
Mean SD r Mean SD r t-value p ES
Ball kick velocity 103.40 4.08 84.40 4.22 9.71 0.00* 0.92
Flexion (low) 77.70 9.77 0.74* 79.20 10.26 0.31 0.32 0.75 0.08
Ankle Dorsiflexion (low) 40.40 5.08 0.70* 59.50 8.09 0.30 6.00 0.00* 0.82
Extention (low) 251.10 43.44 0.82* 299.40 43.80 0.44 2.35 0.03* 0.48
Extension (middle) 149.00 26.81 0.79* 191.90 30.29 0.21 3.18 0.01* 0.60
Extension (high) 105.40 20.28 0.83* 117.40 18.47 –0.12 1.31 0.21 0.30
Extension (total) 505.50 83.56 0.88* 608.70 83.11 0.28 2.63 0.02* 0.53
Flexion (low) 138.30 14.83 0.88* 151.20 24.31 0.38 1.36 0.19 0.31
Flexion (middle) 105.40 14.28 0.62 115.50 13.70 –0.14 1.53 0.14 0.34
Flexion (high) 82.00 12.02 0.54 86.60 16.66 –0.06 0.67 0.51 0.16
Knee
Flexion (total) 325.70 32.45 0.88* 353.30 47.74 0.13 1.43 0.17 0.32
Extention (low) 274.50 54.25 0.93* 318.10 51.61 0.15 1.75 0.10 0.38
Extension (middle) 196.30 51.13 0.56 239.40 58.25 0.14 1.67 0.11 0.37
Extension (high) 133.90 57.49 0.75* 146.80 33.50 0.09 0.58 0.57 0.14
Extension (total) 604.70 145.42 0.84* 704.30 135.34 0.14 1.50 0.15 0.33
Flexion (low) 177.30 44.74 0.47 206.50 21.22 –0.14 1.77 0.09 0.39
Flexion (middle) 137.00 26.59 0.42 165.80 16.64 –0.65* 2.75 0.01* 0.54
Flexion (high) 100.00 21.19 0.78* 105.40 13.47 0.22 0.65 0.53 0.15
Hip
Flexion (total) 414.30 82.71 0.59 477.70 36.74 –0.29 2.10 0.05* 0.44
*p < 0.05. Isokinetic strength: low = 30 deg/sec, middle = 120 deg/sec, high = 240 deg/sec; Unit: ball kick velocity (km/h), isokinetic strength (Nm) ES: effect size.
Discussion
Height and weight showed insignificant differences between
the soccer and the non-soccer groups. However, the soccer group
had inferior knee joint extension (low and middle angular ve-
locities) and hip joint flexion strengths (middle angular velocity)
as compared to the non-soccer group. The non-soccer group in
this study was composed of general competitive athletes (see 2
Subjects in the method). Because sports such as baseball, bas-
ketball, track and field frequently involve running and jumping,
leg strength plays an important role. In Kendo (the Japanese art
of fencing) and American football, athletes need to withstand
rough physical contact. Therefore, it is estimated that leg strength
develops as a result.
Because kicking and running are skills that are frequently
used in soccer, it may be generally assumed that soccer players
have superior leg strength. Tuyama et al. (2007) reported that
their isokinetic knee joint extension strength was significantly
greater than that of archery athletes at low angular velocities
(30 deg/sec). However, because the movements required in arch-
ery are static and do not significantly displace the center of
gravity, archery athletes are not considered to have a great
amount of dynamic leg strength. Hence, from the above report
based on comparison with archery athletes, it cannot be judged
that soccer players have greater leg strength.
It was reported that the mean value of isokinetic knee exten-
sion strength of the Canadian Olympic soccer players was 249.7
Nm (Rhodes, Mosher, McKenzie, Franks, Potts, & Wenger,
1986), isokinetic knee extension and flexion strengths of Greek
elite soccer players were 247.0 ± 29.0 Nm, 146.0 ± 12.0 Nm,
respectively (Poulmedis, 1985), and Japanese university soccer
players were 246.7 ± 36.8 Nm, 139.3 ± 15.3 Nm (Tsuyama,
Kobayashi, Saito, Kiyota & Nakajima, 2007). These were meas-
ured under the same conditions as those used in this study (30
deg/sec). Any mean is almost the same as those of the present
soccer group, and less than that of the present non-soccer group.
From the present results, soccer players may display inferior
leg strength exertion at low velocities to that of general sports
athletes. Furthermore, isokinetic strength of ankle joint dorsi-
flexion at low angular velocities is inferior in soccer players as
compared to non-soccer players (ES = 0.82). This is attributed
to the manner in which the ankle joint is moved. In short, it is
necessary for soccer players to kick the ball while keeping the
ankle joint in a fixed state, so that the force transmitted from
the ankle joint is not dispersed at the moment of impact. For
that, they may have had difficulty exerting the isokinetic leg
strength required to move their ankle joint smoothly toward
dorsiflexion. On the other hand, strength exertion at low and
middle angular velocities differed, and isokinetic strengths of
knee joint extension and hip joint flexion at high angular ve-
locities between the soccer and the non-soccer groups were
different, albeit in insignificant ways. These results differed from
those of strength exertions at low and middle angular velocities,
and may be attributed to the fact that, because shooting a soccer
ball is a swinging action at high velocities, players frequently
use this action during practice and games. From the above, it is
inferred that soccer players possess inferior isokinetic leg strength
at low and medium angular velocities, but have superior or
similar leg strength at high angular velocities as compared to
athletes in other sports.
Furthermore, the soccer group was found to possess inferior
isokinetic leg strength at low and middle velocities in compari-
son to the non-soccer group, but had faster ball kick velocities
(ES = 0.92). In addition, ball kick velocity showed positive and
significant correlations with the following strengths: ankle joint
flexion and dorsiflexion strength (low angular velocity), knee
joint extension strength (low, middle, and high angular veloci-
ties, and total), hip joint extension strength (low and high an-
gular velocities, and total), and flexion strength (high angular
velocity). Significant correlations between the isokinetic strengths

T. NOGUCHI ET AL.
and the ball velocity were found in the soccer group. Hence, it
is inferred that they have excellent technique to give a strong
impact to a ball and players with larger isokinetic strength
could make it reflect the ball velocity. On the other hand, a
significant positive correlation was not found in the non-soccer
group. Even if non-soccer players had large isokinetic strength,
they cannot apply well it to kick velocity due to a lack of ap-
propriate kicking skills. In short, it is considered that the larger
isokinetic strength does not become an important factor deter-
mining ball velocity. Therefore, it is judged that players need to
have adequate kicking techniques in order to possess the isoki-
netic strength contribute to the ball velocity.
Players can gain the unique motor fitness required for a par-
ticular sport by repetitive practice of special movements in
addition to fundamental strength training (Demura, 2011). In
the case of soccer players who mastered appropriate kicking
techniques and shooting movements, the following is consid-
ered: players with superior leg strength generally have a higher
kick velocity. In addition, they may be able to further increase
the ball kick velocity by increasing leg strength. In short, even
if players have superior leg strength, the ball kick velocity will
not improve unless the shooting technique is mastered.
Conclusion
Soccer players have similar or inferior isokinetic leg strength
to non-soccer players, but their instep kick is faster. In the case
of soccer players with superior shooting technique, those with
superior isokinetic leg strength have faster ball kick velocity.
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