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GROUND IMPACT FORCES DURING JOGGING:
Robert U. Newton, Brendan J. Humphries, & I. Barry Ward
Center for Exercise Science and Sport Management
Southern Cross University, Lismore, Australia.
Running Head Shoes with springs
Date of Submission October 30, 1995
Corresponding Author Robert Newton, Centre for Exercise Science and
Sport Management, Southern Cross University PO Box 157, Lismore NSW
2480, Australia · Telephone Int + 61 66 203 234 ·
Facsimile Int + 61 66 203 880 · Email RNEWTON@SCU.EDU.AU
forces experienced during running have been recognised as a source of
injury Kangoo Jumps are a revolution in shoe design which includes a
spring attached to the sole of the shoe.
The aim of this study was to investigate the
effects of wearing Kangoo Jumps on the vertical ground reaction forces
produced during the support phase of jogging.
Seventeen male and seventeen female subject
participated in the study.
Each completed three trials jogging over a force
plate wearing his or her normal training shoes and three trials wearing
Vertical ground reaction force was measured at
750Hz and normalised to the subject?s Body weight.
MANOVA with repeated measures followed by
univariate ANOVA tests were used to determine the effects of the shoe
A criterion alpha lever of p £ 0.01 was
used there was a significant multivariate effect of shoe type and
subsequent univariate analysis revealed that the mean force and 50 ms
impact decreased 5.4 ± 9.3 % and 46.9 ± 14.8
The total impulse, time to peak force, and contact
time increased 16.5 ± 7.5 %.24.2 ± 12.5 % and
49.9 ± 24.8 % respectively.
Peak force was not significantly different between
It was concludes that the Kangoo Jumps
significantly reduced the impact forces experienced while jogging.
Wearing such shoes may have application for the
recreational jogger, cross training for competitive athletes, or as a
rehabilitiation modality for patients with lower limb injuries.
Shoe design, shock absorption, rehabilitation,
The current strategies adopted for sport shoe
constrution are to limit ground reaction forces associated with
repetitive landings (McNeill-Alexander, 1987; Nigg & Segesser,
1992) and optimise energy return (Nigg & Segesser, 1992). Under
normal circumstances of running, jumping and bounding, the elastic
compliance of a sports shoe and the internal structures of the foot,
such as the arch and supporting tendons, reduce impact forces but
provide only 40 to 65% energy return (Mc Neill-Alexander, 1987).
Typically, the average runner impacts the ground at 2-4 times their own
bodyweight with the initial impact producing damaging effects on the
internal tissues and skeletal structures (Nigg, Denoth &
Invertigations with regards to impact forces have
reported that between 27% to 70%.
Of runners or joggers are injured in first year
after commencement of running as a result of external forces (clement
et al., 1981). Other studies have also shown that between 21% and 50%
of tennis players are injured per season (Kuhlund et al., 1979) as a
result of excessive forces. Additionally, research involving the
military found an increased frequency of overuse injuries for soldiers
in relation to the low absorbancy in the hell pad of standard issue
army boots (Joergensen & Hansen, 1989).
Typically, when running, bounding or jumping, the
musculature and joint mechanism involved in the landing process dampen
the impact forces placed on the body. However, it has been reported
that the neuromuscular system has a limited reaction time response,
between 50 to 75 ms, to forces applied to the body (Nigg, Denoth
& Neukomm, 19781; Devita & Skelly, 1992). When a force
is applied to the musculature prior to the response of the
neuromuscular system, the muscles involved are unable to absorb the
shock of landing. This initial sharp peak in the ground impact force
has possible implications for injuries to the lower limbs related to
Landings (Munro, Miller & Fuglevand, 1987; Ricard &
Veatch, 1990). Possible injuries occurring as a result of impact
landings include cartilage degeneration (Radin, et al., 1973), fatigue
fractures, shin splints (Andreasson & Peterson, 1986) and
achilles tendon problems (Joergensen, 1985).
The initial impact forces that occur within this 50
ms time frame of landing are referred to as passive impact forces
(Ricard & Veatch, 1990). It is these passive impact forces that
have been speculated to resut in injuries to the musculature and
skeletal systems (Ricard & Veatch, 1990). The impact forces
that the body sustains from landing appear to be influenced by the
inter-relationship between several mechanical parameters. The height of
the stride, jump of bound (Stacoff, Kaelin & Stuessi, 1988;
Dufek & Bates, 1990) determines the velocity at impact (Valiant
& Cavanagh, 1983; Munro, Miller & Fuglevand, 1987;
McNitt-Gray, 1991; Devita & Skelly, 1992) and therefore the
loading applied to the body (Frederick & Hagy, 1986; Scott
& Winter, 1990). Subsequently it is the momentum attained prior
to ground contact that influences the impact loads upon landing
(McNitt-Gray, 1991). Landing technique (Frederick & Hagy, 1986;
Scott & Winter, 1990; Steele, 1990) and landing surface
(McNeill-Alexander, 1987) have been shown to effect the impact forces
by changing the time period over which the negative work of absorbing
the downwards momentum is reversed to the positive work leading to toe
off. Any device which could attenuate the impact forces associated with
foot strike bears investigation for its possible use for reducing
injury risk during recreational activities and also rehabilitation from
Recently, there has been a fun and fitness shoe
developed, the Kangoo Jumps shoe (Figure 1), that would appear to
attenuate the damaging effects of high impact forces. The shoe is
constructed in a similar fashion to that of an inline roller skate with
the exception of wheels and bearings. Under the shoe is an eliptical
arch stretching from the toe to the heel of the shoe that is bisected
with a removeable band. At each depression of the arch the band absorbs
the energy and returns it in the form of positive work. The design of
these shoes is quite revolutionary and as such the implications for use
in training and rehabilitation need to be investigated. Injury to the
lower extremities an back as a result of chronic exercise involving
ground impact is prevalent in a wide rage of sports and recreational
activities. Further, rehabilitation from injury aims to improve muscle
function, coordination, and cardiovascular fitness without impeding
recovery or exacerbating the injury. The problem is to provide ground
based exercise while maintaining a low impact environment.
Therefore, the purpose of this study was to
investigate the effect of wearing the Kangoo Jumps on the ground impact
forces associated with jogging. Particular attention was focused on the
initial impact impulse and impact spike which have been shown to be
associated with injury.
Seventeen healthy males and seventeen healthy
females volunteered to take part in the study. The subjects were all
undergraduate students and none reported any significant
musculoskeletal disorder. The Subject?s mean (±SD) age,
height and weight were 22.6 ± 6.6 yrs 1.73 ± 0.10
m and 70.7 ± 9.2 kg respectively. The study was approved by
the Ethics Committee of the Southern Cross University, and all subjects
signed an informed consent document prior to the commencement of
The subject?s age, height, weight, and shoe size
were recorded. The subject was then instructed to run at his or her
normal jogging speed over the force plate while trying to ignore the
force plate, that is, without attempting to target the plate. All
subjects began their approach from a minimum of 10 m from the force
plate and continued to jog for 10 m past the force plate. This was to
ensure a consistent gait pattern when crossing the plate. If the
subject missed the plate or the foot contacted the edges of the plate,
the starting position was moved back by the distance that the foot
missed the centre of the plate and the trial was repeated. Each subject
completed three trials wearing the Kangoo Jumps and three trials
wearing their normal training shoes. As none of the subjects had worn
the Kangoo Jumps previously each was allowed an unlimited amount of
time to familiarize themselves with jogging in the boots. Not until the
subject was comfortable did they begin the test trials. The order of
the conditions was randomized between subjects to reduce the possible
confounding effects of learning, fatigue of boredom. During each trial
vertical force data from the force plate was collected and stored for
Normal Training Shoes. The subjects were instructed
to wear his or her normal training shoes. That is , the shoes they
would normally wear when jogging or playing sport. These shoes will be
referred to in the remainder of this paper as normal training shoes.
Kangoo Jumps. The Kangoo Jumps (Kangoo Jumps,
Switzerland) (Figure 1) consist of a rigid boot similar to that used in
a pair of inline skates with a leaf spring configuration attached to
the sole. A plastic band stretches between the hing points of the leaf
springs to provide added stiffness and elastic recoil. Different band
thickness are available and were selected based on the subject?s body
mass and the manufacture?s recommendations. The heavier the subject,
the greater the thickness of band used.
Force Measurement System. Vertical ground reaction
force was measured by means of a force platform (Type 9287) (Kistler,
Switzerland) mounted level with the surface of an articifial running
track. The amplified signals from the charge amplifiers were passed to
a DT01EZ analog to digital card (Data Translation, Marlboro, MA, USA)
in an 80486DX computer running Windows 3.11. The digitized data were
stored on computer disk for later analysis. The force measurement
system was calibrated prior to each testing session. Vertical ground
reaction force was sampled at a frequency of 750 Hz.
The force data were normalized by dividing by the subject?s body weight
in Newtons. The following variables were then calculated to assess the
impact characteristics of the foot contact phase. Peak force was
measured as the highest force recorded. Mean force was calculated as
the average force over the entire contact phase. Total impulse was
calculated byx integrating the force time curve for the contact phase.
The impact over the initial 50 ms was calculated by integrating the
force time curve over the 50 ms following the start of contact. The
time to reach the peak force was measured from the start of contact to
ehen the highest force was recorded. Contact time was the time that the
foot was in contact with the plate. The mean of the three trials for
each variable was then calculated and used in the statistical analysis.
The results for peak force, mean force,
total impulse, 50 ms impact, time to peak force, and contact time were
compared using MANOVA with repeated measures and univariate ANOVA for
follow-up comparisons. The criterion level for significance was set at
The MANOVA revealed no significant effect of gender
on the dependent variables so the data was pooled for all subsequent
analysis. There was a significant multivariate effect of shoetype and
subsequent univariate analysis revealed that the mean force and 50 ms
impact decreased 5.4 ± 9.3 % and 46.9 ± 14.8 %
respectively (Table 1). The total impulse, time to peak force, and
contact time increased 16.5 ± 7.5 %, 24.2 ± 12.5
%, and 49.9 ± 24.8 % respectively (Table 1). There was no
significant difference in peak force (Table 1). Figure 2 contains a
graph of the force time data for a representative subject which shows
that the forces exerted during the contact phase increase more
gradually and are applied over a longer time period for the Kangoo
Jumps compared to the normal training shoe.
Table 1: Impact forces and force time
characteristics foot strike when wearing Kangoo Jumps vesrus normal
* indicates significant difference between normal shoes and the kangoo
Jumps at the 0.01 level.
Figure 2: Ground reaction force during the stance
phase of jogging for a representative subjet wearing normal training
shoes and the Kangoo jumps
The purpose of this study was to investigate the ground reaction force
characteristics when jogging in a pair of Kangoo Jumps compared to
normal training shoes. The results clearly show that the Kangoo Jumps
result in considerably less impact forces being transferred
To the lower limbs compared to the normal training
shoes. In particular, the impulse over the first 50 ms following
initial ground contact was reduced some 47 % which should translate
into reduced risk of impact force induced injury as a result of jogging
in the Kangoo Jumps.
Figure 2 clearly shows that the contact phase is
lengehened such that the forces are applied over a longer period of
time. The force rises more gradually after impact and as can be seen
for the representative subject, the impact spike is not observed in the
Kangoo Jumps trial. Further, the time to achieve th peak force is
increased. Overall, the impact of foot strike is considerably more
gentle than that resulting from normal training shoes.
The peak force was not significantly different
between the two shoes and this was somewhat unexpected, particularly
given that the contact time was lengthened suggesting that a lower
overall force was being produced over greater time, requiring less
magnitude of force. The overall force was lower as indicated by the
lower mean force, however, the total vertical impulse was greater for
the Kangoo Jumps. This indicates that the subjects may have adopted a
more bouncing gait pattern with increased vertical oscillation between
strides. Thus, the greater emphasis on vertical motion may help to
explain the fact that the peak force was not significantly different.
The effect of the Kangoo Jumps on normal gait patterns requires further
This preliminary study shows promise for the use of
Kangoo Jumps for low impact exercise such as recreational jogging and
cross training for athletes. The uninjured person may be able to
continue with a high volume of ground based activity without the impact
injury risk inherent in their usual activity or sport. Further, there
may be application of these shoes in rehabilitating patients with lower
limb injuries. The patients could perform activities similar to normal
running, recovering muscle strength, and maintaining cardiovascular
fitness, but in a low impact situation. Jogging with Kangoo Jumps may
be a good intermediate step in the rehabilitation process between
non-support work and fully loaded running. Such training also has the
advantages of being functionally similar to a normal gait pattern.
The wearing of Kangoo Jumps rather than normal running shoes when
jogging significantly reduces the impact characteristics experienced
during foot contact which have been reported to result in injuries to
the lower extremities. Therefore, the Kangoo Jumps may have application
for recreational jogging as well as providing a safer environment for
rehabilitiation of patients with lower extremity injuries. Further
research work is required to assess the changes in gait pattern that
the Kangoo Jumps may produce, energy efficiency of jogging in the
Kangoo Jumps, and the efficacy of using them in the rehabilitiation
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*indicates significant difference between normal
training shoes and the Kangoo Jumps at the p
<= 0.01 level