THE EFFECT OF GENDER AND FATIGUE ON THE BIOMECHANICS OF BILATERAL
LANDINGS FROM A JUMP: PEAK VALUES
1Division of Physical Therapy, Long Island University, Brooklyn, NY, USA
2Occupational & Industrial Orthopaedic Center, NYU-Hospital for Joint
Diseases, New York, NY, USA
22 June 2006
Journal of Sports Science and Medicine (2007) 6, 77 - 84
Google Scholar for Citing Articles
|Female athletes are substantially more susceptible than males
to suffer acute non-contact anterior cruciate ligament injury. A limited
number of studies have identified possible biomechanical risk factors
that differ between genders. The effect of fatigue on the biomechanics
of landing has also been inadequately investigated. The objective
of the study was to examine the effect of gender and fatigue on peak
values of biomechanical variables during landing from a jump. Thirty-two
recreational athletes performed bilateral drop jump landings from
a 40 cm platform. Kinetic, kinematic and electromyographic data were
collected before and after a functional fatigue protocol. Females
landed with 9° greater peak knee valgus (p = 0.001) and 140% greater
maximum vertical ground reaction forces (p = 0.003) normalized to
body weight compared to males. Fatigue increased peak foot abduction
by 1.7° (p = 0.042), peak rectus femoris activity by 27% (p = 0.018),
and peak vertical ground reaction force (p = 0.038) by 20%. The results
of the study suggest that landing with increased peak knee valgus
and vertical ground reaction force may contribute to increased risk
for knee injury in females. Fatigue caused significant but small changes
on some biomechanical variables. Anterior cruciate ligament injury
prevention programs should focus on implementing strategies to effectively
teach females to control knee valgus and ground reaction force.
WORDS: Anterior cruciate ligament injury, injury prevention,
knee injury, sports biomechanics.
Anterior cruciate ligament (ACL) tear is a debilitating sports
injury with an estimated 80,000 ACL occurrences in the United States
annually (Griffin et al., 2000;
Miyasaka et al., 1991;
Pedowitz et al., 2003).
The literature almost unanimously suggests that females are substantially
more susceptible than males in suffering acute non-contact injury
of the ACL (Arendt and Dick, 1995;
Delfico and Garrett, 1998;
Gray et al., 1985;
Hutchinson and Ireland, 1995;
Messina et al., 1999;
Powell and Barber-Foss, 2000;
Stevenson et al., 1998;
Tillman et al., 2002).
The ACL injury rate in females is higher in a variety of exercise
activities such as soccer (2-6 times higher), basketball (4-10 times
higher) and military training (10 times higher) (Arendt and Dick,
Gray et al., 1985;
Hutchinson and Ireland, 1995;
Messina et al., 1999;
Powell and Barber-Foss, 2000).
A conference on the prevention of ACL injuries sponsored by the
American Orthopaedic Society for Sports Medicine in 1999 issued
a consensus statement suggesting that biomechanical and neuromuscular
factors appear to be the most important factors associated with
ACL injury and the higher incidence of injury in female athletes
A primary recommendation of the conference was that research efforts
should focus on the investigation of biomechanical risk factors
Harmon and Ireland, 2000)
during activities that can cause knee injury, such as landing from
a jump. Two-thirds of ACL injuries occur via a non-contact mechanism,
and the majority of these injuries occur at landing from a jump
(Arendt and Dick, 1995;
Boden et al., 2000;
Gray et al., 1985;
Griffin et al., 2000;
Hewett et al., 1999;
Kirialanis et al., 2003;
Kirkendall and Garrett, 2000).
Although the ACL gender bias is likely multifactorial, three main
theories have been proposed to explain the higher incidence of female
ACL injury: the ligament dominance theory (Hewett et al., 2001),
the quadriceps dominance theory (Hewett et al., 2001),
and the straight knee landing theory (Huston et al., 2001).
The ligament dominance theory suggests that the lower extremity
muscles do not adequately absorb the impact of landing, resulting
in knee valgus which causes increased loading of the ACL (Ford et
The quadriceps dominance theory suggests that females tend to rely
on their quadriceps more than their hamstrings creating excessive
anterior translation of the tibia (Ford et al., 2003;
Hewett et al., 1996;
Huston and Wojtys, 1996).
The straight knee landing theory suggests that females exhibit less
knee flexion at the time of impact that may lead to ACL injury either
by hyperextension or by anterior tibial translation (Decker et al.,
Huston et al., 2001).
The present study investigated whether there is support for these
three theories in a controlled laboratory environment by collecting
biomechanical data for males and females as they are landing from
a drop jump.
Fatigue is another factor that has been linked to athletic injuries.
Several epidemiological studies support the notion that fatigue
is a predisposing factor responsible for increased number of injuries
(Bottini et al., 2000;
Hawkins et al., 2001;
Kersey and Rowan, 1983;
Rahnama et al., 2002).
Despite this, a very limited number of studies have examined the
effect of fatigue on biomechanical variables during drop landing
(Fagenbaum and Darling, 2003;
Madigan and Pidcoe, 2003;
Rozzi et al., 1999a)
and only one of them (Madigan and Pidcoe, 2003)
has used a functional fatigue protocol consisting of tasks that
mimic sports activities such as squat and jumping.
In a study (Rozzi et al., 1999a)
of male and female athletes who were fatigued to 25% of their original
torque with the use of an isokinetic dynamometer, the researchers
found decreased knee proprioception and increased onset of contraction
time for the hamstrings and the gastrocnemius as subjects performed
a landing task. They found no significant effect of gender or fatigue
on balance or anterior tibial translation. However, males exhibited
significantly increased mean vastus lateralis normalized EMG (NEMG)
after fatigue compared to females (Rozzi et al., 1999a).
The authors acknowledged that a significant limitation of their
study was the non-functional fatigue protocol (isokinetic) (Rozzi
et al., 1999a).
Madigan and Pidcoe, 2003
looked at the effects of a functional fatigue protocol on the biomechanics
of landing but all subjects were male and the authors did not collect
frontal plane knee kinematic data.
Fagenbaum and Darling, 2003
concluded that fatigue had a similar effect on males and females
but they used an isokinetic fatigue protocol which may not have
replicated the fatigue that athletes experience during sports. Chappell
et al., 2005
suggested that a fatigue protocol of vertical jumps and sprints
caused subjects to land with increased proximal tibia peak anterior
shear forces and decreased knee flexion at the time that peak anterior
shear forces occur. Moreover, females landed with an external knee
valgus moment that was increased in the post-fatigue condition while
males exhibited an external varus moment. Females also exhibited
a greater external knee flexion moment that the authors suggested
may be due to increased quadriceps contraction, decreased hamstrings
contraction or a combination of both conditions. However, NEMG data
was not collected to further clarify the mechanism that leads to
an increased external knee flexion moment.
The primary aim of the present study was to determine the effect
of gender and fatigue on peak NEMG, kinetic, and kinematic variables
during bilateral drop landings from a 40 cm platform. We hypothesized
that females will exhibit landing biomechanics that predispose them
to knee injury [greater knee valgus, greater vertical ground reaction
force (VGRF)] and that males and females will land with increased
knee valgus, VGRF, and NEMG activity of the rectus femoris and hamstrings
after the fatigue protocol.
study was conducted at the Harkness Dance Center Motion Analysis
Laboratory, NYU - Hospital for Joint Diseases. It was a repeated
measures pre-fatigue and post-fatigue experimental study using measures
of EMG, kinetic, and kinematic data.
Based on a power analysis of the findings of a pilot study (3 males
and 3 females) this study required 32 subjects to answer the hypotheses
with a power of 0.8 and ? level of 0.05. Power analysis was performed
with the use of G Power for knee valgus, VGRF, and rectus femoris
NEMG (Buchner et al., 1997).
Thirty-two subjects were recruited from universities and colleges
in the New York City area via announcements during classes. Only
healthy volunteers between the ages of 20-40 years were recruited
because this age group is more susceptible to ACL injury (Griffin,
The inclusion criteria included participation in recreational sports
at least twice/week for a minimum of 45 min. per practice session.
Exclusion criteria were: obesity (body mass index greater than 30
kg·m-2); a history of injuries and/or diseases that would
render unsafe the execution of the protocol; and a history of injuries
and/or diseases that could affect the biomechanics of landing such
as lower extremity fractures. Subjects were excluded if they had
received specialized training in jumping and landing techniques
such as through participation in gymnastics or dance.
All 32 subjects completed the entire protocol (pre-fatigue data
collection, fatigue protocol, and post-fatigue data collection)
in a single session. Subjects performed bilateral landings on a
force plate from a 40 cm platform. The height was chosen to allow
comparisons with the findings of other investigators who used similar
protocols ( Decker et al., 2003;
Fagenbaum and Darling, 2003;
Ford et al., 2003;
Madigan and Pidcoe, 2003;
Rozzi et al., 1999a;
and as in these studies all subjects landed from the same height
in an effort to minimize variability.
All NEMG and kinematic measurements were in reference to the right
lower extremity. The literature supports that athletes injure the
dominant and non-dominant extremity with equal frequency (Matava
et al., 2002),
and therefore comparisons between the dominant and non-dominant
limb were not performed.
EMG data were collected with the Noraxon Myosystem 1400 (Noraxon
USA, Inc., Scottsdale, AZ). The electrodes were disposable, surface,
passive electrodes (Blue Sensor, Ambu, Inc., Linthicum, MD). The
force plate was an OR6-5 AMTI biomechanical platform (AMTI, Watertown,
MA). Kinematic data were collected with the use of eight Eagle cameras
(Motion Analysis Corp. Santa Rosa, CA) and reflective markers were
placed as per the "Helen Hayes system" (Richards, 2002).
The software for data collection was the EvaRT 4.0 (Motion Analysis
Corp. Santa Rosa, CA). Video data were smoothed using a Butterworth
fourth order low pass filter with a cut-off frequency of 6 Hz. EMG
data were filtered through a low pass 2nd order Butterworth
filter with a 6Hz cut-off frequency.
The force platform was time synchronized to the EMG and the motion
analysis system. The kinetic and EMG data were sampled at 1200 Hz
and the kinematic data were sampled at 240 Hz as appropriate for
fast athletic maneuvers. Before each data collection session the
system was calibrated to the manufacturer's recommendations.
Subjects were verbally informed of the study protocol and all risks
and possible harms as described in the consent form. All subjects
completed a sports activity and medical history questionnaire, signed
a consent form approved by the NYU School of Medicine IRB, and were
measured for height, weight, knee width, foot width, and foot length.
The skin was prepared and the surface electrodes were placed on
the medial gastrocnemius, rectus femoris, biceps femoris, and medial
hamstrings as described elsewhere (Fagenbaum and Darling, 2003).
These sites of electrode placement are consistent with recent guidelines
(Hermens et al., 2000)
and are located between the motor point and the distal tendon in
order to improve intra and inter-subject comparison reliability
(Basmajian and DeLuca, 1985).
Two electrodes were placed on each muscle at a 20 mm distance and
parallel to fiber orientation (Hermens et al., 2000).
Athletic tape was used to fixate the electrodes and decrease movement
artifact (Hermens et al., 2000).
The reflective markers were placed bilaterally on the second metatarsal,
calcaneus, lateral malleolus, fibula, lateral knee joint line, thigh,
anterior superior iliac spine, acromion, lateral humeral epicondyle,
and distal radioulnar joint. Reflective markers were also placed
on the sacrum and the left posterior superior iliac spine (offset)
as per the "Helen Hayes" system (Richards, 2002).
An initial "neutral" standing position of each subject
was used to account for skeletal alignment differences as in similar
studies (Hewett et al., 2005;
Kernozek et al., 2005).
With this technique, zero degree angles were defined as the angles
between adjacent segments during the neutral standing trial.
The subjects were allowed two practice jumps and then performed
three bilateral drop jumps from the 40 cm platform. They were instructed
to drop directly down off the box and land with both legs on the
force plate. Subjects did not receive any instructions on the landing
technique to avoid a coaching effect. The effect of the arms was
minimized by asking the subjects to keep their arms crossed against
their chest (Rodacki et al., 2002;
Decker et al., 2003).
Trials were repeated when they were judged as non-acceptable (such
as when subjects lost their balance or did not land with both feet
on the force plate). Upon completion of three successful jumps,
the wires were disconnected from the electrodes (but the electrodes
were not removed). The subjects followed the fatigue protocol that
consisted of 100 consecutive jumps over short (5-7 cm) obstacles
and 50 maximal vertical jumps. This combination of activities was
chosen to simulate activities commonly performed in sports and because
an eccentric-concentric fatigue protocol is more effective in producing
fatigue than a concentric fatigue protocol (Svantesson et al., 1998).
The fatigue protocol was designed in a way that the fatigue-induced
pattern is applicable to functional activities outside the laboratory
setting. The protocol used in the present study is similar to fatigue
protocols used in recent research ( Chappell et al., 2005;
Madigan and Pidcoe, 2003).
Similar protocols were sufficient in inducing fatigue as measured
by quadriceps force output and jump height (Skurvydas et al., 2000;
and mean EMG frequency (Madigan and Pidcoe, 2003).
Moreover, the demands of games such as soccer are very similar for
males and females in terms of distance covered, sprint duration,
and exercise intensity (Davis and Brewer, 1993)
suggesting that laboratory fatigue protocols have greater applicability
if they fatigue male and female athletes in a similar way as occurs
on the athletic field. After the fatigue protocol was completed,
the wires were re-connected to the EMG electrodes and the same procedure
of landings was repeated for the post-fatigue part of data collection.
All subjects completed all post-fatigue trials within six minutes
after the completion of the fatigue protocol. The landing cycle
was defined as the time between initial contact and peak knee flexion.
The Orthotrak 5.0 (Motion Analysis Corp. Santa Rosa, CA) software
was used to derive kinetic, kinematic, and EMG variables. The peak
value for all variables during the landing cycle were identified
and averaged across the three trials. The VGRF was normalized to
body weight as in previous studies (Hewett et al., 1996;
EMG amplitude was normalized to the maximum linear-enveloped EMG
of each muscle (Arampatzis et al., 2003;
Horita et al., 1999;
Rodacki et al., 2002;
Viitasalo et al., 1998)
exhibited during the landing phase of bilateral landings from a
20 cm platform (mean of three trials).
Gender differences for anthropometric and sports participation variables
were tested with independent sample t-tests. A repeated measures
MANOVA was performed with the use of a statistical software package
(SPSS 12.0, SPSS Inc., Chicago, IL, 60606) with gender and fatigue
as independent variables., The dependent variables were peak values
for knee flexion, knee valgus, foot abduction, VGRF, quadriceps
NEMG, lateral hamstrings NEMG, medial hamstrings NEMG, and gastrocnemius
NEMG as well as knee flexion angle at impact. The data were inspected
and tested to insure that the assumptions for data normality of
the univariate and multivariate repeated measures analysis of variance
(ANOVA and MANOVA) were not violated, Separate univariate repeated
measures ANOVA were performed for each dependent variable when the
MANOVA reached statistical significance (p < 0.05) (Bray and
Cohen's d statistic of effect size was calculated in order to give
a more complete picture of the effect of the independent variables
on the dependent variables. The effect size is defined as trivial
if it is <0.2, small 0.2-0.5, medium 0.5-0.8, and large>0.8
(Portney and Watkins, 2000).
1 shows the descriptive statistics of demographic, anthropometric,
and sports participation data. There were no gender differences
in regards to age and sports activity. As expected, there were differences
in the anthropometric variables between genders.
results of the MANOVA showed that the effects of gender (F9,22 =
5.763, p < 0.001) and fatigue (F9,22 = 2.934, p = 0.019) were
statistically significant but not the interaction of gender and
fatigue (F9,22 = 1.050, p = 0.434).
repeated measures ANOVA revealed that females landed with greater
peak knee valgus (F1,30 = 12.242, p = 0.001) and peak VGRF (F1,30
= 10.548, p = 0.003) but knee flexion at contact was not different
between males and females (F1,30 = 0.003, p = 0.957). After the
fatigue protocol subjects landed with increased peak foot abduction
(F1,30 = 4.534, p = 0. 042), peak VGRF (F1,30 =4.7, p = 0.038),
and peak rectus NEMG (F1,30 = 6.252, p = 0.018). Tables 2
and 3 show the means (95% confidence
intervals) and p-values (Cohen's d effect size statistic) for all
dependent variables grouped by gender and fatigue condition respectively.
objective of this study was to investigate the effects of gender
and fatigue on the kinetics, kinematics, and NEMG of the lower extremity
during landing from a drop jump. Gender had a significant effect
on one kinematic variable (knee valgus) and the sole kinetic variable
studied (VGRF). The findings regarding knee valgus agree with previous
studies (Ford et al., 2003;
Hewett et al., 2004;
Kernozek et al., 2005)
demonstrating that females exhibit greater knee valgus than males
during landing from a jump. Increased knee valgus may produce excessive
stress on the inert structures and lead to traumatic injury, consistent
with the ligament dominance theory (Ford et al., 2003;
Hewett et al., 2004).
Studies have shown that the knee is in a position of valgus at the
time of ACL injury (Boden et al., 2000;
Delfico and Garrett, 1998;
Griffin et al., 2000;
Olsen et al., 2004)
and that females exhibit greater peak knee valgus than males in
a variety of athletic activities (Ferber et al., 2003;
Horita et al., 1999;
Kirkendall and Garrett, 2000;
Zeller et al., 2003).
Moreover, in a prospective study (Hewett et al., 2005),
female athletes who subsequently suffered ACL injury were found
to have increased peak knee valgus compared to female athletes who
did not injure their ACL. The findings of this study provide further
evidence that knee valgus is one of the key gender differences that
may explain the increased incidence of ACL injuries in females.
The effect of gender on VGRF was also significant with females landing
with higher normalized VGRF than males (5.3 BW vs. 3.9 BW). The
VGRF reveals the ability of the athlete to efficiently attenuate
the impact of landing. The lower the VGRF the more optimal the landing
strategy, while high VGRF can lead to knee injuries (Dufec and Bates,
Hewett et al., 1996;
The VGRF findings of the present study show that females experience
greater peak impact forces that may predispose them to non-contact
injuries as they transfer to more proximal joints of the kinetic
chain, such as the knee joint.
To the authors' knowledge, only one more study (Kernozek et al.,
has suggested that females landing from a drop jump have increased
normalized VGRF compared to males. A study by Hewett et al., 1996
showed that a plyometric training program is effective in reducing
peak VGRF in female athletes. VGRF has been shown to be modifiable
with training (Hewett et al., 1996),
linked to injury risk (Dufec and Bates, 1991;
Hewett et al., 1996;
and a significant gender difference as per the findings of the current
study. Injury prevention programs should consider training females
to land with a decreased VGRF in order to decrease risk of ACL injury.
Gender did not have a statistically significant effect on the peak
NEMG of any of the muscles measured. However, females landed with
22% higher rectus femoris NEMG
activity compared to males. It is important to recognize that comparison
of NEMG muscle activity depends on the normalization method. In
the present study, we normalized to peak EMG activity that was exhibited
when each subject performed a similar task (landing from a 20 cm
platform). Task specific EMG normalization has been reported to
be superior to maximum voluntary contraction (MVC) for cyclical
activities (Arendt-Nielsen and Sinkjaer, 1991;
Kamen and Caldwell, 1996)
and to exhibit less variability between and within subjects (Burden
et al., 2003;
Yang and Winter, 1984).
However, the lack of statistical significance in regards to the
effect of gender on rectus femoris NEMG in the present study may
be explained by the similarity of the task that was used for normalization
to the 40 cm landings. That is, females may have landed with higher
rectus femoris activity from the 20 cm platform compared to males;
therefore, the normalization method would have minimized the NEMG
gender differences during the 40 cm landings. A different normalization
method may have resulted in significant gender differences relative
to rectus femoris NEMG. Fagenbaum and Darling, 2003
normalized to MVC and reported that females landed with higher quadriceps
NEMG activity but did not provide details on the magnitude of the
difference which precludes comparisons with the findings of the
present study. Zeller et al., 2003
investigated gender differences during a single leg squat task and
also normalized to MVC and reported that females exhibited 47% higher
mean rectus femoris NEMG than males.
The effect of fatigue on male and female athletes who participated
in the present study was significant relative to three variables:
peak VGRF, peak foot abduction, and peak rectus femoris NEMG. Although
the changes in VGRF were statistically significant, the clinical
significance is questionable; males and females landed with increased
forces after the fatigue protocol by 0.13 BW (3.4% increase) and
0.34 BW (6.5% increase) respectively. It is unclear to what degree
an increase of this magnitude can be said to contribute to injury.
These findings, however, are opposite those of Madigan and Pidcoe,
who reported that fatigue caused a 12% decrease in peak VGRF in
a group of men. The difference in results may be due to the methodology
used by Madigan and Pidcoe, 2003;
they did not test female subjects that contributed most of the peak
VGRF increase in the present study and they fatigued subjects to
exhaustion. Another difference between the two studies is that the
level of fatigue was not measured in the present study; therefore
some subjects may have been fatigued by the protocol more than other
subjects. The VGRF increase in the current study suggests that athletes'
ability to attenuate the impact of landing decreases after fatigue.
In the present study, subjects in the post-fatigue condition exhibited
a significant increase in foot abduction from 6.6° to 8.3° The role
of foot abduction in the occurrence of ACL injury is unclear, however
some have suggested that it leads to increased knee valgus (Lin
et al., 2001)
and subsequent knee injury, although in the present study fatigue
did not cause a significant increase in knee valgus. Further research
is needed to clarify the role of foot abduction on the mechanism
of ACL injury.
Subjects in the post-fatigue condition exhibited a statistically
significant increase of rectus femoris NEMG (F1,30 =
6.252, p = 0.018). This finding, however, does not mean that quadriceps
forces were higher after fatigue. Although the NEMG activity was
higher, the ability of the muscle fibers to develop tension decreases
with fatigue. Dimitrova and Dimitrov, 2003
critically reviewed the literature and reported that fatigue can
cause an increase, decrease, or insignificant change on the NEMG
amplitude during dynamic activities, however, most studies have
shown that fatigue increases the amplitude of quadriceps EMG activity
(Bonnard et al., 1994;
Nummela et al., 1994;
Psek and Cafarelli, 1993;
Rodacki et al., 2001;
Viitasalo et al., 1993).
The findings of the present study also suggest that fatigue causes
an increase in muscle activity when measured by dynamic EMG.
Previous studies (Decker et al., 2003;
Huston et al., 2001)
have provided support to the straight knee landing theory by reporting
that females land with their knees closer to extension than males.
However, the findings of the present study are in agreement with
recent studies (Fagenbaum and Darling, 2003;
McLean et al., 2004)
that do not support the straight knee landing theory. Males and
females landed with very similar knee flexion angles at the time
of impact (20.2° vs. 20.0°, F1,30 = 0.003, p = 0.957).
The effectiveness of sports injury prevention programs has been
well documented both in epidemiological studies that showed a decrease
of athletic injuries (Cerulli et al., 2001;
Hewett et al., 1999;
Myklebust et al., 2002)
and in laboratory studies that showed a decrease in peak VGRF (Hewett
et al., 1996).
However, the outcomes of these programs may improve if they focus
on variables that have been identified by biomechanical studies
as reflecting genuine differences due to gender or fatigue and have
been proven to be modifiable. In the present study, females landed
with greater peak knee valgus and peak VGRF than males. Fatigued
subjects exhibited increased peak VGRF and peak rectus femoris NEMG.
The findings of the present study may be used to guide injury prevention
programs designed to improve the landing technique of female athletes
involved in sports. Control of these variables will likely reduce
landing patterns that result in high VGRF, increased stress on the
passive structures, and subsequently, ligamentous injuries.
The present study was performed in a controlled laboratory environment
where subjects knew exactly what to expect. Although this allows
accurate comparison between groups, it does not closely simulate
the athletic environment. Most ACL injuries are non-contact in nature
but there are additional unexpected factors during a game such as
decreased friction of the floor surface, motion of the opponent,
or miscalculation of ball motion that make landing from a jump more
unpredictable and dangerous than in a laboratory setting. Moreover,
the landing task itself was not identical to the landing technique
the athletic field since we instructed subjects to keep their arms
crossed across their chest and jump down from a platform. These
modifications decrease the generalizability of the findings to the
All subjects were recreational athletes who participated at least
twice per week in a variety of sports that involved jumping. There
were no differences between males and females in regards to hours
of sports participation per week. However, this does not insure
equal proficiency in drop landings; some subjects might have been
more proficient than others in landing from a jump. We also did
not objectively measure the effect of the fatigue protocol on the
volunteers' musculoskeletal system. A more homogenous group of subjects
such as recreational basketball or volleyball players would make
the findings of this study less generalizable but would increase
the internal validity of the study.
Finally, a limitation inherent of this study as well as of most
sports biomechanics studies is that the values used for statistical
analysis were the peak values of the biomechanical variables. Peak
values of kinetic, kinematic and NEMG variables would possess greater
clinical significance if they were shown to occur at the first part
of the landing cycle that coincides with the phase the ACL is loaded
(Pflum et al., 2004)
and injuries are known to occur (Boden et al., 2000;
Olsen et al., 2004).
study investigated the effect of gender and fatigue on the biomechanical
variables of landing from a jump. The findings show that females land
with increased peak knee valgus and VGRF suggesting that the stress
on the inert structures can become excessive and lead to traumatic
injury. Fatigue elicited a similar response in males and females,
resulting in significantly increased peak VGRF, peak foot abduction,
and peak rectus femoris NEMG activity.
Future research should identify where within the landing cycle peak
values occur and more fully examine variables within the early phase
of the cycle where injuries are thought to occur. Consideration should
be given in injury prevention programs to include activities that
train female athletes to control excessive knee valgus and VGRF during
landings from a jump.
athletes landed with increased knee valgus and VGRF which may
predispose them to ACL injury.
elicited a similar response in male and female athletes.
effectiveness of sports injury prevention programs may improve
by focusing on teaching females to land softer and with less knee
Employment: Assistant Professor, Division of Physical Therapy,
Long Island University, Brooklyn, NY.
Degree: PT, PhD.
Research interests: Biomechanics, athletic injuries,
Employment: Research Assistant Professor, Program in Ergonomics
and Biomechanics, New York University, New York, NY.
Research interests: Occupational injuries, electromyography.
Employment: Associate Professor, Division of Physical Therapy,
Long Island University, Brooklyn, NY.
Degree: PT, PhD.
Research interests: Biomechanics, breathing, dance medicine.
Employment: Research Professor, Program in Ergonomics and
Biomechanics, New York University, New York, NY.
Degree: PT, Dr.Med.Sci.
Research interests: Occupational injuries, biomechanics.