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Isokinetics and Exercise Science 19 (2011) 1–6 1
DOI 10.3233/IES-2011-0406
IOS Press
Hamstring to quadriceps strength ratio and
noncontact leg injuries: A prospective study
during one season
Daehan Kimaand Junggi Hongb,∗
aDepartment of Kinesiology, University of Saskatchewan, Saskatchewan, Canada
bDepartment of Exercise Science, Willamette University, Salem, OR, USA
Abstract. Previous studies have proposed that thigh muscle imbalance is a critical risk factor for the athletic non-contact knee
injuries. However, there is a little consensus among prospective studies with regard to the correlation between isokinetic
hamstring to quadriceps strength ratio (HQR) and the non-contact knee injury rates. Most of athletic movements at risk are closed
kinetic chain movements, and compensatory effect among ankle, knee, and hip joints during the closed kinetic chain movement
was observed in the previous literatures. Therefore, it is assumed that hamstrings and quadriceps (H:Q) imbalance can cause
non-contact lower extremity injuries without necessarily causing knee injuries. The purpose of this study was to prospectively
investigate the relationship between H:Q strength imbalance and overall non-contact lower extremity injuries. A prospective
cohort study was conducted on NCAA division III basketball and soccer players during one season. A total of eighty two NCAA
Division III athletes (41 female [19.56 ±1.34 yrs, 68.2 ±10.84 kg, 166.3 ±6.78 cm] and 40 male [19.97 ±1.43 yrs, 75.45 ±
8.23 kg, 173.21 ±7.65 cm]) volunteered to participate in this study which tested Q and H strength at 60◦/s. A trend (p < 0.05)
indicating that lower than 60% of HQR was associated with non-contact leg injuries was apparent. This suggests that the H:Q
imbalance may be of significance in athletic non-contact leg injuries.
Keywords: Kineticintegration, isokinetic strength, neuromuscular, co-contraction, plyometrics, prophylactic
1. Introduction
Co-contraction of agonist and antagonist muscles
is important for joint stabilization during the dynam-
ic movement [8,15,24]. Researchers have consistent-
ly proposed that balance of these opposing muscles is
imperative in maintaining ideal joint position, there-
fore it is a critical factor for avoiding injuries during
the athletic movements such as jumping, pivoting, and
cross-cutting [5,8,28].
The National Collegiate Athletic Association
(NCAA) Injury Surveillance System (ISS) has collect-
ed injury data from various sport activities over a 16-
year time period (1988 through 2004). According to
∗Address for correspondence: J. Hong, Department of Exercise
Science, Willamette University, 900 State Street, Salem, OR97301,
USA. E-mail: jhong@willamette.edu.
its report, more than 50% of all injuries were to the
lower extremity and most of them were non-contact
injuries [17]. Researchers in clinical and exercise
sciences field have focused on developing prevention
strategies of these injuries in an effort to reduce injury
rates and related medical costs over time [10,12,13,22].
One of the most important goals of currently used
prophylactic training programs is to enhance neuro-
muscular balance of hamstring and quadriceps mus-
cles [14,16,23]. While researchers have reported that
preventative conditioning program such as plyomet-
rics and balance exercises not only decreased knee in-
jury rates but also improved balance of hamstring and
quadriceps [12–14], surprisingly, there is little consen-
sus with regard to whether strength ratio of hamstring
to quadriceps (H:Q) can be used as a predictor of non-
contact knee or surrounding tissue injuries [2,9,22].
One explanation of the unclear correlation between
H:Q strength ratio (HQR) and injuries is that imbalance
ISSN 0959-3020/11/$27.50 2011 – IOS Press and the authors. All rights reserved
2D. Kim and J. Hong / Hamstring to quadriceps strength ratio and noncontact leg injuries
of strength between hamstrings and quadriceps have
been retrospectively associated with the injuriesin most
of the previous literatures [6,30]. These retrospective
studies compared HQR of normal and deficient legs [6,
19,20], however, it is unclear if any of the strength im-
balance were present before the injury. Therefore, it
was suggested that thoroughly designed prospective in-
vestigations could clarify the association between HQR
and injuries in knee and surrounding tissues [30].
Currently, few prospective studies are available, but
these studies also reported contradicting results [2,9,
27]. While the role of HQR playing in knee and sur-
rounding tissue injuries remain asan enigma,we cannot
ignore the current emphasis of prophylactic approach
on improving H:Q strength balance. Previous studies
on HQR and susceptibility to injuries have focused on
examining only the knee related injuries. However,
trying to find the direct relationship between a risk fac-
tor and the injuries at corresponding anatomical region
may not be the feasible method because non-contact
athletic leg injuries are multi-factorial. Although ham-
string and quadriceps muscles are directly related to
knee joint stabilization, H:Q strength imbalance may
not necessarily cause knee injuries. Most of the non-
contact athletic lower extremity injuries happen during
the closed kinetic movement such as running, landing
from jumping, pivoting, or cross-cutting. It is well
known that forces acting upon one joint inevitably af-
fect forces exerting on other linked joints during the
closed kinetic movement [31]. Van Ryssegem dis-
cussed that instability at the knee joint can cause dys-
function at ankle, hip, and eventually upper body joints
through the kinetic chain because the person would use
compensatory movement strategies in order to avoid
pain and injuries [29].
In this context, it is inferred that even if an athlete
with low HQR can successfully avoid knee injury, the
strength imbalance still has a considerable potential to
impose undesirable stress on ankle or hip joint, which
can cause non-contact lower extremity injuries. There-
fore, the purpose of this study was to investigate the re-
lationship between H:Q strength imbalance with over-
all non-contact lower extremity injuries. It was our hy-
pothesis that lower HQR would have an effect on lower
leg injuries of Division III male and female basketball
and soccer players.
2. Method
2.1. Participants
Men and women intercollegiate basketball and soc-
cer players were recruited as the participants of the
Table 1
Subject’s demographics
Male Female
Number of participants 40 42
Age (yrs) 19.97 ±1.55 19.56 ±1.34
Height (cm) 178.21 ±8.42 169.3 ±6.78
Weight (kg) 75.45 ±8.2 68.2 ±10.84
study because lower extremity injuries accounted for
approximately one quarter of all injuries in these
sports [17]. In addition, basketball and soccer mainly
involves movements which are at risk of non-contact
leginjuries such as jumping,pivoting and cross-cutting.
A total of eighty two NCAA Division III intercolle-
giate basketball and soccer players volunteered to par-
ticipate in this study (Table 1). Before the commence-
ment of the testing, all participants read and signed an
informed consent form. This study was approved by
the Institutional Review Board.
2.2. Procedure
A Biodex isokinetic dynamometer (Biodex System
3, Biodex Medical Systems, Shirley, NY) was used
to assess Q and H strength. Tests were carried out
at 60◦/s [11] and along a range of motion of at 90◦,
using a knee common protocol (sitting, axes alignment,
stabilization). Gravity correction was performed for
each limb before testing. Once the participants seated
and secured, they performed 3 repetitions of extension
and flexion as a warm-up. A single set of 3 maximal
exertions was performed bilaterally.
In this study, an injury was defined as such providing
1) it occurred as a result of participation in an organized
practice and competition; 2) it prevented the injured
athletes from participating in practices and competition
at least for two weeks; and 3) it required the injured ath-
letes seek medical attention from either athletic trainers
or team doctors [26]. Among the total lower extremity
injuries, we validated only the injuries which were non-
contact in nature. Strain, sprain, and overuse injuries
were included, and contusions were excluded for data
analysis. We also collected the history of ligamentous
injuries.
2.3. Statistical analysis
A statistical analysis was performed using SPSS 17
software (SPSS, Inc., Chicago, IL). The chi-square test
was used to examine the likelihood ratio that legs with
H:Q strength imbalance get injured. An HQR of 0.60
and above was defined as “balance”, while an HQR
D. Kim and J. Hong / Hamstring to quadriceps strength ratio and noncontact leg injuries 3
Table 2
Pre-season hamstring: Quadriceps (H: Q) ratio, in-season lower extremity injuries, and
the pearson chi-square value
HQR Lower extremity injuries Asymp. Sig.
Right Left Right Left Right Left
55.65 ±9.57 54.02 ±8.79 35 32 0.058 0.046∗
∗Indicates significant dependence (Asymp. Sig. <0.05).
Table 2 represents the pre-season mean values ±standard deviation (SD) for the ham-
strings to quadriceps (H:Q) ratios, the number of lower extremity injuries occurred
during the season, and the pearson chi-square value.
Table 3
HQR and injury cross tabulation
Criteria Number of legs Number of injuries % within total
IP1injuries
Right Left Right Left Right Left
HQR <60% 52 55 29 28 63.4% 67.1%
HQR >60% 30 27 6 4 36.6% 32.9%
1IP =Ipsilateral.
Table 3 shows the distribution of H:Q strength ratio among total legs and injured legs.
below 0.60 was defined as “imbalance”. Pearson chi-
square value below 0.05 indicates H:Q strength ratio
and rate of lower extremity injuries are dependent.
3. Results
The mean (SD) of the HQ ratio of total 82 athletes
were 0.55 ±0.09 for the right leg and 0.54 ±0.08 for
the left leg. During season, there were a total of 35
non-contact lower extremity injuries on right legs and
32 on left leg (Table 2).
Outof 35 rightleginjuries,12 weregame-related and
23 were practice-related. For the left leg, out of 32 in-
juries, the respective injuries were 8 and 24. The mean
number of practices per season for men and women’s
basketball team was 75.5, and the number of games
played for both teams was 19. For the soccer players,
the average number of practices was 47.5 and the aver-
age number of games played per season was 19.5. In
recording the number of injury, if athletes had a history
of injury on the same body parts, the injury was not in-
cluded. The results of the analysis showed that 63.4%
of the injured right legs and 67.1% of the injured left
legs had an HQR of less than 0.6 (Table 3, Fig. 1). The
difference in the number of left leg injuries between the
athletes with an HQR <0.6 and those with a ratio >
0.6 was statistically significant (p=0.046). Although
there was a notable difference in the number of right leg
injuries between the athletes with less or more than 0.6,
the pvalue didn’t reveal a significant difference (p=
0.058). However, the chi-square test demonstrated sig-
nificant likelihood ratio in the relationship between the
number of right leg injuries and the right HQR (p=
0.041).
4. Discussion
The question addressed by the present study was
whether the quadriceps and hamstrings isokinetic
strength imbalance was associated with susceptibility
to lower leg injuries. The main finding of the study
is a trend according to which injured athletes had pre-
season HQ ratio of less than 0.6 (p < 0.05). For the left
leg injuries, the result revealed the statistically signifi-
cant relationship between the lower pre-season HQ ra-
tio(<0.6) and the number of the lower leg injuries. For
the right leg injuries, the result showed no statistically
significant relationship but revealed statistically signif-
icant likelihood through the Chi Square test (p=0.03).
This noticeable difference between muscle imbalance
andinjuries is consistentwith previous reports [2,9,11].
Considering that most of the injuries from the study
were the knee joint injuries, a possible explanation for
this demonstrable relationship may arise from the knee
joint mechanism. It has been suggested that the role of
the hamstring muscles during leg extension is to assist
the anterior musculotendinous structures in preventing
anterior tibial force, by pulling the knee joint poste-
riorly, increasing joint stiffness and reducing anterior
laxity force during quadriceps loading [2].
In previous studies, the effects of muscle imbalance
have been reported specifically regarding the suscep-
4D. Kim and J. Hong / Hamstring to quadriceps strength ratio and noncontact leg injuries
Fig. 1. Distribution of HQR within legs (preseason).
tibility of the knee injury; however, in this study, we
included other lower limb injuries to elucidate possible
connections between the thigh muscle imbalance and
other common lower leg injuries among basketball and
soccerplayers. The relationshipbetween low HQR and
overall lower leg injuries shown in our study may as-
cribe to bi-articulate nature of leg muscles and neuro-
muscular compensation among lower extremity joints
in joint stabilization. Dontigny [3] suggested that the
opposing force of hamstring muscles and psoas mus-
cles act as a force couple in stabilizing a pelvis during
thenormal gait. Previousliterature revealedthat a com-
bination of weak hamstring and strong anterior muscles
could cause anterior pelvic tilt, which would demand
muscles and soft tissues around hip and trunk to work
harder in order to stabilize the lumbopelvic complex.
This may explain the result of our study that more than
a quarter of the total leg injuries were to the muscle and
tendons around the hip and knee joints (Table 4). Stabi-
lization of knee and protection of ligaments throughout
the whole flexion angle require simultaneous contrac-
tion of quadriceps, hamstring, and gastrocnemius [25].
Nyland et al. suggested that increased ankle dorsiflex-
ion and eversion moment is due to the compensatory
movement of the ankle joint in order to decelerate the
anterior translation and internal rotation of tibia during
the closed kinetic flexion at the knee joint [24].
The trend describing the dependency between
strengthimbalance and thenon-contact injury observed
in our study suggests that intervention strategies of cor-
recting strength imbalance are urgently required for the
athleteswho haveparticipated in this study,because ap-
proximately 63% of the group demonstrated muscular
imbalance. Previous literatures hinted that quadriceps-
related strength imbalance was likely caused by ha-
bitual quadriceps dominant movement strategies [16,
18,21]. Van Ryssegem emphasized that athletes must
unlearn compensatory movement pattern and learn the
proper movement technique as they train for strength
of the musculature [29]. Therefore, correct movement
training plays an important role in correcting strength
imbalance and preventing athletic non-contact injuries.
For example, traditional jump training suggested for
preventing non-contact injuries should focus more on
proper landing techniques than jumping height in or-
der to unlearn quadriceps dominant movement strate-
gies and learn to properly use hamstrings for knee joint
stabilization during the landing.
4.1. Limitation and suggestion
The speed chosen for the isokinetic strength testing
in the study was 60◦/s. One limitation is not using
other speeds for the isokinetic test. Another limitation
relates to the strength ratio used in the present study.
HQR in the study was only expressed in a conven-
tional manner, which compares concentric quadriceps
muscle actions to concentric hamstring muscle actions.
Recently more functionally relevant protocol (known
as Dynamic Control Ratio or Functional Ratio of HQ)
been suggested as more common parameter in examin-
ing HQ imbalance [1,4,7]. Evaluation of this Dynamic
Control Ratio, which eccentric hamstring muscle ac-
tions are compared to concentric quadriceps actions
(Hecc:Qcon) could have provided more functionally
relevant insights.
5. Clinical implication
To our knowledge, this is the first prospective study
to demonstrate the relationship between H:Q strength
D. Kim and J. Hong / Hamstring to quadriceps strength ratio and noncontact leg injuries 5
imbalance and overall non-contact lower extremity in-
jury rates. The result of our study indicates that an
HQR <0.6 may be a risk factor for non-contact lower
extremity injuries. In Division III setting, athletes re-
ly on unsupervised self-conditioning until the official
practice season begins. Considering the importance
of HQR in preventing lower leg injuries the feasibility
of correcting H:Q strength imbalance through unsuper-
vised training is low. Therefore, thoroughly planned
and supervised conditioning is necessary for division
III athletes. NCAA division III athletes are occupying
more than 40% of the total NCAA athletes [32]. Even
though the rationale of limiting practice seasons in di-
vision III athletes is to protect their academic activi-
ties from excessive practices, it should not be ignored
that radical limitation of supervised conditioning may
lead to engagement in intense athletic activities with
“untrained legs” which may cause more injuries.
Acknowledgments
We would like to sincerely thank the participants,
Guido Van Ryssegem, Stasinos Stavrianeas, Peter
Harmer,Judy Gordon,andGianni Maddalozzo for their
constructive advice and support.
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