ArticlePDF Available

Hamstring to quadriceps strength ratio and noncontact leg injuries: A prospective study during one season

Authors:

Abstract and Figures

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.
Content may be subject to copyright.
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.
References
[1] P. Aagaard, E.B. Simonsen, S.P. Magnusson, B. Larsson
and P. Dyhre-Poulsen, A new concept for isokinetic ham-
string:quadriceps muscle strength ratio, The American Journal
of Sports Medicine 26 (1998), 231–237.
[2] K. Bennell, H. Wajswelner, P. Lew, A. Schall-Riaucour, S.
Leslie, D. Plant and J. Cirone, Isokinetic strength testing does
not predict hamstring injury in Australian Rules footballers,
Br J Sports Med 32 (1998), 309–314.
[3] R. Coombs and G. Garbutt, Developments in the use of the
hamstrings/quadriceps ratio for the assessment of muscle bal-
ance, J Sport Sci Med 1(2002), 56–62.
[4] J. Croisier, B. Forthomme, M. Namurois, M. Vanderthom-
men and J. Crielaard, Hamstring muscle strain recurrence
and strength performance disorders, The American Journal of
Sports Medicine 30 (2002), 199–203.
[5] R.L. Dontigny, Critical analysis ofthe functional dynamics of
the sacroiliac joints as they pertain to normal gait, J Orthop
Med 27 (2005), 3–10.
[6] L.F. Draganich and J.W. Vahey, An in Vitro study of anterior
cruciate ligament strain induced by quadriceps and hamstring
forces, Journal of Orthopaedic Research 8(1990), 57–63.
[7] Z. Dvir, G.Eger, N.Halperin and A. Shklar, Thigh muscles ac-
tivity and ACL insufficiency, Clinical Biomechanics 4(1989),
87–91.
[8] T. Fukubayashi, P.A.Torzilli, M.F.Sherman and R. Warren, An
in Vitro biomechnical evaluation of anterior-posterior motion
of the knee, J Bone Joint Surg 64-A (1982), 258–264.
[9] T.G. Grace, E.R. Sweetser, M.A. Nelson, L.R. Ydens and B.J.
Skipper, Isokinetic muscle imbalance and knee-joint injuries:
a prospective blind study, J Bone Joint Surg Am 66 (1984),
734–740.
[10] L.Y. Griffin, M.J. Albohm and E.A. Arendt, Understanding
and preventing noncontact anterior cruciate ligament injuries:
a review of the Hunt Valley II Meeting, January 2005, Am J
Sports Med 34(9) (2006), 1512–1532.
[11] T.M. Heiser, J. Weber, G. Sullivan, P. Clare and R.R. Jacobs,
Prophylaxis and management of hamstring muscle injuries in
intercollegiate football players, Am J Sports Med 12 (1984),
368–370.
[12] T.E. Hewett, K.R. Ford and G.D. Myer, Anterior cruciate
ligament injuries in female athletes: part 2, a meta-analysis of
neuromuscular interventions aimed at injury prevention, Am J
Sports Med 34(3) (2006), 490–498.
[13] T.E. Hewett, T.N. Lindenfeld, J.V. Riccobene and F.R. Noyes,
The effect of neuromuscular training on the incidence of knee
injury in female athletes: a prospective study, Am J Sports
Med 27 (1999), 699–706.
[14] T.E. Hewett, G.D. Myer and K.R. Ford, Prevention of anterior
cruciate ligament injuries, Current Women’s Health Reports 1
(2001), 218–224.
[15] T.E. Hewett, G.D. Myer, K.R. Ford, R.S. Heidt, A.J. Colosi-
mo, S.G. Mclean, A.J.V. Bogert, M.V. Paterno and P. Succop,
Biomechanical measures of neuromuscular control and valgus
loading of the knee predict anterior cruciate ligament injury
risk in female athletes, Am J Sports Med 33 (2005), 492–501.
[16] T.E. Hewett, A.L. Stroupe, T.A. Nance and F.R. Noyes, Plyo-
metric training in female athletes, Am J Sports Med 24 (1996),
765–773.
[17] J.M. Hootman, R. Dick and J. Agel, Epidemiology of colle-
giate injuries for 15 sports: summary and recommendations
for injury prevention initiatives, Journal of Athletic Training
42(2) (2007), 311–319.
[18] L.J. Huston and E.M. Wojtys, Neuromuscular performance
characteristics in elite female athletes, Am J Sports Med 24(4)
(1996), 427–438.
[19] P. Kannus, Ratio of hamstring to quadriceps femoris muscles’
strength in the anterior cruciate ligament insufficient knee,
Physical Therapy 68(6) (1988), 961–965.
[20] R.C.T. Li, N. Maffulli, Y.C. Hsu and K.M. Chan, Isokinetic
strength of the quadriceps and hamstrings and functional abil-
ity of anterior cruciate deficient knees in recreational athletes,
Br J Sports Med 30 (1996), 161–164.
[21] R.A. Malinzak, S.M. Colby, D.T. Kirkendall, B. Yu and W.E.
Garrett, A comparison of knee joint motion patterns between
men and women in selected athletic tasks, Clin Biomech (Bris-
tol, Avon)16 (2001), 443–445.
[22] D.F.Murphy, D.A.J.Connolly and B.D. Beynnon. Risk factors
for lower extremity injury: a review of the literature, BR J
Sports Med 37 (2003), 13–29.
[23] G.D. Myer, K.R. Ford and T.E. Hewett, Rationale and clinical
techniques for anterior cruciate ligament injury prevention
among female athletes, J Athl Train 39(4) (2004), 352–364.
[24] J.A. Nyland, R. Shapiro, D.N.M. Caborn, A.J. Nitz and T.R.
Malone, The effect of quadriceps femoris, hamstring, and
placebo eccentric fatigue on knee and ankle dynamics during
crossover cutting, J Orthop Sports Phys Ther 25(3) (1997),
171–184.
[25] J.J. O’connor, Can muscle co-contraction protect knee liga-
ments after injury or repair? J Bone Joint Surg (BR)75-B
(1993), 41–48.
6D. Kim and J. Hong / Hamstring to quadriceps strength ratio and noncontact leg injuries
[26] J.B. Shields and A.G. Smith, Cheerleading – Related Injuries
in the United States: A Prospective Surveillance Study, J of
Athl Train 44(6) (2009), 567–577.
[27] K. Soderman, H. Alfredson, T. Pietila and S. Werner, Risk
factors for leg injuries in female soccer players: a prospective
investigation during one out-door season, Knee Surg Sports
Traumatol Arthrosc 9(2001), 313–321.
[28] M. Solomonow and M. Krogsgaard, Sensorimotor control of
knee stability. A review, Scand J Med Sci Sports 11 (2001),
64–80.
[29] G. Van Ryssegem, Kinetic Integrations. Safe Recovery
LLC, 2009. Retrieved 28 January 2009, from http://www.
kineticintegrations.com.
[30] T. Willems, Intrinsic risk factors for sports injuries to the
lower leg and ankle, Diss. Ghent University, Belgium, 2004.
[31] D.A. Winter, Kinematic and kinetic patterns in human gait:
variability and compensating effects, Human Movement Sci-
ence 3(1984), 51–76.
[32] 2009 NCAA Women’s Basketball Attendance, Available at:
http://web1.ncaa.org/web files/stats/w basketball RB/reports/
Attend/09att.pdf. Accessed 10 Jan 2009.
... Different movements (e.g., sliding, jumps, kicks, duels, cutting maneuvers), in both sports, require high levels of lower-body strength [1][2][3][4], especially at the knee joint. There is also evidence that (a) the concentric and eccentric muscle strength of the knee joint is an important parameter to success in basketball and soccer [5,6], and (b) the muscular balance of the knee joint may decrease the predisposition of athletes to knee-related injuries [5,7]. Indeed, a low hamstring-to-quadriceps ratio (below the generally accepted values) may be associated with the presence of hamstring strain and/or anterior cruciate ligament (ACL) injury in young athletes [5,[7][8][9]. ...
... There is also evidence that (a) the concentric and eccentric muscle strength of the knee joint is an important parameter to success in basketball and soccer [5,6], and (b) the muscular balance of the knee joint may decrease the predisposition of athletes to knee-related injuries [5,7]. Indeed, a low hamstring-to-quadriceps ratio (below the generally accepted values) may be associated with the presence of hamstring strain and/or anterior cruciate ligament (ACL) injury in young athletes [5,[7][8][9]. Taking all the above into consideration, the systematic and reliable evaluation of knee extensors' and flexors' muscles, and, as a result, the calculation of conventional and functional reciprocal muscle group torque ratios, must be an integral part of the training and/or rehabilitation process during the developmental years. Isokinetic dynamometers have been widely used in sport and rehabilitation settings as safe (appropriate stabilization during the test), easily applicable following an appropriate familiarization, and acceptably reliable and valid devices for assessing lower limbs muscle strength and endurance in different joints of the human body during the developmental years [10][11][12]. ...
... However, several studies in young and senior soccer or basketball players evaluated and created reference data for conventional and/or functional muscle group torque ratios of the knee joint [18,19,[33][34][35][36][37]. The examination of possible sport-related effect on the development of reciprocal muscle group torque ratios is of utmost importance, as conventional and functional ratios of the knee flexor and extensor muscles may provide valuable information for knee joint stability and function, as well as for injury prevention and rehabilitation in young athletes [5,[7][8][9]. ...
Article
Full-text available
The present study examined and compared the isokinetic peak torque and the reciprocal ratios of the knee joint between young basketball and soccer players. An amount of 100 soccer and 100 basketball players took part in this study and were separated into five equal groups (n = 20), according to their chronological age (12, 13, 14, 15, and 16 years old). The absolute concentric (CON) and eccentric (ECC) peak torque of the knee flexor and extensor muscles (at 60°/s, 180°/s) were assessed using a Cybex Norm dynamometer, and the relative peak torque (per unit of body mass), as well as the conventional (CON/CON; ECC/ECC) and functional (CON/ECC; ECC/CON) ratios, were calculated. Data analysis indicated that the basketball players had higher absolute peak torque values than the soccer players throughout their developmental ages (p < 0.05). When the isokinetic peak torque values were normalized relative to body mass, no differences were observed between basketball and soccer players in any age group (p > 0.05). Additionally, no differences were observed in conventional and functional ratios between soccer and basketball players (p > 0.05). In conclusion, it appears that, during developmental ages (12–16 years old), the isokinetic strength profile (independent of body mass affecting absolute values) of knee extensor and flexor muscles develops similarly in basketball and soccer players.
... Yamaner et al. [41] reported that soccer players are most at risk for lower limb soft tissue injury. It is assumed that an abnormal ratio of muscle strength of the knee flexors to extensors is a predictor of knee joint injury [16]. ...
... It is important that soccer training of adolescent players should lead to their sustainable development. An imbalance in the strength abilities of the knee flexors and extensors is considered as a predictor of injury [16]. In our study, there were no differences in the ratios of the strength of the antagonistic muscle groups of the knee joint in players playing in different positions on the playing field. ...
Article
Purpose Soccer is a sport in which the game is played in a very dynamic manner. It requires soccer players to be able to develop high muscle force in a very short period of time. The aim of the study was to evaluate the strength and jumping abilities of young soccer players playing in different positions on the field. Methods The study included 49 adolescent soccer players: 6 goalkeepers, 15 defenders, 17 midfielders, and 11 strikers. We measured peak torques (PT), total work (TW), and average power (AP) developed by the knee flexors and extensors under isokinetic conditions at angular velocities of 60º*s-1, 180º*s-1, and 300º*s-1 on a Biodex dynamometer, and jump height (H) and maximum power (Pmax) on a force plate. PT, AP, TW, and Pmax scores were normalized relative to body mass. Results There were no statistically significant differences between measurements of basic somatic characteristics (body height and body weight) and age at peak height velocity (APHV) as well as PT, AP, TW, H, and Pmax in players from different positions on the field. Unlike defenders, midfielders showed a significant correlation of isokinetic tests indices with jump height (r = 0.54 ÷ 0.84) and maximum relative power (r = 0.55 ÷ 0.76). Conclusions The differences in correlations are probably due to the different tasks and activities that players in different positions on the field perform during the game.
... It is assumed that H/Q ratio values exceeding 60% can effectively prevent injuries and damage to the anterior cruciate ligament (ACL) and hamstring strains. According to Kim and Hong [19], soccer players with an H/Q ratio exceeding 60% are less likely to suffer from non-contact lower limb injuries. In the event of an injury or contusion, knowledge of the values of biomechanical variables related to the athlete's lower limbs may be an important part of the rehabilitation process, as a rehabilitation target value [26]. ...
Article
Purpose Monitoring and assessing the level of lower limb motor skills using the Biodex System plays an important role in the training of football players and in post-traumatic rehabilitation. The aim of this study is to build and test an artificial intelligence-based model to assess the peak torque of the lower limb extensors and flexors. The model was based on real-world results in three groups: hearing (n = 19) and deaf football players (n = 28) and non-training deaf pupils (n=46). Methods The research used a 4-layer forward CNN neural network with two hidden layers with typical normalization for small data sets and Multilayer Perceptron (MLP) based on MatlabR2023a software with Neural Networks and Deep Learning toolkits and semiautomated learning algorithm selection using ML.NET Results The 70-90% accuracy shown in the article is sufficient here. AI provides a highly accurate, objective and efficient means of assessing neuromuscular performance, which can improve injury prevention and rehabilitation strategies. Conclusions The high accuracy shows that AI-based models can help with this, but their wider practical implementation requires further cross-disciplinary research. AI, and in particular MLP and CNN can support both training methods and various gaming aspects. The contribution of the research is to use an innovative approach to derive computational rules/guidelines from an explicitly given dataset and then identify the relevant physiological torque of the lower limb extensors and flexors in the knee joint. The model complements existing methodologies for describing physiology of peak torque of lower limbs with using fuzzy logic, with a so-called dynamic norm built into the model.
... The current study observed no significant inter-limb asymmetries or bilateral strength deficits in the KF and KE performances. The literature has reported inter-limb asymmetries differences of at least 15% [7] and bilateral strength deficits of at least 10% [40] as problematic for non-contact injuries. The analysis of PT values indicated similar scores between the PL and NPL performance both for KF and KE, which is consistent with previous investigations in young soccer players [18], while the bilateral strength deficit ranged from 1.17 to 2.13% for KF and KE, respectively. ...
Article
Full-text available
Background Muscle strength and balance abilities have been related to game performance injury prevention. This study aimed to (1) assess knee muscle strength performance based on intra- and inter-limb asymmetries, (2) investigate the relationships between knee muscle strength, body composition, and balance, and (3) analyze the variance in the overall stability index (OSI) explained by knee muscle strength indicators after controlling for age and body composition. Methods The sample included 104 young male soccer players (16.0 ± 1.6 years). Body composition, knee muscle strength, and balance ability were assessed. A paired samples t-test was used to examine differences between the preferred leg (PL) and the non-preferred leg (NPL). Pearson correlations and hierarchical multiple regression were conducted to explore the relationships between strength, body composition, and balance. Results No significant inter-limb asymmetries were detected for the knee flexors (KF) and knee extensors (KE) performance. The hamstrings-to-quadriceps ratio does not suggest the existence of intra-limb asymmetries (p = 0.06). Significant and negative correlations were found between KF (r = -0.38, p ≤ 0.01) and KE (r = -0.58, p ≤ 0.01) for the PL. Concerning the NPL, KE also revealed a significant and negative relationship with balance (r = -0.30, p ≤ 0.01). Significant and positive relationships were found between bodyweight, fat-free mass, and balance. After controlling for age and body composition, knee muscle strength could explain between 13% and 30% of the variance observed in the OSI (NPL and PL, respectively). Conclusions The results underline knee muscle strength as an important predictor of balance. Thus, training programs targeting knee muscle strength development should be considered during the season periodization by coaches and their staff throughout the players’ developmental stages.
... Our results showed no significant changes in the H/Q ratio. Research suggests that H/Q ratio values lower than 60-70% are associated with a higher risk of knee injuries, (27) gait asymmetry and variability, and impact on functional tasks. (28,29) We observed that our participants presented adequate results, with values between 70-75%. ...
Article
Full-text available
Background Resistance training with instability (REI) emerged as a promising training modality for older adults aiming to counteract age-related changes. Objectives We compared the effects of 12 weeks of REI and traditional resistance exercise (RE) on muscle strength in older adults with cognitive impairment. We further explored if total training volume (TTV) significantly differs among training groups. Methods This is a secondary analysis of the REI study. Participants were randomly assigned to REI (n=22) or RE (n=23). RE protocol involved moderate-intensity, free-weight, and machines-based resistance exercises (3 sets, 10–15 repetitions). REI received a similar training protocol, in which exercises were simultaneously performed with instability/unstable devices (e.g., squat exercise under a foam pad or Bosu® ball). Maximal isometric strength and isokinetic parameters were assessed at baseline and after completion of a 12-week intervention through a hydraulic handgrip and isokinetic dynamometer, respectively. TTV (sets × repetitions × load) was computed based on external training load over the 12 weeks. Results No differences were observed between groups (p=.35) after the intervention. Over 12 weeks, REI and RE improved isometric handgrip strength (p<.001) and isokinetic performance (p=.04). We also did not find differences in the TTV between training groups (p=.28). Conclusion We demonstrated that both REI and RE training induced similar gains in muscle strength. Combining unstable surfaces/instability devices did not hamper TTV, which may have clinical applications in the context of exercise for older adults.
... ,44 employed 300 degrees per second angular velocity, while only one study44 utilized 180 degrees per second angular velocity. Notably, isokinetic testing at a low angular speed (60 degrees per second) has been deemed a reliable indicator of non-contact leg injuries in National College American Association athletes, as demonstrated by Kim et al.61 . Additionally, Sugiura et al.62 observed a strong correlation between hamstring injuries in elite sprinters and hamstring muscle weakness when testing at lower speeds.62 ...
Article
Full-text available
Background: Hamstring strain injury (HSI) is the most common cause of missing practices and sporting events among running-related athletes. The incidence rate of recurrence in individuals with HSI ranges from 12% to 63%. While various risk factors for HSI have been identified, the alterations and role of biomechanical factors as potential causes of injury have been largely overlooked. Objectives: To report the critical biomechanical parameters assessed among running-related athletes with a recurrent HSI and to present common testing protocols in assessing the biomechanical parameters among running-related athletes with a recurrent HSI. Methods: Eligibility Criteria: Included studies investigated biomechanical parameters assessed among collegiate or elite running-related athletes with recurrent HSI. Sources of Evidence: This scoping review was registered in OSF and was conducted based on PRISMA-ScR. Six electronic databases were systematically searched from 1993 to May 2022. Charting Methods: The reviewers created a data charting tool for the scoping review. Results: Out of 874 articles, a total of 10 articles were included in the scoping review. The critical biomechanical parameters assessed include trunk flexion, hip flexion, and knee extension angles (kinematic variables), flight and stance times and velocity (spatiotemporal variables), and EMG activity of biceps femoris, semitendinosus, semimembranosus, vastus lateralis, and rectus femoris, knee flexion and extension angle peak joint torque (kinetic variables). The most common running test protocols used were the 30-meter overground repeated sprint test, a percentage of maximum running velocity (treadmill), and repeated sprints on a non-motorized treadmill. The most common protocols for isokinetic muscle testing were 60 degrees (concentric), 300 degrees (concentric), and 180 degrees (eccentric) per second angular velocities. Conclusion: The review demonstrated a need for more research on this topic, leading to only limited biomechanical parameters being discussed in the literature. This underscores the need for more rigorous research that could have practical applications for athletes and coaches.
... It has been reported that a hamstring/ quadriceps (H/Q) strength ratio of less than 60% and more than 10-15% of muscle strength asymmetry is associated with lower extremity injuries. In addition, maintaining the strength ratio between the agonist and antagonist muscles in the lower extremities has an important place in both the prevention of sports injuries and the elimination of losses that may occur in athletic performance (8,9,10,15,16,18,19,22). A high incidence of knee injuries has been reported in sports games that require intense physical activity, such as football. ...
Article
Full-text available
Problem Statement: The aim of the study was to compare the angle-specific torque value and the peak torque values of isokinetic knee strength in both lower extremities in extension and flexion phases at different angular velocities between male and female soccer players and to determine whether there is a difference between the genders. Methods: 26 female and male professional football players were included. The knee strengths of both lower extremities of the participants were evaluated using isokinetic dynamometry at 60°/sec and 180°/sec. The peak torque (PT) (Newton meters, Nm), body mass-normalized PT (Nm/kg), and H/Q ratios (%), angle-specific ratio (ASR) at 30° and bilateral strength deficit of the quadriceps and hamstring muscles were recorded for the dominant and non-dominant legs. Results: There was no significant difference in H/Q ratio and ASR between the sexes. There was a moderate correlation between H/Q ratio and ASR. Female players presented significantly higher bilateral deficits for flexor muscles in both angular velocities (p<0.05). Discussion: The results of the study can be summarized as follows: H/Q ratio depends on angular velocity in isokinetic strength testing; compared to men athletes, female athletes have a higher tendency towards asymmetry; and there is a positive correlation between the H/Q ratio and ASR values. Conclusion: The H/Q ratio is different at various knee flexion angles and future studies should investigate if these approaches are better to identify risc factors.
... It is reported that bilateral asymmetry (>10 %) and unilateral asymmetry (hamstrings to quadriceps strength ratio <72 % at an isokinetic velocity of 120 • /s) knee strength ratios are associated with an increased incidence of injuries (Daneshjoo et al., 2013). Hamstrings to quadriceps concentric strength ratio (CSR) is one of the important predictors of knee function (Kim and Hong, 2011). Moreover, strength asymmetry is effect on the gait asymmetry, variability and functional tasks among the older adults Laroche et al., 2012). ...
Article
Background: Asymmetry of lower limb muscle strength and knee proprioception have been linked with risk of falling among elderly with and without history of falling. Objective: This study aimed to determine the comparison of hamstrings to quadriceps strength ratio (CSR) and bilateral knee strength ratio, hamstrings and quadriceps muscles' strength and knee proprioception in elderly male fallers and non-fallers. Methods: Sixty older adults, 65 years and older were recruited into faller (fell twice in the last six months) and non-faller groups. Then, the knee extension and flexion strength and proprioception at 45° knee flexion for the dominant leg (DL) and non-dominant legs (NDL) were measured with a Biodex Isokinetic Dynamometer. Results: The strength of quadriceps and hamstring muscles showed significantly higher values in DL by 5.4 %, 9.2 % and NDL by 11.7 %, 15.5 % in the non-faller compared to the faller (p < 0.05). Significantly greater bilateral asymmetry (>10 % difference) was observed with the quadriceps (p = 0.014, -7.9 %, ES = 0.76) and hamstrings (p < 0.001, -18.4 %, ES = 1.5) as well as reduced CSR (<72 %) by 7.6 % in DL (ES = 0.64) and 11.3 % in NDL (ES = 0.81) with fallers versus non-fallers. Significantly less knee proprioception was found with the DL by -1.5 % (ES = 1.15) and NDL (ES = 1.50) by -2.1 % (p < 0.001) in non-faller compared to faller. Conclusion: It concluded that non-fallers have better strength symmetry, bilateral and unilateral knee strength ratios as well as more sensitive knee proprioception than fallers. It is suggestive that older adult fallers may need to improve bilateral knee strength symmetry and proprioception to prevent the risk of falling.
Article
Background In National Collegiate Athletic Association (NCAA) soccer athletes, men have higher rates of hip and groin strains, whereas women have higher rates of knee ligament injuries. Strength imbalances of the hip and thigh, specifically in agonist–antagonist muscles, are known risk factors for these injuries. Objective To perform hip and thigh strength assessments in NCAA soccer players to evaluate for differences between genders and correlations with gender‐specific injury patterns. Design With a handheld dynamometer, weight‐normalized isometric strength of six muscle groups (hip abductors, hip adductors, hip flexors, hip extensors, knee flexors, knee extensors) was calculated in NCAA soccer players. The strength ratio of each agonist–antagonist muscle was also calculated (hip abductors/adductors, hip flexors/extensors, knee extensors/flexors). Participants Thirty‐six NCAA soccer players (18 men, 18 women) from a single NCAA Division III institution. Interventions Not applicable. Main Outcome Measures Weight‐normalized strength of six muscle groups and their agonist–antagonist strength ratios were compared between genders using linear mixed‐effects models. Results Compared with male players, female players had decreased weight‐normalized strength for hip abduction (0.170 vs. 0.204, p = .012) and hip extension (0.172 vs. 0.211, p = .021). Otherwise, weight‐normalized strength was similar between genders. When comparing agonist–antagonist strength ratios, there was a significant difference between female and male players for hip flexion:extension (1.70 vs. 1.35, p = .008), whereas the hip abduction: adduction ratio did not reach statistical significance (1.45 vs. 1.62, p = .080). Conclusions NCAA male and female soccer players had different hip strength profiles that fit their injury patterns. Male NCAA soccer players have higher rates of hip and groin strains, and men in the cohort had strength ratios that were deficient in the hip flexors and adductors compared with women. Female NCAA soccer players have higher rates of knee sprains and anterior cruciate ligament tears, and women in the cohort had strength ratios that were deficient in the hip abductors and extensors, which function to stabilize the knee. These strength disparities could be the focus of future gender‐specific soccer injury prevention programs.
Article
Full-text available
The purpose of this paper is to describe the basic structure of the sacroiliac joint, the loading sequence of the primary ligaments, its function during normal gait and the supportive muscle functions. The goal of treatment of low back and pelvic pain should be the restoration of normal function and so it is important to understand just how the low back and the pelvis normally function.The sacroiliac joint has been assumed to be structurally so strong as to be immune to injury through minor trauma. Motion in the joint is minimal and its function has been obscure. There is essentially no motion in the sacroiliac joint on a transverse axis when the sacrum is loaded with the superincumbent weight and the pelvis is symmetrical as in relaxed standing. During normal gait, however, when the pelvis moves into asymmetry, the sacrum flexes laterally and rotates toward the side of loading to drive rotation and counter rotation of the trunk during normal gait to decrease the loading impulse. Primary loading o...
Article
Isokinetic moment ratios of the hamstrings (H) and quadriceps (Q) muscle groups, and their implication in muscle imbalance, have been investigated for more than three decades. The conventional concentric H/Q ratio with its normative value of 0.6 has been at the forefront of the discussion. This does not account for the joint angle at which moment occurs and the type of muscle action involved. Advances towards more functional analyses have occurred such that previous protocols are being re-examined raising questions about their ability to demonstrate a relationship between thigh muscle imbalance and increased incidence or risk of knee injury. This article addresses the function of the hamstring-quadriceps ratio in the interpretation of this relationship using the ratios Hecc/Qcon (ratio of eccentric hamstring strength to concentric quadriceps strength, representative of isolated knee extension) and Hcon/Qecc (ratio of concentric hamstring strength to eccentric quadriceps strength, representative of isolated knee flexion).
Article
The purpose of this study was to examine the dynamic relationship between the quadriceps femoris and hamstrings in anterior cruciate ligament (ACL) insufficiency. Thirty-five young active patients with an untreated complete tear of the ACL took part in the study. Using a KINCOM isokinetic dynamometer, the dynamic capacity of each muscle group at 30° in concentric and eccentric exertion in both the deficient and sound knee was measured. Findings demonstrated a significant reduction (P<0.05) in the torque produced by the deficient-side quadriceps compared to the sound side but no significant variations in the hamstring torque. Discussion of the findings considers a possible involvement of neurophysiological inhibition of the quadriceps as a cause for the observed weakness.
Article
In the presence of fairly well defined kinematic patterns in human walking there was considerable variability at the kinetic level. Intra-subject variability of joint moment patterns over the stride period was high at the knee and hip, but low at the ankle and in a recently defined total limb pattern, called support moment. A similar profile of variability was evident for inter-subject trials at slow, natural and fast cadences, with the percentage variability at the knee and hip decreasing as cadence increases. These moment of force patterns were not random, but were highly correlated. Such a finding points to compensating mechanisms by the biarticulate muscles crossing these joints. Also shown was the fact that these compensating patterns were highly predictable from link segment theory.
Article
Background: Women have higher non-contact anterior cruciate ligament injury rate than men do in sport activities. Non-contact anterior cruciate ligament injuries frequently occur in sports requiring cutting tasks. Alternated motor control strategies have identified as a potential risk factor for the non-contact anterior cruciate ligament injuries. The purpose of this study was to compare the patterns of knee kinematics and electromyographic activities in running, side-cutting, and cross-cutting between men and women recreational athletes. Methods: Three-dimensional kinematic data of the knee and electromyographic data of selected muscles across the knee joint were collected for 11 men and 9 women recreational athletes in running, side-cutting, and cross-cutting. Regression analyses with dummy variables for comparison of knee motion patterns between men and women. Results: Women tend to have less knee flexion angles, more knee valgus angles, greater quadriceps activation, and lower hamstring activation in comparison to men during the stance phase of each of the three athletic tasks. Literatures suggest these alternated knee motion patterns of women tend to increase the load on the anterior cruciate ligament. Conclusion: Women on average may have certain motor control strategies that may alter their knee motion patterns. Women's altered knee motion patterns may tend to increase the load on the anterior cruciate ligament in the selected athletic tasks, which may contribute to the increased anterior cruciate ligament injury rate among women. Relevance: Non-contact anterior cruciate ligament injuries frequently occur in sports. Altered motor control strategies and lower extremity motion patterns are likely to play an important role in non-contact anterior cruciate ligament injuries. Non-contact anterior cruciate ligament injuries may be prevented by correcting altered motor control strategies and associated lower extremity motion patterns through certain training programs.
Article
Conventionally, the hamstring:quadriceps strength ratio is calculated by dividing the maximal knee flexor (hamstring) moment by the maximal knee extensor (quadriceps) moment measured at identical angular velocity and contraction mode. The agonist-antagonist strength relationship for knee extension and flexion may, however, be better described by the more functional ratios of eccentric hamstring to concentric quadriceps moments (extension), and concentric hamstring to eccentric quadriceps moments (flexion). We compared functional and conventional isokinetic hamstring: quadriceps strength ratios and examined their relation to knee joint angle and joint angular velocity. Peak and angle-specific (50 degrees, 40 degrees, and 30 degrees of knee flexion) moments were determined during maximal concentric and eccentric muscle contractions (10 degrees to 90 degrees of motion; 30 and 240 deg/sec). Across movement speeds and contraction modes the functional ratios for different moments varied between 0.3 and 1.0 (peak and 50 degrees), 0.4 and 1.1 (40 degrees), and 0.4 and 1.4 (30 degrees). In contrast, conventional hamstring:quadriceps ratios were 0.5 to 0.6 based on peak and 50 degrees moments, 0.6 to 0.7 based on 40 degrees moment, and 0.6 to 0.8 based on 30 degrees moment. The functional hamstring:quadriceps ratio for fast knee extension yielded a 1:1 relationship, which increased with extended knee joint position, indicating a significant capacity of the hamstring muscles to provide dynamic knee joint stability in these conditions. The evaluation of knee joint function by use of isokinetic dynamometry should comprise data on functional and conventional hamstring:quadriceps ratios as well as data on absolute muscle strength.
Article
Cheerleading injuries are on the rise and are a significant source of injury to females. No published studies have described the epidemiology of cheerleading injuries by type of cheerleading team and event. To describe the epidemiology of cheerleading injuries and to calculate injury rates by type of cheerleading team and event. Prospective injury surveillance study. Participant exposure and injury data were collected from US cheerleading teams via the Cheerleading RIO (Reporting Information Online) online surveillance tool. Athletes from enrolled cheerleading teams who participated in official, organized cheerleading practices, pep rallies, athletic events, or cheerleading competitions. The numbers and rates of cheerleading injuries during a 1-year period (2006-2007) are reported by team type and event type. A cohort of 9022 cheerleaders on 412 US cheerleading teams participated in the study. During the 1-year period, 567 cheerleading injuries were reported; 83% (467/565) occurred during practice, 52% (296/565) occurred while the cheerleader was attempting a stunt, and 24% (132/563) occurred while the cheerleader was basing or spotting 1 or more cheerleaders. Lower extremity injuries (30%, 168/565) and strains and sprains (53%, 302/565) were most common. Collegiate cheerleaders were more likely to sustain a concussion (P = .01, rate ratio [RR] = 2.98, 95% confidence interval [CI] = 1.34, 6.59), and All Star cheerleaders were more likely to sustain a fracture or dislocation (P = .01, RR = 1.76, 95% CI = 1.16, 2.66) than were cheerleaders on other types of teams. Overall injury rates for practices, pep rallies, athletic events, and cheerleading competitions were 1.0, 0.6, 0.6, and 1.4 injuries per 1000 athlete-exposures, respectively. We are the first to report cheerleading injury rates based on actual exposure data by type of team and event. These injury rates are lower than those reported for other high school and collegiate sports; however, many cheerleading injuries are preventable.
Article
Strain in the anteromedial fibers of the anterior cruciate ligament [ACL(am)] was studied in six cadaver knees. ACL(am) strain was measured in five knees during the application of isometric quadriceps forces alone and simultaneously applied isometric quadriceps and hamstrings forces at 10 degrees increments from 0 degrees to 90 degrees of knee flexion. ACL(am) strain during muscle loading was measured with respect to the ACL(am) strain measured with the knee in its resting position (neutral or near neutral position). A sixth knee was used to investigate the reproducibility of the resting position and quadriceps-induced ACL(am) strains. The strains induced in the ACL(am) by the quadriceps were significantly greater than 0 at knee flexion angles from 0 to 40 degrees and not significantly different from 0 for 50 to 90 degrees. The ACL(am) strains induced by simultaneously applied hamstrings and quadriceps forces were not significantly different from 0 at any of the knee flexion angles tested. Simultaneously applied hamstrings and quadriceps forces significantly reduced ACL(am) strain at 10, 20, and 90 degrees of knee flexion compared to the ACL(am) strain induced by quadriceps forces alone. The hamstrings are potentially capable of both significantly reducing and negating quadriceps-induced ACL(am) strain at 10 and 20 degrees of knee flexion.