The importance of research in the arena of sports injury prevention
cannot be overstated. Anyone can come forth with a technique or
theory, but while guided by the art of experience and performance,
it should be based on science and research to validate its effectiveness.
By holding a technique or theory to the scrutiny of research, we
can more confidently train athletes in way that is safer and more
effective.
The following are just some of the research studies from the past
20 years or so which have helped shape the approach at Daisey Physical
Therapy and the Center for Human Performance
with regard to sports injury prevention. All of these articles are
accessible through the National Library of Medicine at www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed
KNEE AND ACL INJURY PREVENTION
Females hamstring-quadriceps ratio, jumping form, and landing
forces can improve with specific training, resulting in greater
knee stability during sports performance
Hewett TE, et al: Plyometric training in female athletes: Decreased
impact forces and increased hamstring torques. Am J Sports Med 1996;
24: 765-76.
Landmark study showing that a training protocol emphasizing soft
landing forces, hamstring training, and correct jumping mechanics
resulted in the following changes in a group of female athletes:
- Peak knee
landing forces from a volleyball block jump decreased 22%
- Knee adduction
and abduction moments (medially and laterally directed torques)
decreased approximately 50%
- Hamstring
muscle power increased 44% with training on the dominant side
and 21% on the non-dominant
- Peak torque
ratios of male athletes were significantly greater than those
of untrained female athletes, but similar to those of trained
females
- Mean vertical
jump height increased approximately 10%.
Females
who train to improve landing forces, hamstring-quadriceps ratio, and
jumping form have less non-contact injuries while playing sports
Hewitt TE, et al: Neuromuscular training and knee injury in female
athletes: A prospective study. Am J Sports Med 1999; 27: 699-705.
Monitored three groups of female athletes: one that trained in the
program outlined in the 1996 study by Hewitt before sports participation,
one that did not train in the program, and a group of untrained male
athletes throughout the high school soccer, volleyball, and basketball
seasons. There were 14 serious knee injuries in the 1263 athletes
tracked through the study. Ten of 463 untrained female athletes sustained
serious knee injuries (8 non-contact). Two of 366 trained female athletes
sustained serious knee injuries (0 non-contact), Two of 434 male athletes
sustained serious knee injuries (1 non-contact). Untrained female
athletes had a 3.6 times higher incidence of knee injury than trained
female athletes and 4.8 times higher than male athletes. The incidence
of knee injury in trained female athletes was not significantly different
from that in untrained male athletes. First study of this scale to
show a decreased incidence of knee injury in female athletes after
a specific plyometric training program.
Male and
female athletes activate their leg muscles differently, which could
increase the likelihood of knee injury in females
Zeller BL, McCrory JL, Kibler WB, Uhl TL: Differences in Kinematics
and Electromyographic Activity Between Men and Women during the Single-Legged
Squat. Am J Sports Med 2003; 31:449-456.
Male and female were asked to perform a single leg squat. Muscle activation
patterns and joint positions during the squat were measured.
- The knee
of the squat leg turned inward (valgus movement) much more with
the female athletes because the femur moved inward (hip adduction).
- The gluteal
muscles (gluteus medius) were much less active (47% less) in females.
This would contribute greatly to the inward motion of the femur
and knee.
- The quadriceps
muscles were much more active in the female athletes (30-56% more
active, depending on which part of the quadriceps).
- The hamstring
muscle tested was 36% less active in the female athletes
Generalized
joint laxity, hyperextension of the knee and a low hamstring-to-quadriceps
ratio increase the risk of injury in soccer players
Soderman K , et al: Risk factors for leg injuries in female soccer
players: a prospective investigation during one out-door season.
Knee Surg Sports Traumatol Arthrosc. 2001 Sep;9(5):313-21.
Studied age, anatomical alignment, generalized joint laxity, thigh
muscle torque, muscle flexibility, ligamentous laxity of the knee
and ankle joints, recent injuries, and duration of soccer exposure
to predict soccer injury. In 50 players there were 61 traumatic injuries,
and 17 players sustained 19 overuse injuries. Variables significantly
increasing the risk of traumatic leg injuries included generalized
joint laxity, low postural sway of the legs, hyperextension of the
knee joint, and a low hamstring-to-quadriceps ratio during concentric
action. All five players who suffered an anterior cruciate ligament
injury during the study period had a lower hamstring-to-quadriceps
ratio during concentric action on the injured side than on their non-injured
side.
Demonstrated
the role of the hamstrings as an ACL protector
More RC, et al: Hamstrings - an anterior cruciate ligament protagonist:
An in-vitro study. Am J Sports Med 1993; 21: 231-7.
Study
that suggested it is possible to prevent ACL injuries among handball
players with a specific neuromuscular training program
Myklebust G, et al: Prevention of anterior cruciate ligament injuries
in female team handball players: a prospective intervention study
over three seasons. Clin J Sport Med. 2003 Mar;13(2):71-8.
Females
land with greater ground reaction forces to the knee than males
Salci Y, Kentel BB, Heycan C, Akin S, Korkusuz F: Comparison of
landing maneuvers between male and female college volleyball players.
Clin Biomech (Bristol, Avon). 2004 Jul;19(6):622-8.
Eight female and eight male college volleyball players performed spike
and block landings from 40 and 60 cm height platforms. Lower extremity
joint kinetics and kinematics, and leg muscle strengths were recorded.
Females demonstrated significantly lower knee and hip flexion angles
compared to their male counterparts in knee flexion at 40 cm spike
and hip flexion at 40 cm block landings. Group comparison also revealed
that male players' peak knee extensor moment at 60 cm block landing
was significantly different than female players. Additionally, female
players applied significantly higher normalized ground reaction forces
and males knee flexion angles and thigh muscle strength results positive
and highly correlated but relation could not found in females. It
is likely that females may not use their thigh muscles as effective
as males in landing. CONCLUSION: Female volleyball players initiate
different lower extremity mechanics during landings than that of males.
Comparing
Leg Extension to the Squat and Leg Press. Showed high anterior shear
forces (248N) at the knee during open chain knee extension (ACL stress).
High posterior shear forces (ACL protective) and much greater hamstring
forces with squat and leg press
Wilk KE, et al: A comparison of tibiofemoral joint forces and
electromyographic activity during open and closed kinetic chain exercises.
Am J Sports Med 1996 Jul-Aug;24(4):518-27
Female
athletes have greater knee valgus/varus (side-to-side) motion during
landing as compared to males
Ford KR, Myer GD, Hewett TE: Valgus knee motion during landing
in high school female and male basketball players. Med Sci Sports
Exerc. 2003 Oct;35(10):1745-50.
Eighty-one high school basketball players, 47 female and 34 male.
Valgus knee motion and varus-valgus angles during a drop vertical
jump (DVJ) were calculated for each subject. Female athletes landed
with greater total valgus knee motion and a greater maximum valgus
knee angle than male athletes. Female athletes had significant differences
between their dominant and nondominant side in maximum valgus knee
angle. CONCLUSION: The absence of dynamic knee joint stability may
be responsible for increased rates of knee injury in females but is
not normally measured in athletes before participation.
Differences
in females vs. males during sidestep cutting
McLean SG, Lipfert SW, van den Bogert AJ: Effect of gender and
defensive opponent on the biomechanics of sidestep cutting. Med Sci
Sports Exerc. 2004 Jun;36(6):1008-16.
Eight male and eight female subjects performed sidestep cuts with
and without a static defensive opponent while 3D motion and ground
reaction force data were recorded. Females had less hip and knee flexion,
hip and knee internal rotation, and hip abduction. Females had higher
knee valgus and foot pronation angles, and increased variability in
knee valgus and internal rotation. Increased medial ground reaction
forces and flexion and abduction in the hip and knee occurred with
the defensive player for both genders. CONCLUSIONS: A simulated defense
player causes increased lower limb movements and forces, and should
be a useful addition to laboratory protocols for sidestepping. Gender
differences in the joint kinematics suggest that increased knee valgus
may contribute to ACL injury risk in women, and that the hip and ankle
may play an important role in controlling knee valgus during sidestepping.
Consideration of the entire lower extremity contributes to an understanding
of injury mechanisms and may lead to better training programs for
injury prevention.
IMPORTANCE OF HIP MUSCLE DOMINANCE
TO INJURY PREVENTION
Decreased unilateral hip extension strength found in female
athletes who were injured or complained of low back pain
Nadler SF et al: The relationship between lower extremity injury,
low back pain, and hip muscle strength in male and female collegiate
athletes. Clin J Sport Med 2000 Apr;10(2):89-97
A significant difference in side-to-side symmetry of maximum hip extension
strength was observed in female subjects who reported LE injury or
LBP as compared to those who did not. Side-to-side difference in hip
strength, however, did not differ between male athletes, regardless
of reported LE injury or LBP status.
Female
athletes with weak hip abductors were more likely to require treatment
for low back pain.
Nadler SF et al: Hip muscle imbalance and low back pain in athletes:
influence of core strengthening. Med Sci Sports Exerc 2002 Jan;34(1):9-16
No significant advantage was found with core strengthening in reducing
LBP occurrence.
Female
athletes have more hip internal rotation maximum displacement during
single-leg land and forward hop
Lephart SM et al: Gender differences in strength and lower extremity
kinematics during landing. Clin Orthop 2002 Aug;(401):162-9
Study that looked at kinematic, vertical ground reaction forces, and
strength variables in healthy collegiate female basketball, volleyball,
and soccer players compared with matched male subjects. During the
single-leg land and forward hop, females had:
- Significantly
more hip internal rotation maximum angular displacement
- Less lower
leg internal rotation time to maximum angular displacement
- Significantly
less peak torque to body mass for the quadriceps and hamstrings
than males
Females
demonstrated significantly less peak hip abduction than did males.
Otherwise, there were no gender differences in selected peak hip and
knee joint kinematics and moment
Pollard CD, Davis IM, Hamill J: Influence of gender on hip and knee
mechanics during a randomly cued cutting maneuver. Clin Biomech (Bristol,
Avon). 2004 Dec;19(10):1022-31.
Injury
prevention effect from plyometric training may occur due to greater
hip activation strategies of hip abductor/adductor co-activation
Chimera NJ, Swanik KA, Swanik CB, Straub SJ: Effects of Plyometric
Training on Muscle-Activation Strategies and Performance in Female
Athletes. J Athl Train. 2004 Mar;39(1):24-31.
Twenty healthy National Collegiate Athletic Association Division I
female athletes. CONCLUSIONS: The increased preparatory adductor activity
and abductor-to-adductor co-activation represent preprogrammed motor
strategies learned during the plyometric training. These data strongly
support the role of hip-musculature activation strategies for dynamic
restraint and control of lower extremity alignment at ground contact.
Plyometric exercises should be incorporated into the training regimens
of female athletes and may reduce the risk of injury by enhancing
functional joint stability in the lower extremity.
HAMSTRING INJURY
Muscle imbalances of the legs, hamstring strength, and the
ratio of the knee flexors to extensors are related to the occurrence
of hamstring strains
Yamamoto T. Relationship between hamstring strains and leg muscle
strength. A follow-up study of collegiate track and field athletes.
Sports Med Phys Fitness 1993 Jun;33(2):194-9.
Strength
imbalances in the hamstrings can lead to injury in sports
Knapik JJ et al: Preseason strength and flexibility imbalances
associated with athletic injuries in female collegiate athletes.
Am J Sports Med 1991 Jan-Feb;19(1):76-81
Athletes experienced more lower extremity injuries if they had: 1)
a right knee flexor 15% stronger than the left knee flexor at 180
deg/sec; 2) a right hip extensor 15% more flexible than the left hip
extensor; 3) a knee flexor/knee extensor ratio of less than 0.75 at
180 deg/sec. There was a trend for higher injury rates to be associated
with knee flexor or hip extensor imbalances of 15% or more on either
side of the body.
Occurrence
of hamstring strains was much lower in a group of soccer players who
engaged in a pre-season eccentric strength training program
Askling C, Karlsson J, Thorstensson A: Hamstring injury occurrence
in elite soccer players after preseason strength training with eccentric
overload. Scand J Med Sci Sports. 2003 Aug;13(4):244-50.
Occurrence of hamstring strain injuries was lower a the training group
(3/15) than in a control group (10/15). There were significant increases
in strength and speed in the training group. However, there were no
obvious coupling between performance parameters and injury occurrence.
Results indicate that the addition of specific preseason strength
training for the hamstrings - including eccentric overloading - would
be beneficial for elite soccer players, both from an injury prevention
and from performance enhancement point of view.
Effective methods
for hamstring rehabilitation
Sherry MA, Best TM: A comparison of 2 rehabilitation programs
in the treatment of acute hamstring strains. J Orthop Sports Phys
Ther. 2004 Mar;34(3):116-25.
CONCLUSIONS: A rehabilitation program consisting of progressive agility
and trunk stabilization exercises is more effective than a program
emphasizing isolated hamstring stretching and strengthening in promoting
return to sports and preventing injury recurrence in athletes suffering
an acute hamstring strain.
STRETCHING AND THE RELATIONSHIP
TO INJURY PREVENTION
Pre-exercise muscle stretching did not prevent injury
in army recruits. Fitness level and age predicted injury risk
Pope RP, et al: A randomized trial of pre-exercise stretching
for prevention of lower-limb injury. Med Sci Sports Exerc 2000 Feb;32(2):271-7
CONCLUSION: A typical muscle stretching protocol performed during
pre-exercise warm-ups does not produce clinically meaningful reductions
in risk of exercise-related injury in army recruits. Fitness may be
an important, modifiable risk factor.
Past injury,
and posture, but not flexibility predisposes athletes to further injury
Watson AW: Sports injuries related to flexibility, posture, acceleration,
clinical defects, and previous injury, in high-level players of body
contact sports. Int J Sports Med. 2001 Apr;22(3):222-5.
Study analyzed 82 players of gaelic football, soccer and hurling over
two seasons. Days of injury during the second 12-month period could
be predicted from (1) the days of injury during the first 12-month
period, (2) posture, (3) acceleration over 10m from a standing start,
and (4) the number of musculo-skeletal clinical defects. Flexibility
scores were not found to be significant predictors of injury.
Nice review
article on sports injury prevention
Parkkari J, Kujala UM, Kannus P. Is it possible to prevent sports
injuries? Review of controlled clinical trials and recommendations
for future work. Sports Med 2001;31(14):985-95
Found among other things:
The general injury rate can be reduced by a multifactorial injury
prevention program in soccer, or by ankle disk training, combined
with a thorough warm-up. Ankle sprains can be prevented by ankle
supports (i.e. semirigid orthoses or air-cast braces) in high-risk
sporting activities, such as soccer and basketball, and stress fractures
of the lower limb by the use of shock-absorbing insoles in footwear.
Soccer
athletes with tight hamstrings and quadriceps are more likely to injure
them playing soccer. Did not apply to the calf or groin.
Witvrouw E, et al: Muscle flexibility as a risk factor for developing
muscle injuries in male professional soccer players. A prospective
study. Am J Sports Med. 2003 Jan-Feb;31(1):41-6.
Does not show that stretching before competition would lead to an
injury prevention effect.
Excellent
review of stretching and the non-relationship to injury prevention
Shrier I. Stretching before exercise does not reduce the risk
of local muscle injury: a critical review of the clinical and basic
science literature. Clin J Sport Med 1999 Oct;9(4):221-7
- Three (all
prospective) of the four clinical articles that suggested stretching
was beneficial included a co-intervention of warm-up. The fourth
study (cross-sectional) found stretching was associated with less
groin/buttock problems in cyclists, but only in women.
- Five studies
suggesting no difference in injury rates between stretchers and
nonstretchers (3 prospective, 2 cross-sectional)
- Three suggested
stretching was detrimental (all cross-sectional).
The
review of the basic science literature suggested five reasons
why stretching before exercise would not prevent injuries.
- In animals,
immobilization or heating-induced increases in muscle compliance
cause tissues to rupture more easily.
- Stretching
before exercise should have no effect for activities in which
excessive muscle length is not an issue (e.g., jogging).
- Stretching
will not affect muscle compliance during eccentric activity, when
most strains are believed to occur.
- Stretching
can produce damage at the cytoskeleton level.
- Stretching
appears to mask muscle pain in humans.
CONCLUSION: The
basic science literature supports the epidemiologic evidence that
stretching before exercise does not reduce the risk of injury.
Another
excellent review on the role of stretching as it relates to injury
prevention
Herbert RD, Gabriel M. Effects of stretching before and after
exercising on muscle soreness and risk of injury: systematic review.
BMJ. 2002 Aug 31;325(7362):468.
Hamstring
strains were associated with hamstring weakness, but not flexibility
Orchard J, et al: Pre-season hamstring muscle weakness associated
with hamstring muscle injury in Australian footballers. Am J Sports
Med. 1997 Jan-Feb;25(1):81-5.
Injuries to
soccer players were decreased 21 – 30% with an intervention program
that included an improved warm-up, cool-down, taping of unstable ankles,
adequate rehabilitation, and performance of drills to improve balance,
stability of the ankle, and strength & flexibility of the trunk,
hips.
Junge A, et al: Prevention of soccer injuries: a prospective intervention
study in youth amateur players. Am J Sports Med. 2002 Sep-Oct;30(5):652-9.
MISCELLANEOUS
Athletes who did not participate in an injury prevention
for ankle stability training were 5.9 times more likely to be injured
(traumatic and overuse injuries) among handball players
Wedderkopp N, et al: Prevention of injuries in young female players
in European team handball. A prospective intervention study. Scand
J Med Sci Sports. 1999 Feb;9(1):41-7.
Decreased Shoulder internal rotation strength and range-of-motion
in symptomatic swimmers
Bak K, Magnusson SP Shoulder strength and range of motion in symptomatic
and pain-free elite swimmers. Am J Sports Med. 1997 Jul-Aug;25(4):454-9.
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