ACL Non-Contact Injuries Part III (by guest contributor Anna Napolitano)

The third and final installment of the ACL Non-Contact injury series by Guest Contributor Anna Napolitano. Thanks Anna for a great series!


Studies show volleyball and basketball female athletes are at increased risk of NCACL injury due to ankle, knee and hip joint kinematic/kinetic asymmetries during jump landings.  Therefore it should be safe to state ALL jumping activities can place the athlete at greater risk of NCACL injury.  However, this is not true with female dancers.  It has been reported dancers have a much lower incidence of NCACL injuries (0.009 NCACL injuries per 1000 exposures) compared with team sports like basketball and volleyball (0.07-0.31 NCACL injuries per 1000 exposures) (Orishimo, 2009).  This is a substantial difference in the injury rates considering both groups of athletes perform jump landing skills regularly.  Also, no clear gender difference has been identified within the dance population which is unique to this sport compared with other sports like basketball and volleyball (Orishimo, 2009).  Further investigation of the kinematics and kinetics of dancers during jump landings will help determine why NCACL risk is lower in this population.

Understanding the training background of dancers is important when trying to analyze jump landings.  Dancers are trained early “in highly specific jumping/landing techniques” (Orishimo, 2009).  They are trained to land with their lower extremities in full extension, their spine vertical and maximum plantar flexion occurring at the ankle joint during initial contact of the jump landing (Orishimo, 2009).  Previous research with basketball and volleyball female athletes has indicated the negative effects of landing with lower extremities in full extension.  However, dancers have been trained to land on their phalanges and metatarsal heads and then to rotate through their heels using eccentric control to achieve quiet landings (Orishimo, 2009).  This is contrary to female basketball and volleyball athletes who would increase knee flexion and hip flexion to achieve “softer” or quiet landings.  Dancers have also been able to exhibit the ability to control their patellar alignment (over the second ray of the foot) during jump landings (Orishimo, 2009).  Proper alignment of the patella protects the knee joint from unwanted forces acting on the joint and protects soft tissue structures from risk of injury.

Leg stiffness is another common variable seen among dancers.  Defined as “tissue compressibility and individual joint angular stiffness,” leg stiffness is dependent on kinematic and kinetic events occurring in the lower extremity (Kulig, 2010).  Ground reaction forces, joint reaction forces and sagittal/frontal plane kinematics are some variables affecting leg stiffness in dancers.  In Kulig et al, dancers were able to modify their joint angular stiffness during landings (2010).  This was also seen with volleyball and basketball athletes when they were instructed to land soft.  However, the vertical ground reaction forces were subconsciously modified with dancers.  As joint angular stiffness increased so does the ability of the dancer to use stored elastic energy “from the weight acceptance sub phase through the propulsion sub phase” (Kulig, 2010).  Therefore, increasing knee angular stiffness may be optimal for take-off phase and decreasing knee angular stiffness allows for protection of the joint during landing phase (Kulig, 2010).  Take off jump kinematics were not studied for basketball and volleyball athletes so no comparison can be made.

Leg stiffness can also be associated with neuromuscular training, a method of training allowing the body to more efficiently use sport like patterns and combine muscular strengthening with dynamic stabilization exercises.  The result would be the body being able to respond more efficiently to opposing forces as seen during athletic movements like jump landings.  Dancers learn specific jumping and landing techniques during their training.  They are able to activate their medial hamstrings early in the landing and lateral quadriceps and gastrocnemius later (Ambegaonkar, 2011).  Both aspects help represent the neuromuscular timing and cooperation of the hip and ankle joint during jump landings.  Female basketball and volleyball athletes have not demonstrated these neuromuscular timing and cooperation abilities in studies.  However, with the proper intervention program, basketball and volleyball athletes could decrease their NCACL risk by increasing their hip and ankle joint neuromuscular stability.  Orishimo et al determined a large peak hip abduction moment experienced during single jump landing may be due to the dancers’ ability to limit frontal plane hip range of motion through increased neuromuscular control of associated joints (2009).  This study highlights the technical training dancers receive and how it appears to help decrease their risk of NCACL injury.

The purpose of this paper was to examine the biomechanics of jump landings and determine why basketball and volleyball athletes and dancers differ in their risk for NCACL injury.  While effective intervention programs have been established, basketball and volleyball athletes are more prone to NCACL injury due to their technical training in jump landings, or lack of.  Dancers have been taught at an early age the proper technique and appearance of jump landings.  Minimal jump training programs exist for young athletes wanting to learn how to play basketball and volleyball.  Instead they are taught the fundamentals of the game and not the fundamentals of jump landings.  Dancers are trained more from a neuromuscular standpoint as well.  Meaning their training protocol involves dynamic strength and stabilization training.  Basketball and volleyball athletes may or may not even complete any type of strength training depending on the program and/or team they are associated with.  So much emphasis is placed on proper technique during dance for the pure purposes of appearance that it translates into better training methods overall.  Basketball and volleyball athletes are not encouraged to be “graceful” or “delicate” when they compete.  They are instructed to go after the ball in a manner according to which the sport they are playing demands it.  If female basketball and volleyball athletes were to be placed on a neuromuscular training program similar to the demands of their sport with the addition of more dynamic stabilization exercises at an earlier age, it would be interesting to see how much their NCACL injury risk would decrease (if at all).


ACL Non-Contact Injuries Part II (by guest contributor Anna Napolitano)


Much emphasis has been placed on proper landing techniques for female volleyball and basketball athletes.  Body position and alignment during jump landings along with proper joint angles and range of motion are important factors to investigate.  Studies have found that NCACL injury possibly occurs in all three planes of motion due to increased knee internal rotation, increased knee valgus and decreased knee flexion during jump landings (Laughlin et al, 2011).  Valgus collapse (knee valgus) may result due to poor timing of the activation of the gluteus medius.  Valgus collapse is also associated with increased ankle pronation and subtalar joint eversion especially during a jump landing.  Decreased knee flexion (most often seen with decreased hip flexion) leads to increased anterior shear forces or increased anterior translation of the tibia over the femur.  With minimal hip and knee flexion occurring, a greater force of the quadriceps occurs to absorb the momentum of the jump landing therefore pulling the tibia forward over the femur.  If the hamstrings are unable to counter this force, then a NCACL injury may occur.  Joseph et al. found increased frontal plane motion during a drop jump test occurring more in females than males and found female athletes exhibiting greater valgus angular velocity (2011).  Increased angular velocity generally occurs during sport specific drills forcing female athletes to adapt to ever changing environments at a quick pace.

Most studies have investigated basketball or volleyball landings separately.  Few studies have compared jump landings between the two sports at one time.  Lee Herrington (2011) investigated knee valgus angles during jump landings between volleyball and basketball athletes.  The results could help identify possible sport specific situations that would place females at greater NCACL risk.  The Herrrington study found no difference between single and bilateral jumping tasks in volleyball athletes (2011).  Basketball athletes showed a decrease in knee valgus angle during the unilateral jump tasks (2011).  A decrease in knee valgus shows greater dynamic hip and knee joint stability and strength.  During the unilateral jumping task volleyball athletes exhibited greater knee valgus than basketball athletes for both the left and right knees (2011).  In contrast the female basketball athletes displayed greater knee valgus angle control during the unilateral task (2011).  The differences here could be related to sport specific skills and demands found unique to that sport.  During volleyball, especially at the middle blocker position, knee, hip and ankle joints are placed at greater risk as the blocker moves across the net to defend the opposing attackers.  Often times when blockers move to the outside or right side of the net to block, their ensuing footwork requires the athlete to maintain stabilization and move quickly to their necessary target.  If there are any imbalances within the lower extremity muscle chain then the forces experienced by the athlete as they move across the net places he/she at possible higher risk of NCACL injury.

Kinematic asymmetries, although not desired, are common among athletes.  Single limb dominance is a common theme however strong research to support it does not exist.  Females could present with greater kinematic asymmetries than males when performing jump landing tasks explaining their “dominance” in NCACL injuries.  During forward jump landings, females displayed greater asymmetry than males in knee valgus and ankle abduction (Pappas and Carpes, 2011).  Ankle abduction increases stress along the medial aspect of the knee joint therefore possibly increasing the amount of knee valgus measured.  Also, the asymmetry presented could have been right limb vs. left limb dominance during landings.  Navicular drop and subtalar pronation are associated with ankle abduction (Pappas and Carpes, 2011).  Females displayed greater asymmetries than males with ankle joint kinematics in the frontal plane as well (Pappas and Carpes, 2011).  Ankle motion in the frontal plane is necessary for shock absorption.  Increased ankle movement leads to internal rotation of the tibia and preloading of the ACL (Pappas and Carpes, 2011).  If the ankle is unable to absorb the extra movements and forces the lower extremity experiences during jump landings, more stress will be placed on the knee and hip joints placing the ACL at greater risk for injury.


ACL non-contact injuries in female athletes: a three (3) part series

The following is a three part series devoted to the female athlete, specifically ACL injuries of the non-contact variety. Guest contributor Anna Napolitano explores some of the reasoning behind this frequent injury and the role of dance as a possible protection against such injuries. Anna is a 1998 graduate of the University of Michigan with a Bachelor of Science in Athletic Training and Movement Science and is licensed as an AT.  She has her CSCS from the NSCA and her PES-NASM through the National Academy of Sports Medicine.  Anna owns Innovative Training Solutions, LLC ( where she works with middle and high school athletes on sports performance training with her specialty being in ACL prevention and post ACL rehab.  I hope you enjoy this series.




Injuries are a possible outcome experienced by athletes participating in sports of all types with some athletes at a greater risk for injuries than others.  According to Hughes et al, women competing in the same sport as men are reported to be six to eight times more likely to experience a non-contact anterior cruciate ligament (NCACL) tear than men (Hughes, 2009).  Numerous studies have attempted to gain a better understanding of this phenomenon.  The majority of female NCACL injuries occur during jump landings as seen in the sports of basketball and volleyball (Pappas and Carpes, 2011).  Another study by Hootman et al found female basketball athletes and volleyball athletes experienced NCACL injuries but at different exposure rates (Herrington, 2011).  Many more studies have documented and investigated jump landing biomechanics of female basketball and volleyball athletes.  However, not all jump landing athletes are prone to NCACL injuries. 

Dancers may not be considered athletes as this form of physical activity is often classified under the “arts”.  However, their training protocol places them at risk for soft tissue joint injuries similar to those of traditionally defined athletes.  “Dancers may perform more than 200 jumping and landing activities throughout their daily training and practice.” (Orishimo, 2009).  Training at this caliber could place female dancers at increased risk of NCACL injury.  However, the incidence of NCACL injuries among female dancers is much lower than that of female basketball and volleyball athletes (Orishimo, 2009).  Biomechanics of jumping styles may play a role in the difference between female basketball and volleyball athletes and dancers.  The purpose of this report is to examine the biomechanics of jump landings and determine why basketball and volleyball athletes are a greater risk for NCACL injury than female dancers.


Before evaluating the biomechanics of jump landings, a thorough understanding of the mechanics of NCACL injuries occur needs to be discussed.  Simply explained, NCACL injuries occur when there is too much stress on the ligament (i.e., anterior cruciate ligament, ACL) leading to failure of the tensile strength of the ligament (Hashemi et al, 2011).  Stress factors include the magnitude of the stress as well as the rate of loading of this stress.  NCACL injuries may occur during practices, games or competitions.  Research has identified not one but numerous risk factors associated with NCACL injuries.  Factors found to “affect both ACL strength and the loads applied to it” include anterior shear force, hyperextension, axial compressive loads, internal rotation of tibia, valgus collapse mechanism, combination of anterior and valgus shear forces, and combination of external tibia torque and valgus forces (Hashemi et al, 2011).  These factors can be found in sport movements especially jump landings.


The biomechanics of a jump landing involves observation of the ankle, knee and hip joints and the kinetics/kinematics occurring at these structures.  At initial contact of the jump landing the body experiences forces from the ground absorbed through the lower extremities.  Gravity is pulling the athlete down and ground reaction forces are pushing back on the athlete as the athlete lands from the jump.  Great ground reaction forces during landing tasks result in an increase on the load of the passive structures (ACL) of the knee (Hughes, 2009).  The muscles of the hip and knee joint become a protective mechanism at this point.  Some studies have attempted to determine if a decrease in ground reaction forces can result by having female athletes perform “soft” landing or “stiff” landings.  “Soft” landings are defined as maximizing knee flexion and “stiff” landings are defined as minimizing knee flexion (Lauglin et al, 2011).  This same study determined that soft landings allowed the lower extremity to absorb the ground reaction forces experienced by the body.  The ability to absorb the ground reaction forces may be due to increased muscle activation during the jump landings and may be protective of the passive structures (i.e., ACL).  The “soft” landing may provide an increase in posterior shear force by the hamstrings to counter the anterior shear force created by the quadriceps and tibio femoral joint (Laughlin et al, 2011).  This counterbalance between the quadriceps and hamstrings protects the ACL from damage.  Hughes et al found an increase in ground reaction forces during the first 40% of landing phase and a decrease in ground reaction forces during the final 60% of the landing phase while observing females landing from volleyball block jumps (2009).  The higher absorption of the ground reaction forces at initial contact of landing phase coincide with the athlete’s proper body position and alignment as well as joint positions.  The majority of the ground reaction forces was absorbed initially and then subsided as the velocity of the jump decreased.    Coincidently, most NCACL tears occur immediately upon ground contact, as the athlete lands or makes a sudden change in direction.