The third and final installment of the ACL Non-Contact injury series by Guest Contributor Anna Napolitano. Thanks Anna for a great series!
DANCERS AND RISK OF NON CONTACT ACL INJURY:
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).