Peak Lower Extremity Landing Kinematics in Dancers and Nondancers
Authors: Hansberger Bethany L. , Acocello Shellie , Slater Lindsay V. , Hart Joseph M. , Ambegaonkar Jatin P. 
Published: March 2018

Context:
Anterior cruciate ligament (ACL) injuries often occur during jump landings and can have detrimental short-term and long-term functional effects on quality of life. Despite frequently performing jump landings, dancers have lower incidence rates of ACL injury than other jump-landing athletes. Planned versus unplanned activities and footwear may explain differing ACL-injury rates among dancers and nondancers. Still, few researchers have compared landing biomechanics between dancers and nondancers.

Objective:
To compare the landing biomechanics of dancers and nondancers during single-legged (SL) drop-vertical jumps.

Design:
Cross-sectional study.

Setting:
Laboratory.

Patients or Other Participants:
A total of 39 healthy participants, 12 female dancers (age = 20.9 ± 1.8 years, height = 166.4 ± 6.7 cm, mass = 63.2 ± 16.4 kg), 14 female nondancers (age = 20.2 ± 0.9 years, height = 168.9 ± 5.0 cm, mass = 61.6 ± 7.7 kg), and 13 male nondancers (age = 22.2 ± 2.7 years, height = 180.6 ± 9.7 cm, mass = 80.8 ± 13.2 kg).

Intervention(s):
Participants performed SL–drop-vertical jumps from a 30-cm–high box in a randomized order in 2 activity (planned, unplanned) and 2 footwear (shod, barefoot) conditions while a 3-dimensional system recorded landing biomechanics.

Main Outcome Measure(s):
Overall peak sagittal-plane and frontal-plane ankle-, knee-, and hip-joint kinematics (joint angles) were compared across groups using separate multivariate analyses of variance followed by main-effects testing and pairwise-adjusted Bonferroni comparisons as appropriate (P &lt; .05).

Results:
No 3-way interactions existed for sagittal-plane or frontal-plane ankle (Wilks λ = 0.85, P = .11 and Wilks λ = 0.96, P = .55, respectively), knee (Wilks λ = 1.00, P = .93 and Wilks λ = 0.94, P = .36, respectively), or hip (Wilks λ = 0.99, P = .88 and Wilks λ = 0.97, P = .62, respectively) kinematics. We observed no group × footwear interactions for sagittal-plane or frontal-plane ankle (Wilks λ = 0.94, P = .43 and Wilks λ = 0.96, P = .55, respectively), knee (Wilks λ = 0.97, P = .60 and Wilks λ = 0.97, P = .66, respectively), or hip (Wilks λ = 0.99, P = .91 and Wilks λ = 1.00, P = .93, respectively) kinematics, and no group × activity interactions were noted for ankle frontal-plane (Wilks λ = 0.92, P = .29) and sagittal- and frontal-plane knee (Wilks λ = 0.99, P = .81 and Wilks λ = 0.98, P = .77, respectively) and hip (Wilks λ = 0.88, P = .13 and Wilks λ = 0.85, P = .08, respectively) kinematics. A group × activity interaction (Wilks λ = 0.76, P = .02) was present for ankle sagittal-plane kinematics. Main-effects testing revealed different ankle frontal-plane angles across groups (F2,28 = 3.78, P = .04), with male nondancers having greater ankle inversion than female nondancers (P = .05).

Conclusions:
Irrespective of activity type or footwear, female nondancers landed with similar hip and knee kinematics but greater peak ankle eversion and less peak ankle dorsiflexion (ie, positions associated with greater ACL injury risk). Ankle kinematics may differ between groups due to different landing strategies and training used by dancers. Dancers' training should be examined to determine if it results in a reduced occurrence of biomechanics related to ACL injury during SL landing.