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drop landing

Influence of Generalized Joint Laxity on Landing Ground Reaction Force in Ballet and Modern Dancers

Generalized joint laxity (GJL) is a condition in which most joints of the body move beyond the accepted normal range of motion. It allows for greater flexibility, which is beneficial to sports such as dance, but can lead to musculoskeletal injuries and decreases in strength. The ability to control landings with strength and stability is key to high level dance performance. Therefore, the purpose of this study was to evaluate differences in peak ground reaction force (GRF; vertical, medial-lateral, and anterior-posterior), during landing between dancers with and without GJL. Twenty healthy female volunteers with experience in ballet or modern dance were screened for GJL using the Beighton Scale. 10 subjects with GJL (score of 6 or higher) and 10 without GJL (score of 3 or below) were selected for testing. Subjects performed three forward, unshod, single-leg drop landings from a height of 40 cm onto a portable force plate (Bertec Corporation, OH, USA). Peak GRF for each landing was found and averaged for each subject, and for each group. No significant differences were found in peak GRF in any direction (p=0.71). We believe the similarity in peak forces between groups is due to dancers’ training and technique, as dancers are expected to control and soften their landings. GRF provides information about the load placed on the body, but lacks details related to landing technique. Further research describing 3D landing kinematics, joint moments, and muscle activation is required to determine if different landing techniques exist between dancers with and without GJL.
Listed In: Biomechanics

Static Foot Structure May Predict Midfoot Mechanics

INTRODUCTION: Clinical interventions for foot injury prevention are often prescribed based on static measures of foot structure. However, this convention merits further investigation as the static-dynamic relationship has only been explored in walking and running. The primary aim of this study was to explore the relationship between static foot structure and dynamic midfoot kinematics and kinetics during a barefoot single-leg landing. METHODS: 48 females (age=20.4±1.8 yr, height=1.6±0.06 m, weight=57.3±5.5 kg) completed the study. Standing arch height index (AHI) was measured using the Arch Height Index Measurement System. Skin markers were attached using a multi-segment foot model by Bruening et al.1 A14-camera motion capture system (Vicon) was used to sample kinematic data at 250Hz while two force platforms (AMTI) sampled kinetic data at 1000Hz. A static trial was captured then subjects hung from wooden rings and performed barefoot single-leg drop landings from a height of 0.4m. Metrics were calculated in Visual 3D (C-motion, Inc.) to obtain static midfoot angle (MA), midtarsal range of motion (ROM), and midtarsal work. PCCs were calculated for static and dynamic variables using paired t-tests in SAS. RESULTS: AHI was correlated negatively with sagittal plane midtarsal ROM (r=-0.32032, p=0.0264) and positively with midtarsal work (r=0.33180, p=0.0212). MA was correlated positively with sagittal plane midtarsal ROM (r=0.48336, p=0.0005) and negatively with midtarsal work (r=-0.32321, p=0.0250). DISCUSSION/CONCLUSION: Static foot structure may be a valuable clinical tool in assessing midfoot function relating to injury risk in athletes, who participate in high-impact loading activities, as well as in pathological populations.