Luke Hopper

Dance floor mechanical properties and dancer injuries in a touring professional ballet company

OBJECTIVES The mechanical properties of the floors used by dancers have often been suggested to be associated with injury, yet limited etiological evidence is available to support this hypothesis. The dance floors at three theatres regularly used by a touring professional ballet company were mechanically quantified with the aim of comparing floor properties with injury incidence in dancers. DESIGN Cross sectional. METHODS Test points on the floors were quantified in accordance with European Sports Surface Standard protocols for force reduction. Injuries and associated variables occurring within the ballet company dancers during activity on the three floors were recorded by the companys medical staff. An injury was recorded if a dancer experienced an incident that restricted the dancer from performing all normal training or performance activities for a 24 h period. Injuries were delimited to those occurring in the lower limbs or lumbar region during non-lifting tasks. RESULTS Floor construction varied between venues and a range of floor mechanical properties were observed. None of the floors complied with the range of force reduction values required by the European Sport Surface Standards. The highest injury rate was observed on the floor with the greatest variability of force reduction magnitudes. No difference in injury frequency was observed between the venues with the highest and lowest mean force reduction magnitudes. CONCLUSIONS Professional dancers can be required to perform on floors that may be inadequate for safe dance practice. Intra-floor force reduction variability may have a stronger association with injury risk than mean floor force reduction magnitude.

A comparison of the physical and anthropometric qualities explanatory of talent in the elite junior Australian football development pathway

OBJECTIVES To compare the physical and anthropometric qualities explanatory of talent at two developmental levels in junior Australian football (AF). DESIGN Cross-sectional observational. METHODS From a total of 134 juniors, two developmental levels were categorised; U16 (n=50; 15.6±0.3 y), U18 (n=84; 17.4±0.5 y). Within these levels, two groups were a priori defined; talent identified (U16; n=25; 15.7±0.2 y; U18 n=42; 17.5±0.4 y), non-talent identified (U16; n=25; 15.6±0.4 y; U18; n=42; 17.3±0.6 y). Players completed seven physical and anthropometric assessments commonly utilised for talent identification in AF. Binary logistic regression models were built to identify the qualities most explanatory of talent at each level. RESULTS A combination of standing height, dominant leg dynamic vertical jump height and 20m sprint time provided the most parsimonious explanation of talent at the U16 level (AICc=60.05). At the U18 level, it was a combination of body mass and 20m sprint time that provided the most parsimonious explanation of talent (AICc=111.27). CONCLUSIONS Despite similarities, there appears to be distinctive differences in physical and anthropometric qualities explanatory of talent at the U16 and U18 level. Coaches may view physical and anthropometric qualities more (or less) favourably at different levels of the AF developmental pathway. Given these results, future work should implement a longitudinal design, as physical and/or anthropometric qualities may deteriorate (or emerge) as junior AF players develop.

Lower limb kinematic variability in dancers performing drop landings onto floor surfaces with varied mechanical properties

Elite dancers perform highly skilled and consistent movements. These movements require effective regulation of the intrinsic and extrinsic forces acting within and on the body. Customized, compliant floors typically used in dance are assumed to enhance dance performance and reduce injury risk by dampening ground reaction forces during tasks such as landings. As floor compliance can affect the extrinsic forces applied to the body, secondary effects of floor properties may be observed in the movement consistency or kinematic variability exhibited during dance performance. The aim of this study was to investigate the effects of floor mechanical properties on lower extremity kinematic variability in dancers performing landing tasks. A vector coding technique was used to analyze sagittal plane knee and ankle joint kinematic variability, in a cohort of 12 pre-professional dancers, through discrete phases of drop landings from a height of 0.2m. No effect on kinematic variability was observed between floors, indicating that dancers could accommodate the changing extrinsic floor conditions. Future research may consider repeat analysis under more dynamic task constraints with a less experienced cohort. However, knee/ankle joint kinematic variability was observed to increase late in the landing phase which was predominantly comprised of knee flexion coupled with the terminal range of ankle dorsiflexion. These findings may be the result of greater neural input late in the landing phase as opposed to the suggested passive mechanical interaction of the foot and ankle complex at initial contact with a floor. Analysis of joint coordination in discrete movement phases may be of benefit in identifying intrinsic sources of variability in dynamic tasks that involve multiple movement phases.

Dancer perceptions of quantified dance surface mechanical properties

Dance floor surfaces are important environmental factors in dance activity and have been suggested to be a factor in the aetiology of dance injury. Measurement of the injury risk associated with floor surfaces is difficult as the validity of the relationship between mechanical surface measures and human–surface interactions is unclear. Dancer perceptions of the mechanical properties of floor surfaces were investigated with reference to mechanical quantification measures. Student (n = 27) and professional (n = 27) dancers completed a questionnaire investigating their perceptions of the force reduction, vertical deformation, energy restitution and overall ratings of five sample dance floors. Dance floor mechanical properties were quantified using sport surface testing apparatus, the Advanced Artificial Athlete (AAA) (Metaalmaatwerk, Netherlands). Student and professional cohort perceptions were not significantly different for 18 of the 20 perception variables. Vertical deformation was the only mechanical variable to differ between cohort perceptions. Dancers demonstrated a preference for floors with greater force reduction magnitudes than specified by European sport surface standards, suggesting that bespoke floor standards for dance may be beneficial. Considerable discrepancies were found between particular dancer perceptions and related AAA outputs, highlighting the need for further investigation of valid mechanical tests that are used to represent human–surface interactions.

Dance floor force reduction influences ankle loads in dancers during drop landings

OBJECTIVES Dance floor mechanical properties have the potential to influence the high frequency of ankle injuries in dancers. However, biomechanical risk factors for injury during human movement on hard, low force reduction floors have not been established. The aim of this study was to examine the ankle joint mechanics of dancers performing drop landings on dance floors with varied levels of force reduction. DESIGN Repeated measures cross sectional study. METHODS Fourteen dancers performed drop landings on five custom built dance floors. Ankle joint mechanics were calculated using a three dimensional kinematic model and inverse dynamics approach. RESULTS Ankle joint kinematic (dorsiflexion; range of motion, peak angular velocity and acceleration) and kinetic (plantar flexion; peak joint moments and power) variables significantly increased with a decrease in floor force reduction. Many of the observed changes occurred within a latency of <0.1s post-contact with the floor and were associated with increased vertical ground reaction forces and decreased floor vertical deformation. CONCLUSIONS The observed mechanical changes are interpreted as an increase in the load experienced by the energy absorbing structures that cross the ankle. The short latency of the changes represents a high intensity movement at the ankle during a period of limited cognitive neuromuscular control. It is suggested that these observations may have injury risk implications for dancers that are related to joint stabilization. These findings may be of benefit for further investigation of dance injury prevention and support the notion that bespoke force reduction standards for dance floors are necessary.

Biological maturity and the anthropometric, physical and technical assessment of talent identified U16 Australian footballers

This study compared biological maturation, anthropometric, physical and technical skill measures between talent and non-talent identified junior Australian footballers. Players were recruited from the under 16 Western Australian Football League and classified as talent (state representation; n = 25, 15.7 ± 0.3 y) or non-talent identified (non-state representation; n = 25, 15.6 ± 0.4 y). Players completed a battery of anthropometric, physical and technical skill assessments. Maturity was estimated using years from peak height velocity calculations. Binary logistic regression was used to identify the variables demonstrating the strongest association with the main effect of ‘status’. A receiver operating characteristic curve was used to assess the level of discrimination provided by the strongest model. Talent identified under 16 players were biologically older, had greater stationary and dynamic leaps and superior handball skill when compared to their non-talent identified counterparts. The strongest model of status included standing height, non-dominant dynamic vertical jump and handball outcomes (AUC = 83.4%, CI = 72.1%–95.1%). Biological maturation influences anthropometric and physical capacities that are advantageous for performance in Australian football; talent identification methods should factor biological maturation as a confound in the search for junior players who are most likely to succeed in senior competition.

Single-leg squats can predict leg alignment in dancers performing ballet movements in "turnout"

The physical assessments used in dance injury surveillance programs are often adapted from the sports and exercise domain. Bespoke physical assessments may be required for dance, particularly when ballet movements involve “turning out” or external rotation of the legs beyond that typically used in sports. This study evaluated the ability of the traditional single-leg squat to predict the leg alignment of dancers performing ballet movements with turnout. Three-dimensional kinematic data of dancers performing the single-leg squat and five ballet movements were recorded and analyzed. Reduction of the three-dimensional data into a one-dimensional variable incorporating the ankle, knee, and hip joint center positions provided the strongest predictive model between the single-leg squat and the ballet movements. The single-leg squat can predict leg alignment in dancers performing ballet movements, even in “turned out” postures. Clinicians should pay careful attention to observational positioning and rating criteria when assessing dancers performing the single-leg squat.

Kinematic repeatability of a multi-segment foot model for dance

Abstract The purpose of this study was to determine the intra and inter-assessor repeatability of a modified Rizzoli Foot Model for analysing the foot kinematics of ballet dancers. Six university-level ballet dancers performed the movements; parallel stance, turnout plié, turnout stance, turnout rise and flex-point-flex. The three-dimensional (3D) position of individual reflective markers and marker triads was used to model the movement of the dancers’ tibia, entire foot, hindfoot, midfoot, forefoot and hallux. Intra and inter-assessor reliability demonstrated excellent (ICC ≥ 0.75) repeatability for the first metatarsophalangeal joint in the sagittal plane. Intra-assessor reliability demonstrated excellent (ICC ≥ 0.75) repeatability during flex-point-flex across all inter-segmental angles except for the tibia-hindfoot and hindfoot-midfoot frontal planes. Inter-assessor repeatability ranged from poor to excellent (0.5 > ICC ≥ 0.75) for the 3D segment rotations. The most repeatable measure was the tibia-foot dorsiflexion/plantar flexion articulation whereas the least repeatable measure was the hindfoot-midfoot adduction/abduction articulation. The variation found in the inter-assessor results is likely due to inconsistencies in marker placement. This 3D dance specific multi-segment foot model provides insight into which kinematic measures can be reliably used to ascertain in vivo technical errors and/or biomechanical abnormalities in a dancer’s foot motion.

Eccentric loading increases peak torque angle of the ankle plantar flexors in healthy volunteers

Eccentric loading of the ankle plantar Flexor’s (PF) has demonstrated clinical efficacy in the conservative treatment of Achilles tendinopathy, however, its mechanism of therapeutic benefit remains unclear. The purpose of this study was to examine the effects of PF eccentric loading on PF angle to peak torque (AtPT), peak torque (PT) and lower limb vertical stiffness. Thirty healthy volunteers were randomised to an eccentric (n=15) or concentric (n=13) exercise group. A 10-week loading programme of the ankle plantar flexors was completed. AtPT, PT and vertical stiffness were compared within and between groups before and after the interventions. AtPT increased in the eccentric group by 3.2 ° dorsiflexion (p=0.001) and decreased by 0.7 ° dorsiflexion (p=0.528) for the concentric group with significant post-intervention group differences (p 0.2); however, postintervention the eccentric group showed a greater PT than the concentric group (p>0.05). Between group comparison showed no significant difference in vertical stiffness (p>0.5). However, the concentric group demonstrated a vertical stiffness increase of 765kNm ¹ (p ≥ 0.05). This study demonstrates that a clinicallyderived eccentric loading programme can produce an adaptive shift in AtPT of the ankle plantar flexors in a healthy population. These results support the theory that in part, eccentric loading derives its therapeutic benefit from mechanisms that influence plantar flexor motor performance.

Fatigue effects on quadriceps and hamstrings activation in dancers performing drop landings

Fatigue may reduce a dancers ability to maintain the muscle synergies required for stable human movement. Therefore, fatigue presents as a potential risk factor for injury in dancers. Activation patterns of the quadriceps and hamstrings muscle groups in athletic populations have been consistently reported to alter in response to fatigue during landing tasks. It is unknown whether dancers demonstrate similar muscle activation patterns, nor if dancers respond to fatiguing protocols, with regard to muscle activation, in the same manner as their athletic counter-parts. The purpose of this study was to assess quadriceps and hamstrings activation levels in a cohort of dancers performing drop landings before and after completion of a dance-specific fatigue protocol, the High Intensity Dance Performance Fitness Test. Quadriceps and hamstrings co-contraction ratios significantly increased between pre- and post-fatigue conditions in a similar fashion to that reported in the literature. Therefore, the neuromuscular activation of the knee extensors and flexors in dancers changed in response to the dance-specific fatiguing protocol. Furthermore, quadriceps and hamstrings co-contraction ratios were substantially greater than previously reported in other athletic populations, due to low hamstrings activation levels. Future investigation of dancer biomechanical adaptations to fatigue would be beneficial to further examine the potential implications for injury risk.