The effects of acute physical fatigue on sauté jump biomechanics in dancers.

Dancers spend large amounts of time practicing and performing, where fatigue may occur, resulting in adverse movement patterns. The purpose of this study was to compare sauté landings before and after acute physical fatigue in experienced female dancers. Twenty-one dancers completed 10 sauté jumps before and after a dance-specific fatigue protocol. A 12-camera motion capture system and a force plate were utilized to collect three-dimensional kinematic and kinetic data. After fatigue, dancers demonstrated an increase in mediolateral centre of mass displacement, pelvis excursion, peak knee abduction, peak ankle eversion and external rotation, as well as decreased peak metatarsophalangeal (MTP) joint extension, indicating less desirable movement patterns. Peak vertical ground reaction force was decreased after fatigue due to a softer landing strategy, demonstrated by increased peak hip flexion, knee flexion, and ankle dorsiflexion. There was some indication of shifting demands demonstrated by an increased peak knee extensor moment and decreased peak MTP flexor moment after fatigue. With jump landing kinematics and kinetics affected after only an average of 5 minutes of dancing, dancers may benefit from developing greater endurance and more eccentric strength to allow them to slow down properly while landing and to sustain the aesthetic demands throughout performance.

What goes up must come down, part II: Consequences of jump strategy modification on dance leap landing biomechanics.

Knee injuries are common in jumping athletes; modifying jump strategy may impact loads placed on the body and reduce injury risk. The purpose of this study was to determine if modifying strategy in a saut de chat leap to focus on height would decrease sagittal plane knee loading. Biomechanical data were collected while 28 dancers performed saut de chat leaps with instructions to jump far (FAR) or jump high (UP). In the UP condition, there was greater vertical GRF and less braking GRF. Also in UP, lower extremity contact angle was greater (71.3 ± 2.9º FAR; 75.8 ± 3.3º UP; p = 0.0178), peak knee extensor moment was greater (2.8 ± 0.7 Nm FAR; 3.2 ± 0.8 Nm UP; p = 0.01), and peak ankle plantar flexor moment was lower (3.19 ± 0.4 Nm FAR; 2.94 ± 0.4 Nm UP; p < 0.01). A more acute LECA was related to greater braking force and braking force was related to greater knee extensor moments. Despite these relationships, we observed greater knee extensor moments in UP. While the relationship among these whole-body variables and knee joint loading exists, it may not be the primary factor driving load distribution during dance leap landings.

Evaluation of Overhand Throwing Among College Students With and Without Autism Spectrum Disorder.

Children with autism spectrum disorder (ASD) typically demonstrate deficits in gross motor skills such as the overhand throw. It has not been determined whether such deficits persist into adulthood. Therefore, the purpose of this study was to examine the kinematics and developmental level of overhand throws among young adults with and without ASD. Three-dimensional motion-capture data were collected during overhand throwing trials performed by 20 college students (10 students with ASD). Individuals with ASD demonstrated similar throw duration, stride length, and step width but a longer acceleration phase and slower ball velocity than individuals without ASD. Young adults with ASD also performed the overhand throw with less developmental proficiency than those without ASD. Specifically, individuals with ASD exhibited developmental deficits in the backswing and composite throwing score. Motor skill interventions for individuals with ASD should address throwing skills, with a particular focus on the preparatory phase of the overhand throw.

What goes up must come down: Consequences of jump strategy modification on dance leap take-off biomechanics.

Chronic foot and ankle injuries are common in dancers; understanding how lower extremity loading changes in response to altered task goals can be beneficial for rehabilitation and injury prevention strategies. The purpose of this study was to examine mechanical demands during jump take-offs when the task goal was modified to focus on either increasing jump distance or increasing jump height. It was hypothesized that a jump strategy focused on height would result in decreased energetic demands on the foot and ankle joints. Thirty healthy, experienced female dancers performed saut de chat leaps while travelling as far as possible (FAR) or jumping as high as possible (UP). Ground reaction force (GRF) impulses and peak sagittal plane net joint moments and sagittal plane mechanical energy expenditure (MEE) of the metatarsophalangeal (MTP), ankle, knee, and hip joints were calculated. During take-off, vertical and horizontal braking GRF impulses were greater and horizontal propulsive GRF impulse was lower in the UP condition. MEE at the MTP, ankle, and hip joints was lower in UP, and MEE at the knee was higher in UP. These results suggest that a strategy focused on height may be helpful in unloading the ankle and MTP joints during dance leaps.

Achieving the Split Position in a Saut de Chat Leap.

OBJECTIVES: Dancers frequently perform complex jumping skills that involve achieving specific body positions while in the air. An examination of how skilled dancers achieve these aesthetic demands can provide information useful for dance training. The purpose of this study was to examine the temporal coordination of the hip and knee joints during the flight phase of a saut de chat leap, where dancers aim to achieve a split position in the air when the center of mass (COM) reaches peak height. METHODS: Thirty healthy, experienced dancers with 22.5±4.5 years of dance training performed 5 saut de chat leaps. The timing of peak hip and knee joint angles and velocities for the takeoff and leading legs were extracted and compared to the time when COM reached peak height in the leap using a repeated measures ANOVA, with post-hoc comparisons made using paired t-tests. RESULTS: Dancers demonstrated significant differences in timing associated with achieving the split position (main effect p<0.001), with only peak leading leg hip flexion occurring at a similar time to the COM reaching peak height (paired t-test p=0.074). CONCLUSIONS: The results of this study provide insight into coordination patterns used by trained dancers. Trained dancers demonstrate patterns in timing that may be important for successful performance. The hip and knee coordination patterns during flight demonstrate how dancers work to achieve the desired aesthetics of a saut de chat leap. However, it appears that dancers do not reach the full split position at the height of the leap, as would be aesthetically desirable.

What Do We Know About How Acute Physical Fatigue Affects Movement in Dancers?: A Systematic Review of the Literature.

BACKGROUND: Dancers are skilled athletes who train, rehearse, and perform extensively and often repeat the same sequences of movements in class or while learning and rehearsing choreography. Fatigue is thought to be related to an increased risk of injury due to altered movement patterns and distributions of joint forces. However, little research has examined the effects of fatigue on dance performance. AIMS: The purpose of this study was to review the relevant literature and characterize what is known about how the movement patterns of trained dancers are affected by induced acute physical fatigue. METHODS: Four electronic databases were searched for studies that investigated any protocol or method designed to induce acute fatigue and examined the effects fatigue had on dancers. Two reviewers independently assessed the methodological quality of and extracted data from the included studies. RESULTS: Of 440 search results, 12 studies were included in the final review. The mean score for methodological quality was 9.2/13. A variety of methods have been used in an effort to induce fatigue in dancers, but many of the fatigue protocols or movements studied were not specific to dance or have not been studied using a functional approach. Several studies identified changes in mechanics after fatigue, but a consistent pattern is not yet apparent in the literature. CONCLUSIONS: Studies examining fatigue in dancers have found contradictory results in terms of shifting contributions from the lower extremity joints, indicating that more research is needed to determine the effects of fatigue on jump mechanics in dancers.

Interlimb Force Coordination in Bipedal Dance Jumps: Comparison Between Experts and Novices.

Bipedal tasks require interlimb coordination that improves with practice and acquisition of skills. The purpose of this study was to compare interlimb force coordination during dance-specific rate-controlled consecutive bipedal jumps (sautés) between expert dancers and nondancers. To analyze coordination of vertical ground reaction forces recorded under each leg, the vector coding approach was used. Although there were no differences in the patterns of interlimb force coordination between groups, the dancers exhibited less variability of interlimb force coordination during the transition phase from weight acceptance to propulsion as well as during the propulsion phase itself. The interlimb force coordination variability was associated with task performance only during the transition phase, which highlights the potential importance of control during this phase. In conclusion, expert dancers were better at reducing interlimb force coordination variability during the task-relevant transition phase, which was related to better performance at maintaining jump rate and jump height consistency.

Kinematic and kinetic analyses of the toes in dance movements.

Due to the significant amount of time dancers spend on the forefoot, loads on the metatarsophalangeal joints are likely high, yet vary between dance movements. The purpose of this study was to compare joint motion and net joint moments at the metatarsophalangeal joints during three different dance movements ranging in demands at the foot and ankle joints. Ten healthy, female dancers (27.6 ± 3.2 years; 56.3 ± 6.9 kg; 1.6 ± 0.1 m) with an average 21.7 ± 4.9 years of dance training performed relevés (rising up onto the toes), sautés (vertical bipedal jumps), and saut de chat leaps (split jumps involving both vertical and horizontal components). Metatarsophalangeal joint kinematics and kinetics in the sagittal plane were calculated. Total excursion and peak net joint moments during rising or push-off were compared between the three dance movements. Greater extension of the metatarsophalangeal joints was seen during relevés compared to sautés or saut de chat leaps, and the largest metatarsophalangeal net joint moments were seen during saut de chat leaps. The metatarsophalangeal joints frequently and repetitively manage external loads and substantial metatarsophalangeal extension during these three dance movements, which may contribute to the high rate of foot and ankle injuries in dancers.

Lower Extremity Biomechanical Demands During Saut de Chat Leaps.

In dance, high demands are placed on the lower extremity joints during jumping tasks. The purpose of this study was to compare biomechanical demands placed on the lower extremity joints during the takeoff and landing phases of saut de chat leaps. METHODS: Thirty healthy, experienced dancers with 20.8±4.9 yrs of dance training performed 5 saut de chat leaps. A three-dimensional motion analysis system and force plates were used to collect kinematic and kinetic data. Ground reaction force (GRF) peaks and impulse and sagittal plane kinematics and kinetics of the hip, knee, ankle, and metatarsophalangeal (MTP) joints were calculated for the takeoff and landing phases of each leap. RESULTS: Saut de chat takeoffs demonstrated greater braking GRF impulse (p<0.001), while landings demonstrated greater peak vertical GRF (p<0.001). During takeoff, greater kinetic demands were placed on the MTP (p<0.001) and ankle (p<0.001) joints, while during landing greater kinetic demands were placed on the hip (p=0.037) joint. CONCLUSIONS: Both the takeoff and landing phases of saut de chat leaps place significant demands on a dancer's body. Takeoff involves greater demands on the more distal joints and requires more braking forces, while the landing phase involves greater demands on the more proximal joints of the lower extremity and requires the dancer to absorb more vertical force. These demands, combined with extensive repetition of movements during training, may contribute to the high number of chronic injuries seen in dance.

Pointing the foot without sickling: an examination of ankle movement during jumping.

The sauté is a relatively simple dance jump that can be performed by both highly skilled dancers and non-dancers. However, there are characteristics of jumping unique to trained dancers, especially in terms of foot and ankle movement during flight. Dancers are trained not to "sickle, " or to avoid the anatomically coupled ankle inversion that occurs with plantar flexion, maintaining the appearance of a straight line through the lower leg and foot. The purpose of this study was to examine ankle movements in elite dancers compared to non-dancers. Twenty healthy females, 10 with no prior dance training and 10 professional dancers, performed 20 consecutive sautés while three-dimensional kinematic data were collected. Sagittal and frontal plane kinematics were calculated and vector coding methods were used to quantify coordination patterns within the ankle in the sagittal and frontal planes. This pattern was chosen for analysis to identify the avoidance of a sickled foot by trained dancers. Peak ankle positions and coordination patterns between groups were examined using independent t-tests (a <0.05). Dancers demonstrated greater peak plantar flexion (p<0.01) and less change in ankle angle during the flight phase (p= 0.01), signifying holding the pointed foot position during flight. There was no statistically significant difference in sagittal and frontal plane ankle coupling (p= 0.15); however, the Cohen's d effect size for the difference in coupling was medium-to-large (0.73). Dynamic analysis of the foot and ankle during jumping demonstrates how elite dancers achieve the aesthetic requirements of dance technique.

Toe Flexor Strength, Flexibility and Function and Flexor Hallucis Longus Tendon Morphology in Dancers and Non-Dancers.

Tendinopathy of the flexor hallucis longus (FHL), colloquially referred to as "dancer's tendinitis," is a common condition in dancers and attributed to high demand on this muscle in positions of extreme ankle plantarflexion and metatarsophalangeal (MTP)) flexion and extension. Despite such a high prevalence, there has been little research into preventative or nonsurgical interventions. As a means to identify potential targets for prevention and intervention, this study aimed to characterize toe flexors in dancers by measuring strength, flexibility, function, and FHL tendon morphology. Dancers (n=25) were compared to non-dancers (n=25) in toe flexor isometric strength, first MTP joint range of motion, foot longitudinal arch flexibility, balance ability, endurance during modified heel raises without use of the toes, and FHL tendon thickness, cross-sectional area, and peak spatial frequency. Significant differences were found in functional first MTP joint extension (dancers 101.95°, non-dancers 91.15°, p<0.001), balance ability during single-leg stance on the toes (dancers 11.43 s, non-dancers 5.90 s, p=0.013), and during modified heel raises (dancers 22.20 reps, non-dancers 28.80 reps, p=0.001). Findings indicate that dancers rely on toe flexors more than non-dancers to complete balance and heel raise tasks. Efficacy of using this modified heel raise task with the toes off the edge of a block as a means to train larger plantarflexors and as a nonsurgical intervention should be studied in the future. Improving interventions for FHL tendinopathy will be impactful for dancers, in whom this condition is highly prevalent.

Exploring Active and Passive Contributors to Turnout in Dancers and Non-Dancers.

OBJECTIVE: Lower-extremity external rotation, or turnout, is a fundamental skill in dance. Active standing turnout has previously been measured using low-friction turnout disks. Turnout is influenced by passive range of motion (ROM) and strength, with passive ROM a function of bony morphology and ligamentous/capsular restraints. PURPOSE: Our study explored the relationship between standing active turnout and femoral bony morphology, hip passive ROM, and strength among dancers and non-dancers. METHODS: Cross-sectional cohort study. Twenty-three female dancers and 13 female non-dancers aged 18 to 30 yrs were recruited. Standing active turnout on reduced-friction disks, ultrasound images of femoral version, supine passive turnout, and hip abductor and external rotator strength were collected. RESULTS: Dancers demonstrated greater standing turnout (107° ± 18°) than non-dancers (92° ± 28°), but the difference was not statistically significant (p=0.054). A significant difference was found for femoral version (p<0.001), 4.7° ( ± 2.8°) for dancers vs 12.1° ( ± 4.6°) for non-dancers. Dancers demonstrated greater supine turnout, 102.7°±18.8°, compared to non-dancers, 84.3° ± 30.4° (p=0.031). Dancers were able to achieve greater peak force in turnout compared to non-dancers: 2.44 ± 0.44 N/kg and 1.72 ± 0.59 N/kg, respectively (p<0.0001). Supine total turnout was the best predictor of active turnout, contributing 48% of the variance (r=0.696, p<0.001). CONCLUSION: Our findings suggest supine turnout is the largest predictor for standing turnout. Investigating dancers and non-dancers independently, our finding were similar to previous studies suggesting the femoro-acetabular complex may be influenced by dance training, contributing to differences in bony morphology between dancers and non-dancers. Although strength did not significantly contribute to active standing turnout, dancers demonstrated greater peak force compared to non-dancers.

Trunk coordination in dancers and nondancers.

Variability, or how a task changes across trials, may reveal differences between athletes of differing skill levels. The purpose of this study was to examine trunk and lower extremity (LE) single joint kinematic variability and intersegmental coordination variability in dancers and nondancers during bipedal vertical dance jumps (sautés). Twenty healthy females, 10 with no formal dance training and 10 professional dancers, performed 20 consecutive sautés. Single joint kinematic variability was assessed using mean standard deviation of angular displacement, and intersegmental coordination variability was assessed using angular deviation of the coupling angle between segments. Within the context of the standard error of measure, there was no difference in single joint kinematic variability between dancers and nondancers. Intersegmental coordination variability in the trunk was higher than variability in LE couplings for both groups. Dancers had lower intersegmental coordination variability than nondancers for LE sagittal, frontal, and transverse plane couplings, and sagittal plane trunk couplings. Trunk adjustments may be important for successful performance, but lower intersegmental coordination variability in expert dancers indicates a higher level of control. Trunk coordination and postural control may be important factors to investigate in skilled athletes.

Dancers exhibit decreases in postural control after fatigue.

Dancers require exceptional postural control to combat mechanically unstable positions. Dancers are prone to developing fatigue, which may increase the risk of injury. We investigated the effects of a dance-specific fatigue protocol on static postural control in a passé stance in 15 healthy dancers. A 12-camera video motion analysis system and a force plate were used to collect kinematic and kinetic data. After fatigue, significant increases in centre of pressure displacement were observed in the anterior-posterior direction on both legs (4.13 ± 0.71 mm pre-fatigue, 5.57 ± 1.9 mm post-fatigue dominant; p = 0.005; 4.41 ± 1.19 mm pre-fatigue, 5.24 ± 1.16 mm post-fatigue non-dominant; p = 0.018) and the medio-lateral direction on the non-dominant leg (3.18 ± 0.49 mm pre-fatigue, 3.37 ± 0.57 mm post-fatigue; p = 0.033). Sway area was significantly increased in the non-dominant leg only (52.1 ± 19.6 mm2 pre-fatigue, 64.1 ± 18.9 mm2 post-fatigue; p = 0.006). Significant increases in joint excursion for both legs were observed at the hip in the sagittal and frontal planes and the knee in the sagittal plane. There were significant increases in excursion for the non-dominant ankle in the sagittal plane. Static postural control was significantly affected by the fatigue protocol; the dominant leg appears to be more resistant to fatigue than the non-dominant leg. Therefore, dancers should include stability training that induces fatigue to increase balance recovery.

Evaluation of Skipping in College Students with and without Autism Spectrum Disorder.

Children with Autism Spectrum Disorder (ASD) demonstrate motor skill deficits in comparison to their neurotypically developing peers. However, it is unknown whether these motor skill deficits persist into adulthood. We evaluated skipping kinematics and motor performance in college students with and without ASD. We collected kinematic data from 20 college students, 10 with ASD and 10 without ASD, using a 12-camera three-dimensional motion capture system while participants completed three skipping trials. We scored skipping performance using Everyone Can! and the Halverson Developmental Sequences for Skipping, and we processed data using Cortex, Visual 3D, and MATLAB. We extracted data for center of mass excursion, peak velocity of joint extension, and peak joint angles of the hip, knee, and ankle of the dominant leg. Independent t-tests and Mann-Whitney U tests were used to examine differences between groups with an alpha level of p ≤ 0.05. We found no statistically significant differences for peak sagittal plane joint angles, velocities, or vertical center of mass excursion. However, the ASD group demonstrated greater medio-lateral center of mass displacement (ASD M = .08, SD = .1 m; Control M = .03, S = .03 m; p = .026) and greater frontal plane knee excursion (ASD M = 11.49, SD = 6.23°; Control M = 5.29, SD = 2.44°; p = .01) than participants without ASD. Similarly, the ASD group performed less proficiently in skipping than the group without ASD, as assessed by the developmental scoring methods (Everyone Can! composite score medians [interquartile range]: ASD M = 10.5, SD = 8; Control M = 15.0, SD = 0, p = .008). Despite many similarities in skipping kinematics between groups, participants with ASD were less proficient in skip performance than participants without ASD. Interventions for individuals with ASD addressing skipping proficiency or the performance of other locomotor skills, such as running and jumping, may promote participation in activities that involve complex motor skills and help individuals with ASD lead more physically active lives.

Validity of inertial measurement units for tracking human motion: a systematic review.

Human motion is often tracked using three-dimensional video motion tracking systems, which have demonstrated high levels of validity. More recently, inertial measurement units (IMUs) have been used to measure human movement due to their ease of access and application. The purpose of this study was to systematically review the literature regarding the validity of inertial sensor systems when being used to track human motion. Four electronic databases were used for the search, and eleven studies were included in the final review. IMUs have a high level of agreement with motion capture systems in the frontal and sagittal planes, measured with root mean square error (RMSE), intraclass correlation coefficient, and Pearson's correlation. However, the transverse or rotational planes began to show large discrepancies in joint angles between systems. Furthermore, as the intensity of the task being measured increased, the RMSE values began to get much larger. Currently, the use of accelerometers and inertial sensor systems has limited application in the assessment of human motion, but if the precision and processing of IMU devices improves further, it could provide researchers an opportunity to collect data in less synthetic environments, as well as improve ease of access to biomechanically analyse human movement.