Ground reaction force as a factor responsible for the topography of injuries in professional dance. An analysis of three dance styles: classical dance, modern dance, and folk dance.

OBJECTIVE: The study aimed to identify the effects of ground reaction forces (GRF) recorded during landing in typical elements of three dance styles, including classical, modern, and folk dance, on injuries` topography. METHODS: The research involved a survey and measurements of GRF generated during landing after the jump. The survey involved a group of 90 professional dancers. In the questionnaire, the dancers marked areas of the human body that were affected at least once by injuries. Biomechanical tests of the GRF recording were conducted on a group of 15 professional dancers. The analysis focused on the following parameters: a maximum value of the vertical variable of the GRF relative to body weight (maxGRFz), the time between the moment from first foot contact with the ground to the moment of reaching the maxGRFz (tmaxGRFz), and the loading rate of the GRF relative to body weight (LRGRFz). RESULTS: Regardless of dance style and sex, the lower spine, knee joints, ankle joints and feet were the areas most affected by injuries among professional dancers. The level of maxGRFz, tmaxGRFz and LRGRFz during typical jumps in classical, modern, and folk dance was statistically significantly different (P<0.01*). The highest mean maxGRFz values were recorded for jumps performed by classical dancers. Furthermore, the sum of injury-affected areas differed significantly across various dance styles and was connected with the impact forces transferred by the dancer's musculoskeletal system. CONCLUSION: The level of GRF is one of the decisive factors affecting the topography of professional dance injuries.

Is the Symmetry of Classical Ballet Positions Perfect?

OBJECTIVE: It is expected that in classical ballet dancers would be able to execute all the techniques symmetrically from the right as well as from the left side of the body. This study aimed to evaluate the symmetry of kinematic parameters of hip joints, knee joints, and foot progression angle of the left and right lower extremities (LE) in five classical ballet positions, as well as the symmetry of active and passive turnout and range of passive hip external rotation. METHODS: The experimental testing involved 12 female pre-professional ballet dancers. Three measurements of range of motion, made using a standard goniometer, were carried out to characterize the study group. Kinematic data of left and right LE in the five classical ballet positions were recorded using a motion capture system. RESULTS: The comparisons revealed significantly lower (p < 0.01) hip external rotation values by 9.8% (1st position), 5.4% (2nd position), and 8.5-11.8% (3rd position) for the right LE than the left LE. Moreover for 3rd, 4th and 5th positions, there was significantly higher (p < 0.05) hip external rotation values by 7.0%-27.2% in the back LE than the front LE. In 4th position there was asymmetry in foot progression angle with significantly lower values (p < 0.01) by 5.3% in the front LE (left) than the back LE (right). In case of goniometric measurements, the results showed significantly higher (p < 0.05) passive hip external rotation values by 10.8% for the right LE than the left LE. CONCLUSION: The perfect ballet symmetry pursued by dancers is not in fact so ideal. The most astonishing result was the existence of statistically significant differences in hip external rotation in the case of the 1st and 2nd positions.

Effect of strengthening and weakening of abdominal and dorsal muscles on lumbar spine loads in parents of disabled children.

Pain in the lower part of the back is one of the most common chronic illnesses globally. This work aimed to determine the impact of the reinforcement of particular groups of abdominal and dorsal muscles on the loads exerted on the lumbar section of the spine in 30 mothers of children with motor disabilities. An optical Ariel Performance Analysis System recorded and processed the kinematics data of everyday activities. Tests investigating the effects of the strengthening or weakening of abdominal and dorsal muscles on loading in the lumbar section of the spine utilized the AnyBody Modelling System. Input data for the simulations included mean values of body positions, while the effects of strengthening or weakening of muscles were simulated in the muscle forces model by introducing different values for muscle physiological cross-sectional area (PCSA). Simulations used decreasing or increasing PCSA values of abdominal muscles and the erector spinae. The analysis involved component and resultant force values on the lumbosacral joint (L5-S1) of the spine and intra-abdominal pressure values. The highest reduction of the resultant reaction value in L5-S1 was observed in the simulations that increased the PCSA of the transverse abdominal (TrA). Indeed, a double increase in the TrA cross-section caused a reduction of the resultant reaction in L5-S1 by 30% and the anterior-posterior and proximal-distal forces by approximately 20-30%. Increased PCSA of the erector spinae exerted higher loads on the spine. These results indicate that strengthening weakened abdominal muscles, particularly TrA, in parents of children with motor disabilities reduces lower spinal loads during daily activities.

Lower Extremities Strength Differences in Female Volleyball Players With Stage 1 Patellar Tendinopathy.

ABSTRACT: Kabacinski, J, Murawa, M, Fryzowicz, A, Gorwa, J, and Dworak, LB. Lower extremities strength differences in female volleyball players with stage 1 patellar tendinopathy. J Strength Cond Res 36(8): 2230-2235, 2022-The main purpose of the study was to compare the muscle strength between the involved knee (IK) and uninvolved knee (UK) in 12 female volleyball players with stage 1 chronic patellar tendinopathy. Evaluation included the isometric maximal strength to body mass (MS/BM) of the lower extremities extensors for unilateral and bilateral conditions, concentric isokinetic peak torque to body mass (PT/BM) of the hamstrings and quadriceps at 60°·s -1 and 180°·s -1 , IK to UK extensors maximal strength ratio (SR), IK to UK hamstrings (or quadriceps) peak torque ratio (TR), and hamstrings to quadriceps peak TR (H/Q). The results indicated a significantly lower unilateral and bilateral MS/BM of lower extremities extensors for IK than UK ( p < 0.001). However, there were no significant differences in SR variable between the unilateral condition and bilateral condition ( p = 0.448). Only at the 60°·s -1 velocity, significantly lower quadriceps PT/BM for IK compared with the UK ( p < 0.001) and the control group ( p < 0.001) were observed. Torque ratio related to the quadriceps group was significantly lower at 60°·s -1 than 180°·s -1 ( p = 0.004). Furthermore, significantly higher H/Q for IK compared with UK ( p < 0.001) and control group ( p = 0.008) only at 60°·s -1 was found. These findings show a significant isometric strength asymmetry for both unilateral and bilateral conditions and a significant concentric strength asymmetry at the low velocity. This study suggests strengthening the weaker quadriceps group and balancing the strength between hamstrings and quadriceps within the knee with patellar tendinopathy.

Comparison of isokinetic knee torque and bioelectrical activity for hamstrings, quadriceps and erector spinae muscles in elite rowers.

In sweep rowers, the lower extremities muscle strength translates into the driving force of the boat. Therefore, isokinetic assessment of muscle torque is used by coaches as an indicator of the level of athletes' preparation for competitions. A total of 22 elite sweep rowers performed an isokinetic test of knee joint flexors and extensors, and a test on an asymmetric ergometer with the electromyography measures. Significantly higher quadriceps peak torque was shown during the beginning than the end of the preparatory period (p < 0.05). However, there was no significant knee peak torque difference between the lower extremities (p = 0.398). In the case of the electromyography test of quadriceps, hamstrings and lumbar erector spinae, analysis demonstrated significant bioelectrical activity differences between the sides (p < 0.05). Lower values of quadriceps peak torque at the end of the preparatory period may result from a decrease in the number of power training units during the entire preparatory period. A similar muscle strength between both lower extremities seems to be the correct result in the context of injury prevention. In turn, significant bioelectrical activity differences between the sides possibly are associated with the asymmetric movement pattern in sweep rowers.

Biomechanical Effects of Flamenco Footwork.

Footwork is one of the basic features of flamenco dancing and is performed in traditional high-heeled shoes. The purpose of this study was to analyse the mechanical profile of flamenco dancing in terms of vertical ground reaction force, and knee joint kinematics of the supporting limb in footwork technique in order to understand causes which predispose injuries derived from the practice of flamenco dancing. The participant in our study was a professional female flamenco dancer (34 years, 58 kg, 1.65 m) who performed the ZAP 3 test, a sequence of single strikes of the feet performed continuously for 15 s. 3D lower extremity kinematic data were collected using a five-camera motion analysis system (Vicon; Oxford Metrics Ltd., Oxford, UK). Ground reaction forces were recorded using a Kistler force plate. Our analysis was based on 30 cycles of each lower limb consisting of 177 footwork steps. The vertical component of the ground reaction force did not reveal any significant differences between the left and the right limb. The most dynamic strike was provided by the heel (twice the participant's body weight). The mean angular displacement of the supporting limb's knee was ~27°. Results reveal that these impacts could make the knee joint more prone to injuries.

In Pursuit of the Perfect Dancer's Ballet Foot. The Footprint, Stabilometric, Pedobarographic Parameters of Professional Ballet Dancers.

This work aims to assess footprint parameters in a group of professional ballet dancers and to determine the correlation between the aforementioned parameters and lateralization, stabilometric parameters, pedobarographic parameters and work environment conditions. A group subjected to tests consisted of 44 elite professional ballet dancers and the reference group was composed of 44 students. The test of balance and thrust under feet involved 30 s-long free standing with open eyes on a podographic platform. The research-related analysis was concerned with footprint parameters (foot length and width, Clarke angle, and Weissflog index), stabilometric parameters (path length and ellipse field, mean value of the velocity and deflection of the displacement of the center of the foot pressure on the ground) and pedobarographic parameters (percentage thrust on the right, left foot as well as the front and rear part the foot). Statistically significant differences between the groups were observed in relation to the stabilometric parameters, the percentage pressure of the left forefoot and the right heel, as well as the value of the Clarke angle (p ≤ 0.05). The longitudinal arch of the foot and the width of the foot in ballet dancers are not dependent on the total and professional career duration and weekly training volume.

Biomechanical Description of Zapateado Technique in Flamenco.

The main purpose of this study was to identify a dancer's body alignment while performing flamenco footwork to provide a detailed description that could be used by flamenco practitioners: teachers, instructors and students of different levels of advancement. The zapateado technique performed by a professional flamenco dancer was analyzed. The biomechanical analysis was based on 30 cycles composed of six repeating sequences of strikes. Kinematic recordings were performed using a Vicon system, while the measurement of the ground reaction forces (GRF) was accomplished with a Kistler force plate. The following parameters were analyzed: the time of each foot strike, the maximal value of the vertical component of GRF normalized to body weight (BW) for subsequent footwork steps, the impulse of the GRF and the kinematics of pelvis and lower limb joints, and an exemplary waveform view of the sound of footwork strikes was shown. The average values of the vertical component of GRF ranged between 0.6 and 2.7 BW. The maximal anterior pelvic tilt was 29°, with a 6° range of motion (RoM). This mobility was accompanied by 20° hip RoM and by ~40° knee RoM throughout flexion. The conclusions provide practical information that a teacher and flamenco student should receive.

How to teach safe landing after the jump? The use of biofeedback to minimize the shock forces generated in elements of modern dance.

PURPOSE: The aim of the study was to assess the possible use of biofeedback (information on the course and values of ground reaction forces (GRF) during landing following the performance of a dance evolution) for training minimising impact loads after a jump in modern dance. METHODS: The tests involved the analysis of a total of 60 expressive elements of modern dance performed by 5 soloists. The tests involved the recording of the vertical component of GRF (GRFz) vector using Kistler platform in the landing phase following the performance of modern dance jumps. The dancers performed the above-named jumps three times in successive tests: a reference test (without biofeedback) and the next two tests with biofeedback, after the obtainment of information about the vertical value of GRF. After each performance, the dancers watched a course of GRF and films showing the recorded landing phase. RESULTS: Applying of a proposed didactic laboratory session led to: extension of contact time and of time preceding the obtainment of the maximum value of GRFz, reduction of the maximum values of the vertical components of the GRF, reduction of the loading rate of the ground reaction force, increase of an impulse of the vertical component of GRF in the entire stance phase and in the shock absorption phase. CONCLUSIONS: Proposed didactic laboratory session with biofeedback may result in the change of the post-jump shock absorption technique.

Classic and indicative methods in the analysis of the foot arch and foot loads in professional folklore dancers on the basis of stabilographic tests.

PURPOSE: The proper shape of the foot determines its proper functioning and efficiency, which is significant as far as dancers are concerned. The aim of the study was to identify the arch of feet based on the Arch Index (AI), ability to maintain balance on the basis of stabilometric parameters and the distribution of loads acting on the feet of professional folk dancers. METHODS: The study group was composed of 37 folk dancers and the reference group consisted of 56 healthy adults aged 19-45. Balance measurements were performed using the Zebris FDM-S measurement platform, Romberg test with eyes open. Test results were exported to the Matlab 2019b computing environment. The algorithm developed by the Authors in relation was used to calculate Arch Index for the right and left foot, for each test participant separately. RESULTS: Statistical tests did not reveal statistically relevant differences between stabilometric parameters and loads affecting feet in the reference group and that of the dancers. The statistical tests revealed that the value of the AI differed significantly in the reference group and in the group of professional folk dancers ( p = 0.05). The differences were also observed in the group of females ( p = 0.003). No statistically relevant differences were observed in relation to the group of males ( p = 0.116). The percentage of the feet with high arch in the group of dancers amounted to 26%; 33% of dancers' feet were classified as the feet with low arch. CONCLUSIONS: The feet of professional folk dancers have a statistically more arched foot than the reference group.

Muscle activation varies between high-bar and low-bar back squat.

BACKGROUND: Differences in the muscular activity between the high-bar back squat (HBBS) and the low-bar back squat (LBBS) on the same representative group of experienced powerlifters are still scarcely investigated. The main purpose of the study was to compare the normalized bioelectrical activity and maximal angles within single homogeneous group between the HBBS and LBBS for 60% one repetition maximum (1RM), 65% 1RM and 70% 1RM. METHODS: Twelve healthy men (age 24.3  ± 2.8 years, height 178.8  ± 5.6 cm, body mass 88.3  ± 11.5 kg), experienced in powerlifting performed HBBS and LBBS with comparable external loads equal 60% 1RM, 65% 1RM, and 70% 1RM. Electromyography (EMG) signals of muscle groups were synchronously recorded alongside kinematic data (joints angle) by means of a motion capture system. RESULTS: EMG activity during eccentric phase of squat motion were significantly higher during LBBS than in HBBS for all selected muscles (60% 1RM and 65% 1RM) (p < 0.05). All examined muscles were more activated during concentric phase of the squat cycle (p < 0.05). In the concentric phase, significant differences between the loads were generally not observed between just 5% 1RM change in load level for LBBS. CONCLUSIONS: Our results confirmed significant differences in muscles activation between both squat techniques. Muscle activity during eccentric phase of squat motion were significantly higher during LBBS than HBBS. The differences are crucial for posterior muscle chain during eccentric phase of squat cycle.

On the track of the ideal turnout: Electromyographic and kinematic analysis of the five classical ballet positions.

The turnout of the lower extremities is the major component of the classical ballet positions (CPs) and correctly is initiated in the hips. The aim of this research was to determine the differences in the electromyographic and kinematic variables in the five CPs in ballet students with greater and lesser amount of passive hip external rotation (HER). A group of 14 female pre-professional ballet dancers 11-16 years of age participated in the study. Based on the amount of passive HER, participants with higher values made up greater rotation group (n = 7) whereas those with lesser values formed lesser rotation group (n = 7). Electromyographic activity of 14 muscles from right side of the trunk and right lower extremity was recorded with the surface electrodes while subjects were standing in all five CPs (CP1-CP5). The external rotation of the hips, knees and feet were recorded with the motion capture system. The kinematic differences between the groups were revealed in asymmetric positions CP4 and CP5 where foot progression angle was significantly lesser in forward than backward setting only in lesser rotation group. In lesser rotation group the ankle and back muscles were more engaged in CPs while abdominal and hip muscles less when compared with greater rotation group. This finding suggests that in the group with lesser passive HER the mechanism of forced turnout was employed. The most remarkable finding in our work was that various electromyographic patterns can be observed between groups in all CPs, while kinematic differences may be marked only in asymmetric positions.

Gait Kinematics Index, Global Symmetry Index and Gait Deviations Profile: Concept of a new comprehensive method of gait pathology evaluation.

PURPOSE: The objective of the work was to define a new comprehensive method of evaluating gait pathology (Gait Kinematics Index, Global Symmetry Index and Gait Deviations Profile). METHODS: The article presents in detail a mathematical algorithm of a new comprehensive method of evaluating gait pathology. Input data for the algorithm are the kinematic parameters of gait. The method is based on the determination of the following parameters: standardized angular variables (Wji), kinematic indicators of gait (KIj), gait cycle indicators (GCIi), Gait Kinematic Index (GKI), Gait Deviations Profile (GDP, GDPj), Global Symmetry Index (GSI) and Symmetry Indices (SIj) for kinematic gait values. The algorithm is based on the determination of the difference between results obtained in relation to the kinematics of movement of a given patient and the average value obtained in relation to the standard in each percentage of a gait cycle. The proposed method was tested using results obtained for 59 healthy persons and one patient with locomotor function disorder. RESULTS: The GKI values for the reference group amounted to 0.89 ± 0.23. Information which can be obtained using the proposed gait assessment method was presented using an example of a patient with the disorder of locomotor functions. Areas of gait deviations, which were identified on the basis of the determined indicators, were presented in a graphic form using GDP. CONCLUSIONS: The new gait assessment method makes it possible to identify gait using a single numerical value, evaluate movements in individual joints and in subsequent moments as well as to assess the symmetry of gait.

Which of the five classical ballet positions is the most demanding for the dancer's body? An electromyography-based study to determine muscular activity.

PURPOSE: The study aimed to determine which of the five classical ballet positions is the most demanding regarding muscular activity, values of external rotation in the hip joints, angular values of foot progression as well as the inclination (tilt) of the pelvis in the sagittal plane. METHODS: In this cross-sectional study, 14 female pre-professional ballet dancers (aged 11-16) participated. Participants were tasked with the sequential adoption of five classical ballet positions (CP1-CP5). The electromyographic activity of the muscles of the trunk and the lower limb was recorded with surface electrodes. Kinematic data including hip and knee external rotation, foot progression angle and pelvic tilt were collected using a motion capture system. RESULTS: Symmetric positions CP1 and CP2 were not as demanding as asymmetric CP3-CP5. Higher values of hip and foot external rotation without greater muscular effort in CP2 than CP1 was noticed. Considering asymmetric positions, CP3 did not trigger a greater activity of hip or foot muscular groups than CP4 and CP5. CP4 was characterised by the greatest pelvic anterior tilt and the lowest activity of GM in the forward lower limb. In CP5, forward lower limb entailed a higher activity of muscles supporting the foot than in the remaining positions. CONCLUSION: In terms of biomechanics, the most demanding classical ballet position in pre-professional dancers is CP4, followed by CP5, CP3, CP1 and CP2. This finding can be applied in educational methodology of dancers, figure skaters, synchronized swimmers, acrobatic gymnasts, rhythmic gymnasts or cheerleaders.

Decreased Bone Mineral Density in Forearm vs Loaded Skeletal Sites in Professional Ballet Dancers.

AIMS: To compare the differences in bone mineral density (BMD) at loaded and non-loaded skeletal sites in professional ballet dancers. We hypothesized that in both male and female elite ballet dancers, a significant difference in BMD will be observed between impact and non-impact sites. METHODS: 44 elite ballet dancers, 22 men (age 26.4±5.9 yrs) and 22 women (age 24.9±5.3 yrs), were examined. BMD measurements were performed using dual-energy x-ray absorptiometry at three skeletal sites-forearm (FA), lumbar spine (LS), and femoral neck (FN)-and analyzed using t-tests, ANOVA, and linear regression models. Information about career duration, training volume, health habits, and menstrual disorders (women) was collected. RESULTS: Z-scores for LS and FN were significantly higher in men than in women. However, Z-scores for FA were similar in men and women and fell below the expected range for age (<-2.0), and they were significantly lower than those for LS and FN. With longer career duration, a trend was observed towards lower Z-scores for FN in men and towards higher Z-scores for FA in women. CONCLUSION: In ballet dancers, FA mineralization is extremely low compared to loaded skeletal sites. Male dancers may have lowered forearm BMD despite the absence of risk factors present in female dancers (menstrual disorders). Professional ballet dancers may be at risk of local osteopenia due to the "local non-impact" characteristics of ballet dance, and use of the 33% distal radius region for the accurate assessment of bone mineral status should be investigated further in this population.

Is it possible to reduce loads of the locomotor system during the landing phase of dance figures? Biomechanical analysis of the landing phase in Grand Jeté, Entrelacé and Ballonné.

PURPOSE: The objective of the work was to determine biomechanical parameters influencing loads affecting the musculoskeletal system and shock absorption during the landing phase in Grand Jeté, Entrelacé and Ballonné. METHODS: Motion kinematics measurements of the landing phase in GrandJeté, Entrelacé and Ballonné were carried out using the optical APAS system, and measurements of the GRF components - using Kistler platform. The research was carried out for three professional dancers. Kinematic and kinetic parameters of the landing were analysed. RESULTS: The mean maximum GRF value in relation to the classical dancer amounted to 8.16 ± 1.37 N/BW. During landing, the joints of the lower limb are affected by external force moments of high values (ankle - 3.04 ± 0.54 [Nm/BW], knee - 7.56 ± 5.53 [Nm/BW], hip - 10.97 ± 6.80 [Nm/BW]). The maximum value of the external force moments in the joint were strongly negatively correlated with the value of the angle in the hip joint at the moment of the first contact with the ground. It was noticed that the obtainment of maxGRF was preceded by a decrease in kinetic energy of approximately 50%. CONCLUSIONS: Factors affecting loads present in the musculoskeletal system during the shock absorption of a leap are: GRF values, the values of external force generated inside the joints and a change in the value of kinetic energy. The safe shock absorption after landing is influenced by properly positioned limb at the moment of the first contact, a greater range of movements in the joints and longer time from the moment of the first contact to the obtainment of maxGRF.

Kinematic analysis of modern dance movement "stag jump" within the context of impact loads, injury to the locomotor system and its prevention.

BACKGROUND: This paper presents a case study of kinematic analysis of the modern dance movement known as the "stag jump". Detailed analysis of the kinematic structure of this movement as performed by the dancers, accompanied by measurements of impact forces during landing, will allow the authors to determine, in subsequent model-based research phases, the forces acting in knee joints of the lower landing limb. MATERIAL AND METHODS: Two professional modern dancers participated in the study: a male and a female. The study consisted in recording the values of ground reaction and body motion, and then determining and analyzing kinematic parameters of performed movements. RESULTS: The results of measurement of joint angles in the landing lower limb, pelvis, and foot position in relation to the ground, as well as the level of vertical components of ground reaction, provided insight into the loading response phase of the "stag jump". The measurements and obtained results show differences between the man and woman in ground reactions and kinematic quantities. CONCLUSIONS: The results obtained during the research may be used in the development and teaching of dancing movements. Training sessions, carried out in the biomechanical laboratory, with active participation of dancing teachers, could form a basis for a prevention model of injuries and physical overloads occurring within this occupational group. Primary differences in the "stag jump" performance technique probably result from the different educational path the man and the woman went through.