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.

Exploring the impact of body mass change on fatigue and activity of the muscular system during daily routine.

BACKGROUND: Correct body weight is one of the factors that allows you to maintain a properly functioning body. Abnormal body weight can cause muscle tissue remodelling, affecting activity and muscle fatigue. Changes in the muscular system can cause occurrence of functional limitations. OBJECTIVE: To determine the effect of weight change on fatigue and activity of the muscular system during daily activities. METHODS: The evaluation of musculoskeletal functioning was based on the results of computer simulations conducted in the AnyBody Modeling System. The following activities were analysed: standing, sitting down and getting up from a chair, holding and lifting an object, and walking. The simulations of the activities were carried out using averaged kinematic data, and by changing body mass in the range of 50 kg to 100 kg by increments of 2 kg, to map different nutritional status from excessive thinness to extreme obesity. Identification of loads in the musculoskeletal system was based on solving an inverse dynamics problem and then the estimation of muscle force values using static optimization. The simulation results allowed to determine the value of muscle fatigue and the level of muscle activity. RESULTS: For activities (i.e., standing, walking, sitting down and getting up from a chair) it was observed that the value of muscle fatigue increases with increasing body mass. However, for activities that cause more load on the musculoskeletal system, i.e. lifting and holding an object, the highest value of muscle fatigue was observed in underweight individuals. CONCLUSION: The change in body weight alters the functioning of the muscular system and thus the ability to perform activities. It was shown that in case of underweight, overweight or obese people, abnormal body weight can be the reason for occurrence of difficulties in performing the activities of lifting and holding a 20 kg object, as well as walking.

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.

Thoracic surgery may alter body static balance via diaphragm dysfunction.

Many diseases and conditions can alter an ability to maintain body balance. The aim of the present study was to investigate whether thoracic surgery may elicit diaphragm dysfunction thereby impairing postural stability. 40 patients qualified to video-assisted thoracoscopy (VATS) lobectomy or lobectomy via thoracotomy due to pulmonary carcinoma were examined two times: a day before lung resection and 3-5 days after surgical procedure. Diaphragm assessment was performed using ultrasonography, while postural sways were evaluated by Zebris FDM-S stabilometric platform. Thoracic surgery was associated with decrease of diaphragm thickness and movement, as well as, with deterioration of static body balance maintenance. Upper lobe resection was linked with greater diaphragm excursion restriction and worse body sway parameters than middle and lower lobe resection. VATS lobectomy was associated with better postoperative diaphragm function and better postural sway parameters than lobectomy via thoracotomy. Patients after lobectomy via thoracotomy had significantly more load on lower limb on the operated side than patients after VATS lobectomy. Impairment of diaphragm function is closely associated with equilibrium impairment after pulmonary resection. VATS lobectomy was less invasive than lobectomy via thoracotomy in terms of primary respiratory muscle function and body balance maintenance parameters.

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.

A sitting or standing position - which one exerts more loads on the musculoskeletal system of the lumbar spine? Comparative tests based on the methods of mathematical modelling.

PURPOSE: The work aimed to assess the functioning of the musculoskeletal system within the lumbar spine in relation to everyday postures of sitting and standing. METHODS: The comparative analysis was based both on experimental tests and computer simulations performed in the AnyBody Modeling System environment. Input data used to prepare models were based on the information obtained in experimental tests. The test participants were tasked with adopting two postures: 1) standing position and 2) sitting position. Kinematics measurements were performed using the Zebris ultrasonic system. During sitting position, the tests additionally involved the use of a dynamometric platform measuring reaction forces occurring between buttocks and the seat. RESULTS: The comparative analysis included measurements of the trunk inclination angle and the pelvic inclination angle as well as results of computer simulations. The sitting posture is responsible for increased trunk inclination and a change in the position of the pelvis. In terms of the sitting position, it was possible to observe an increase in the loads affecting individual intervertebral joints of the lumbar spine by 155-184% in comparison with the standing posture (100%). Simulations revealed an increased muscle activity of the erector spinae, abdominal internal oblique muscles and abdominal external oblique muscles. CONCLUSIONS: Adopting a sitting position increases the loads on the lumbar spine and increases the activity of the erector spinae and abdominal muscles compared to the standing position, which is caused by change in the position of the pelvis and the curvature of the lumbar region.

Effectiveness of the power and speed dry-land training in female swimmers aged 15-16.

PURPOSE: This work aimed to define the impact of the introduction of power and speed dry-land training in female swimmers aged 15-16 on the rise of time results at a distance of 200 m and on the increase of the strength level of the muscle groups in the elbow joint. METHOD: The investigations were conducted on a group of 28 junior female swimmers: group 1 (aged 13-14) with speed and endurance training based on "water" exercises; group 2 (aged 15-16) with extra power and speed dry-land training. The following parameters were analyzed: time results, the moments of muscle forces in the elbow joint at the extension and flexion movements in isokinetic conditions and the ratio of the values of moments of muscle forces of flexors in relation to extensors. RESULTS: Statistically significant differences between groups were found for the following parameters: the time results from swimming 200 m with ( p < 0.001) and without using lower limbs ( p = 0.031), the ratio of the moments of muscle forces of flexors to extensors ( p < 0.05). CONCLUSIONS: The results of the correlation analysis show that the higher the moments of muscle forces of flexors and extensors of the elbow joint, the shorter the time obtained in swimming 200 m in the freestyle stroke.

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.

Effect of Short-Term Metro-Rhythmic Stimulations on Gait Variability.

The aim of the study was to define the effect of different short-term metro-rhythmic stimulations on the time and spatial parameters of gait. The secondary goal was to test whether prior instructions on how to respond to stimulations played a significant role in the stimulation by sound stimuli. Experimental tests of gait were conducted on a group of 36 healthy participants: group 1-subjects who were not informed how to react after hearing sound stimuli, group 2-subjects who received a clear instruction before the test to adjust the frequency of taking steps to the rhythm of the music. The gait research was carried out on a Zebris FDM-S (zebris Medical Gmbh, Isny, Germany) treadmill for various sound stimuli (arrhythmic stimulus, rhythmic stimuli at different rate). It was shown that a short-term influence of metro-rhythmic stimulations changes the time and spatial parameters of gait, i.e., gait frequency, length and duration of the gait cycle. The greatest impact on the modification of the time-space parameters of walking is exerted by rhythmic stimuli at a pace different from the frequency of gait at a preferred velocity. Providing information on how to respond to sounds heard may be important in gait therapy with RAS (rhythmic auditory stimulation).

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.

A numerical study to determine the effect of strengthening and weakening of the transversus abdominis muscle on lumbar spine loads.

This work aimed to determine the influence of strengthening or weakening of the transversus abdominis (TrA) muscle on loads in the lumbar spine using musculoskeletal modelling methods. The input kinematic data of two positions (a standing position and a position during a sitting-down task) were angles in the elbow joint (0°;4°), shoulder joint (0°;3°), hip joint (0°;75°) and knee joint (0°;69°) as well as the torso tilt angle (0°;32°). It was shown that a change in the TrA physiological cross section area (PCSA) has a crucial impact on lumbar spine loads (2xTrA PCSA causes a reduction in the force in joint L5-S1 by 11% for a standing position and by 25% for a sitting-down position) and value of intra-abdominal pressure.

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.

The effect of the pelvis position in the sagittal plane on loads in the human musculoskeletal system.

PURPOSE: The research work aimed to perform the mathematical modelling-based assessment concerning the effect of the position of the pelvis in the sagittal plane on loads present in the musculoskeletal system in the standing position. METHODS: The analysis of the effect of various positions of the pelvis was performed using the Free Posture Model in the AnyBody Modeling System software. Simulated positions involving various values of pelvis inclination ranged from the extreme pelvic retroposition (-7°) through normative values (0-23°) to the extreme pelvic anteversion (33°). RESULTS: The lowest resultant reaction forces in the intervertebral joints recorded for an angle of inclination restricted within the range of 9-27° and segment L5-S1 amounted to less than 0.7 BW. A change in the pelvic inclination from the normative values towards retroposition or anteversion resulted in the increased muscular activity of the erector spinae, transverse abdominal muscles as well as internal and external oblique muscles. Regarding the lower limbs, changes in the activity were observed in the biceps femoris muscle, iliac muscle, gluteus minimus, gluteus medius and the gluteus maximus. CONCLUSION: The results obtained in the research-related tests confirmed that the pelvic inclination affects loads present in the musculoskeletal system. The abovenamed results will be used to develop therapeutic exercises aimed to reduce loads present in the musculoskeletal system. The aforesaid exercises will be used to teach participants how to properly position their pelvis and how to activate individual groups of muscles.

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.