Article

Does local dynamic stability of kayak paddling technique affect the sports performance? A pilot study

Wiley
European Journal of Sport Science
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Abstract

During competition, kayak athletes must optimally adapt to environmental factors (e.g. wind, waves) to achieve peak performance. However, the ability to adapt to such perturbations has never been assessed in kayak paddling. Therefore, the aim of the current study was to evaluate the local dynamic stability in sports technique of youth sprint kayak athletes. In a cross-sectional study, 14 healthy male athletes were recruited from an elite youth sprint kayak squad. During an incremental kayak ergometer test, mean power, heart rates and local dynamic technique stability of hands, arms, trunk and paddle were registered and the association with the athletes 2000 m free-water times were estimated using mixed models. The 2000 m free-water performance significantly predicted the paddles (p = .037) local dynamic stability whereas no association was found for the trunk or the upper extremity kinematics. In conclusion, kayak athletes with high-performance capability over 2000 m paddling depict high local dynamic technique stability. This emphasizes the importance of a stable technique for advanced kayak skills, especially regarding paddling movements.

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... The mean sample size was 26.1 participants, ranging from 10 to 42. In total, eight of the ten studies enrolled participants of both sexes: one study involved only male participants [21], and one study enrolled only female participants [22] (Table 2). ...
... Regarding the assessed tasks (Table 2), four studies analysed walking [23][24][25][26]; of those, two studies assessed normal walking (NW) and tandem walking (TW) [25,26]. The remaining studies focused on the analysis of stair descent walking [22], a quiet upright stance [27], trunk and upper limb movement [21], swimming [28,29], and long swinging on a high bar [30]. Three studies that assessed walking [23][24][25][26] or stair descent walking [22] used a self-selected speed. ...
... Three studies that assessed walking [23][24][25][26] or stair descent walking [22] used a self-selected speed. The tasks were carried out in real contexts, namely schools [22,[24][25][26][27], training centres [21,23,30], and aquatic environments [28,29]. ...
Article
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Nonlinear measures have increasingly revealed the quality of human movement and its behaviour over time. Further analyses of human movement in real contexts are crucial for understanding its complex dynamics. The main objective was to identify and summarize the nonlinear measures used in data processing during out-of-laboratory assessments of human movement among healthy adolescents. Summarizing the methodological considerations was the secondary objective. The inclusion criteria were as follows: According to the Population, Concept, and Context (PCC) framework, healthy teenagers between 10 and 19 years old that reported kinetic and/or kinematic nonlinear data-processing measurements related to human movement in non-laboratory settings were included. PRISMA-ScR was used to conduct this review. PubMed, Science Direct, the Web of Science, and Google Scholar were searched. Studies published between the inception of the database and March 2022 were included. In total, 10 of the 2572 articles met the criteria. The nonlinear measures identified included entropy (n = 8), fractal analysis (n = 3), recurrence quantification (n = 2), and the Lyapunov exponent (n = 2). In addition to walking (n = 4) and swimming (n = 2), each of the remaining studies focused on different motor tasks. Entropy measures are preferred when studying the complexity of human movement, especially multiscale entropy, with authors also carefully combining different measures, namely entropy and fractal analysis.
... The flat-water kayaking stroke is an asymmetrical movement with one side being in a water phase, propelling the kayak, while the other side is in an aerial phase. Several studies have identified trunk, pelvis and shoulder kinematics as crucial for kayak propulsion during the paddling performance (Bjerkefors, Rosén, Tarassova, & Arndt, 2019;Hamacher, Krebs, Meyer, & Zech, 2018;Wassinger et al., 2011). However, researchers have also demonstrated that lower limbs kinematics must be taken into account as an influential factor for successful performance since they are not only a passive link with the kayak but instead, they actively contribute to pelvis and trunk rotation through an alternated pedaling motion (Begon et al., 2010;Nilsson & Rosdahl, 2016). ...
... The trunk plays a dominant role in the sprint kayak technique Hamacher et al., 2018;Limonta et al., 2010). Good trunk mobility can affect the overall performance since it is strictly related to the upper limb's capacity to produce propulsive power during the pull phase (Michael et al., 2009;Wassinger et al., 2011). ...
Article
Success in sprint kayaking depends on the propulsive power generated by trunk, pelvis, shoulder and lower limb movements. However, no studies have examined whole-body kinematics over a simulated distance. We aimed to study the changes in movement patterns of kayakers performing a 500-m kayak sprint. Eleven young K1 sprint kayakers (3 females; age: 16.5 ± 1.9 years, height: 174.1 ± 7.1 cm, weight: 66.1 ± 6.2 kg) performed an incremental test on a kayak ergometer to assess their Peak Oxygen Uptake (V̇O2peak). They then performed a 500-m sprint trial on the same ergometer, and the positions of 40 reflective markers were recorded to assess whole-body kinematics. Joint angles over time were computed for the trunk and right shoulder, hip, knee, and ankle. Changes of joint kinematics during the test were assessed with Statistical Parametric Mapping, calculating at each time node the linear regression between joint angles waveforms and the time of the rowing cycle, p<0.05. Cardiometabolic responses confirmed that the participants achieved a maximal effort (V̇O2 and HR reached 99 ± 11% and 94 ± 6% of peak values, respectively). Paddle velocity negatively correlated with sprint time. The shoulder (elevation, rotation and flexion), trunk (lateral flexion and rotation) and hip (abduction) angles significantly changed over time in different phases of the stroke cycle during the simulated sprint. No significant differences over time were found for knee and ankle flexion. A high-intensity sprint may affect shoulder, trunk and hip kinematics of kayak paddling. The kinematic analysis of kayakers’ paddling during simulated metabolic-demanding tasks can provide useful insights to coaches and athletes.
... Electrodes were placed on the following kayaking muscles on the right and left sides: the latissimus dorsi, medial deltoid, pectoralis major, brachial biceps, rectus femoris, biceps femoris, and external oblique abdominal. The EMG signal lies in the frequency range from 0-500 Hz [13] In all cases, we checked the individual electrodes by asking the kayaker to use the tested muscle. Footrest also was checked with the maximal foot compression by the athletes. ...
... All the measured data were simultaneously streamed, synchronized and registered by a central computer [13][14][15][16]. The Vicon analysis has been made with 100 frame per second. ...
Article
The purpose of this study was to gain a better understanding of the importance of footrest use and the symmetry of kayaking motions. Method: Measurements were performed on 11 professional male Hungarian kayakers (n = 11), with a mean age of 24 years (range: 18–30 years), a mean height of 184, 5 cm (range: 172–197 cm), and a mean weight of 84 kg (72–96 kg). Weba sport kayak ergometer, Vicon MXT 3D camera system and surface electromyography were used for the measurements. The unique part of the study was the dynamometer, built into the footrest of the ergometer. The right and left sides differed significantly in terms of range of motion in the joints and activity of the muscles involved. Statistically significant differences were observed in the force applied to the footrest between the right and left sides. There were significant differences between the right and left stroke lengths in most athletes. There was a positive correlation between force applied to the footrest, the stroke length and the kayakers’ power output. Our study identified differences and correlations between the parameters of kayaking motion, highlighting the importance of the footrest. Better and more precise footrest use allows correct technique to be applied with high performance.
... Nowadays, non-linear measures are frequently used in the analysis of human walkingfor instance to determine gait stability in elderly people and to distinguish between fallers and nonfallers (Hamacher, Hamacher, Singh, Taylor, & Schega, 2015;Hamacher, Singh, Van Dieen, Heller, & Taylor, 2011;Mehdizadeh, 2018;Toebes, Hoozemans, Furrer, Dekker, & van Dieen, 2012). There are also some studies addressing LDS in cyclic sports techniques, such as kayak paddling (Hamacher, Krebs, Meyer, & Zech, 2018) or cross-country skiing (Cignetti, Schena, & Rouard, 2009). ...
... With regard to literature (Asgari, Sanjari, & Esteki, 2017;Cignetti et al., 2009;Granata & Gottipati, 2008), our hypothesis was that local dynamic running stability (measured by the largest Lyapunov exponent λ) decreases during exercise due to fatigue. As it was already shown that LDS may positively correlate with sports performance (Hamacher et al., 2018), we hypothesise that recreational runners show a pronounced decrease in local dynamic stability during running compared to competitive runners. ...
Article
In the analysis of human walking, the assessment of local dynamic stability (LDS) has been widely used to determine gait stability. To extend the concepts of LDS to the analysis of running biomechanics, this study aimed to compare LDS during exhaustive running between competitive and recreational runners. Fifteen recreational and fifteen competitive runners performed an exhaustive 5000 m run. Inertial measurement units at foot, pelvis, and thorax were used to determine local dynamic running stability as quantified by the largest Lyapunov exponent. In addition, we measured running velocity, lactate levels, perceived exertion, and foot strike patterns. LDS at the start, mid, and end of a 5000 m run was compared between the two groups by a two-way repeated-measures analysis of variance (ANOVA). Local dynamic stability increased during the run (thorax, pelvis) in both recreational and competitive runners (PThorax = 0.006; PPelvis = 0.001). During the whole run, competitive runners showed a significantly higher LDS (P = 0.029) compared to recreational runners at the foot kinematics. In conclusion, exhaustive running can lead to improvements in LDS, indicating a higher local dynamic stability of the running technique with increasing exhaustion. Furthermore, LDS of the foot differs between the two groups at all measurement points. The results of this study show the value of determining LDS in athletes as it can give a better understanding into the biomechanics of running.
... They were literature reviews focusing on the areas of biomechanics, physiology, and injury epidemiology in rowing. Another study that can be recognized was the one that examined the ability to adapt to environmental factors in kayaking, such as wind and waves (Hamacher et al., 2018). This study focused on the local dynamic stability of kayak paddling techniques. ...
... The inertial measurement units (IMUs) can now be applied to human body segments, enabling the ability to track human kinematics in real-time during specific activities [69][70][71]. Therefore, IMU technology has made its way into biomechanics, and several studies have utilized the Xsens system to investigate kinematics [69][70][71][72][73][74][75][76][77][78][79]. Therefore, utilizing inertial motion capture systems to record athletes in their natural ecological conditions can underpin relevant and as-yetunknown aspects of the kayak paddlers' kinematics (Study I). ...
Thesis
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Sprint kayak is a competitive sport in which the ability to generate propulsion through efficient kayaking locomotion, which involves technique and power, is essential for performance. The technique predominantly utilizes upper-body muscles in the dynamic movement. However, studies have illustrated that cyclic leg movement is crucial as well. Several studies have investigated the kinetics of the paddle, while few studies have examined kinetics in the footrest and seat. These forces are essential as well, as forces produced by the paddlers must travel through the seat and footrest to be translated from force to velocity. Several studies have investigated kayak kinetics and kinematics through on-ergometer testing, while only a few have investigated these factors in the ecological conditions on the water. Studies have determined that the physiological responses with on-ergometer testing accurately simulate the physiological response of on-water kayaking. However, a few studies have suggested that the biomechanical response may differ between the two conditions. This PhD project's overall aim was initiated to investigate the kinematics and kinetics of on-water sprint kayaking. Study I investigated the kinematics of on-water and on-ergometer kayaking and differences in stroke rate. Study II developed a force-sensitive footrest and seat that could be utilized on the water. Finally, Study III investigated leg force in relation to performance in on-water kayaking in a team of elite kayakers. In summary, Study I demonstrates that on-water and on-ergometer kayaking differs in the elbow, shoulder, and knee kinematics. Concurrently, a significantly higher stroke rate was observed during a 2-min all-out effort on the ergometer than on the water. Study II developed, designed, and tested a device that measures forces applied to the footrest during on-water kayaking. The developed seat presents unacceptable values of hysteresis and system weight. Therefore, it must be redesigned if it is to be utilized further in research and testing. The developed seat was not included in the Study II. Study III has demonstrated that sprint kayakers exhibit a positive relationship between leg forces and velocity. The present thesis provides the first kinematic comparison of on-water and on-ergometer kayaking. Furthermore, it the first to provide on-water leg force data from a team of elite kayakers.
... Physical exercise and learning are the central question for the disabled people and have to be investigated for every quantitative and qualitative performances (Raiola, 2020ab;Raiola et al., 2018). In this discipline, it is essential to have a stable technique for advanced kayaking skills, especially as regards paddling movements (Hamacher et al., 2018). Flatwater kayak sprint performance can be assessed by analysing the average boat speed a paddler can produce, which has been shown to be directly related to force production levels. ...
... Indonesian rowing athletes, both men, have a height below 175 cm, even female athletes have an average height of less than 170 cm. The height that is not ideal will greatly affect the performance of national kayaking athletes who have not been maximal at the Sea Games, Asian Games, and even the Olympic level (Akca & Muniroglu, 2008;Hamacher et al., 2018;López-Plaza et al., 2019;McKean & Burkett, 2014;Pickett et al., 2018). ...
Article
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The purpose of this study was to find out the impact of balance exercises on the achievements of kayaking athletes 200 meters. The method used in this study is a survey using correlational. The sample selected was by criteria of the number of kayakers participating in the National Training Center for rowing in 2019, as many as 28 male athletes. Data analysis using a simple correlation with a significant level of 0.05, overall analysis of this data uses the help of SPSS program version 20.00. The finding is that the R Square value (determination coefficient) is 0.712, which means 71.2% of the total performance variation of 200m kayakers is caused by a simple correlate relationship with variable balance. This means that 71.2% of balance data has a direct influence on the performance of kayakers 200m in 2019 and the remaining 28.8% or (100% - 71.2% = 28.8%) caused by other factors such as weather conditions, mental condition, boat conditions, nutrition, recovery, athlete health conditions, and others
... In the literature, the focus of kayaking research has been primarily on individual K1 boat. [17][18][19] To the authors' best knowledge, this is the first study examining the effect of seat order on stroke characteristics in K2 crew boat. Findings from the present study can add knowledge to the limited body of literature in K2 sprint kayaking. ...
Article
Full-text available
The purpose of this study was to investigate the how seat order in a K2 crew boat could influence the performance time and stroke synchronization during high intensity sprint kayaking. Sixteen national team sprint kayakers formed eight K2 crews based on preference. Each crew performed two 200-m segments at high intensity in their preferred order (e.g. Paddler A in front, Paddler B behind), and then the reversed order (i.e. Paddler B in front, Paddler A behind). Video analysis identified stroke synchronization based on a four-position model. Magnitude-based inferences were used for statistical analysis. The preferred seat order was 0.5 ± 1.8 s faster than the reversed seat order but the effect was possibly trivial. As four crews were faster in the reversed seat order, data were also rearranged to compare between the slower and faster trials. The faster trials were 1.5 ± 0.5 s quicker than the slower trials, which was a very likely effect. There was no clear effect of seat order on stroke synchronization between the two paddlers. Since faster timing does not always correspond with the preferred sear order, sprint kayak athletes are recommended to try both possible seat orders in a K2 crew boat rather than relying on preference alone.
... During competition, kayak athletes must optimally adapt to environmental factors (e.g. wind, waves) to achieve peak performance [20]; ...
Article
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The purpose of the research is to substantiate scientifically the structure and content of tourists’ physical training at the stage of preliminary basic training. Material and methods . The study involved athletes aged 12-13 years. The control and experimental groups consist of 32 young men in each group. Results . It was developed and experimentally substantiated the structure and content of athletes-tourists’ physical training. It was determined the content and volumes of physical training types (general, special and additional). It was developed the complexes of training exercises with a rational correlation of general and additional physical training means. The ratio of the main types of training was as follows: general physical training - 35%, special - 15% and additional - 50%. Conclusions . The rock climbing and slacklining were offered for the preparatory period as the means of additional physical training. These means are based on the structure of motor activity and preferential orientation focused on the development of coordination, power, speed and speed-power qualities.
... Even though pulling forces at the foot-rest only explained 4 % of the variance in power in our study, this may still make a difference for elite kayakers where the differences between competitors are small. In highly trained athletes can it be hard to increase VO 2 peak further to get advantages during competition [20][21][22][23]. ...
Article
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The aim of this study was to determine the forces applied at the foot-rest during ergometer kayaking and their correlation to power, VO2peak and competition time. Ten competitive kayakers (7 men, 3 women) participated voluntarily in the study. Exercise capacity was measured as maximal oxygen consumption (VO2peak) and peak power during two and four minutes all-out exercise test on a kayak ergometer. External force sensors were attached to the wires connecting the paddle to the fan of the kayak ergometer. Foot-rests were built to enable measurements of pushing and pulling forces and to distinguish between the left and right foot. Paddle forces correlated significantly to power, VO2peak and on-water competition time at 500 meter but not at 1000 meter. Pulling forces on the foot-rests correlated significantly to power, VO2peak and competition time at 500 and 1000 meters, whereas no significant correlations were found for pushing forces on the foot-rest. No significant correlation was found between forces in the paddle and the foot-rest. To the best of our knowledge, we have for the first time demonstrated that pulling forces at the foot-rest influence kayaking performance.
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In the current study, we quantified biological movement variability on the start and early acceleration phase of sprinting. Ten male athletes aged 17-23 years (100-m personal best: 10.87 +/- 0.36s) performed four 10-m sprints. Two 250-Hz cameras recorded the sagittal plane action to obtain the two-dimensional kinematics of the block start and initial strides from subsequent manually digitized APAS motion analysis. Infra-red timing lights (80Hz) were used to measure the 10-m sprinting times. The coefficient of variation (CV%) calculation was adjusted to separate biological movement variability (BCV%) from estimates of variability induced by technological error (SEM%) for each individual sprinter and measure. Pearson's product-moment correlation and linear regression analysis were used to establish relationships between measures of BCV% and 10-m sprint start performance (best 10-m time) or 10-m sprint start performance consistency (10-m time BCV%) using SPSS version 12.0. Measurement error markedly inflated traditional measures of movement variability (CV%) by up to 72%. Variability in task outcome measures was considerably lower than that observed in joint rotation velocities. Consistent generation of high horizontal velocity out of the blocks led to more stable and faster starting strides.
Book
How Does the Body's Motor Control System Deal with Repetition? While the presence of nonlinear dynamics can be explained and understood, it is difficult to be measured. A study of human movement variability with a focus on nonlinear dynamics, Nonlinear Analysis for Human Movement Variability, examines the characteristics of human movement within this framework, explores human movement in repetition, and explains how and why we analyze human movement data. It takes an in-depth look into the nonlinear dynamics of systems within and around us, investigates the temporal structure of variability, and discusses the properties of chaos and fractals as they relate to human movement. Providing a foundation for the use of nonlinear analysis and the study of movement variability in practice, the book describes the nonlinear dynamical features found in complex biological and physical systems, and introduces key concepts that help determine and identify patterns within the fluctuations of data that are repeated over time. It presents commonly used methods and novel approaches to movement analysis that reveal intriguing properties of the motor control system and introduce new ways of thinking about variability, adaptability, health, and motor learning. In addition, this text: Demonstrates how nonlinear measures can be used in a variety of different tasks and populations Presents a wide variety of nonlinear tools such as the Lyapunov exponent, surrogation, entropy, and fractal analysis Includes examples from research on how nonlinear analysis can be used to understand real-world applications Provides numerous case studies in postural control, gait, motor control, and motor development Nonlinear Analysis for Human Movement Variability advances the field of human movement variability research by dissecting human movement and studying the role of movement variability. The book proposes new ways to use nonlinear analysis and investigate the temporal structure of variability, and enables engineers, movement scientists, clinicians, and those in related disciplines to effectively apply nonlinear analysis in practice.
Article
Background Extreme levels of gait variability and local dynamic stability of walking are associated with risk of falling and reduced executive functions. However, it is not sufficiently investigated how gait variability and local dynamic stability of human walking develop in the course of a motor-cognitive intervention. As dancing implies high demands on (and therewith trains) executive functioning and motor control, it might increase local dynamic stability or reduce gait variability. Methods 32 older healthy participants were randomly assigned to either a health-related exercise group (age: mean = 68.33 years, standard deviation = 3.17 years; BMI: mean = 27.46, standard deviation= 2.94; female/male: 10/6) or a dancing group (age: mean = 66.73 years, standard deviation = 3.33 years; BMI: mean = 26.02, standard deviation = 3.55; female/male: 11/5). Based on angular velocity data of trunk kinematics, local dynamic stability and stride-to-stride variability in level overground walking were assessed prior to and after the specific intervention. The data were analysed by a blinded observer using two-way repeated measures ANOVAs. Based on one-way ANOVAs, time and group effects were determined. Findings Regarding the variability of trunk movements, no interaction effect was observed (F 1,30 = 0.506, p = .482; η2 = 0.017). For local dynamic stability of trunk movements, an interaction effect in favour of the dancing group was observed (F 1,30 = 5,436; p = .026 ; η2 = 0.146). Interpretation Our data indicate that a dancing programme (which combines cognitive and motor efforts) might increase local dynamic stability in older people.
Article
Local dynamic stability is a critical aspect of stable gait but its assessment for use in clinical settings has not yet been sufficiently evaluated, particularly with respect to inertial sensors applied on the feet and/or trunk. Furthermore, key questions remain as to which state-space reconstruction is most reliable and valid. In this study, we evaluated the reliability as well as the ability of different sensor placement and state-spaces to distinguish between local dynamic stability in young and older adults. Gait data of 19 older and 20 young subjects were captured with inertial sensors twice within the first day as well as after seven days. 21 different signals (and combinations of signals) were used to span the system's state-space to calculate different measures of local dynamic stability. Our data revealed moderate or high effect sizes in 12 of the 21 old vs. young comparisons. We also observed considerable differences in the reliability of these 12 results, with intra-class correlation coefficients ranging from 0.09 to 0.81. Our results demonstrate that in order to obtain reliable and valid estimates of gait stability λ of walking time series is best evaluated using trunk data or 1-dimensional data from foot sensors.
Article
Detecting the presence of chaos in a dynamical system is an important problem that is solved by measuring the largest Lyapunov exponent. Lyapunov exponents quantify the exponential divergence of initially close state-space trajectories and estimate the amount of chaos in a system. We present a new method for calculating the largest Lyapunov exponent from an experimental time series. The method follows directly from the definition of the largest Lyapunov exponent and is accurate because it takes advantage of all the available data. We show that the algorithm is fast, easy to implement, and robust to changes in the following quantities: embedding dimension, size of data set, reconstruction delay, and noise level. Furthermore, one may use the algorithm to calculate simultaneously the correlation dimension. Thus, one sequence of computations will yield an estimate of both the level of chaos and the system complexity.
Article
During kayak paddling, athletes attempt to maximize kayak velocity with the generation of optimal paddle forces. The aim of the current study was to examine ten elite kayakers and identify a number of key biomechanical performance variables during maximal paddling on a custom kayak simulator. These included analysing the effect of side (left and right) and period (beginning, middle, and end of the kayak simulation) on paddle force, paddle angle, mechanical efficiency, and stroke timing data. Paddle kinetics and kinematics were measured with strain gauge force transducers attached to either end of the ergometer paddle and using a 3D motion analysis system respectively. Results indicated a significantly greater mechanical efficiency during the right paddle stroke compared with the left (P < 0.025). In addition, analysing the effect of period, peak paddle force demonstrated a significant reduction when comparing the beginning to the middle and end of the simulated race respectively (P < 0.025). Examination of individual force profiles revealed considerable individuality, with significant variation in the time course of force application. Analysis of the profiles presented may provide meaningful feedback for kayakers and their coaches.
Article
Repeated episodes of giving way at the ankle may be related to alterations in movement variability. Eighty-eight recreational athletes (39 males, 49 females) were placed in 4 groups: mechanically unstable, functionally unstable, copers, and controls based on ankle injury history, episodes of giving way, and joint laxity. Lower extremity kinematics and ground reaction forces were measured during single leg landings from a 50% maximum vertical jump in the anterior, lateral, and medial directions. Ensemble curves of 10 trials were averaged and coefficients of variation were identified for ankle, knee, hip, and trunk motion in 3 planes. A log(e) (ln) transformation was performed on the data. Mixed model analyses of variance (ANOVAs) with Tukey post-hoc tests were utilized with Bonferroni corrections to α ≤ 0.008. At the knee, controls were more variable than functionally unstable and copers for knee rotation before initial contact, and were more variable during stance than functionally unstable in knee rotation (P ≤ 0.008). Interactions during stance revealed controls were more variable than functionally unstable in lateral jumps for hip flexion, and than mechanically and functionally unstable in hip abduction in the anterior direction (P≤0.008). Controls were more variable than all other groups in hip flexion and than mechanically unstable in hip abduction (P ≤0 .008). Individuals with ankle instability demonstrated less variability at the hip and knee compared to controls during single leg jump landings. Inability to effectively utilize proximal joints to perform landing strategies may influence episodes of instability.
Article
Fields studying movement generation, including robotics, psychology, cognitive science, and neuroscience utilize concepts and tools related to the pervasiveness of variability in biological systems. The concept of variability and the measures for nonlinear dynamics used to evaluate this concept open new vistas for research in movement dysfunction of many types. This review describes innovations in the exploration of variability and their potential importance in understanding human movement. Far from being a source of error, evidence supports the presence of an optimal state of variability for healthy and functional movement. This variability has a particular organization and is characterized by a chaotic structure. Deviations from this state can lead to biological systems that are either overly rigid and robotic or noisy and unstable. Both situations result in systems that are less adaptable to perturbations, such as those associated with unhealthy pathological states or absence of skillfulness.
Article
The aim of the study was to examine the inter-cycle variability in cross-country skiing gait and its evolution with fatigue. Both issues were investigated to understand the flexibility capabilities of the neuromuscular system. Four women and four men skied on a treadmill, up to exhaustion. The angular displacements of the arms and legs movements were obtained for 40s period at the beginning and end of the skiing test. Mean inter-cycle standard deviation (SD(c)), largest Lyapunov exponent (lambda(1)) and correlation dimension (D(c)) were computed for each time series and surrogate counterpart to evaluate the magnitude and nature of the variability. For any experimental time series, lambda(1) was positive, D(c) greater than 1 and both were found to be different from their surrogate counterparts, confirming that the temporal variations of the data had a deterministic origin. More, larger SD(c), D(c) and lambda(1) values were observed at the end of the test, indicating more variability, noise and local dynamic instability in the data with fatigue. Hence, the fluctuations of limb angular displacements displayed a chaotic behavior, which reflected flexibility of the neuromuscular system to adapt to possible perturbations during skiing. However, such chaotic behavior degraded with fatigue, making the neuromuscular system less adaptable and more unstable.
Article
Several efforts have been made to study gait stability using measures derived from nonlinear time-series analysis. The maximum finite time Lyapunov exponent (lambda(max)) quantifies how a system responds to an infinitesimally small perturbation. Recent studies suggested that slow walking leads to lower lambda(max) values, and thus is more stable than fast walking, but these studies suffer from methodological limitations. We studied the effects of walking speed on the amount of kinematic variability and stability in human walking. Trunk motions of 15 healthy volunteers were recorded in 3D during 2 min of treadmill walking at different speeds. From those time series, maximum Lyapunov exponents, indicating short-term and long-term divergence (lambda(S-stride) and lambda(L-stride)), and mean standard deviation (MeanSD) were calculated. lambda(S-stride) showed a linear decrease with increasing speed for forward-backward (AP) movements and quadratic effects (inverted U-shaped) for medio-lateral (ML) and up-down (VT) movements. lambda(L-stride) showed a quadratic effect (inverted U-shaped) of walking speed for AP movements, a linear decrease for ML movements, and a linear increase for VT movements. Moreover, positive correlations between lambda(S) and MeanSD were found for all directions, while lambda(L-stride) and MeanSD were correlated negatively in the AP direction. The different effects of walking speed on lambda(S-stride) and lambda(L-stride) for the different planes suggest that slow walking is not necessarily more stable than fast walking. The absence of a consistent pattern of correlations between lambda(L-stride) and MeanSD over the three directions suggests that variability and stability reflect, at least to a degree, different properties of the dynamics of walking.
Article
The aim of this study was to compare within-individual variability in baseball pitching among various levels of competition. It was hypothesized that variability decreases as level of competition increases. Five fastballs were analysed for 93 healthy male baseball pitchers (20 youth, 19 high school, 20 college, 20 Minor League, and 14 Major League level pitchers). Eleven kinematic, four temporal, and six kinetic parameters were quantified with a 240-Hz automated digitizing system. Three multiple analyses of variance were used to compare individual standard deviations for kinematic, temporal, and kinetic parameters among the five competition levels. There was a significant overall difference in kinematics and in six of the eleven kinematic parameters analysed: foot placement, knee flexion, pelvis angular velocity, elbow flexion, shoulder external rotation, and trunk forward tilt. Individual standard deviations tended to be greatest for youth pitchers, and decreased for higher levels of competition. Thus pitchers who advanced to higher levels exhibited less variability in their motions. Differences in temporal variation were non-significant; thus variability in pitching coordination was not improved at higher levels. Differences in kinetic variation were non-significant, implying no particular skill level has increased risk of injury due to variation in joint kinetics.
Article
The mutual information I is examined for a model dynamical system and for chaotic data from an experiment on the Belousov-Zhabotinskii reaction. An N logN algorithm for calculating I is presented. As proposed by Shaw, a minimum in I is found to be a good criterion for the choice of time delay in phase-portrait reconstruction from time-series data. This criterion is shown to be far superior to choosing a zero of the autocorrelation function.
Article
We examine the issue of determining an acceptable minimum embedding dimension by looking at the behavior of near neighbors under changes in the embedding dimension from {ital d}{r arrow}{ital d}+1. When the number of nearest neighbors arising through projection is zero in dimension {ital d}{sub {ital E}}, the attractor has been unfolded in this dimension. The precise determination of {ital d}{sub {ital E}} is clouded by noise,'' and we examine the manner in which noise changes the determination of {ital d}{sub {ital E}}. Our criterion also indicates the error one makes by choosing an embedding dimension smaller than {ital d}{sub {ital E}}. This knowledge may be useful in the practical analysis of observed time series.
Article
A ubiquitous characteristic of elderly and patients with gait disabilities is that they walk slower than healthy controls. Many clinicians assume these patients walk slower to improve their stability, just as healthy people slow down when walking across ice. However, walking slower also leads to greater variability, which is often assumed to imply deteriorated stability. If this were true, then slowing down would be completely antithetical to the goal of maintaining stability. This study sought to resolve this paradox by directly quantifying the sensitivity of the locomotor system to local perturbations that are manifested as natural kinematic variability. Eleven young healthy subjects walked on a motorized treadmill at five different speeds. Three-dimensional movements of a single marker placed over the first thoracic vertebra were recorded during continuous walking. Mean stride-to-stride standard deviations and maximum finite-time Lyapunov exponents were computed for each time series to quantify the variability and local dynamic stability, respectively, of these movements. Quadratic regression analyses of the dependent measures vs. walking speed revealed highly significant U shaped trends for all three mean standard deviations, but highly significant linear trends, with significant or nearly significant quadratic terms, for five of the six finite-time Lyapunov exponents. Subjects exhibited consistently better local dynamic stability at slower speeds for these five measures. These results support the clinically based intuition that people who are at increased risk of falling walk slower to improve their stability, even at the cost of increased variability.
Article
The focus of this study was to examine the role of walking velocity in stability during normal gait. Local dynamic stability was quantified through the use of maximum finite-time Lyapunov exponents, lambda(Max). These quantify the rate of attenuation of kinematic variability of joint angle data recorded as subjects walked on a motorized treadmill at 20%, 40%, 60%, and 80% of the Froude velocity. A monotonic trend between lambda(Max) and walking velocity was observed with smaller lambda(Max) at slower walking velocities. Smaller lambda(Max) indicates more stable walking dynamics. This trend was evident whether stride duration variability remained or was removed by time normalizing the data. This suggests that slower walking velocities lead to increases in stability. These results may reveal more detailed information on the behavior of the neuro-controller than variability-based analyses alone.
Canoe sprint -summer Olympic sport
International Olympic Committee. (2017). Canoe sprint -summer Olympic sport. Retrieved from https://www.olympic.org/canoesprint.
A practical method for calculating largest Lyapunov exponents from small data sets Application of thermovisual body image analysis in the evaluation of paddöing effects on a kayak ergometer
  • M T Rosenstein
  • J J Collins
  • C J M De Luca
  • P Korman
  • P Zurek
  • T Rynkiewicz
Rosenstein, M. T., Collins, J. J., & De Luca, C. J. (1993). A practical method for calculating largest Lyapunov exponents from small data sets. Physica D: Nonlinear Phenomena, 65(1-2), 117-134. doi:10.1016/0167-2789(93)90009-P Rynkiewicz, M., Korman, P., Zurek, P., & Rynkiewicz, T. (2015). Application of thermovisual body image analysis in the evaluation of paddöing effects on a kayak ergometer. Medicina Dello Sport, 68, 31-42.
Identifying the control structure of multijoint coordination during pistol shooting Identification of interindividual and intraindividual movement patterns in handball players of varying expertise levels
  • J P Scholz
  • G Schöner
  • M L J Latash
  • J Baker
  • F Fath
  • T Jaitner
Scholz, J. P., Schöner, G., & Latash, M. L. (2000). Identifying the control structure of multijoint coordination during pistol shooting. Experimental Brain Research, 135(3), 382-404. doi:10.1007/ s002210000540 Schorer, J., Baker, J., Fath, F., & Jaitner, T. (2007). Identification of interindividual and intraindividual movement patterns in handball players of varying expertise levels. Journal of Motor Behavior, 39(5), 409-421. doi:10.3200/JMBR.39.5.409-422
  • Stergiou N.