USING COORDIN'ATlON MEASURES FOR MOVEMENT ANALYSIS

Traditionally, in biomechanics we have investigated the actions of single joints or segments without taking into account the interactions of these structures. A dynamical systems approach has been increasingly used in biomechanics to give a different perspective on the interaction of specific structures in human movement. That is, the study of coordination has become more prominent in the biomechanics literature based on the work of Bernstein (1967). Coordination is defined as overcoming excessive degrees of freedom thereby turning individual movement elements into a controllable system. In this paper, we will' describe a theoretical framework for analyzing coordination, present examples in the literature and discuss future developments for this type of analysis

OVERUSE INJURIES IN RUNNING: DO COMPLEX ANALYSES HELP OUR UNDERSTANDING?

The purpose of this paper is to discuss the change in focus in biomechanics from relatively simple analysis techniques to more complex techniques. Overuse injuries, linked to rearfoot motion, will be used as an example. In the early development of biomechanical techniques, the angle magnitudes were presented to suggest the mechanisms of overuse injuries. Later, coupling rearfoot motion with actions of the knee became commonplace. In these analyses, the timing and ratios of the angular movements were expressed. However, none of these measures provided a sufficient explanation for injury mechanisms. New techniques, derived from dynamical systems theory, have provided a more salient explanation of the overuse injury mechanism through assessing the role of variability in movement coordination

Within-day repeatability of coordination variability measures across the running gait cycle

The purpose of this study was to identify the within-day repeatability of coordination variability calculated using a velocity ellipse area method. Twenty participants attended two data collection sessions within 6 hours. At each session, a marker based motion capture system measured kinematics whilst participants ran at 12 km/h on a treadmill. The minimum detectable change in coordination variability was calculated for four commonly researched joint/segment couplings. Of the couplings investigated, thigh flexion/extension – shank flexion/extension and hip flexion/extension – knee flexion/extension were most repeatable. But in the most repeatable coupling, an average change of 75% across the gait cycle would be required between sessions to detect a meaningful change. This indicated poor repeatability and possible causes are discussed

Postural Stability is Reduced in People with Multiple Sclerosis due to Walking-imposed Fatigue

The most limiting symptoms reported by individuals with multiple sclerosis (MS) are impaired balance and symptomatic fatigue. We have reported greater postural sway and reduced stability following local muscular fatigue in individuals with MS, suggesting that these symptoms may be related. However, it is unknown whether a similar relationship exists with modest increases in fatigue resulting from an activity of daily living (ADL). Thus, the purpose of this study was to determine whether walking has a greater impact on balance during postural tasks in people with MS (PwMS) compared to those without. Seven PwMS (43±12 yrs, 6F/1M) and 10 controls (CON; 42±12 yrs, 7F/3M) performed postural tasks (quiet stance, fixed/maximal reaches) pre/post 30 minutes of treadmill walking at a range of speeds (0.6-1.4 m/s). Individuals rated their fatigue pre/post walking using a Visual Analog Scale. Kinematic data were recorded using a passive marker system (Qualysis AB) and kinetic data were recorded using two forceplates (AMTI), one under each foot. The net center of pressure was analysed using a time to contact analysis to assess postural stability. Following prolonged walking PwMS demonstrated greater reductions in stability than the CON group during the most challenging task (P=0.04), that may be related to increased fatigue (P\u3c0.0001) following walking. PwMS demonstrated greater stability than the CON group for maximal reaches (backward, P=0.009; forward, P=0.03 frontal plane only), which may be explained by reduced reach distances performed by the PwMS (backward, P=0.2; forward, P=0.008). These findings suggest that PwMS place a higher priority on stability, than maximal reach distance, which could relate to fall-related fear or specific disease-related limitations. These findings indicate that postural stability is reduced in PwMS following a common ADL, thus individuals with MS should be counseled on the increased likelihood of balance loss with heightened fatigue, even at relatively low levels

New Concepts A dynamical systems approach to lower extremity running injuries

Abstract In this paper, we are presenting an alternative approach to the investigation of lower extremity coupling referred to as a dynamical systems approach. In this approach, we calculate the phase angle of each segment and joint angle. Pairing the key segment/ joint motions, we use phase angles to determine the continuous relative phase and the variability of the continuous relative phase. Data from two studies illustrate the ecacy of the dynamical systems approach. Individuals who were asymptomatic, even though they may have anatomical aberrant structural problems (i.e. high Q-angle vs low Q-angle) showed no dierences in the pattern of the continuous relative phase or in the variability of the continuous phase. However, dierences in the variability of the continuous relative phase were apparent in comparing individuals who were symptomatic with patellofemoral pain with non-injured individuals. Patellofemoral pain individuals showed less variability in the continuous relative phase of the lower extremity couplings than did the healthy subjects. We hypothesize that the lower variability of the couplings in the symptomatic individuals indicates repeatable joint actions within a very narrow range. Relevance We claim that the traditional view of the variability of disordered movement is not tenable and suggest that there is a functional role for variability in lower extremity segment coupling during locomotion. While the methods described in this paper cannot determine a cause of the injury, they may be useful in the detection and treatment of running injuries.

Sagittal hip-knee coordination during a 45 degree cutting task

Concurrent extension at the hip and flexion at the knee has been suggested as a high risk coordination pattern for the anterior cruciate ligament (ACL). Nine elite female athletes performed ten 45" cutting tasks before and alter a multi-directional fatiguing protocol. Force and kinematic data were captured. Vector coding was used to calculate sagittal hip - knee coordination for the first 40 ms of foot contact of the dominant limb and percentage time spent in each coordination pattern was extracted. Hip extension - knee flexion was the dominant coordination pattern pre- and post-fatigue ( P less than 0.05)t the time spent in this coordination pattern did not change as a result of fatigue. The hypothesised high risk hip extension - knee flexion was the dominant coordination pattern during the 45' cutting task

New developments in vector coding methods for assessing coordination variability

The purpose of this study is to propose modifications to current methods for the assessment of coordination variability through vector coding techniques. Commonly, vector coding starts from calculating the vector difference between adjacent data points on an angle-angle plot. This initial stage is analogue to estimating angular velocities from displacement, but with the limitation of differentiating the three axial components in isolation. Instead, the calculation of angular velocities from 3D data should take into account movement in other planes of motion. This study suggests the use of angular velocities in vector coding in place of the difference calculations and demonstrates how using this method can be integrated with recent developments which involve the use of ellipses for calculating coordination variability of angle-angle diagrams

Coordination as a function of skill level in the gymnastics longswing

The purpose of this study was to investigate the nature of inter-joint coordination at different levels of skilled performance to: (1) distinguish learners who were successful versus unsuccessful in terms of their task performance; (2) investigate the pathways of change during the learning of a new coordination pattern and (3) examine how the learner’s coordination patterns relate to those of experts in the longswing gymnastics skill. Continuous relative phase of hip and shoulder joint motions was examined for longswings performed by two groups of novices, successful (n = 4) and unsuccessful (n = 4) over five practice sessions, and two expert gymnasts. Principal component analysis showed that during longswing positions where least continuous relative phase variability occurred for expert gymnasts, high variability distinguished the successful from the unsuccessful novice group. Continuous relative phase profiles of successful novices became more out-of-phase over practice and less similar to the closely in-phase coupling of the expert gymnasts. Collectively, the findings support the proposition that at the level in inter-joint coordination a technique emerges that facilitates successful performance but is not more like an expert’s movement coordination. This finding questions the appropriateness of inferring development towards a “gold champion” movement coordination