[Show abstract][Hide abstract] ABSTRACT: The purpose of this study was to investigate the integration of bimanual rhythmic movements and posture in expert marching percussionists. Participants (N=11) performed three rhythmic manual tasks [1:1, 2:3, and 2:3-F (2:3 rhythm played faster at a self-selected tempo)] in one of three postures: sitting, standing on one foot, and standing on two feet. Discrete relative phase, postural time-to-contact, and coherence analysis were used to analyze the performance of the manual task, postural control, and the integration between postural and manual performance. Across all three rhythms, discrete relative phase mean and variability results showed no effects of posture on rhythmic performance. The complexity of the manual task (1:1 vs. 2:3) had no effect on postural time-to-contact. However, increasing the tempo of the manual task (2:3 vs. 2:3-F) did result in a decreased postural time-to-contact in the two-footed posture. Coherence analysis revealed that the coupling between the postural and manual task significantly decreased as a function of postural difficulty (going from a two-footed to a one-footed posture) and rhythmic complexity (1:1 vs. 2:3). Taken together, these results demonstrate that expert marching percussionists systematically decouple postural and manual fluctuations in order to preserve the performance of the rhythmic movement task.
Full-text · Article · Jan 2016 · Human movement science
[Show abstract][Hide abstract] ABSTRACT: Clinical disorders often are characterized by a breakdown in dynamical processes that contribute to the control of upright standing. Disruption to a large number of physiological processes operating at different time scales can lead to alterations in postural center of pressure (COP) fluctuations. Multiscale entropy (MSE) has been used to identify differences in fluctuations of postural COP time series between groups with and without known physiological impairments at multiple time scales. The purpose of this paper is to: 1) review basic elements and current developments in entropy techniques used to assess physiological complexity; and 2) identify how MSE can provide insights into the complexity of physiological systems operating at multiple time scales that underly the control of posture. We review and synthesize evidence from the literature providing support for MSE as a valuable tool to evaluate the breakdown in the physiological processes that accompany changes due to aging and disease in postural control. This evidence emerges from observed lower MSE values in individuals with multiple sclerosis, idiopathic scoliosis, and in older individuals with sensory impairments. Finally, we suggest some future applications of MSE that will allow for further insight into how physiological deficits impact the complexity of postural fluctuations; this information may improve the development and evaluation of new therapeutic interventions.
No preview · Article · Jan 2016 · Journal of Sport and Health Science
[Show abstract][Hide abstract] ABSTRACT: Traditional biomechanical analyses of human movement are generally derived from linear mathematics. While these methods can be useful in many situations, they do not describe behaviors in human systems that are predominately nonlinear. For this reason, nonlinear analysis methods based on a dynamical systems approach have become more prevalent in recent literature. These analysis techniques have provided new insights into how systems (1) maintain pattern stability, (2) transition into new states, and (3) are governed by short and long-term (fractal) correlational processes at different spatio-temporal scales. These different aspects of system dynamics are typically investigated using concepts related to variability, stability, complexity, and adaptability. The purpose of this paper is to compare and contrast these different concepts and demonstrate that, although related, these terms represent fundamentally different aspects of system dynamics. In particular, we argue that variability should not uniformly be equated with stability or complexity of movement. In addition, current dynamic stability measures based on nonlinear analysis methods (such as the finite maximal Lyapunov exponent) can reveal local instabilities in movement dynamics, but the degree to which these local instabilities relate to global postural and gait stability and the ability to resist external perturbations remains to be explored. Finally, systematic studies are needed to relate observed reductions in complexity with aging and disease to the adaptive capabilities of the movement system and how complexity changes as a function of different task constraints.
Preview · Article · Jan 2016 · Journal of Sport and Health Science
[Show abstract][Hide abstract] ABSTRACT: Traditional biomechanical analyses of human movement are generally derived from linear mathematics. While these methods can be useful in many situations, they do not describe behaviors in human systems that are predominately nonlinear. For this reason, nonlinear analysis methods based on a dynamical systems approach have become more prevalent in recent literature. These analysis techniques have provided new insights into how systems (1) maintain pattern stability, (2) transition into new states, and (3) are governed by short- and long-term (fractal) correlational processes at different spatio-temporal scales. These different aspects of system dynamics are typically investigated using concepts related to variability, stability, complexity, and adaptability. The purpose of this paper is to compare and contrast these different concepts and demonstrate that, although related, these terms represent fundamentally different aspects of system dynamics. In particular, we argue that variability should not uniformly be equated with stability or complexity of movement. In addition, current dynamic stability measures based on nonlinear analysis methods (such as the finite maximal Lyapunov exponent) can reveal local instabilities in movement dynamics, but the degree to which these local instabilities relate to global postural and gait stability and the ability to resist external perturbations remains to be explored. Finally, systematic studies are needed to relate observed reductions in complexity with aging and disease to the adaptive capabilities of the movement system and how complexity changes as a function of different task constraints.
Full-text · Article · Jan 2016 · Journal of Sport and Health Science
[Show abstract][Hide abstract] ABSTRACT: The presence of long-range correlations (self-similarity) in the stride-to-stride fluctuations in running stride interval has been used as an indicator of a healthy adaptable system. Changes to footfall patterns when running with minimalist shoes could cause a less adaptable running gait. The purpose of this study was to investigate stride interval variability and the degree of self-similarity of stride interval in runners wearing minimalist and conventional footwear. Twenty-six trained habitual rearfoot footfall runners, unaccustomed to running in minimalist footwear, performed 6-min sub-maximal treadmill running bouts at 11, 13 and 15 km·h−1 in minimalist and conventional shoes. Force sensitive resistors were placed in the shoes to quantify stride interval (time between successive foot contacts). Footfall position, stride interval mean and coefficient of variation (CV), were used to assess performance as a function of shoe type. Long-range correlations of stride interval were assessed using detrended fluctuation analysis (α). Mean stride interval was 1-1.3% shorter (P = 0.02) and 27% of runners adopted a midfoot footfall (MFF) in the minimalist shoe. There was a significant shoe effect on α and shoe*speed*footfall interaction effect on CV (P < 0.05). Runners that adopted a MFF in minimalist shoes, displayed reduced long-range correlations (P < 0.05) and CV (P < 0.06) in their running stride interval at the 15 km·h−1 speed. The reduced variability and self-similarity observed for runners that changed to a MFF in the minimalist shoe may be suggestive of a system that is less flexible and more prone to injury.
[Show abstract][Hide abstract] ABSTRACT: Loss of postural center-of-pressure complexity (COP complexity) has been associated with reduced adaptability that accompanies disease and aging. The aim of this study was to identify if COP complexity is reduced: (1) in those with Multiple Sclerosis (MS) compared to controls; (2) when vision is limited compared to remaining intact; and (3) during more demanding postural conditions compared to quiet standing. Additionally, we explored the relationship between the COP complexity and disease severity, fatigue, cutaneous sensation and central motor drive. Twelve women with MS and 12 age-matched controls were tested under quiet standing and postural maximal lean conditions with normal and limited vision. The key dependent variable was the complexity index (CI) of the center of pressure. We observed a lower CI in the MS group compared to controls in both anterior-posterior (AP) and medio-lateral (ML) directions (p's < 0.002), during the performance of maximal self-regulated leans (AP: p < 0.001; ML: p = 0.018), and under limited vision (AP: p = 0.001; ML: p = 0.006). No group-by-vision interaction (p > 0.05) was observed, indicating that limiting vision did not impact COP complexity differently in the two groups. Decreased cutaneous sensitivity was associated with lower CI values in the AP direction among those with MS (r2 = 0.57); all other measures did not exhibit significant relationships. The findings reported here suggest that (1) MS is associated with diminished COP complexity under both normal and challenging postures, and (2) complexity is strongly correlated with cutaneous sensitivity, suggesting the unique contribution of impaired somatosensation on postural control deficits in persons with MS.
[Show abstract][Hide abstract] ABSTRACT: 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.
No preview · Article · Jun 2015 · Journal of Sports Sciences
[Show abstract][Hide abstract] ABSTRACT: This study investigated timing and coordination during the swing phase of swing leg, body center of mass (CoM) and head during walking in n=19 people with multiple sclerosis (MS; n=19) and controls (n=19). The MS group showed differences in swing phase timing at all speeds. At imposed but not preferred speeds, the MS group had less time to prepare for entry into the unstable equilibrium, as the CoM entered this phase of swing earlier. Time-to-contact coupling, quantifying the coordination between the CoM and the swing foot, was not different between groups. The projection of head motion on the ground occurred earlier after toe-off and was positioned closer to the body in the MS group, illustrating increased reliance on visual exproprioception in which vision of the body in relation to the surface of support is established. Finally, prospective control, linking head movements to the swing foot time-to-contact and next step landing area, was impaired in the MS group at higher gait speeds.
[Show abstract][Hide abstract] ABSTRACT: Excessive pronation, because of its coupling with tibial internal rotation (TIR), has been implicated as a risk factor in the development of anterior knee pain (AKP). Traditionally this coupling has been expressed as a ratio between the eversion range of motion and the TIR range of motion (Ev/TIR) that occurs during stance. Currently, this technique has not been used to evaluate specific injuries or the effects of gender. Additionally, Ev/TIR is incapable of detecting coupling changes that occur throughout stance. Therefore, the purpose of this study was to compare the coupling between eversion and TIR in runners with (n = 19) and without AKP (n = 17) and across gender using the Ev/TIR ratio, and more continuously using vector coding. When using vector coding, significant coupling differences were noted in runners with AKP (34-38% stance), with runners with AKP showing relatively more TIR than eversion. Similarly significant differences were noted across gender (14-25 & 36-47% stance) with males transitioning from a loading to propulsive coordination pattern using a proximal to distal strategy, while female runners used a distal to proximal strategy. These differences were only detected when evaluating this coupling relationship using a continuous technique such as vector coding.
No preview · Article · Nov 2014 · Journal of applied biomechanics
[Show abstract][Hide abstract] ABSTRACT: People living with multiple sclerosis (MS) consistently rate balance and gait impairments as having the greatest negative impacts on their quality of life. Our research aims to understand the sensorimotor contributions to balance dysfunction and difficulty with walking in people with MS, with specific attention paid to how fatigue, muscle weakness, and sensory loss interact to limit physical function and mobility. Here, we relate aspects of somatosensory loss and symptomatic fatigue to balance function, and provide new insights in our understanding of the mechanisms of balance and gait dysfunction in MS through the use of novel analytical methods and experimental paradigms. We first review the existing methods and paradigms to assess postural and gait stability in research on MS. Next, we introduce novel measures to assess the stability and adaptability of posture and gait in people with MS that are based on nonlinear and complex systems methods. These novel methods include (1) boundary-relevant measures of postural stability and control (postural “time to contact”), and (2) entropy measures for assessing postural and gait adaptability. These novel methods allow us to differentiate between postural and gait variability caused by dysfunction that may interfere with movement control, and variability that is functional and provides stable and adaptable movement patterns. Finally, we discuss how these methods and paradigms could help to develop innovative treatments for balance and gait dysfunction in people with MS.
No preview · Article · Oct 2014 · Advances in Experimental Medicine and Biology
[Show abstract][Hide abstract] ABSTRACT: Background:
Clinically, plantar fasciitis (PF) is believed to be a result and/or prolonged by overpronation and excessive loading, but there is little biomechanical data to support this assertion. The purpose of this study was to determine the differences between healthy individuals and those with PF in (1) rearfoot motion, (2) medial forefoot motion, (3) first metatarsal phalangeal joint (FMPJ) motion, and (4) ground reaction forces (GRF).
We recruited healthy (n=22) and chronic PF individuals (n=22, symptomatic over three months) of similar age, height, weight, and foot shape (p>0.05). Retro-reflective skin markers were fixed according to a multi-segment foot and shank model. Ground reaction forces and three dimensional kinematics of the shank, rearfoot, medial forefoot, and hallux segment were captured as individuals walked at 1.35 ms(-1).
Despite similarities in foot anthropometrics, when compared to healthy individuals, individuals with PF exhibited significantly (p<0.05) (1) greater total rearfoot eversion, (2) greater forefoot plantar flexion at initial contact, (3) greater total sagittal plane forefoot motion, (4) greater maximum FMPJ dorsiflexion, and (5) decreased vertical GRF during propulsion.
These data suggest that compared to healthy individuals, individuals with PF exhibit significant differences in foot kinematics and kinetics. Consistent with the theoretical injury mechanisms of PF, we found these individuals to have greater total rearfoot eversion and peak FMPJ dorsiflexion, which may put undue loads on the plantar fascia. Meanwhile, increased medial forefoot plantar flexion at initial contact and decreased propulsive GRF are suggestive of compensatory responses, perhaps to manage pain.
No preview · Article · Jun 2014 · Journal of Biomechanics
[Show abstract][Hide abstract] ABSTRACT: This study examined the prospective control of the swing phase in young healthy adults while walking at preferred speed over unobstructed ground and during obstacle clearance. Three aspects of swing were examined: (1) the relation of the body Center of Mass (CoM) to the stability boundaries at the base of support; (2) a dynamic time-to-contact analysis of the CoM and swing foot to these boundaries; and (3) the role of head movements in the prospective control of gait and field of view assessment. The time-to-contact analysis of CoM and swing foot showed less stable swing dynamics in the trail foot compared to the lead foot in the approach to the unstable equilibrium, with the CoM leading the swing foot and crossing the anterior stability boundary before the swing foot. Compensations in temporal coupling occurred in the trail limb during the late swing phase. Time-to-contact analysis of head movement showed stronger prospective control of the lead foot, while fixation of the field of view occurred earlier in swing and was closer to the body in the obstacle condition compared to unobstructed walking. The dynamic time-to-contact analysis offers a new approach to assessing the unstable swing phase of walking in different populations.
No preview · Article · May 2014 · Human Movement Science
[Show abstract][Hide abstract] ABSTRACT: 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
[Show abstract][Hide abstract] ABSTRACT: Multiple Sclerosis (MS) is a chronic auto-immune disorder characterized by demyelination of neurons of the central nervous system. MS-related reductions in neural activity have been associated with reductions in balance control and limitations in mobility. Multiscale entropy (MSE) analysis has been used to identify reductions in complexity of the postural control system in various disorders. The purpose of this study was to examine if center-of-pressure fluctuations, analyzed through MSE, differ between persons with MS and healthy controls. We hypothesized that MSE would be reduced in MS compared to controls in all postural tasks in both anterior-posterior (AP) and medio-lateral (ML) directions. Eight persons with MS (7 female, 1 male) and matched controls completed the testing procedures. The MS subjects had minimal functional impairment (Patient Determined Disease Steps, range 0-3). Quiet standing and fixed distance forward and backward reaches were assessed for 30 s. MSE was computed across 30 time scales (range .01-.25s). Effect size (ES) statistics were used to assess differences between MS and control groups. Quiet standing revealed moderate reductions in complexity among persons with MS compared to controls in the AP direction (ES = .71). The backward reach demonstrated moderate and strong reductions in complexity in the AP and ML direction in the MS group (ES = .74 and 1.0, respectively). Moderate reductions in ML complexity were also observed in the forward reach condition in the MS group (ES = .68). These results support the hypothesis that persons with MS display lower postural complexity compared to those without MS. MSE analysis is a promising new tool for detecting MS-related changes in postural complexity. These changes in postural complexity appear to precede locomotor impairment, as assessed by the patient determined disease steps, and may provide novel insight into MS progression.
[Show abstract][Hide abstract] ABSTRACT: Abstract Recent literature has related differences in pelvis-trunk coordination to low back pain (LBP) status. In addition, repetitive motions involving bending and twisting have been linked to high incidence of LBP. The purpose of this study was to examine trunk sagittal motion - axial rotation ('bend and twist') coordination during locomotion in three groups of runners classified by LBP status (LBP: current low back pain; RES: resolved low back pain and CTR: control group with no history of LBP). Trunk kinematic data were collected as running speed was systematically increased on a treadmill. Within-segment coordination between trunk sagittal and transverse planes of motion (trunk lean and axial rotation, respectively) was calculated using continuous relative phase (CRP), and coordination variability was defined as the between stride cycle standard deviation of CRP (CRPvar). Bend-twist coordination was more in-phase for the LBP group than CTR (p = 0.010) regardless of running speed. No differences in CRPvar were found between the groups. The results from our coordination (CRP) analysis were sensitive to LBP status and suggest that multi-plane interactions of the trunk should be considered in the assessment of LBP. This analysis also has potential for athletically oriented tasks that involve multi-plane interactions of the trunk, particularly ones that contain asymmetric action, such as sweep rowing or a shot on goal in field hockey or ice hockey.