Walking Speed Affects Gait Coordination and Variability Among Older Adults With and Without Mobility Limitations.

OBJECTIVE: To determine if poorer gait variability and gait coordination among mobility-limited older adults is related to their slower walking speed. DESIGN: Cross-sectional analysis. SETTING: University research laboratory. PARTICIPANTS: Community-dwelling adults (N=69) 68 years or older with (Short Physical Performance Battery score ≤9; n=37) and without (n=32) mobility limitations. INTERVENTIONS: Not applicable. MAIN OUTCOME MEASURES: The variability of step length, swing time percent, and step width. Gait coordination was assessed along with the Phase Coordination Index. RESULTS: The usual pace gait speed of those without mobility limitations was faster (1.22±0.14m/s vs 0.71±0.14m/s; P<.001) and less variable in all gait characteristics (all P<.001), with the exception of step width (P=.185), than those with limitations. When those without limitations slowed their walking pace (0.71m/s±0.14), their gait coordination became poorer (P<.001), and the variability of all gait characteristics increased (all P<.001) except for step width, which decreased (P=.002). When those without mobility limitations walked at a slow pace, they had better gait coordination (P=.008) and less variable step length (P=.014) and swing time percent (P=.036). The variability of stride time (P=.260) and step width (P=.385) were not significantly different than that of their peers with limitations. CONCLUSIONS: Increased variability in some gait characteristics of mobility-limited older adults appears to be related to their slower walking speed. Gait coordination and the variability of step length and swing time percent may reflect intrinsic differences in mobility-limited older adults that are independent of walking speed.

Ankle control differentiation as a mechanism for mobility limitations.

Independent control of the right and left ankles (differentiation) may be a motor control mechanism linking impaired coordination and mobility limitations. We tested the hypotheses that motor control differentiation of the ankles, as measured using Cross-Sample Entropy, during antiphase coordination at two movement frequencies, is associated with impaired coordination (high ankle coordination variability) and mobility limitations (Short Physical Performance Battery score ≤9). We conducted a cross-sectional study of community-dwelling older adults (N = 133) aged 80.04 (±4.67) years. In linear regression modeling, low ankle Cross-Sample Entropy (low motor control differentiation) was associated with poor (i.e., high) coordination variability at the slower (P = 0.026), but not the faster (P = 0.447), ankle movement frequency. In logistic regression modeling, low Cross-Sample Entropy at the slower (OR = 1.67; 95 % CI: 1.07-2.59) and faster (OR = 2.38; 95 % CI: 1.43-3.94) ankle movement frequencies were associated with increased odds for mobility limitations. Our findings support the hypothesis that ankle differentiation may be a motor control mechanism that links impaired coordination with mobility limitations.

Small arteries stay stiff for a longer period following vibration exercises in combination with blood flow restriction.

PURPOSE: The aim of this study was to assess the effect of isometric exercises performed during whole-body vibration (WBV) with and without blood flow restriction (BFR) on arterial elasticity and hemodynamic variables. METHODS: Eight male subjects performed static upper body (UB) and lower body (LB) exercises on a vibration platform with and without BFR. During BFR sessions, BFR cuffs were placed on the arms or legs and inflated to a target pressure. Exercises consisted of eight 45-s sets for UB, and ten 1-min sets for LB. Arterial elasticity and hemodynamic variables were assessed before, at 10 min and 40 min postexercise. Repeated measures ANOVA was used to test the mean differences in related variables. RESULTS: A significant condition (BFR versus no-BFR) main effect was detected for small arterial elasticity (P<0·05). For heart rate (HR), there were significant time (P<0·01), condition (P = 0·02) and body (P = 0·04) main effects during exercise and condition (P<0·04) and time (P<0·01) main effects following exercise. Significantly lower values in systemic vascular resistance were detected at 10 min post compared to 40 min post (P<0·02) and UB compared to LB (P = 0·02). CONCLUSIONS: Results showed that small arteries stayed stiffer for a longer period of time after vibration exercises with BFR and BFR placed a greater demand on cardiovascular system. Findings also indicated that the type of exercises performed and/or the measurement location are very important and should be taken into account when examining arterial response.

Coordination Impairments Are Associated With Falling Among Older Adults.

Background/Study Context: Approximately one third of older adults over the age of 65, and over 40% of those over 80 years, fall each year, leading to fractures, morbidity, and mortality. Annual direct medical costs due to falls in the United States are approximately $19.2 billion. The identification of new treatable risk factors for falls has the potential to advance their prevention and rehabilitation. METHODS: A cross-sectional study of 127 community-dwelling adults aged 67-99 years was conducted. An electronic gait walkway was used to assess gait coordination, measured as the Phase Coordination Index during normal speed walking. A motion capture system was used to assess rhythmic interlimb antiphase ankle coordination, measured as the standard deviation of ankle relative phase. Having fallen in the previous year was self-reported retrospectively. Odds ratios for falling as a function of coordination quartiles were determined using multivariable logistic regression. RESULTS: Adjusting for age, sex, body mass index, number of chronic conditions, Mini-Mental State Examination score, gait speed, and the variability of step length, time, and width, the odds ratios for falling based upon being in the 4th (the poorest) quartiles of gait or ankle coordination were 5.5 (95% confidence interval [CI]: 1.2-24.7) and 8.2 (95% CI: 2.2-31.3), respectively, and 3.7 (95% CI: 1.0-13.8) for the 3rd quartile of gait coordination, compared with the best (the 1st) coordination quartiles. Similar results were found in regression without adjustment for gait characteristics. CONCLUSION: The results support the hypothesis that impaired gait and rhythmic interlimb ankle coordination are associated with a history of falls in the past year. Prospective longitudinal research is needed to determine the possible direction of causality between falls and impaired coordination.

Rhythmic Interlimb Coordination Impairments Are Associated With Mobility Limitations Among Older Adults.

Background/Study Context: Mobility limitations affect more than 25% of adults aged 70 years or older. This study tested the hypothesis that impairments in ankle and shoulder coordination are associated with mobility limitations among older adults. METHODS: his study consisted of conducted a cross-sectional analysis from a sample of community-dwelling older adults (N = 130) aged ≥67 years. Motion capture equipment was used to collect kinematic data during rhythmic antiphase coordination of the right and left: (a) ankles moving in dorsi-plantarflexion; and (b) glenohumeral ("shoulder") moving in flexion-extension while paced by an auditory metronome. Coordination variability was measured as the standard deviation of the relative phase between right and left body segments. Mobility limitations were defined as a score of ≤9 on the Short Physical Performance Battery (SPPB). Odds ratios for mobility limitations as a function of coordination variability quartiles were determined using multivariable logistic regression. RESULTS: Adjusting for age, gender, body mass index, number of chronic conditions and Mini-Mental State Examination score, the odds ratios for mobility limitation (SPPB score ≤9) were 7.38 (95% confidence interval [CI]: 2.20-24.78) and 15.40 (95% CI: 4.31-55.07) for the 3rd and 4th (the poorest) ankle coordination quartiles, respectively, and 6.73 (95% CI: 2.11-21.51) for the 4th shoulder coordination quartile, compared with the best (the 1st) coordination quartiles. CONCLUSION: The results supported the hypothesis that impaired interlimb ankle and shoulder coordination are associated with the manifestation of mobility limitations. These findings indicate the need for further study of the role of coordination impairments as potential contributors to poor mobility among older adults.

Rhythmic Interlimb Coordination Impairments and the Risk for Developing Mobility Limitations.

BACKGROUND: The identification of novel rehabilitative impairments that are risk factors for mobility limitations may improve their prevention and treatment among older adults. We tested the hypothesis that impaired rhythmic interlimb ankle and shoulder coordination are risk factors for subsequent mobility limitations among older adults. METHODS: We conducted a 1-year prospective cohort study of community-dwelling older adults (N = 99) aged 67 years and older who did not have mobility limitations (Short Physical Performance Battery score > 9) at baseline. Participants performed antiphase coordination of the right and left ankles or shoulders while paced by an auditory metronome. Using multivariable logistic regression, we determined odds ratios (ORs) for mobility limitations at 1-year follow-up as a function of coordination variability and asymmetry. RESULTS: After adjusting for age, sex, body mass index, Mini-Mental State Examination score, number of chronic conditions, and baseline Short Physical Performance Battery score, ORs were significant for developing mobility limitations based on a 1 SD difference in the variability of ankle (OR = 1.88; 95% confidence interval [CI]: 1.16-3.05) and shoulder (OR = 1.96; 95% CI: 1.17-3.29) coordination. ORs were significant for asymmetry of shoulder (OR = 2.11; 95% CI: 1.25-3.57), but not ankle (OR = 0.95; 95% CI: 0.59-1.55) coordination. Similar results were found in unadjusted analyses. CONCLUSIONS: The results support our hypothesis that impaired interlimb ankle and shoulder coordination are risk factors for the development of mobility limitations. Future work is needed to further examine the peripheral and central mechanisms underlying this relationship and to test whether enhancing coordination alters mobility limitations.

Mobility limitations and fear of falling in non-English speaking older Mexican-Americans.

OBJECTIVE: To determine whether older Mexican-Americans who cannot speak and/or understand spoken English have higher rates of mobility limitations or fear of falling than their English-speaking counterparts. DESIGN: We conducted a cross-sectional analysis of 1169 community-dwelling Mexican-Americans aged 72-96 years from the 2000-2001 wave of the Hispanic Established Population for the Epidemiological Study of the Elderly. Mobility limitations were defined as having a Short Physical Performance Battery score ≤9, and fear of falling by participant report of being somewhat, fairly, or very afraid of falling. We determined the rates and odds ratios, for having mobility limitations and fear of falling as a function of English ability in those who were 72-96, <80, and ≥80 years of age. RESULTS: Among participants who were unable to speak and/or understand spoken English 85.7% had mobility limitations and 61.6% were afraid of falling, compared to 77.6% and 57.5%, respectively, of English speakers. Before adjusting for covariates, participants who did not speak and/or understand spoken English were more likely to have mobility limitations (odds ratio: 1.7; 95% CI: 1.3-2.4) but not fear of falling, compared to English speakers. Among those aged ≥80 years, but not those <80 years, who did not speak or understand English were more likely to have mobility limitations (odds ratio: 4.8; 95% CI:2.0-11.5) and fear of falling (odds ratio: 2.0; 95% CI:1.3-3.1). CONCLUSION: Older Mexican-Americans who do not speak or understand spoken English have a higher rate of mobility limitations and fear of falling than their English-speaking counterparts.

Gait coordination impairment is associated with mobility in older adults.

BACKGROUND: Impairments to body systems contribute to mobility limitations. The objective of this study was to determine whether impaired gait coordination, as measured by the Phase Coordination Index (PCI), is significantly associated with mobility limitations in older adults, even after adjusting for other gait features. METHODS: We conducted a cross-sectional analysis of performance-based measures of mobility in older adults (N=164) 77-101years of age, participants in the population-based MOBILIZE Boston Study. Mobility outcomes included the Short Physical Performance Battery (SPPB) and each of its three components. Multivariable linear regression models, adjusting for age and gender, were used to examine the associations of PCI and the coefficients of variation of stride length, width and time, stance time, and step width with each outcome. RESULTS: PCI accounted for more variance in SPPB score (R(2)=0.21), gait speed (R(2)=0.17), chair rise score (R(2)=0.10), and balance score (R(2)=0.09) than any of the other gait measures. Impaired gait coordination was significantly associated with performance on the SPPB and each of its component tasks, even after accounting for gait measures previously linked to mobility tasks (all P<0.05). In multivariable linear regression modeling PCI accounted for an additional 9% of the variance in SPPB score (P<0.001), after accounting for the other gait variables, age, and gender. CONCLUSIONS: This study shows that impaired gait coordination is associated with poorer mobility performance in older adults, independent of other gait variables previously linked to mobility tasks.

Effects of practice variability on unimanual arm rotation.

High variability practice has been found to lead to a higher rate of motor learning than low variability practice in sports tasks. The authors compared the effects of low and high levels of practice variability on a simple unimanual arm rotation task. Participants performed rhythmic unimanual internal-external arm rotation as smoothly as possible before and after 2 weeks of low (LV) or high (HV) variability practice and after a 2-week retention interval. Compared to the pretest, the HV group significantly decreased hand, radioulnar, and shoulder rotation jerk on the retention test and shoulder jerk on the posttest. After training the LV group had lower radioulnar and shoulder jerk on the posttest but not the retention test. The results supported the hypothesis that high variability practice would lead to greater learning and reminiscence than low variability practice and the theoretical prediction of a bifurcation in the motor learning dynamics.

Nonstationarity of stable States in rhythmic bimanual coordination.

The HKB model and its variants characterize bimanual coordination with fixedpoint dynamics and predict stationarity of the mean and variance of relative phase in stable coordinative states. In the current study, participants performed in-phase and antiphase coordination modes in rhythmic bimanual finger and elbow flexionextension tasks. The results of runs tests revealed that discrete relative phase was nonstationary in 49.25%, 50.25%, and 54% of time-series in the 10, 20, and 30 box runs tests, respectively. In all individual Task conditions >38% of time-series were nonstationary. These findings contradicted model predictions that the mean and variance of relative phase are stationary in bimanual coordination and distinguish the concept of dynamical stability from statistical stationarity. The findings indicated that relative phase was not attracted to a stationary fixed-point and that fluctuations in relative phase are not Gaussian white noise as in existing models of bimanual coordination.

Short-term differential training decreases postural sway.

Differential training has been shown to enhance motor learning in sports skills. In the present study differential training was applied to the minimization of postural sway. A differential training group performed 15 one minute practice trials, each with different postural movement instructions. A repetitive practice group performed 15 trials standing as still as possible for one minute. Pre- and post-tests were performed standing as still as possible in 1 and 2-leg stance. Accelerometry data were collected approximately at the level of the center of mass (COM) and at the head. The root mean square jerk (RMSJ) of movement at the COM and head was estimated for the anteroposterior and mediolateral axes of motion. A significant Group × Test interaction revealed that the differential training led to lower anteroposterior RMSJ on the post-test than on the Pre-test in both the 1 and 2-leg stance tasks. A significant Group × Effector × Test interaction revealed that the decrease in anteroposterior RMSJ with differential training occurred in the RMSJ of the head but not the COM. The repetitive practice did not lead to a significant change in anteroposterior RMSJ at either the COM or the head. Neither form of training led to a significant change in mediolateral RMSJ. The results indicated that differential training can enhance motor learning not only in complex sports skills but in relatively simple motor tasks such as maintaining quiet stance.

A model of postural coordination dynamics.

Prior research has shown that voluntary postural movement is characterized by stable in-phase and antiphase hip-ankle coordination modes. Prior modeling of coordination dynamics does not capture the stable fixed-points, phase transitions and hysteresis found in hip-ankle coordination. In this article a model was created to capture the dynamics of hip-ankle postural coordination. The present model follows the synergetic approach and uses two nonlinear oscillators to capture the dynamics of hip-ankle coordination. Terms for symmetry breaking and additive stochastic noise are included in the model. The model captures phase transitions from in-phase to antiphase coordination as movement frequency is scaled up and from antiphase to in-phase coordination as movement frequency is scaled down. The model also exhibits hysteresis, with phase transitions occurring at different movement frequencies as the control parameter is scaled up and down.

Vascular restriction decreases EMG regularity during walking.

Prior research has found that the level of regularity in the output of numerous physiological systems is lowest in healthy young adults and higher in groups such as the elderly and those with various diseases. Vascular restriction has been found to stimulate exercise induced responses, including greater muscle activation, hypertrophy and increased strength. However, the time-dependent properties of muscular activation with vascular restriction have not previously been examined. In the present study participants (N=9) performed two 10 minute bouts of treadmill walking with and without vascular restriction while surface EMG was used to examine the level of activation of the vastus lateralis. Regularity was found to increase over bouts of exercise. A significant vascular restriction×bout×minute interaction in EMG regularity also occurred, with vascular restriction leading to a slower increase in regularity than without vascular restriction. These results suggest that, in addition to previously identified effects, vascular restriction decreases the regularity of muscular activation patterns during walking.

Metastable postural coordination dynamics.

The present study examined the coordination dynamics of the head and center of mass (COM) using accelerometry in quiet 1 and 2 leg stance with and without vision. The root mean square jerk of effectors was greater in 1 leg stance and without vision, and was greater for the head in 2 leg stance and greater at the COM for 1 leg stance. The coordination of the COM and head was more variable in 1 leg stance with vision than in the other stance and vision combinations. Both grouped and individual participant data showed metastable coordination dynamics with the presence of ghost attractors on both axes of motion that varied with the task. The findings indicated that stance and visual information conditions acted as control parameters, with increments in task difficulty increasing relative phase variability until a bifurcation in the metastable dynamics occurred in 1 leg stance without vision.

Dimensionality in rhythmic bimanual coordination.

Newell and Vaillancourt (2001) hypothesized that the dimensionality of motor behavior is a function of the level of task performance and the task dynamic. The present study examined high (in-phase), moderate (antiphase) and low (45°, 90°, and 135° relative phase) levels of task performance in bimanual coordination. Estimates of dimensionality were calculated for the component (effector movements), coupling of components (coupling of effectors), and task output (the produced relative phase) levels of analysis. The in-phase coordination mode had lower Approximate Entropy within, and lower Cross-Approximate Entropy between, effector movements than all other modes. The in-phase mode had higher relative phase Approximate Entropy than all other modes. These findings indicate lower effector and coupling dimensionality, and higher relative phase dimensionality, in the in-phase mode. These results support the hypothesis that at the levels of analysis with limit-cycle dynamics high levels of task performance are characterized by lower dimensionality than lower levels of performance. The results also support the hypothesis that high task performance of the fixed-point task goal of maintaining a constant relative phase is characterized by higher dimensionality than low level performance. Together, these findings support and generalize the Newell and Vaillancourt hypothesis to the component, coupling, and task output levels of analysis.

Dynamical degrees of freedom and correlations in isometric finger force production.

Prior research has concluded that the correlations of isometric finger forces represent the extent to which the fingers are controlled as a single unit. If this is the case, finger force correlations should be consistent with estimates of the controlled (dynamical) degrees of freedom in finger forces. The present study examined the finger force correlations and the dynamical degrees of freedom in four isometric force tasks. The tasks were to produce a preferred level of force with the (a) Index, (b) Ring, (c) Both fingers and also to (d) Rest the fingers on the load cells. Dynamical degrees of freedom in finger forces were lowest in the Both finger force task and progressively higher in the Ring, Index and Resting finger force tasks. The finger force correlations were highest in the Resting and lowest in the Index and Ring finger tasks. The results for the dynamical degrees of freedom in finger forces were consistent with a reduction in degrees of freedom in response to the degrees of freedom problem and the task constraints. The results for the finger force correlations were inconsistent with a reduction in the dynamical degrees of freedom. These findings indicate that finger force correlations do not necessarily reflect the coupling of finger forces. The findings also highlight the value of time-domain analyses to reveal the organization of control in isometric finger forces.

Fixed-point drift and hysteresis in frequency-scaled unimanual coordination.

Research on human rhythmic coordination has shown that the in-phase and antiphase coordination modes are typically stable and that the coordination of asymmetric effectors frequently exhibits fixed-point drift. The author extended research on symmetry breaking in coordination dynamics by examining a frequency-scaled unimanual pronation-supination task. The results showed symmetry breaking and fixed-point drift, with the radioulnar joint increasingly more phase advanced than the shoulder with increments in movement frequency. Hysteresis was also observed, as the relative phase patterns produced at 3 of the 4 movement frequencies were lower in the upward frequency scaling direction than in the downward direction. These results showed that the dynamic properties of symmetry breaking and fixed-point drift in unimanual pronation-supination movements were consistent with prior research and modeling. The hysteresis effect was explained as potentially being due to the control structures that organize this redundant coordination task.

Body movement instructions facilitate synergy level motor learning, retention and transfer.

Prior work has suggested that the findings of research on attentional focus during human motor learning research generalize to the use of instructions regarding body movement. However, research on focus of attention has generally not included the use of instructions that prescribe body movement. The present study examined the effect of instructions regarding body movement or movement outcome in a motor task that principally relied upon the organization of an effective movement pattern, with little demand to adapt the movement to environmental task constraints. The use of instructions for efficient body movement produced an improvement in a seated turning range-of-motion task within the first 5 movement trials. This improvement was retained 24 h later and transferred across sitting positions. The instructions to optimize the movement outcome improved the turning range-of-motion significantly on the post-test but not on the retention or transfer tests. These findings indicate that instructions regarding movement form can be more advantageous than instructions regarding movement outcome in a task that relies upon the organization of an effective movement pattern with little demand to adapt this pattern to environmental constraints of the task. The results are interpreted with respect to task constraints and Bernstein's (1996) hierarchy of control.

Hierarchical control in redundant and non-redundant postural tasks.

Prior studies of postural coordination have shown inconsistencies between hip-ankle coordination in redundant and non-redundant coordination tasks as well as predictions of the HKB model. These inconsistencies were investigated by testing the hypothesis that there are different hierarchical control structures for redundant (multiple potential task solutions) and non-redundant (a single task solution) coordination tasks (Bernstein, 1996). The transfer between a non-redundant postural tracking task and a redundant scanning task consisting of 16 hip-ankle relative phase patterns from 0° to 337.5° was investigated. The results showed that the transfer between the tasks was transitory, negative and occurred only from the non-redundant to the redundant task. This finding supports the hypothesis that inconsistencies between redundant and non-redundant coordination dynamics may be due to a hierarchical relation between control structures for the performance of these types of tasks.

Time dependence of coupling in frequency-scaled bimanual coordination.

Prior research has shown that fluctuations in the relative phase of bimanual coordination do not reflect a white Gaussian noise process. The present study furthered the examination of time-dependent properties in bimanual coordination by comparing the magnitude of relative phase variability and the degree of effector independence within the time domain. The original Kelso (1984) [10] bimanual frequency-scaling protocol was reproduced in which phase transitions from antiphase to in-phase were induced with increasing movement frequency. The results showed that as movement frequency was scaled-up the amount of relative phase variability increased and the effector movements became more dependent prior to the transition. This is consistent with previous modeling showing that stronger effector coupling can prevent the occurrence of phase transitions when long range correlations in relative phase are present. It appears that, as movement frequency is scaled up, increases in effector coupling strength minimize loss of pattern stability and delay the onset of phase transitions.