Spatiotemporal walking performance in different settings: effects of walking speed and sex

Background

Understanding the factors that influence walking is important as quantitative walking assessments have potential to inform health risk assessments. Wearable technology innovation has enabled quantitative walking assessments to be conducted in different settings. Understanding how different settings influence quantitative walking performance is required to better utilize the health-related potential of quantitative walking assessments.

Research question

How does spatiotemporal walking performance differ during walking in different settings at different speeds for young adults?

Methods

Forty-two young adults [21 male (23 ± 4 years), 21 female (24 ± 5 years)] walked in two laboratory settings (overground, treadmill) and three non-laboratory settings (hallway, indoor open, outdoor pathway) at three self-selected speeds (slow, preferred, fast) following verbal instructions. Six walking trials of each condition (10 m in laboratory overground, 20 m in other settings) were completed. Participants wore 17 inertial sensors (Xsens Awinda, Movella, Henderson, NV) and spatiotemporal parameters were computed from sensor-derived kinematics. Setting × speed × sex repeated measures analysis of variance were used for statistical analysis.

Results

Regardless of the speed condition, participants walked faster overground when compared to while on the treadmill and walked faster in the indoor open and outdoor pathway settings when compared to the laboratory overground setting. At slow speeds, participants also walked faster in the hallway when compared to the laboratory overground setting. Females had greater cadence when compared to males, independent of settings and speed conditions.

Significance

Particularly at slow speeds, spatiotemporal walking performance was different between the settings, suggesting that setting characteristics such as walkway boundary definition may significantly influence spatiotemporal walking performance.

The measurement properties of the Lean-and-Release test in people with incomplete spinal cord injury or disease

OBJECTIVE

To evaluate test-retest reliability, agreement, and convergent validity of the Lean-and-Release test for the assessment of reactive stepping among individuals with incomplete spinal cord injury or disease (iSCI/D).

DESIGN

Multi-center cross-sectional multiple test design.

SETTING

SCI/D rehabilitation hospital and biomechanics laboratory.

PARTICIPANTS

Individuals with motor incomplete SCI/D (iSCI/D).

INTERVENTIONS

None.

OUTCOME MEASURES

Twenty-six participants attended two sessions to complete the Lean-and-Release test and a battery of clinical tests. Behavioral (i.e. one-step, multi-step, loss of balance) and temporal (i.e. timing of foot off, foot contact, swing of reactive step) parameters were measured. Test-retest reliability was determined with intraclass correlation coefficients, and agreement was evaluated with Bland-Altman plots. Convergent validity was assessed through correlations with clinical tests.

RESULTS

The behavioral responses were reliable for the Lean-and-Release test (ICC = 0.76), but foot contact was the only reliable temporal parameter using data from a single site (ICC = 0.79). All variables showed agreement according to the Bland-Altman plots. The behavioral responses correlated with scores of lower extremity strength (0.54, P<0.01) and balance confidence (0.55, P < 0.01). Swing time of reactive stepping correlated with step time (0.73, P < 0.01) and cadence (-0.73 P < 0.01) of over ground walking.

CONCLUSIONS

The behavioral response of the Lean-and-Release test is a reliable and valid measure for people with iSCI/D. Our findings support the use of the behavioral responses to evaluate reactive stepping for research and clinical purposes.

TRIAL REGISTRATION

ClinicalTrials.gov identifier: NCT02960178.

The Associations Among Self-Compassion, Self-Esteem, Self-Criticism, and Concern Over Mistakes in Response to Biomechanical Feedback in Athletes

Athletes regularly face the possibility of failing to meet expectations in training and competition, and it is essential that they are equipped with strategies to facilitate coping after receiving performance feedback. Self-compassion is a potential resource to help athletes manage the various setbacks that arise in sport over and above other psychological resources. The primary purpose of this research was to explore how athletes respond to objective biomechanical feedback given after a performance. Specifically, we investigated if levels of self-compassion, self-esteem, self-criticism, and concern over mistakes were related to one another before and after a series of sprint tests interspersed with biomechanical feedback, and whether self-compassionate athletes achieved a better sprint performance after receiving and implementing biomechanical feedback. Forty-eight athletes (20 female: M_age = 19.8 years, SD = 3.1; 28 male: M_age = 23.6 years, SD = 7.8) completed online measures of self-compassion, self-esteem, self-criticism and concern over mistakes before performing four sets of 40-m sprints. Participants received personalized biomechanical feedback after each sprint that compared their performance to gold standard results. Following all sprints, they then completed measures of self-criticism, and reported emotions, thoughts, and reactions. Self-compassion was positively correlated with self-esteem (r = 0.57, p < 0.01) and negatively related to both self-criticism (r = −0.52, p < 0.01) and concern over mistakes (r = −0.69, p < 0.01). We also found that athletes with higher levels of self-compassion prior to sprint performance experienced less self-critical thoughts following biomechanical feedback and subsequent sprint trials (r = −0.38, p < 0.01). Although the results of this study provide some support for the effectiveness of self-compassion in promoting healthy emotions, thoughts, and reactions in response to sprint performance-based biomechanical feedback, a moderated regression analysis between the first and fourth sprint time variables revealed that self-compassion was not a moderator for change in sprint performance (R² = 0.64, ΔR² = 0.10, p > 0.05). These findings suggest that there are likely longer-term benefits of athletes using self-compassion to cope with biomechanical feedback, but that any benefits might be limited in a short series of sprint trials.

Design characteristics and inclusion of evidence-based exercise recommendation in fall prevention community exercise programs for older adults in Canada: a national descriptive self-report study

BACKGROUND

Training balance through exercise is an effective strategy to reduce falls in community-dwelling older adults. Evidence-based fall prevention exercise recommendations have been proposed, specifying that exercise programs should: (1) provide a high challenge to balance, (2) be offered for a least three hours per week, (3) be provided on an ongoing basis. Community exercise programs have the potential to deliver effective fall prevention exercise; however, current design characteristics and whether they include the recommendations is not known. This study described design characteristics of fall prevention community exercise programs for older adults (50 years and older) across Canada, and explored whether these programs included the three evidence-based exercise recommendations.

METHODS

Instructors of fall prevention community exercise programs completed electronic self-report questionnaires following a modified Dillman recruitment approach. Questions explored program characteristics, exercise content, target population, and program and instructor demographic information. Using a previously developed coding scheme based on recommendations, exercises were coded for balance challenge.

RESULTS

One hundred fourty completed eligible questionnaires were analyzed (74% response rate). One hundred thirty-three programs (95%) included the challenge recommendation by prescribing mostly moderate or high challenge balance exercises, 16 programs (11%) included at least three hours of exercise a week, and 59 programs (42%) were offered on an ongoing basis. Eight programs (6%) included all three recommendations.

CONCLUSIONS

Most programs included at least one recommendation for effective fall prevention exercise. Future studies should examine organizational barriers and facilitators to incorporating evidence-based exercise recommendations and explore the use of mixed home/in-class strategies to include the recommendations.

Adding Light Touch While Walking in Older Adults: Biomechanical and Neuromotor Effects

Adding haptic input may improve balance control and help prevent falls in older adults. This study examined the effects of added haptic input via light touch on a railing while walking. Participants (N = 53, 75.9 ± 7.9 years) walked normally or in tandem (heel to toe) with and without haptic input. During normal walking, adding haptic input resulted in a more cautious and variable gait pattern, reduced variability of center of mass acceleration and margin of stability, and increased muscle activity. During tandem walking, haptic input had minimal effect on step parameters, decreased lower limb muscle activity, and increased cocontraction at the ankle closest to the railing. Age was correlated with step width variability, stride length variability, stride velocity, variability of medial-lateral center of mass acceleration, and margin of stability for tandem walking. This complex picture of sensorimotor integration in older adults warrants further exploration into added haptic input during walking.

The effects of light touch on gait and dynamic balance during normal and tandem walking in individuals with an incomplete spinal cord injury

STUDY DESIGN

Prospective cross-sectional study OBJECTIVES: To investigate the effect of adding haptic input during walking in individuals with incomplete spinal cord injury (iSCI).

SETTING

Research laboratory.

METHODS

Participants with iSCI and age- and sex-matched able-bodied (AB) individuals walked normally (SCI n = 18, AB n = 17) and in tandem (SCI n = 12, AB n = 17). Haptic input was added through light touch on a railing. Step parameters, and mediolateral and anterior-posterior margins of stability (means and standard deviations) were calculated. Surface electromyography data were collected bilaterally from the tibialis anterior (TA), soleus (SOL), and gluteus medius (GMED) and integrated over a stride. Repeated measures ANOVAs examined within- and between-group differences (α = 0.05). Cutaneous and proprioceptive sensation of individuals with iSCI were correlated to changes in outcome measures that were affected by haptic input.

RESULTS

When walking normally, adding haptic input decreased stride velocity, step width, stride length, MOS_ML, MOS_ML_SD, MOS_AP, and MOS_AP_SD, and increased GMED activity on the limb opposite the railing. During tandem walking, haptic input had no effect; however, individuals with iSCI had a larger step width SD and MOS_ML_SD compared with the AB group. Sensory abilities of individuals with iSCI were not correlated to any of the outcome measures that significantly changed with added haptic input.

CONCLUSIONS

Added haptic input improved balance control during normal but not in tandem walking. Sensory abilities did not impact the use of added haptic input during walking.

Haptic input and balance control: An exploratory study examining normative messaging

This study examined the effect of descriptive norm messaging information on the relationship between haptic input and balance control. Participants were randomly assigned to either a message group where they balanced with haptic input after receiving a descriptive norm message about the positive effect of haptic input or a control group. Findings from an analysis of covariance revealed a significant difference between the two groups. Those in the descriptive norm message group had better balance control than those in the control group. These findings suggest that efforts designed to improve balance control through haptic input may be enhanced through normative messaging.

Are there attentional demands associated with haptic modalities while walking in young, healthy adults?

STUDY DESIGN

A prospective, observational study.

OBJECTIVES

To assess the attentional demands of using haptic modalities during walking using a multi-task paradigm in young, healthy adults.

SETTING

Biomechanics of Balance and Movement (BBAM) Lab, University of Saskatchewan.

METHODS

Twenty-two (12 male) young, healthy adults performed walking trials with and without a verbal reaction time (VRT) task, as well as with and without the use of haptic anchors and light touch on a railing. Walking performance was evaluated using normalized stride velocity and step width, and dynamic stability was evaluated using step width variability and medial-lateral margin of stability (ML MOS) and its variability.

RESULTS

There were no significant differences in VRT when walking with and without added haptic input and no interactions between the added VRT task and added haptic input. Step width increased and variability of the ML MOS increased during trials with the VRT task compared to trials without the VRT task. The ML MOS decreased when using both haptic tools with a greater decrease when using light touch on the railing compared to when using the haptic anchors. Normalized stride velocity and step width decreased when using light touch on the railing only.

CONCLUSION

Both haptic tools affected stability during walking. Using the railing to add haptic input had a greater effect on walking stability and was the only haptic tool to affect walking performance. Attentional demands should be considered in future research and applications of adding haptic input during walking.

To what extent do older adult community exercise programs in Winnipeg, Canada address balance and include effective fall prevention exercise? A descriptive self-report study

Background

Effective fall prevention exercise for community-dwelling older adults requires (i) challenging balance exercise, (ii) offered at least 3 hrs/ week, and (iii) on an ongoing basis, to reduce falls. Community exercise programs are a potential implementation strategy for fall prevention exercise; however, the extent to which they address balance and include effective fall prevention exercise is unknown. Study objectives were to describe program delivery, exercise design, and assessment characteristics of older adult community exercise programs in Winnipeg, Canada; determine if they included effective fall prevention exercise; determine the balance challenge and components of postural control addressed in the most- and least-frequently reported exercises.

Methods

A public inventory of older adult community exercise programs served as the sampling frame for cross-sectional telephone questionnaires exploring program, exercise, and assessment characteristics. Exercises were coded independently by two investigators for balance challenge level and components of postural control. Programs were categorized by number of effective fall prevention exercise components established by evidence-based recommendations. Descriptive statistics were calculated.

Results

Thirty-three eligible programs were identified and nine individuals participated. Most programs (n = 5, 56%) identified as general exercise, and two (22%) as fall prevention exercise. Most programs (n = 5, 56%) were offered two or more times/ week and reported exercise intensity as somewhat challenging. Exercise time offered ranged between 1 and 3 h/ week. Assessments were conducted in two programs (22%). Only one program (general exercise) included all components of effective fall prevention exercise. Two programs (22%) included the component of being offered at least 3 hrs/ week. Three programs (33%) included the component of being offered on an ongoing basis. Seven programs (78%) prescribed mostly moderate challenge balance exercise, and one program (11%) prescribed mostly high challenge exercise. Most of the 19 most-frequently prescribed exercises (n = 17, 89%) targeted static stability and none targeted reactive postural control.

Conclusions

Most of the older adult community exercise programs participating in this study did not focus on fall prevention, and did not include all components of effective fall prevention exercise. Future studies should focus on fall prevention programs and explore factors influencing implementation of effective fall prevention exercise components to facilitate planning.

Electronic supplementary material

The online version of this article (10.1186/s12877-019-1224-x) contains supplementary material, which is available to authorized users.

Comparing the effect of haptic modalities on walking balance control: Is using one or two arms better?

BACKGROUND

Adding haptic input by lightly touching a railing or using haptic anchors may improve walking balance control. Typical use of the railing(s) and haptic anchors requires the use of one and two arms in an extended position, respectively. It is unclear whether it is arm configuration and/or the number of arms used or the addition of sensory input that affects walking balance control.

RESEARCH QUESTION

This study examined whether using one arm or two arms to add haptic input through light touch on a railing or using the haptic anchors affects walking balance control.

METHODS

In this study, young adults (n = 24) walked while using (actual use) or pretending to use (pretend use) the railing(s) and haptic anchors with one or two arms. Inertial-based sensors (Mobility Lab, APDM) were used to measure stride velocity, relative time spent in double support (%DS), and peak normalized medio-lateral trunk velocity (pnMLTV).

RESULTS

Using two arms lead to a decrease in pnMLTV compared to using one arm and pnMLTV was lower in the actual use trials compared to the pretend use trials for the anchors only. Stride velocity and %DS did not change between trials when one or two arms were used or when participants actually or pretended to use the haptic tools. Participants walked slower when using the railing compared to the anchors.

SIGNIFICANCE

The importance of considering the number of arms is highlighted in the improved balance control when using two arms with either tool. The augmented sensory input adds to the stabilizing effect of arm configuration for the anchors but not the railings. These results have implications for future research and rehabilitation efforts emphasizing sensorimotor integration to improve walking balance control.

Modulation of the Hoffmann reflex in the tibialis anterior with a change in posture

Hoffmann (H-) reflex amplitudes in plantar flexor soleus muscle are modulated by posture, yet dorsiflexor tibialis anterior (TA) H-reflex parameters have sparingly been studied. The purpose was to investigate modulation of the TA H-reflex when postural demands are increased from sitting to standing. In this study, data from 18 participants (Age: 25 ± 4 years, Height: 170.9 ± 9.5 cm, Weight: 75.9 ± 17.2 kg) allowed comparison of two experimental conditions involving different postures (i.e. sitting and standing). Maximal amplitude of the TA H-reflex (Hmax ) as a percent of the maximal M-wave amplitude (Mmax ) (Hmax (% Mmax )) during sitting and standing was compared using ANOVA. Modulation of TA H-reflex amplitude was found: Eleven participants showed facilitation and seven showed no change of reflex amplitudes. Only participants in the facilitation group showed modulation related to changes in posture (sitting: 8.7 ± 2.9%; standing: 14.8 ± 6.7%, P = 0.005). These data provide evidence of the sensitivity to posture of TA H-reflexes. As with task-dependent changes in soleus H-reflexes, presynaptic regulation of Ia afferent transmission is a possible mechanism. Further investigations into causes of modulation are warranted.

The effect of light touch on balance control during overground walking in healthy young adults

Balance control is essential for safe walking. Adding haptic input through light touch may improve walking balance; however, evidence is limited. This research investigated the effect of added haptic input through light touch in healthy young adults during challenging walking conditions. Sixteen individuals walked normally, in tandem, and on a compliant, low-lying balance beam with and without light touch on a railing. Three-dimensional kinematic data were captured to compute stride velocity (m/s), relative time spent in double support (%DS), a medial-lateral margin of stability (MOS_ML) and its variance (MOS_MLCV), as well as a symmetry index (SI) for the MOS_ML. Muscle activity was evaluated by integrating electromyography signals for the soleus, tibialis anterior, and gluteus medius muscles bilaterally. Adding haptic input decreased stride velocity, increased the %DS, had no effect on the MOS_ML magnitude, decreased the MOS_MLCV, had no effect on the SI, and increased activity of most muscles examined during normal walking. During tandem walking, stride velocity and the MOS_MLCV decreased, while %DS, MOS_ML magnitude, SI, and muscle activity did not change with light touch. When walking on a low-lying, compliant balance beam, light touch had no effect on walking velocity, MOS_ML magnitude, or muscle activity; however, the %DS increased and the MOS_MLCV and SI decreased when lightly touching a railing while walking on the balance beam. The decreases in the MOS_MLCV with light touch across all walking conditions suggest that adding haptic input through light touch on a railing may improve balance control during walking through reduced variability.

Measuring balance confidence after spinal cord injury: the reliability and validity of the Activities-specific Balance Confidence Scale

CONTEXT/OBJECTIVE

The study objectives were to evaluate the test-retest reliability, convergent validity, and discriminative validity of the Activities-specific Balance Confidence (ABC) scale in individuals with incomplete spinal cord injury (iSCI).

DESIGN

Prospective, cross-sectional study.

SETTING

Laboratory.

PARTICIPANTS

Twenty-six community-dwelling individuals with chronic iSCI (20 males, 59.7 + 18.9 years old) and 26 age- and sex-matched able-bodied (AB) individuals participated.

INTERVENTIONS

None.

OUTCOME MEASURES

Measures of balance and gait were collected over two days. Clinical measures included the ABC scale, Mini-Balance Evaluation System's Test, 10-meter Walk Test, SCI Functional Ambulation Profile, manual muscle testing of lower extremity muscles, and measures of lower extremity proprioception and cutaneous pressure sensitivity. Biomechanical measures included the velocity and sway area of centre of pressure (COP) movement during quiet standing.

RESULTS

The ABC scale demonstrated high test-retest reliability (intraclass correlation coefficient = 0.93) among participants with iSCI. The minimal detectable change was 14.87%. ABC scale scores correlated with performance on all clinical measures (ρ=0.60-0.80, P<0.01), with the exception of proprioception and cutaneous pressure sensitivity (P=0.20-0.70), demonstrating convergent validity. ABC scale scores also correlated with overall COP velocity (ρ=-0.69, P<0.001) and COP velocity in the anterior-posterior direction (ρ=-0.71, P<0.001). Participants with iSCI scored significantly lower on the ABC scale than the AB participants (P<0.001), and the area under the receiver operating characteristic curve was 0.95, demonstrating discriminative validity.

CONCLUSION

The ABC scale is a reliable and valid measure of balance confidence in community-dwelling, ambulatory individuals with chronic iSCI.

Validation of a commercial inertial sensor system for spatiotemporal gait measurements in children

Although inertial sensor systems are becoming a popular tool for gait analysis in both healthy and pathological adult populations, there are currently no data on the validity of these systems for use with children. The purpose of this study was to validate spatiotemporal data from a commercial inertial sensor system (MobilityLab) in typically-developing children. Data from 10 children (5 males; 3.0-8.3 years, mean=5.1) were collected simultaneously from MobilityLab and 3D motion capture during gait at self-selected and fast walking speeds. Spatiotemporal parameters were compared between the two methods using a Bland-Altman method. The results indicate that, while the temporal gait measurements were similar between the two systems, MobilityLab demonstrated a consistent bias with respect to measurement of the spatial data (stride length). This error is likely due to differences in relative leg length and gait characteristics in children compared to the MobilityLab adult reference population used to develop the stride length algorithm. A regression-based equation was developed based on the current data to correct the MobilityLab stride length output. The correction was based on leg length, stride time, and shank range-of-motion, each of which were independently associated with stride length. Once the correction was applied, all of the spatiotemporal parameters evaluated showed good agreement. The results of this study indicate that MobilityLab is a valid tool for gait analysis in typically-developing children. Further research is needed to determine the efficacy of this system for use in children suffering from pathologies that impact gait mechanics.

The Relationship of Anticipatory Gluteus Medius Activity to Pelvic and Knee Stability in the Transition to Single-Leg Stance

BACKGROUND

The knee abduction moment in a weight-bearing limb is an important risk factor of conditions such as patellofemoral pain and knee osteoarthritis. Excessive pelvic drop in single-leg stance can increase the knee abduction moment. The gluteus medius muscle is crucial to prevent pelvic drop and must be activated in anticipation of the transition from double-leg to single-leg stance.

OBJECTIVE

To examine the relationship of anticipatory activity of the gluteus medius to pelvic drop and knee abduction moment.

DESIGN

Observational, cross-sectional correlational study.

SETTING

Research laboratory.

PARTICIPANTS

Twenty female adults (mean age 22.6 years, standard deviation 2.5) were recruited and fully participated. Participant selection was limited to healthy women who did not have a history of knee and ankle ligament injuries, any indication of knee, hip, and/or low back pain, and/or knowledge of the proper squat technique.

METHODS

Participants performed 16 single-leg mini squats on their nondominant leg.

MAIN OUTCOME MEASURES

The onset and magnitude of anticipatory gluteus medius activity were measured in relation to toe-off of the dominant leg during the transition from double-leg to single-leg stance. Preplanned correlations between anticipatory gluteus medius onset and its activation magnitude, pelvic obliquity, and knee abduction moment were examined.

RESULTS

The magnitude of anticipatory gluteus medius activity was significantly correlated with the knee abduction moment (rs (18) = -0.303, P < .001) and pelvic obliquity (rs (18) = 0.361, P < .001), whereas gluteus medius onset was not significantly correlated with either knee abduction moment or pelvic obliquity.

CONCLUSIONS

The amount of gluteus medius activity is more important for controlling knee and pelvic stability in the frontal plane than the onset of activation.

Evaluation of an inertial sensor system for analysis of timed-up-and-go under dual-task demands

Functional tests, such as the timed-up-and-go (TUG), are routinely used to screen for mobility issues and fall risk. While the TUG is easy to administer and evaluate, its single time-to-completion outcome may not discriminate between different mobility challenges. Wearable sensors provide an opportunity to collect a variety of additional variables during clinical tests. The purpose of this study was to assess a new wearable inertial sensor system (iTUG) by investigating the effects of cognitive tasks in a dual-task paradigm on spatiotemporal and kinematic variables during the TUG. No previous studies have looked at both spatiotemporal variables and kinematics during dual-task TUG tests. 20 healthy young participants (10 males) performed a total 15 TUG trials with two different cognitive tasks and a normal control condition. Total time, along with spatiotemporal gait parameters and kinematics for all TUG subtasks (sit-to-stand, walking, turn, turn-to-sit), were measured using the inertial sensors. Time-to-completion from iTUG was highly correlated with concurrent manual timing. Spatiotemporal variables during walking showed expected differences between control and cognitive dual-tasks while trunk kinematics appeared to show more sensitivity to dual-tasks than reported previously in straight line walking. Non-walking TUG subtasks showed only minor changes during dual-task conditions indicating a possible attentional shift away from the cognitive task. Stride length and some variability measures were significantly different between the two cognitive tasks suggesting an ability to discriminate between tasks. Overall, the use of the iTUG system allows the collection of both traditional and potentially more discriminatory variables with a protocol that is easily used in a clinical setting.

Control of dynamic stability during gait termination on a slippery surface in Parkinson's disease

This study investigated how Parkinson's disease (PD) affects the ability to switch from locomotion to gait termination (GT) during planned and cued GT and examined the effect of PD on the integration of a reactive, balance maintenance strategy into voluntary GT. After a series of stops on a stable surface, eight participants with and 10 without PD stopped on a surface, which slid quickly and unexpectedly forward mimicking a slippery surface. PD caused instability during the completely voluntary nonslippery stops (P = 0.012) but not during the slippery stops, which required a reactive movement. The PD group walked slower [0.9-1.0 m/s vs. 1.3 m/s, respectively (P < 0.001)] with shorter steps during the first step of nonslippery GT (P = 0.016) and with wider steps during all steps of nonslippery GT (P <or= 0.05). Similar to controls, the PD group increased lateral stability during planned GT compared to cued GT (P = 0.007). The timing of gait termination was similar between groups in all conditions. During the unexpected perturbation, both groups used a generalized slip response to regain balance after the perturbation. PD did not affect the ability to stop walking or to integrate a balance-correcting response into GT but did affect movement speed, size, and stability of the voluntary movement.

Compensatory postural adaptations during continuous, variable amplitude perturbations reveal generalized rather than sequence-specific learning

We examined changes in the motor organization of postural control in response to continuous, variable amplitude oscillations evoked by a translating platform and explored whether these changes reflected implicit sequence learning. The platform underwent random amplitude (maximum +/- 15 cm) and constant frequency (0.5 Hz) oscillations. Each trial was composed of three 15-s segments containing seemingly random oscillations. Unbeknownst to participants, the middle segment was repeated in each of 42 trials on the first day of testing and in an additional seven trials completed approximately 24 h later. Kinematic data were used to determine spatial and temporal components of total body centre of mass (COM) and joint segment coordination. Results showed that with repeated trials, participants reduced their magnitude of COM displacement, shifted from a COM phase lag to a phase lead relative to platform motion and increased correlations between ankle/platform motion and hip/platform motion as they shifted from an ankle strategy to a multi-segment control strategy involving the ankle and hip. Maintenance of these changes across days provided evidence for learning. Similar improvements for the random and repeated segments, indicated that participants did not exploit the sequence of perturbations to improve balance control. Rather, the central nervous system may have been tuning into more general features of platform motion. These findings provide important insight into the generalizabilty of improved compensatory balance control with training.

Control of dynamic stability during gait termination on a slippery surface

There are three common ways by which to successfully terminate gait: decreased acceleration of whole-body center of mass (COM) through a flexor synergy in the trail leg, increased deceleration of whole-body COM through an extensor synergy in the front limb, and an energy/momentum transfer to dissipate any remaining momentum if the first two strategies are unsuccessful. Healthy individuals were asked to stop on a slippery surface while we examined their unexpected response to the slippery surface. Kinetic data from the forceplates revealed lower braking forces in the slip trials compared with normal gait-termination trials. Subjects were unable to control their center of pressure (COP) to manipulate the COM as revealed by increased deviations and maximum absolute ranges of COP movement. Subject COM deviated farther in both horizontal planes and lowered further during the slip compared with normal gait-termination trials. Arm movements were effective in dissipating forward COM movement. In addition, there likely was a transfer of forward to lateral momentum to stop forward progression. All recorded muscle activity in the lower limbs and back increased during the slip to provide support to the lower limbs and correct upright balance. The trailing limb shortened its final step to provide support to the lowering COM. The balance-correction response seen here resembles previous reactions to perturbations during locomotion suggesting there is a generalized strategy employed by the nervous system to correct for disturbances and maintain balance.