Trunk Velocity Changes in Response to Physical Perturbations Are Potential Indicators of Gait Stability.

Response to challenging situations is important to avoid falls, especially after medial perturbations, which require active control. There is a lack of evidence on the relationship between the trunk's motion in response to perturbations and gait stability. Eighteen healthy adults walked on a treadmill at three speeds while receiving perturbations of three magnitudes. Medial perturbations were applied by translating the walking platform to the right at left heel contact. Trunk velocity changes in response to the perturbation were calculated and divided into the initial and the recovery phases. Gait stability after a perturbation was assessed using the margin of stability (MOS) at the first heel contact, MOS mean, and standard deviation for the first five strides after the perturbation onset. Faster speed and smaller perturbations led to a lower deviation of trunk velocity from the steady state, which can be interpreted as an improvement in response to the perturbation. Recovery was quicker after small perturbations. The MOS mean was associated with the trunk's motion in response to perturbations during the initial phase. Increasing walking speed may increase resistance to perturbations, while increasing the magnitude of perturbation leads to greater trunk motions. MOS is a useful marker of resistance to perturbations.

Machine Learning-Based Peripheral Artery Disease Identification Using Laboratory-Based Gait Data.

Peripheral artery disease (PAD) manifests from atherosclerosis, which limits blood flow to the legs and causes changes in muscle structure and function, and in gait performance. PAD is underdiagnosed, which delays treatment and worsens clinical outcomes. To overcome this challenge, the purpose of this study is to develop machine learning (ML) models that distinguish individuals with and without PAD. This is the first step to using ML to identify those with PAD risk early. We built ML models based on previously acquired overground walking biomechanics data from patients with PAD and healthy controls. Gait signatures were characterized using ankle, knee, and hip joint angles, torques, and powers, as well as ground reaction forces (GRF). ML was able to classify those with and without PAD using Neural Networks or Random Forest algorithms with 89% accuracy (0.64 Matthew's Correlation Coefficient) using all laboratory-based gait variables. Moreover, models using only GRF variables provided up to 87% accuracy (0.64 Matthew's Correlation Coefficient). These results indicate that ML models can classify those with and without PAD using gait signatures with acceptable performance. Results also show that an ML gait signature model that uses GRF features delivers the most informative data for PAD classification.

Joint Angle Variability Is Altered in Patients with Peripheral Artery Disease after Six Months of Exercise Intervention.

Supervised exercise therapy (SET) is a conservative non-operative treatment strategy for improving walking performance in patients with peripheral artery disease (PAD). Gait variability is altered in patients with PAD, but the effect of SET on gait variability is unknown. Forty-three claudicating patients with PAD underwent gait analysis before and immediately after a 6-month SET program. Nonlinear gait variability was assessed using sample entropy, and the largest Lyapunov exponent of the ankle, knee, and hip joint angle time series. Linear mean and variability of the range of motion time series for these three joint angles were also calculated. Two-factor repeated measure analysis of variance determined the effect of the intervention and joint location on linear and nonlinear dependent variables. After SET, walking regularity decreased, while the stability remained unaffected. Ankle nonlinear variability had increased values compared with the knee and hip joints. Linear measures did not change following SET, except for knee angle, in which the magnitude of variations increased after the intervention. A six-month SET program produced changes in gait variability toward the direction of healthy controls, which indicates that in general, SET improved walking performance in individuals with PAD.

Task specificity impacts dual-task interference in older adults.

BACKGROUND: Task prioritization is an important factor determines the magnitude and direction of dual-task interference in older adults. Greater dual-task cost during walking may lead to falling, sometimes causing lasting effects on mobility. AIMS: We investigated dual-task interference for walking and cognitive performance. METHODS: Twenty healthy, older adults (71 ± 5 years) completed three cognitive tasks: letter fluency, category fluency, and serial subtraction during seated and walking conditions on a self-paced treadmill for 3 min each, in addition to walking only condition. Walking speed, step length and width were measured during walking and each dual-task condition. RESULTS: Comparing the percentage of correct answers in cognitive tasks across single and dual-task conditions, there was a main effect of cognitive task (p = 0.021), showing higher scores during letter fluency compared to serial subtraction (p = 0.011). Step width was significantly wider during dual-task letter fluency compared to walking alone (p = 0.003), category fluency (p = 0.001), and serial subtraction (p = 0.007). DISCUSSION: During both fluency tasks, there was a cost for gait and cognition, with category showing a slightly higher cognitive cost compared to letter fluency. During letter fluency, to maintain cognitive performance, gait was sacrificed by increasing step width. During serial subtraction, there was a cost for gait, yet a benefit for cognitive performance. CONCLUSION: Differential effect of cognitive task on dual-task performance is critical to be understood in designing future research or interventions to improve dual-task performance of most activities of daily living.

COPD Patients Have a Restricted Breathing Pattern That Persists with Increased Metabolic Demands.

A healthy respiratory system has variability from breath-to-breath and patients with COPD (PwCOPD) have abnormal variability in breath cycles. The aim of this study was to determine if interbreath-interval and tidal-volume variability, and airflow regularity change as metabolic demands increase (seated, standing, and walking) in PwCOPD as compared to controls. Sixteen PwCOPD (64.3 ± 7.9 yr, 61.3 ± 44.1% FEV1%predicted) and 21 controls (60.2 ± 6.8 yr, 97.5 ± 16.8% FEV1%predicted) sat, stood, and walked at their preferred-pace for five-minutes each while breathing patterns were recorded. The mean, standard deviation, and coefficient of variation of interbreath-intervals and tidal-volume, and the regularity (sample entropy) of airflow were quantified. Results were subjected to ANOVA analysis. Interbreath-interval means were shorter in PwCOPD compared to controls (p = 0.04) and as metabolic demand increased (p < 0.0001), standard deviation was decreased in PwCOPD compared to controls during each condition (p's < 0.002). Mean tidal-volume did decrease as metabolic demand increased across groups (p < 0.0001). Coefficient of variation findings (p = 0.002) indicated PwCOPD decline in tidal-volume variability from sitting to standing to walking; whereas, controls do not. There was an interaction for airflow (p = 0.02) indicating that although, PwCOPD had a more regular airflow across all conditions, control's airflow became more irregular as metabolic demand increased. PwCOPD's airflow was always more regular compared to controls (p = 0.006); although, airflow became more irregular as metabolic demand increased (p < 0.0001). Healthy respiratory systems have variability and irregularity from breath-to-breath decreases with adaptation to demand. PwCOPD have more regular and restricted breathing pattern that may affect their ability to adjust in demanding situations.

Optic flow improves step width and length in older adults while performing dual task.

BACKGROUND: Dual-task paradigms are used to investigate gait and cognitive declines in older adults (OA). Optic-flow is a virtual reality environment where the scene flows past the subject while walking on a treadmill, mimicking real-life locomotion. AIMS: To investigate cost of environment (no optic-flow v. optic-flow) while completing single- and dual-task walking and dual-task costs (DTC; single- v. dual-task) in optic-flow and no optic-flow environments. METHODS: Twenty OA and seven younger adults (YA) walked on a self-paced treadmill in 3-min segments per task and both environments. Five task conditions included: no task, semantic fluency (category), phonemic fluency (letters), word reading, and serial-subtraction. RESULTS: OAs had a benefit of optic-flow compared to no optic-flow for step width (p = 0.015) and step length (p = 0.045) during letters compared to the YA. During letters, OA experienced improvement in step width DTC; whereas YA had a decrement in step width DTC from no optic-flow to optic-flow (p = 0.038). During serial-subtraction, OA had less step width DTC when compared to YA in both environments (p = 0.02). DISCUSSION: During letters, step width and step length improved in OA while walking in optic-flow. Also, step width DTC differed between the two groups. Sensory information from optic-flow appears to benefit OA. Letters relies more on verbal ability and word knowledge, which are preserved in aging. However, YA use a complex speech style during dual tasking, searching for complex words and an increased speed of speech. CONCLUSIONS: OA can benefit from optic-flow by improving spatial gait parameters, specifically, step width, during dual-task walking.

Enhancing walking performance in patients with peripheral arterial disease: An intervention with ankle-foot orthosis.

Lower extremity peripheral artery disease (PAD) is a cardiovascular condition manifesting from narrowed or blocked arteries supplying the legs. Gait is impaired in patients with PAD. Recent evidence suggests that walking with carbon fiber ankle foot orthoses (AFOs) can improve patient mobility and delay claudication time. This study aimed to employ advanced biomechanical gait analysis to evaluate the impact of AFO intervention on gait performance among patients with PAD. Patients with claudication had hip, knee, and ankle joint kinetics and kinematics assessed using a cross-over intervention design. Participants walked over the force platforms with and without AFOs while kinematic data was recorded with motion analysis cameras. Kinetics and kinematics were combined to quantify torques and powers during the stance period of the gait cycle. The AFOs effectively reduced the excessive ankle plantar flexion and knee extension angles, bringing the patients' joint motions closer to those observed in healthy individuals. After 3 months of the AFO intervention, the hip range of motion decreased, likely due to changes occurring within the ankle chain. With the assistance of the AFOs, the biological power generation required from the ankle and hip during the push-off phase of walking decreased. Wearing AFOs resulted in increased knee flexor torque during the loading response phase of the gait. Based on this study, AFOs may allow patients with PAD to maintain or improve gait performance. More investigation is needed to fully understand and improve the potential benefits of ankle assistive devices.

Diagnosis of disease affecting gait with a body acceleration-based model using reflected marker data for training and a wearable accelerometer for implementation.

This paper demonstrates the value of a framework for processing data on body acceleration as a uniquely valuable tool for diagnosing diseases that affect gait early. As a case study, we used this model to identify individuals with peripheral artery disease (PAD) and distinguish them from those without PAD. The framework uses acceleration data extracted from anatomical reflective markers placed in different body locations to train the diagnostic models and a wearable accelerometer carried at the waist for validation. Reflective marker data have been used for decades in studies evaluating and monitoring human gait. They are widely available for many body parts but are obtained in specialized laboratories. On the other hand, wearable accelerometers enable diagnostics outside lab conditions. Models trained by raw marker data at the sacrum achieve an accuracy of 92% in distinguishing PAD patients from non-PAD controls. This accuracy drops to 28% when data from a wearable accelerometer at the waist validate the model. This model was enhanced by using features extracted from the acceleration rather than the raw acceleration, with the marker model accuracy only dropping from 86 to 60% when validated by the wearable accelerometer data.

Sampling rate influences the regularity analysis of temporal domain measures of walking more than spatial domain measures.

BACKGROUND: The spatiotemporal dynamics of stepping can provide useful information about walking performance. Most often, the identification of gait motion is performed using 3-D cinematography. The sampling rate of motion capture systems may influence the accuracy of these measures albeit in varying degrees for measures within the spatial versus temporal domain. RESEARCH QUESTION: What are the effects of sampling frequency on common analysis methods of measures within the spatial and temporal domain? METHODS: Specifically, mean, variability (i.e. standard deviation), and regularity (i.e. sample entropy) of step length (i.e. spatial domain) and step time (i.e. temporal domain) measures were assessed following ten minutes of preferred-speed treadmill walking in eleven young adults. RESULTS: The spatiotemporal mean measures were not affected by changing sampling frequencies. Frequencies ≥120 Hz showed consistent results for spatial variability measures, while temporal variability increased due to decreased resolution in capturing variability when data was sampled at 120 Hz or less. In assessing regularity, poor temporal resolution at lower sampling rates led to "binning", limiting the variety of vector patterns. As a result, more vectors were classified as similar, leading to a signal appearing more periodic. For the spatial domain, sample entropy was not affected, indicating the greater sensitivity of step time to sampling rate compared to step length. SIGNIFICANCE: Sampling rate influenced recognition of gait events. By reducing the sampling rate, the time intervals were increased and reduced the resolution leading to less accurate gait event detection in the temporal domain. The sampling rate of 120 Hz is the minimum sampling rate that should be used to calculate spatiotemporal data for variability and sample entropy.

Margin of Stability May Be Larger and Less Variable during Treadmill Walking Versus Overground.

Margin of stability (MOS) is considered a measure of mechanical gait stability. Due to broad application of treadmills in gait assessment experiments, we aimed to determine if walking on a treadmill vs. overground would affect MOS during three speed-matched conditions. Eight healthy young participants walked on a treadmill and overground at Slow, Preferred, and Fast speed-matched conditions. The mean and variability (standard deviation) of the MOS in anterior-posterior and mediolateral directions at heel contact were calculated. Anterior-posterior and mediolateral mean MOS values decreased with increased speed for both overground and treadmill; although mediolateral mean MOS was always wider on the treadmill compared to overground. Due to lack of optic flow and different proprioceptive inputs during treadmill walking, subjects may employ strategies to increase their lateral stability on treadmill compared to overground. Anterior-posterior MOS variability increased with speed overground, while it did not change on treadmill, which might be due to the fixed speed of treadmill. Whereas, lateral variability on both treadmill and overground was U-shaped. Walking at preferred speed was less variable (may be interpreted as more stable) laterally, compared to fast and slow speeds. Caution should be given when interpreting MOS between modes and speeds of walking. As sagittal plane walking is functionally unstable, this raises the consideration as to the meaningfulness of using MOS as a global measure of gait stability in this direction.

Chronic obstructive pulmonary disease patients increase medio-lateral stability and limit changes in antero-posterior stability to curb energy expenditure.

BACKGROUND: A relationship exists between step width and energy expenditure, yet the contribution of dynamic stability to energy expenditure is not completely understood. Chronic obstructive pulmonary disease (COPD) patients' energy expenditure is increased due to airway obstruction. Further, they have a higher prevalence of falls and balance deficits compared to controls. RESEARCH QUESTION: Is dynamic stability different between COPD patients and controls; and is the association between dynamic stability and energy expenditure different between groups? METHODS: Seventeen COPD patients (64.3 ±â€¯7.6years) and 23 controls (59.9 ±â€¯6.6years) walked on a treadmill at three speeds: self-selected walking speed (SSWS), -20%SSWS, and +20%SSWS. Mean and variability (standard deviation) of the anterior-posterior (AP) and medio-lateral (ML) margins of stability (MOS) were compared between groups and speed conditions, while controlling for covariates. Additionally, their association to metabolic power was examined. RESULTS: The association between stability and power did not significantly differ between groups. However, increased metabolic power was associated with decreased MOS AP mean (p < 0.0001), independent of speed. Increased MOS AP variability (p = 0.01) and increased SSWS (p's < 0.05) were associated with increased metabolic power. The MOS ML mean for COPD patients was greater than that of healthy patients (p = 0.02). MOS AP mean decreased as speed increased and differed by group (p = 0.048). For COPD patients, a plateau was observed at SSWS and did not decrease further at +20%SSWS compared to controls. MOS AP variability (p < 0.0001), MOS ML mean (p < 0.0001), and MOS ML variability (p = 0.003) decreased as speed increased and did not differ by group. SIGNIFICANCE: Patients with COPD operate at the upper limit of their metabolic reserve due to an increased cost of breathing. To compensate for their lack of stability, they walked with larger margins of stability in the ML direction, instead of changing the stability margins in the AP direction, due to its association with energy expenditure.

Effect of motor-assisted elliptical training speed and body weight support on center of pressure movement variability.

BACKGROUND: A motor-assisted elliptical trainer is being used clinically to help individuals with physical disabilities regain and/or retain walking ability and cardiorespiratory fitness. Unknown is how the device's training parameters can be used to optimize movement variability and regularity. This study examined the effect of motor-assisted elliptical training speed as well as body weight support (BWS) on center of pressure (CoP) movement variability and regularity during training. METHODS: CoP was recorded using in-shoe pressure insoles as participants motor-assisted elliptical trained at three speeds (20, 40 and 60 cycles per minute) each performed at four BWS levels (0 %, 20 %, 40 %, and 60 %). Separate two-way repeated measures ANOVAs (3 × 4) evaluated impact of training speed and BWS on linear variability (standard deviation) and non-linear regularity (sample entropy) of CoP excursion (anterior-posterior, medial-lateral) for 10 dominant limb strides. FINDINGS: Training speed and BWS did not significantly affect the linear variability of CoP in the anterior-posterior or medial-lateral directions. However, sample entropy in both directions revealed the main effect of training speed (p < 0.0001), and a main effect of BWS was observed in the medial-lateral direction (p = 0.004). Faster training speeds and greater levels of BWS resulted in more irregular CoP patterns. INTERPRETATION: The finding that speed and BWS can be used to manipulate CoP movement variability when using a motor-assisted elliptical has significant clinical implications for promoting/restoring walking capacity. Further research is required to determine the impact of motor-assisted elliptical speed and BWS manipulations on functional recovery of walking in individuals who have experienced a neurologic injury or illness.

Strength of Plantar- and Dorsiflexors Mediates Step Regularity During a High Cognitive Load Situation in a Cross-sectional Cohort of Older and Younger Adults.

BACKGROUND AND PURPOSE: Completing simultaneous tasks while standing or walking (ie, a high cognitive load situation [HCLS]) is inevitable in daily activities and can lead to interference in task performances. Age-related physical and cognitive changes may confound performance variability during HCLS in older and younger adults. Identification of these confounding effects may reveal therapy targets to maintain optimal physical function later in life. The aim of this study was to investigate the effect of increasing the difficulty levels of an additional motor task and restricting visual information, on gait parameters in younger and older adults while considering the effect of cognitive and physical covariates. METHODS: Fifteen healthy younger and 14 healthy older adults were asked to complete assessments of cognitive function, balance, and strength. They were then asked to walk on a self-paced treadmill with or without carrying a plastic tray. Opaqueness of the tray (vision) and the presence of water in glasses placed on the tray (increasing task difficulty) were varied. Mean, standard deviation, and regularity (sample entropy) of step width and length were compared across conditions and groups using repeated-measures analyses of variance with and without covariate analysis. Only significantly correlated covariates of cognition, balance, and strength were entered into each model. RESULTS AND DISCUSSION: Older adults had greater step width irregularity compared with younger adults across all conditions when controlling for concentric plantar- and dorsiflexion strength. A decline in strength may likely alter neuromuscular control of gait, specifically control of step width, which has been associated with fall risk in older adults. Adjusting for the same covariates revealed increased regularity of step length, as visual feedback from the feet was restricted. Specifically, step length was more regular while carrying an opaque tray compared with not carrying a tray. Visual restriction was a contributing factor, which led to more predictable gait kinematics, indicating the role of sensory information to enhance the adaptability during walking under HCLS. CONCLUSION: The knowledge of the regularity behavior of human movement can expand physical therapists' treatment approaches to promote further interactivity and coordination across body systems that model behavior of healthy young individuals. Targeting strength during therapy may provide additional benefits for gait performance under HCLS.