A Simple and Valid Method to Calculate Wheelchair Frame Rotation Using One Wheel-Mounted IMU.

Wheelchair sports have been using Inertial Measurement Units (IMU) to measure mobility metrics during training, testing and competition. Presently, the most suitable solution to calculate wheelchair speed and frame rotation is the 3IMU method as there is uncertainty about the ability of a one wheel-mounted IMU (1IMU) approach to calculate wheelchair frame rotational kinematics. A new method for calculating wheelchair frame rotational kinematics using a single wheel-mounted IMU is presented and compared to a criterion measurement using a wheelchair-frame-mounted IMU. Goodness-of-fit statistics demonstrate very strong linear relationships between wheelchair frame angular velocity calculated from the wheel-mounted IMUs and a wheelchair-frame-mounted IMU. Root mean square error (RMSE), mean absolute error (MAE) and Bland-Altman analysis show very small differences between the wheelchair frame angular velocity calculated from the wheel-mounted IMUs and the wheelchair-frame-mounted IMU. This study has demonstrated a simple and accurate approach to estimating wheelchair frame rotation using one wheel-mounted IMU during an elite wheelchair athlete agility task. Future research is needed to reexamine and compare wheelchair mobility metrics determined using the 3IMU and 1IMU solutions using this new approach.

Wheelchair Rugby Sprint Force-Velocity Modeling Using Inertial Measurement Units and Sport Specific Parameters: A Proof of Concept.

BACKGROUND: Para-sports such as wheelchair rugby have seen increased use of inertial measurement units (IMU) to measure wheelchair mobility. The accessibility and accuracy of IMUs have enabled the quantification of many wheelchair metrics and the ability to further advance analyses such as force-velocity (FV) profiling. However, the FV modeling approach has not been refined to include wheelchair specific parameters. PURPOSE: The purpose of this study was to compare wheelchair rugby sprint FV profiles, developed from a wheel-mounted IMU, using current mono-exponential modeling techniques against a dynamic resistive force model with wheelchair specific resistance coefficients. METHODS: Eighteen athletes from a national wheelchair rugby program performed 2 × 45 m all-out sprints on an indoor hardwood court surface. RESULTS: Velocity modelling displayed high agreeability, with an average RMSE of 0.235 ± 0.07 m/s-1 and r2 of 0.946 ± 0.02. Further, the wheelchair specific resistive force model resulted in greater force and power outcomes, better aligning with previously collected measures. CONCLUSIONS: The present study highlights the proof of concept that a wheel-mounted IMU combined with wheelchair-specific FV modelling provided estimates of force and power that better account for the resistive forces encountered by wheelchair rugby athletes.

Age-related erosion of obstacle avoidance reflexes evoked with electrical stimulation of tibial nerve during walking.

In young healthy adults, characteristic obstacle avoidance reflexes have been demonstrated in response to electrical stimulation of cutaneous afferents of the foot during walking. It is unknown whether there is an age-related erosion of this obstacle avoidance reflex evoked with stimulation to the tibial nerve innervating the sole of the foot. The purpose of this study was to identify age-dependent differences in obstacle avoidance reflexes evoked with electrical stimulation of the tibial nerve at the ankle during walking in healthy young and older (70 yr and older) adults with no history of falls. Toe clearance, ankle and knee joint displacement and angular velocity, and electromyograms (EMG) of the tibialis anterior, medial gastrocnemius, biceps femoris, and vastus lateralis were measured. A significant erosion of kinematic and EMG obstacle avoidance reflexes was seen in the older adults compared with the young. Specifically, during swing phase, there was reduced toe clearance, ankle dorsiflexion, and knee flexion angular displacement in older adults compared with the young as well as changes in muscle activation. These degraded reflexes were superimposed on altered kinematics seen during unperturbed walking in the older adults including reduced toe clearance and knee flexion and increased ankle dorsiflexion compared with the young. Notably, during mid-swing the toe clearance was reduced in the older adults compared with the young by 2 cm overall, resulting from a combination of 1-cm reduced reflex response in the older adults superimposed on 1-cm less toe clearance during unperturbed walking. Together, these age-related differences could represent the prodromal phase of fall risk. NEW & NOTEWORTHY This study demonstrated age-dependent erosion of obstacle avoidance reflexes evoked with electrical stimulation of the tibial nerve at the ankle during walking. There was significant reduction in toe clearance, ankle dorsiflexion, and knee flexion reflexes as well as changes in muscle activation during swing phase in older adults with no history of falls compared with the young. These degraded reflexes, superimposed on altered kinematics seen during unperturbed walking, likely represent the prodromal phase of fall risk.

Erosion of Stumble Correction Evoked with Superficial Peroneal Nerve Stimulation in Older Adults during Walking.

In healthy young adults, electrical stimulation of the superficial peroneal cutaneous nerve (SPn) innervating the dorsum of the foot has been shown to elicit functionally relevant reflexes during walking that are similar to those evoked by mechanical perturbation to the dorsum of the foot during walking and are referred to as stumble corrective (obstacle avoidance) responses. Though age-related differences in reflexes induced by mechanical perturbation have been studied, toe clearance has not been measured. Further, age-related differences in reflexes evoked by electrical stimulation of SPn have yet to be determined. Thus, the purpose of this study was to characterize age-related differences between healthy young adults and older adults with no history of falls in stumble correction responses evoked by electrical stimulation of the SPn at the ankle during walking. Toe clearance relative to the walking surface along with joint displacement and angular velocity at the ankle and knee and EMG of the tibialis anterior, medial gastrocnemius, biceps femoris and vastus lateralis were measured. The combined background and reflex toe clearance was reduced in the older adults compared with the young in mid-early swing (p = 0.011). These age-related differences likely increase fall risk in the older adult cohort. Further, age-related changes were seen in joint kinematics and EMG in older adults compared with the young such as decreased amplitude of the plantarflexion reflex in early swing in older adults (p < 0.05). These altered reflexes reflect the degradation of the stumble corrective response in older adults.

A Comparison of Bioelectric and Biomechanical EMG Normalization Techniques in Healthy Older and Young Adults during Walking Gait.

This study compares biomechanical and bioelectric electromyography (EMG) normalization techniques across disparate age cohorts during walking to assess the impact of normalization methods on the functional interpretation of EMG data. The biomechanical method involved scaling EMG to a target absolute torque (EMGTS) from a joint-specific task and the chosen bioelectric methods were peak and mean normalization taken from the EMG signal during gait, referred to as dynamic mean and dynamic peak normalization (EMGMean and EMGPeak). The effects of normalization on EMG amplitude, activation pattern, and inter-subject variability were compared between disparate cohorts, including OLD (76.6 yrs N = 12) and YOUNG (26.6 yrs N = 12), in five lower-limb muscles. EMGPeak normalization resulted in differences between YOUNG and OLD cohorts in Biceps Femoris (BF) and Medial Gastrocnemius (MG) that were not observed with EMGMean or EMGTS normalization. EMGPeak and EMGMean normalization also demonstrated interactions between age and the phase of gait in BF that were not seen with EMGTS. Correlations showed that activation patterns across the gait cycle were similar between all methods for both age groups and the coefficient of variation comparisons found that EMGTS produced the greatest inter-subject variability. We have shown that the normalization technique can influence the interpretation of findings when comparing disparate populations, highlighting the need to carefully interpret functional differences in EMG between disparate cohorts.

Detecting differences in gait initiation between older adult fallers and non-fallers through multivariate functional principal component analysis.

Gait initiation (GI) is an important locomotor transition task that includes anticipatory postural adjustments and the joint propulsion necessary for the first step of walking. Discrete variable analysis between GI of fallers and non-fallers has shown important between-group differences. More complex time series analysis, such as functional principal component analysis (FPCA) may highlight group differences not detectable using discrete comparisons alone. This study aims to characterize the differences between fallers and non-fallers by examining the kinematics and kinetics of gait initiation using multivariate FPCA (mFPCA). A sample of 56 community-dwelling older adults completed five walking trials where GI was measured by force platforms. mFPCA of center of pressure kinematics and kinetics was conducted and functional principal component scores were compared between groups. Overall mFPCA provided a comprehensive assessment of GI that supports and enhances previous findings with respect to differences between faller and non-faller cohorts. During weight transfer and forward progress, fallers demonstrate a greater range of mediolateral movement and lower lateral force than non-fallers. During the first step, fallers have a more gradual rise in vertical force, as well as a greater lateral movement toward the edge of their base of support. Fallers also demonstrate a shorter step length, indicating an altered approach to GI, where mediolateral and anteroposterior stability may be prioritized over forward advancement.

Comparing executive function, evoked hemodynamic response, and gait as predictors of variations in mobility for older adults.

OBJECTIVE: Falls represent a major concern for older adults and may serve as clinically salient index events for those presenting in the prodromal stages of mild cognitive impairment. Declines in executive function performance and in gait consistency have shown promise in predicting fall risk; however, associated neurophysiological underpinnings have received less attention. In this study, we used a multimodal approach to assess fall risk in a group of older adults with and without a previous fall history. METHOD: Processing speed, inductive reasoning, verbal fluency, crystallized ability, episodic memory, and executive functioning were assessed using standardized neuropsychological tests. Cognitive interference was assessed using the Multi-Source Interference Task. Spatiotemporal gait parameters were assessed with and without cognitive load using a 6.4-m instrumented walkway. Hemodynamic responses were measured using functional near-infrared spectroscopy. RESULTS: Whereas no group differences were observed in cognitive behavioral performance, during a cognitive interference task fallers displayed more oxygenated hemoglobin across the prefrontal cortex than nonfallers, suggesting that engaging in the cognitive task was more effortful for them overall, therefore eliciting greater cortical activation. Between-group differences in spatial as well as temporal gait parameters were also observed. CONCLUSIONS: These results are in keeping with assertions that diminished executive control is related to fall risk. Notably, the group differences observed in prefrontal cortical activation and in gait parameters may ultimately precede those observed in cognitive behavioral performance, with implications for measurement sensitivity and early identification.

Accurate and Reliable Gait Cycle Detection in Parkinson's Disease.

There is a growing interest in the use of Inertial Measurement Unit (IMU)-based systems that employ gyroscopes for gait analysis. We describe an improved IMU-based gait analysis processing method that uses gyroscope angular rate reversal to identify the start of each gait cycle during walking. In validation tests with six subjects with Parkinson disease (PD), including those with severe shuffling gait patterns, and seven controls, the probability of True-Positive event detection and False-Positive event detection was 100% and 0%, respectively. Stride time validation tests using high-speed cameras yielded a standard deviation of 6.6 ms for controls and 11.8 ms for those with PD. These data demonstrate that the use of our angular rate reversal algorithm leads to improvements over previous gyroscope-based gait analysis systems. Highly accurate and reliable stride time measurements enabled us to detect subtle changes in stride time variability following a Parkinson's exercise class. We found unacceptable measurement accuracy for stride length when using the Aminian et al gyro-based biomechanical algorithm, with errors as high as 30% in PD subjects. An alternative method, using synchronized infrared timing gates to measure velocity, combined with accurate mean stride time from our angular rate reversal algorithm, more accurately calculates mean stride length.