Estimating upper extremity joint loads of persons with spinal cord injury walking with a lower extremity powered exoskeleton and forearm crutches.

Lower extremity powered exoskeletons with crutch support can provide upright mobility to persons with complete spinal cord injury (SCI); however, crutch use for balance and weight transfer may increase upper extremity (UE) joint loads and injury risk. This research presented the first exoskeleton-human musculoskeletal model to estimate upper extremity biomechanics, driven by 3D motion data of persons with complete SCI walking with an exoskeleton and crutch assistance. Forearm crutches instrumented with strain gauges, force plates, and a 3D motion capture system were used to collect kinematic and kinetic data from five persons with complete SCI while walking with the ARKE exoskeleton. Model output estimated participant upper extremity kinematics, kinetics, and crutch forces. Compared to inverse dynamic biomechanical crutch model studies of persons with incomplete SCI, exoskeleton users walked with more anterior trunk tilt and twice the shoulder flexion angle. Anterior tilt increased forces and moments at the crutch, shoulder, and elbow. Crutch floor contact periods were 30-40% longer, resulting in upper extremity joint impulses 5 to 12 times greater than previously reported. Reducing UE joint loading is important to reduce overuse injuries associated with ambulatory assistive devices. Incorporating a variable assist ankle joint or more experience with exoskeleton walking may reduce UE joint loads, and minimise injury risk. Study outcomes provide a quantitative understanding of UE dynamics during exoskeleton walking that can be used to improve device design, training, and rehabilitation.

Lower limb sagittal kinematic and kinetic modeling of very slow walking for gait trajectory scaling.

Lower extremity powered exoskeletons (LEPE) are an emerging technology that assists people with lower-limb paralysis. LEPE for people with complete spinal cord injury walk at very slow speeds, below 0.5m/s. For the able-bodied population, very slow walking uses different neuromuscular, locomotor, postural, and dynamic balance control. Speed dependent kinetic and kinematic regression equations in the literature could be used for very slow walking LEPE trajectory scaling; however, kinematic and kinetic information at walking speeds below 0.5 m/s is lacking. Scaling LEPE trajectories using current reference equations may be inaccurate because these equations were produced from faster than real-world LEPE walking speeds. An improved understanding of how able-bodied people biomechanically adapt to very slow walking will provide LEPE developers with more accurate models to predict and scale LEPE gait trajectories. Full body motion capture data were collected from 30 healthy adults while walking on an instrumented self-paced treadmill, within a CAREN-Extended virtual reality environment. Kinematic and kinetic data were collected for 0.2 m/s-0.8 m/s, and self-selected walking speed. Thirty-three common sagittal kinematic and kinetic gait parameters were identified from motion capture data and inverse dynamics. Gait parameter relationships to walking speed, cadence, and stride length were determined with linear and quadratic (second and third order) regression. For parameters with a non-linear relationship with speed, cadence, or stride-length, linear regressions were used to determine if a consistent inflection occurred for faster and slower walking speeds. Group mean equations were applied to each participant's data to determine the best performing equations for calculating important peak sagittal kinematic and kinetic gait parameters. Quadratic models based on walking speed had the strongest correlations with sagittal kinematic and kinetic gait parameters, with kinetic parameters having the better results. The lack of a consistent inflection point indicated that the kinematic and kinetic gait strategies did not change at very slow gait speeds. This research showed stronger associations with speed and gait parameters then previous studies, and provided more accurate regression equations for gait parameters at very slow walking speeds that can be used for LEPE joint trajectory development.

Modeling and Simulation of a Lower Extremity Powered Exoskeleton.

Lower extremity powered exoskeletons (LEPEs) allow people with spinal cord injury (SCI) to stand and walk. However, the majority of LEPEs walk slowly and users can become fatigued from overuse of forearm crutches, suggesting LEPE design can be enhanced. Virtual prototyping is a cost-effective way of improving design; therefore, this research developed and validated two models that simulate walking with the Bionik Laboratories' ARKE exoskeleton attached to a human musculoskeletal model. The first model was driven by kinematic data from 30 able-bodied participants walking at realistic slow walking speeds (0.2-0.8 m/s) and accurately predicted ground reaction forces (GRF) for all speeds. The second model added upper limb crutches and was driven by 3-D-marker data from five SCI participants walking with ARKE. Vertical GRF had the strongest correlations (>0.90) and root-mean-square error (RMSE) and mediolateral center of pressure trajectory had the weakest (<0.35), for both models. Strong correlations and small RMSE between predicted and measured GRFs support the use of these models for optimizing LEPE joint mechanics and improving LEPE design.

Temporal-spatial gait parameter models of very slow walking.

This study assessed the relationship between walking speed and common temporal-spatial stride-parameters to determine if a change in gait strategy occurs at extremely slow walking speeds. Stride-parameter models that represent slow walking can act as a reference for lower extremity exoskeleton and powered orthosis controls since these devices typically operate at walking speeds less than 0.4 m/s. Full-body motion capture data were collected from 30 health adults while walking on a self-paced treadmill, within a CAREN-Extended virtual reality environment. Kinematic data were collected for 0.2-0.8 m/s, and self-selected walking speed. Eight temporal stride-parameters were determined and their relationship to walking speed was assessed using linear and quadratic regression. Stride-length, step-length, and step-frequency were linearly related to walking speed, even at speeds below 0.4 m/s. An inflection point at 0.5 m/s was found for stride-time, step-time, stance-time, and double support time. Equations were defined for each stride-parameter, with equation outputs producing correlations greater than 0.91 with the test data. This inflection point suggests a change in gait strategy at very slow walking speeds favouring greater ground contact time.

Neuromuscular adaptations in older males and females with knee osteoarthritis during weight-bearing force control.

BACKGROUND: Females exhibit significantly greater incidence, prevalence, and severity of osteoarthritis (OA) compared to males. Despite known biological, morphological, and functional differences between males and females, there has been little sex-related investigation into sex-specific biomechanical and neuromuscular responses to OA. OBJECTIVE: To identify sex-related differences in OA-affected adults and within-sex differences between healthy and OA-affected adults' muscular activation patterns during lower limb loading. METHODS: Thirty adults with OA and 36 controls completed a standing ground reaction force (GRF) matching protocol requiring participants to expose equal body weight to each leg and modulate horizontal GRFs while maintaining constant joint positions. Electromyography was plotted as a function of GRF direction to depict muscle activation patterns. Muscles were classified as a general joint stabilizer, specific joint stabilizer or moment actuator by quantifying activation patterns with a test of asymmetry, specificity index and mean direction of activity. Lower limb kinematics and kinetics were also recorded. RESULTS: In general, muscle roles as it relates to joint stability did not differ between groups. Compared to controls, both males and females with OA demonstrated greater rectus femoris activity and reduced knee rotation moments. Females with OA had significantly greater biceps femoris and gastrocnemius activity during respective lateral, and anterior-medial loading directions compared to males with OA. CONCLUSIONS: We identified fundamental differences in muscular stabilization strategies in older adults with OA as well as sex-related changes in neuromuscular function that may influence joint loading conditions and provide insight into the greater incidence of knee OA in females.

Sex-related differences in neuromuscular control: Implications for injury mechanisms or healthy stabilisation strategies?

Sex-related differences in neuromuscular activation have been previously identified and are thought to be an underlying contributor to the ACL injury mechanism. During dynamic tasks evaluating the role of muscle action as it relates to joint stability is difficult since individual muscle contributions to force generation are confounded by biomechanical factors of movement. The purpose of this study was to examine sex-related differences in knee muscle action during a weight-bearing isometric exercise and identify the stabilising role of these muscles. Healthy young adults stood with their dominant leg in a boot fixed to a force platform. A force matching protocol required participants to modulate normalised ground reaction forces in various combinations of anterior-posterior, medial-lateral loads while maintaining a constant joint position. Normalised electromyographic data of eight muscles crossing the knee joint were displayed in polar plots. Patterns were quantified with an orientation analysis and mean activation magnitudes were computed. Females demonstrated symmetrical activation patterns with significantly greater activation in the rectus femoris (p = 0.037), lateral gastrocnemius (p = 0.012), and tensor fascia lata (p = 0.005) compared to males. High between-subject reliability (ICC = 0.772-0.977) was observed across groups suggesting we have identified fundamental sex-related differences in knee joint stabilisation strategies.

Reliability of knee joint muscle activity during weight bearing force control.

We developed a novel approach that requires subjects to produce and finely tune ground reaction forces (GRFs) while standing. The aim of this study was to examine the reliability of electromyographic data recorded during these tasks. Healthy young adults stood with their dominant leg in a boot fixed to a force platform. A target matching protocol required subjects to control both the direction and magnitude of GRF along the horizontal plane while maintaining constant inferior-superior loads of 50% body-weight (BW). Each target matching task was repeated three times in a random order. Subjects were retested with the same protocol 2-3 days later. Normalised electromyography data of eight muscles crossing the knee joint was collected for each successful target match. A random model, single measures intra-class correlation analysed the reliability for both test-retest and intra-day results, in addition to inter-subject reliability. The GRFs required to meet the targets were comparable to a range of activities of daily living, ranging from 0.48 to 0.58 N/kg of BW in the horizontal plane while maintaining 50% BW in the vertical plane. We observed moderate to high ICC values (0.60-0.993) for most muscles in most directions, indicating low within-subject variance. In addition, moderate to high between-subject reliability was observed in all eight muscle activation profiles, indicating subjects used similar neuromuscular control strategies to achieve the desired GRFs. In conclusion, our protocol identifies non-random weight-bearing motor control strategies while generating direction dependent GRFs. These results provide reliable insight into knee joint stabilisation strategies during weight bearing.