Physics-based predictive simulations of human movement have the potential to support personalized medicine, but large computational costs and difficulties to model control strategies have limited their use. We have developed a computationally efficient optimal control framework to predict human gaits based on optimization of a performance criterion without relying on experimental data. The framework generates three-dimensional muscle-driven simulations in 36 min on average—more than 20 times faster than existing simulations—by using direct collocation, implicit differential equations and algorithmic differentiation. Using this framework, we identified a multi-objective performance criterion combining energy and effort considerations that produces physiologically realistic walking gaits. The same criterion also predicted the walk-to-run transition and clinical gait deficiencies caused by muscle weakness and prosthesis use, suggesting that diverse healthy and pathological gaits can emerge from the same control strategy. The ability to predict the mechanics and energetics of a broad range of gaits with complex three-dimensional musculoskeletal models will allow testing novel hypotheses about gait control and hasten the development of optimal treatments for neuro-musculoskeletal disorders.

Objective: To compare gait parameters in Parkinson's disease (PD) during the on-phase of medication cycle with those of healthy elderly control subjects.Design: A group-comparison study. Setting: Gait analysis laboratory of a university hospital. Participants: Fifteen patients with PD and 9 healthy elderly controls.Interventions: Not applicable. Main Outcome Measures: Spatiotemporal, kinematic, and kinetic gait parameters.Results: The PD spatiotemporal results showed a significant reduction in step length and walking velocity compared with controls. In the kinematics, the major feature of the PD group was a markedly reduced ankle plantarflexion excursion (at 50%-60% of the gait cycle). Most important, the kinetics showed reduced ankle push-off power and hip pull-off power. Unlike the control subjects, the patients with PD did not show any correlation between ankle generation (push-off) power and stride length (rϭ.19) or with gait speed (rϭ.29). Correction for walking velocity did not result in significant changes in the kinetics between the groups.Conclusions: Reduced ankle (push-off) power generation and reduced hip flexion (pull-off) power persisted in PD gait despite being tested in the on-phase of the medication cycle. Lack of a correlation between ankle and hip power generation and walking velocity suggests that peripheral and central factors contribute to lack of forward progression. Patients with PD may benefit from intervention strategies that correct the kinematic and the kinetic gait components.

While limited walking speed characterizes gait in the majority of persons post-stroke, the potential to increase walking speed can also be markedly impaired and has not been thoroughly investigated. We hypothesized that failure to effectively recruit both hip flexor and plantarflexor muscles of the paretic side limits the potential to increase walking speed in lower functioning hemiparetic subjects. To test this hypothesis, we measured gait kinematics and mechanics of twelve persons with poststroke hemiparesis at self-selected and fast walking conditions. Two groups were identified: 1) lower functioning subjects (n=6) who increased normalized walking speed from 0.52 leg lengths/sec (ll/s, SEM: 0.04) to 0.72 ll/s (SEM: 0.03) and 2) higher functioning subjects (n = 6) who increased walking speed from 0.88 ll/s (SEM:0.04) to 1.4 ll/s (SEM 0.03). Changes in spatiotemporal parameters, joint kinematics and kinetics between self-selected and fast walking were compared to control data collected at matched speeds (0.35 ll/s (SEM: 0.03) -0.63 ll/s (SEM: 0.03) -0.92 ll/s (SEM: 0.04) and 1.4 ll/s (SEM: 0.04)). Similar to speed-matched control subjects, the higher functioning hemiparetic subjects increased paretic limb hip flexion power and ankle plantarflexion power to increase walking speed. The lower functioning subjects demonstrated impaired ankle power generation combined with excessive power generation at the paretic hip during pre-swing at their self selected speed. This lower functioning group did not increase power generation at the hip or ankle to increase walking speed. This observation suggests that impaired ankle power generation combined with saturation of hip power generation, limits the potential to increase walking speed in lower functioning hemiparetic subjects.

The aim of this study was to characterize the specifics of the sprint technique during the transition from start block into sprint running in well-trained sprinters. Twenty-one sprinters (11 men and 10 women), equipped with 74 spherical reflective markers, executed an explosive start action. An opto-electronic motion analysis system consisting of 12 MX3 cameras (250 Hz; 325,000 pixels) and two Kistler force plates (1000 Hz) was used to collect the three-dimensional (3D) marker trajectories and ground reaction forces (Nexus, Vicon). The 3D kinematics, joint kinetics, and power were calculated (Opensim) and were time normalized to 100% from the first action after gunshot until the end of second stance after block clearance (Matlab). The results showed that during the first stance, power generation at the knee plays a significant role in obtaining an effective transition, representing 31% of power generation in the lower limb, in the absence of preceding power absorption. Furthermore, the sprinter actively searches a more forward leaning position to maximize horizontal velocity. Since success during sprinting from the second stance onwards involves high hip and ankle activation, the above-mentioned three characteristics are specific skills required to successfully conclude the transition from start block into sprint running.

It is recognized that objective gait analysis is of great value in planning a multilevel botulinum toxin type A (BTX-A) treatment. After BTX-A treatment, objective outcome measures can provide new and interesting information for each individual child with cerebral palsy (CP). Moreover, by studying group results, we may evaluate our treatment hypotheses. The present prospective study attempts to document the effect of integrated multilevel BTX-A treatment 1 on objective gait parameters and to de®ne the optimal strategy for the combined treatment of BTX-A with casting in children with cerebral palsy. Objective three-dimensional gait analysis (3DGA) data were collected pre-and 2 months post-treatment, in two randomized patient groups: a ®rst group of 17 children treated with lower leg casting prior to BTX-A injections, and a second group of 17 patients who received casting immediately after injections. The present study demonstrates that improved gait can be achieved after a multilevel BTX-A treatment, combined with casting, using a set of 90 gait parameters. The most pronounced improvement was seen at the ankle joint. The results in the knee, hip and pelvis imply that multilevel treatment of the child with CP should start at an early age, in order to prevent development of muscle contractures. Slightly more pronounced bene®ts, mainly in the proximal joints, were seen for the children who were casted after injections as compared to the children who were casted before injections.

Recommendations on backpack loading advice restricting the load to 10% of body weight and carrying the load high on the spine. The effects of increasing load (0%-5%-10%-15% of body weight) and changing the placement of the load on the spine, thoracic vs. lumbar placement, during standing and gait were analysed in 20 college-aged students by studying physiological, biomechanical and subjective data. Significant changes were: (1) increased thorax flexion; (2) reduced activity of M. erector spinae vs. increased activation of abdominals; (3) increased heart rate and Borg scores for the heaviest loads. A trend towards increased spinal flexion, reduced pelvic anteversion and rectus abdominis muscle activity was observed for the lumbar placement. The subjective scores indicate a preference for the lumbar placement. These findings suggest that carrying loads of 10% of body weight and above should be avoided, since these loads induce significant changes in electromyography, kinematics and subjective scores. Conclusions on the benefits of the thoracic placement for backpack loads could not be drawn based on the parameter set studied.

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ObjectiveTo systematically review the biomechanical deficits after ACL reconstruction (ACLR) during single leg hop for distance (SLHD) testing and report these differences compared with the contralateral leg and with healthy controls.DesignSystematic review with meta-analysis.Data sourcesA systematic search in Pubmed (Ovid), EMBASE, CINAHL, Scopus, Web of Science, PEDro, SPORTDiscus, Cochrane Library, grey literature and trial registries, was conducted from inception to 1 April 2018.Eligibility criteria for selecting studiesStudies reporting kinematic, kinetic and/or electromyographic data of the ACLR limb during SLHD with no language limits.ResultsThe literature review yielded 1551 articles and 19 studies met the inclusion criteria. Meta-analysis revealed strong evidence of lower peak knee flexion angle and knee flexion moments during landing compared with the uninjured leg and with controls. Also, moderate evidence (with large effect size) of lower knee power absorption during landing compared with the uninjured leg. No difference was found in peak vertical ground reaction force during landing. Subgroup analyses revealed that some kinematic variables do not restore with time and may even worsen.ConclusionDuring SLHD several kinematic and kinetic deficits were detected between limbs after ACLR, despite adequate SLHD performance. Measuring only hop distance, even using the healthy leg as a reference, is insufficient to fully assess knee function after ACLR.PROSPERO trial registration number CRD42018087779.