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The foot is more than a spring: human foot muscles perform work to adapt to the energetic requirements of locomotion.
Riddick, R, Farris, DJ, Kelly, LA
Journal of the Royal Society, Interface. 2019;(150):20180680
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Abstract
The foot has been considered both as an elastic mechanism that increases the efficiency of locomotion by recycling energy, as well as an energy sink that helps stabilize movement by dissipating energy through contact with the ground. We measured the activity of two intrinsic foot muscles, flexor digitorum brevis (FDB) and abductor hallucis (AH), as well as the mechanical work performed by the foot as a whole and at a modelled plantar muscle-tendon unit (MTU) to test whether these passive mechanics are actively controlled during stepping. We found that the underlying passive visco-elasticity of the foot is modulated by the muscles of the foot, facilitating both dissipation and generation of energy depending on the mechanical requirements at the centre of mass (COM). Compared to level ground stepping, the foot dissipated and generated an additional -0.2 J kg-1 and 0.10 J kg-1 (both p < 0.001) when stepping down and up a 26 cm step respectively, corresponding to 21% and 10% of the additional net work performed by the leg on the COM. Of this compensation at the foot, the plantar MTU performed 30% and 89% of the work for step-downs and step-ups, respectively. This work occurred early in stance and late in stance for stepping down respectively, when the activation levels of FDB and AH were increased between 69 and 410% compared to level steps (all p < 0.001). These findings suggest that the energetic function of the foot is actively modulated by the intrinsic foot muscles and may play a significant role in movements requiring large changes in net energy such as stepping on stairs or inclines, accelerating, decelerating and jumping.
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A single session of trip-specific training modifies trunk control following treadmill induced balance perturbations in stroke survivors.
Nevisipour, M, Grabiner, MD, Honeycutt, CF
Gait & posture. 2019;:222-228
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Abstract
BACKGROUND Individuals with stroke are at significant risk of falling. Trip-specific training is a targeted training approach that has been shown to reduce falls in older adults and amputees by enhancing the compensatory stepping response required to prevent a fall. Still, individuals with stroke have unique deficits (e.g. spasticity) which draws into question if this type of training will be effective for this population. OBJECTIVE Evaluate if a single session of trip-specific training can modify the compensatory stepping response (trunk movement, step length/duration, reaction time) of individuals with chronic stroke. METHODS Sixteen individuals with unilateral chronic stroke participated in a single session of trip-specific training consisting of 15 treadmill perturbations. A falls assessment consisting of 3 perturbations was completed before and after training. Recovery step kinematics measured during the pre- and post-test were compared using a repeated measures design. Furthermore, Fallers (those who experienced at least one fall during the pre- or post-test) were compared to Non-fallers. RESULTS Trip-specific training decreased trunk movement post perturbation. Specifically following training, Trunk flexion was 48 and 19 percent smaller on the small and medium perturbations at the end of the first compensatory step. Fallers (9 out of 16 subjects) post-training resembled Non-Fallers pre-training. Specifically, Trunk flexion at the completion of the first step during small and medium perturbations was not different between Fallers post-training and Non-Fallers pre-training. Still enthusiasm was tempered because Trunk flexion at the largest perturbation (where most falls occurred) was not changed and therefore total falls were not reduced as a result of this training. SIGNIFICANCE Our results indicate that trip-specific training modifies the dynamic falls response immediately following trip-like treadmill perturbations. However, the incidence of falls was not reduced with a single training session. Further study of the implications and length of the observed intervention effect are warranted.
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The effect of age and speed on foot and ankle kinematics assessed using a 4-segment foot model.
van Hoeve, S, Leenstra, B, Willems, P, Poeze, M, Meijer, K
Medicine. 2017;(35):e7907
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Abstract
BACKGROUND The effects of age and speed on foot and ankle kinematics in gait studies using foot models are not fully understood, whereas this can have significant influence. We analyzed these variables with the 4-segment Oxford foot model. METHODS Twenty-one healthy subjects (aged 20-65 years) were recruited for gait analysis. The effect of speed on foot and ankle kinematics was assessed by comparing results during slow walking and fast walking. To assess the effect of age, a group of 13 healthy young adults (aged 20-24 years) were compared with a group of 8 older adults (aged 53-65 years). Also, the interaction between age and speed was analyzed. RESULTS Regarding speed, there was a significant difference between forefoot/hindfoot motion in the sagittal plane (flexion/extension) during both loading- and push-off phase (P = .004, P < .001). Between hindfoot/tibia, there was a significant difference for all parameters except for motion in the sagittal plane (flexion/extension) during push-off phase (P = .5). Age did not significantly influence kinematics. There was no interaction between age and speed. CONCLUSION Our analysis found that speed significantly influenced the kinematic outcome parameters. This was more pronounced in the ankle joint. In contrast, no significant differences were found between younger and older healthy subjects.
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Contribution of feedback and feedforward strategies to locomotor adaptations.
Lam, T, Anderschitz, M, Dietz, V
Journal of neurophysiology. 2006;(2):766-73
Abstract
The aim of this study was to examine the strategies used by human subjects to adapt their walking pattern to a velocity-dependent resistance applied against hip and knee movements. Subjects first walked on a treadmill with their lower limbs strapped to an exoskeletal robotic gait orthosis with no resistance against leg motions (null condition). Afterward, a velocity-dependent resistance was applied against left hip and knee movements (force condition). Catch trials were interspersed throughout the experiment to track the development of adaptive changes in the walking pattern. After 188 steps in the force condition, subjects continued to step in the null condition for another 100 steps (washout period). Leg muscle activity and joint kinematics were recorded and analyzed. The adaptive modifications in the locomotor pattern suggest the involvement of both feedback and feedforward control strategies. Feedback-driven adaptations were reflected in increases in rectus femoris and tibialis anterior activity during swing, which occurred immediately, only in the presence of resistance, and not during the catch trials. Locomotor adaptations involving feedforward strategies were reflected in enhanced pre-swing activity in the biceps femoris and medial hamstrings muscles, which required experience and persisted in the catch trials. During washout subjects showed a gradual deadaptation of locomotor activity to control levels. In summary, adaptive changes in the walking pattern were driven by both feedback and feedforward adjustments in the walking pattern appropriate for overcoming the effects of resistance.
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Functional roles of lower-limb joint moments while walking in water.
Miyoshi, T, Shirota, T, Yamamoto, S, Nakazawa, K, Akai, M
Clinical biomechanics (Bristol, Avon). 2005;(2):194-201
Abstract
OBJECTIVE To clarify the functional roles of lower-limb joint moments and their contribution to support and propulsion tasks while walking in water compared with that on land. DESIGN Sixteen healthy, young subjects walked on land and in water at several different speeds with and without additional loads. BACKGROUND Walking in water is a major rehabilitation therapy for patients with orthopedic disorders. However, the functional role of lower-limb joint moments while walking in water is still unclear. METHODS Kinematics, electromyographic activities in biceps femoris and gluteus maximums, and ground reaction forces were measured under the following conditions: walking on land and in water at a self-determined pace, slow walking on land, and fast walking in water with or without additional loads (8 kg). The hip, knee, and ankle joint moments were calculated by inverse dynamics. RESULTS The contribution of the walking speed increased the hip extension moment, and the additional weight increased the ankle plantar flexion and knee extension moment. CONCLUSIONS The major functional role was different in each lower-limb joint muscle. That of the muscle group in the ankle is to support the body against gravity, and that of the muscle group involved in hip extension is to contribute to propulsion. In addition, walking in water not only reduced the joint moments but also completely changed the inter-joint coordination. RELEVANCE It is of value for clinicians to be aware that the greater the viscosity of water produces a greater load on the hip joint when fast walking in water.
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Differences in the EMG pattern of leg muscle activation during locomotion in Parkinson's disease.
Albani, G, Sandrini, G, Künig, G, Martin-Soelch, C, Mauro, A, Pignatti, R, Pacchetti, C, Dietz, V, Leenders, KL
Functional neurology. 2003;(3):165-70
Abstract
In this pilot study, EMG patterns of leg muscle activation were studied in five parkinsonian patients with (B1) and five without (B2) freezing. Gastrocnemius medialis (GM) and tibialis anterior (TA) activity was analysed, by means of surface electromyography (EMG), during treadmill walking at two different belt speeds. Both groups showed reduced GM activity and an overactive TA at the lower speed compared with controls. Upon increasing the speed, the B2 patients showed a marked GM response (increment index 100%), while a moderate change was observed in the B1 group. Poor recruitment of the GM characterises parkinsonian gait in general; this pattern is much more marked in parkinsonian patients with freezing of gait, who show a loss of GM adaptation to variation of locomotion speed.
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Trajectories of leg strength and gait speed among sedentary older adults: longitudinal pattern of dose response.
Purser, JL, Pieper, CF, Poole, C, Morey, M
The journals of gerontology. Series A, Biological sciences and medical sciences. 2003;(12):M1125-34
Abstract
BACKGROUND Current theory about how an older adult's leg strength influences walking speed is based primarily on nonlinear patterns of association observed in cross-sectional data. Compared with adults with normal or high levels of leg muscle strength, weak older adults are thought to have a greater capacity for functional change in response to changes in lower extremity strength. Longitudinal data, however, have not been applied to study this putative pattern of dose response. METHODS Three repeated measures of leg strength, gait speed, and covariates were evaluated in a cohort of 134 sedentary, community-dwelling male and female participants (aged >64 years) of a randomized exercise intervention. Empirical Bayes methods were used to evaluate the association between trajectories of strength and gait speed during the course of the study. RESULTS We observed a potentially clinically important, positive linear association between strength change and gait speed change. Each additional unit increase in the monthly rate of strength change increased the rate of gait speed change by 0.29 meters/minute/month (95% CI [confidence interval] = 0.03, 0.55 m/min/mo). Absolute change in walking velocity due to strength changes in the cohort ranged from a gain of approximately 15 m/min to a loss of approximately 13 m/min over the 9-month period (changes of -18% to +20% relative to a normal walking speed of 72 m/min). CONCLUSIONS In this cohort, change in functional walking speed depended more on the rate of strength change observed than on the amount of muscle weakness present at baseline. These results have important implications for screening and intervention programs designed to change functional walking ability among sedentary older adults.
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Determination of the effectiveness of materials in attenuating high frequency shock during gait using filterbank analysis.
Gillespie, KA, Dickey, JP
Clinical biomechanics (Bristol, Avon). 2003;(1):50-9
Abstract
OBJECTIVE To develop an accurate method for quantifying the frequency content of the ground reaction force transient. DESIGN Repeated measures design comparing the impact severity during walking with different insole materials. BACKGROUND The body experiences a brief but sizeable impact upon heel strike during walking. This impact transient is believed to result in musculoskeletal injuries. It is important to accurately quantify this impact as a step towards decreasing the risk of injury. METHODS Seven subjects walked barefoot at their normal cadence across a force platform, while insole materials (Spenco, Microcel-puff, and Plastazote) were placed on the surface of the force platform. A filterbank program was developed to determine the percent root mean square in 10 Hz frequency bands from zero to 400 Hz. Analysis focused on the impact transient contained in a 20 ms window after heel contact. RESULTS The high frequency (>60 Hz) power was significantly larger in the barefoot condition compared to the insole conditions. The barefoot condition also resulted in significantly higher initial peak forces and force loading rates. CONCLUSIONS The frequency content of the ground reaction force can be effectively quantified using a filterbank approach. Shoe insole materials can reduce the initial peak force, force loading rate, and frequency content of the impact transient in walking. The frequency content of the initial ground reaction force extends up to 400 Hz in some footwear conditions. RELEVANCE The new filterbank procedure illustrates that the vertical ground reaction force in walking has a higher frequency content than previously thought. This signal requires high sampling rates to avoid aliasing, and appropriate signal processing algorithms, such as filter banks, for analysis.