Self-selected step length asymmetry is not explained by energy cost minimization in individuals with chronic stroke.

BACKGROUND: Asymmetric gait post-stroke is associated with decreased mobility, yet individuals with chronic stroke often self-select an asymmetric gait despite being capable of walking more symmetrically. The purpose of this study was to test whether self-selected asymmetry could be explained by energy cost minimization. We hypothesized that short-term deviations from self-selected asymmetry would result in increased metabolic energy consumption, despite being associated with long-term rehabilitation benefits. Other studies have found no difference in metabolic rate across different levels of enforced asymmetry among individuals with chronic stroke, but used methods that left some uncertainty to be resolved. METHODS: In this study, ten individuals with chronic stroke walked on a treadmill at participant-specific speeds while voluntarily altering step length asymmetry. We included only participants with clinically relevant self-selected asymmetry who were able to significantly alter asymmetry using visual biofeedback. Conditions included targeting zero asymmetry, self-selected asymmetry, and double the self-selected asymmetry. Participants were trained with the biofeedback system in one session, and data were collected in three subsequent sessions with repeated measures. Self-selected asymmetry was consistent across sessions. A similar protocol was conducted among unimpaired participants. RESULTS: Participants with chronic stroke substantially altered step length asymmetry using biofeedback, but this did not affect metabolic rate (ANOVA, p = 0.68). In unimpaired participants, self-selected step length asymmetry was close to zero and corresponded to the lowest metabolic energy cost (ANOVA, p = 6e-4). While the symmetry of unimpaired gait may be the result of energy cost minimization, self-selected step length asymmetry in individuals with chronic stroke cannot be explained by a similar least-effort drive. CONCLUSIONS: Interventions that encourage changes in step length asymmetry by manipulating metabolic energy consumption may be effective because these therapies would not have to overcome a metabolic penalty for altering asymmetry.

Spring-like Ankle Foot Orthoses reduce the energy cost of walking by taking over ankle work.

In patients with central neurological disorders, gait is often limited by a reduced ability to push off with the ankle. To overcome this reduced ankle push-off, energy-storing, spring-like carbon-composite Ankle Foot Orthoses (AFO) can be prescribed. It is expected that the energy returned by the AFO in late stance will support ankle push-off, and reduce the energy cost of walking. In 10 patients with multiple sclerosis and stroke the energy cost of walking, 3D kinematics, joint power, and joint work were measured during gait, with and without the AFO. The mechanical characteristics of the AFO were measured separately, and used to calculate the contribution of the AFO to the ankle kinetics. We found a significant decrease of 9.8% in energy cost of walking when walking with the AFO. With the AFO, the range of motion of the ankle was reduced by 12.3°, and the net work around the ankle was reduced by 29%. The total net work in the affected leg remained unchanged. The AFO accounted for 60% of the positive ankle work, which reduced the total amount of work performed by the leg by 11.1% when walking with the AFO. The decrease in energy cost when walking with a spring-like energy-storing AFO in central neurological patients is not induced by an augmented net ankle push-off, but by the AFO partially taking over ankle work.

Quantification of energy expenditure during gait in children affected by cerebral palsy.

AIM: Children affected by cerebral palsy (CP) are generally characterised by some movement limitations and abnormalities that compromised gait pattern. These disabilities during deambulation may lead to excessive energy cost and so to a compromised energy efficiency. METHODS: In this study oxygen expenditure was evaluated during walking in 20 children affected by CP and in 20 healthy children, using Cosmed K4b2 (Cosmed, Italy). From obtained data about energy consumption, some parameters (heart rate, energy expenditure index, oxygen consumption, oxygen cost) were extracted, first in order to quantify energy cost during gait in pathological and healthy subjects and then to underline differences between the 2 groups of children. RESULTS: In particular, the results obtained revealed that heart rate (bpm) and oxygen consumption (mL/kg/min) mean values didn't differ significantly between normal subjects and those with CP; instead, energy expenditure index (b/m) and oxygen cost (mL/kg/m) presented higher mean values rather than control group at a statistically level and so they revealed to be significant parameters, in order characterized energy expenditure in children affected by CP. CONCLUSIONS: This inefficiency characteristic of CP deambulation is probably directly connected to the presence of simultaneous contraction of agonist and antagonist muscle in these patients.

Energy cost of walking in low lumbar myelomeningocele.

The aim of this study was to determine whether it is more efficient for adolescents with low lumbar myelomeningocele (MM) to walk with a reciprocal or a swing-through gait pattern. Energy measurements for subjects with MM were compared for reciprocal and swing-through gait and also with an able-bodied control group. The rate of oxygen consumption (in milliliters per kilogram per minute) was higher for both the reciprocal and swing-through conditions compared with the control group, but there was no difference in the rate of consumption between the two modes of walking. Walking velocities (in meters per minute) were slower for both the reciprocal and swing-through conditions compared with the control group, with reciprocal walking significantly slower than swing-through gait. Oxygen cost (in milliliters per kilogram per meter) was higher for both the reciprocal and the swing-through conditions compared with the control group. Oxygen cost was higher for reciprocal walking than for swing-through gait. Swing-through gait proved to be the more efficient walking pattern in this group of subjects with MM.