Background: In people with calf muscle weakness, the stiffness of dorsal leaf spring ankle–foot orthoses (DLS-AFO) needs to be individualized to maximize its effect on walking. Orthotic suppliers may recommend a certain stiffness based on body weight and activity level. However, it is unknown whether these recommendations are sufficient to yield the optimal stiffness for the individual. Therefore, we assessed whether the stiffness following the supplier’s recommendation of the Carbon Ankle7 (CA7) dorsal leaf matched the experimentally optimized AFO stiffness. Methods: Thirty-four persons with calf muscle weakness were included and provided a new DLS-AFO of which the stiffness could be varied by changing the CA7® (Ottobock, Duderstadt, Germany) dorsal leaf. For five different stiffness levels, including the supplier recommended stiffness, gait biomechanics, walking energy cost and speed were assessed. Based on these measures, the individual experimentally optimal AFO stiffness was selected. Results: In only 8 of 34 (23%) participants, the supplier recommended stiffness matched the experimentally optimized AFO stiffness, the latter being on average 1.2 ± 1.3 Nm/degree more flexible. The DLS-AFO with an experimentally optimized stiffness resulted in a significantly lower walking energy cost (− 0.21 ± 0.26 J/kg/m, p < 0.001) and a higher speed (+ 0.02 m/s, p = 0.003). Additionally, a larger ankle range of motion (+ 1.3 ± 0.3 degrees, p < 0.001) and higher ankle power (+ 0.16 ± 0.04 W/kg, p < 0.001) were found with the experimentally optimized stiffness compared to the supplier recommended stiffness. Conclusions: In people with calf muscle weakness, current supplier’s recommendations for the CA7 stiffness level result in the provision of DLS-AFOs that are too stiff and only achieve 80% of the reduction in energy cost achieved with an individual optimized stiffness. It is recommended to experimentally optimize the CA7 stiffness in people with calf muscle weakness in order to maximize treatment outcomes. Trial registration Nederlands Trial Register 5170. Registration date: May 7th 2015. http://www.trialregister.nl/trialreg/admin/rctview.asp?TC=5170.

Objective: To describe the orthotic properties and evaluate the effects of ankle-foot orthoses for calf muscle weakness in persons with non-spastic neuromuscular disorders compared with shoes-only. Design: Cross-sectional study. Subjects: Thirty-four persons who used ankle-foot orthoses for non-spastic calf muscle weakness. Methods: The following orthotic properties were measured: ankle-foot orthosis type, mass, and ankle and footplate stiffness. For walking with shoes- only and with the ankle-foot orthoses, walking speed, energy cost and gait biomechanics were assessed. Results: Four types of ankle-foot orthosis were identified: shaft-reinforced orthopaedic shoes (n = 6), ventral ankle-foot orthoses (n = 10), dorsal leaf ankle-foot orthoses (n = 12) and dorsiflexion-stop ankle-foot orthoses (n = 6). These types differed significantly with regards to mass, ankle-and footplate stiffness. Compared with shoes-only, all anklefoot orthoses/orthopaedic shoes groups combined increased walking speed by 0.18 m/s (95% confidence interval (95% CI) 0.13-0.23), reduced energy cost by 0.70 J/kg/m (95% CI 0.48-0.94) and limited ankle dorsiflexion by -3.0° (95% CI 1.3-4.7). Higher ankle-foot orthoses ankle stiffness correlated with greater reductions in walking energy cost and maximal ankle dorsiflexion angle. Conclusion: Ankle-foot orthoses for persons with non-spastic calf muscle weakness vary greatly in properties and effects on gait. The large variation in effectiveness may be due to differences in ankle stiffness, although this requires further prospective evaluation.

In persons with calf muscle weakness, walking energy cost is commonly increased due to persistent knee flexion and a diminished push-off. Provided ankle-foot orthoses (AFOs) usually lower walking energy cost. To maximize the reduction in energy cost, AFO bending stiffness should be individually optimized, but this is not common practice. Therefore, we aimed to evaluate whether individually stiffness-optimized AFOs reduce walking energy cost compared to conventional AFOs in persons with non-spastic calf muscle weakness and, secondarily, whether stiffness-optimized AFOs improve walking speed and gait biomechanics. Thirty-seven persons with non-spastic calf muscle weakness using a conventional AFO were included. Participants were provided a new, individually stiffness-optimized AFO. Walking energy cost, speed and gait biomechanics were assessed, at delivery and 3-months follow-up. Stiffness-optimized AFOs reduced walking energy cost with 9.2% (-0.42J/kg/m, 95%CI: 0.26 to 0.57) compared to the conventional AFOs while walking speed increased with 5.2% (+0.05m/s, 95%CI: 0.03 to 0.08). In bilateral affected persons the effects were larger compared to unilateral affected persons (difference effect energy cost: 0.31J/kg/m, speed: +0.09m/s). Although individually gait biomechanics changed considerably, no significant group differences were found (p > 0.118). We demonstrated that individually stiffness-optimized AFOs considerably and meaningfully reduced walking energy cost compared to conventional AFOs, which was accompanied by an increase in walking speed. Especially in bilateral affected persons large effects of stiffness-optimization were found. The individual differences in gait changes substantiate the recommendation that the AFO bending stiffness should be individually tuned to minimize walking energy cost.

BACKGROUND: To improve gait, persons with calf muscle weakness can be provided with a dorsal leaf spring ankle foot orthosis (DLS-AFO). These AFOs can store energy during stance and return this energy during push-off, which, in turn, reduces walking energy cost. Simulations indicate that the effect of the DLS-AFO on walking energy cost and gait biomechanics depends on its stiffness and on patient characteristics. We therefore studied the effect of varying DLS-AFO stiffness on reducing walking energy cost, and improving gait biomechanics and AFO generated power in persons with non-spastic calf muscle weakness, and whether the optimal AFO stiffness for maximally reducing walking energy cost varies between persons. METHODS: Thirty-seven individuals with neuromuscular disorders and non-spastic calf muscle weakness were included. Participants were provided with a DLS-AFO of which the stiffness could be varied. For 5 stiffness configurations (ranging from 2.8 to 6.6 Nm/degree), walking energy cost (J/kg/m) was assessed using a 6-min comfortable walk test. Selected gait parameters, e.g. maximal dorsiflexion angle, ankle power, knee angle, knee moment and AFO generated power, were derived from 3D gait analysis. RESULTS: On group level, no significant effect of DLS-AFO stiffness on reducing walking energy cost was found (p = 0.059, largest difference: 0.14 J/kg/m). The AFO stiffness that reduced energy cost the most varied between persons. The difference in energy cost between the least and most efficient AFO stiffness was on average 10.7%. Regarding gait biomechanics, increasing AFO stiffness significantly decreased maximal ankle dorsiflexion angle (- 1.1 ± 0.1 degrees per 1 Nm/degree, p < 0.001) and peak ankle power (- 0.09 ± 0.01 W/kg, p < 0.001). The reduction in minimal knee angle (- 0.3 ± 0.1 degrees, p = 0.034), and increment in external knee extension moment in stance (- 0.01 ± 0.01 Nm/kg, p = 0.016) were small, although all stiffness' substantially affected knee angle and knee moment compared to shoes only. No effect of stiffness on AFO generated power was found (p = 0.900). CONCLUSIONS: The optimal efficient DLS-AFO stiffness varied largely between persons with non-spastic calf muscle weakness. Results indicate this is caused by an individual trade-off between ankle angle and ankle power affected differently by AFO stiffness. We therefore recommend that the AFO stiffness should be individually optimized to best improve gait. TRIAL REGISTRATION NUMBER: Nederlands Trial Register 5170. Registration date: May 7th 2015. http://www.trialregister.nl/trialreg/admin/rctview.asp?TC=5170.

Background: Patients with calf muscle weakness due to neuromuscular disorders have a reduced ankle push-off work, which leads to increased energy dissipation at contralateral heel-strike. Consequently, compensatory positive work needs to be generated, which is mechanically less efficient. It is unknown whether neuromuscular disorder patients compensate with their ipsilateral hip and/or contralateral leg; and if such compensatory joint work is related to walking energy cost. Research question: Do patients with calf muscle weakness compensate for the increase in negative joint work by increasing positive ipsilateral hip work and/or positive contralateral leg work? And is the total mechanical work related with walking energy cost? Methods: Seventeen patients with unilateral flaccid calf muscle weakness and 10 healthy individuals performed the following two tests: i) a barefoot 3D gait analysis at comfortable speed and matched control speed (i.e. 0.4 non-dimensional) to assess lower limb joint work and ii) a 6-minute walk test at comfortable speed to assess walking energy cost. Results: Patients had a lower comfortable walking speed compared to healthy individuals (1.05 vs 1.36 m/s, p < 0.001) and did not increase positive lower limb joint work at comfortable speed. At matched speed (1.25 m/s), patients showed increased positive work at their ipsilateral hip (0.38 ± 0.08 vs 0.27 ± 0.07, p = 0.001) and/or contralateral leg (0.99 ± 0.14 vs 0.69 ± 0.14, p < 0.001). Patients with weakest plantar flexors used both strategies. No relation between total positive work and walking energy cost was found (r = 0.43, p = 0.122). Significance: Patients with unilateral calf muscle weakness compensated for reduced ankle push-off work by lowering their comfortable walking speed or, at matched speed, by generating additional positive joint work at the ipsilateral hip and/or contralateral leg. The additional positive joint work at matched speed did not explain the elevated walking energy cost at comfortable speed, which needs further exploration.

Impaired calf muscle strength in patients with neuromuscular diseases typically reduces ankle work during push-off, leading to increased energy dissipation (i.e. negative work) at contralateral heel-strike [1]. To overcome the reduced push-off work and consequent energy dissipation, patients have to compensate by producing more positive work elsewhere to maintain their walking speed. Increments in positive hip work in the affected leg and positive total work in the non-affected leg have been proposed as possible compensation strategies in patients with spastic calf muscle weakness [2] and in below knee amputees [3]. However, knowledge about which compensations are used in neuromuscular disease patients exhibiting flaccid calf muscle weakness is currently lacking, and may be useful to inform treatment decisions, including the specs of orthotic devices.

Introduction: In patients with neuromuscular disorders and subsequent calf muscle weakness, metabolic walking energy cost (EC) is nearly always increased, which may restrict walking activity in daily life. To reduce walking EC, a spring-like ankle-footorthosis (AFO) can be prescribed. However, the reduction in EC that can be obtained from these AFOs is stiffness dependent, and it is unknown which AFO stiffness would optimally support calf muscle weakness. The PROOF-AFO study aims to determine the effectiveness of stiffness-optimised AFOs on reducing walking EC, and improving gait biomechanics and walking speed in patients with calf muscle weakness, compared to standard, non-optimised AFOs. A second aim is to build a model to predict optimal AFO stiffness. Methods and analysis: A prospective intervention study will be conducted. In total, 37 patients with calf muscle weakness who already use an AFO will be recruited. At study entry, participants will receive a new custom-made spring-like AFO of which the stiffness can be varied. For each patient, walking EC (primary outcome), gait biomechanics and walking speed (secondary outcomes) will be assessed for five stiffness configurations and the patient's own (standard) AFO. On the basis of walking EC and gait biomechanics outcomes, the optimal AFO stiffness will be determined. After wearing this optimal AFO for 3 months, walking EC, gait biomechanics and walking speed will be assessed again and compared to the standard AFO. Ethics and dissemination: The Medical Ethics Committee of the Academic Medical Centre in Amsterdam has approved the study protocol. The study is registered at the Dutch trial register (NTR 5170). The PROOF-AFO study is the first to compare stiffness-optimised AFOs with usual care AFOs in patients with calf muscle weakness. The results will also provide insight into factors that influence optimal AFO stiffness in these patients. The results are necessary for improving orthotic treatment and will be disseminated through international peer-reviewed journals and scientific conferences.