Plantarflexion Resistance Research Articles

An articulated ankle–foot orthosis with adjustable plantarflexion resistance, dorsiflexion resistance and alignment: A pilot study on mechanical properties and effects on stroke hemiparetic gait

Mechanical properties of an articulated ankle–foot orthosis (AFO) are closely related to gait performance in individuals post-stroke. This paper presents a pilot study on the mechanical properties of a novel articulated AFO with adjustable plantarflexion resistance, dorsiflexion resistance and alignment, and its effect on ankle and knee joint kinematics and kinetics in an individual post-stroke during gait. The mechanical properties of the AFO were quantified. Gait analysis was performed using a 3D motion capture system with a split-belt instrumented treadmill under 12 different settings of the mechanical properties of the AFO [i.e. 4 plantarflexion resistances (P1<P4), 4 dorsiflexion resistances (D1<D4), 4 initial alignments (A1<A4)]. The AFO demonstrated systematic changes in moment–angle relationship in response to changes in AFO joint settings. The gait analysis demonstrated that the ankle and knee angle and moment were responsive to changes in the AFO joint settings. Mean ankle angle at initial contact changed from −0.86° (P1) to 0.91° (P4) and from −1.48° (A1) to 4.45° (A4), while mean peak dorsiflexion angle changed from 12.01° (D1) to 6.40° (D4) at mid-stance. The novel articulated AFO appeared effective in influencing lower-limb joint kinematics and kinetics of gait in the individual post-stroke.

Influences of Fascicle Length During Isometric Training on Improvement of Muscle Strength.

Tanaka, H, Ikezoe, T, Umehara, J, Nakamura, M, Umegaki, H, Kobayashi, T, Nishishita, S, Fujita, K, Araki, K, and Ichihashi, N. Influences of fascicle length during isometric training on improvement of muscle strength. J Strength Cond Res 30(11): 3249-3255, 2016-This study investigated whether low-intensity isometric training would elicit a greater improvement in maximum voluntary contraction (MVC) at the same fascicle length, rather than the joint angle, adopted during training. Sixteen healthy women (21.8 ± 1.5 years) were randomly divided into an intervention group and a control group. Before (Pre) and after (Post) training, isometric plantarflexion MVCs were measured every 10° through the range of ankle joint position from 20° dorsiflexion to 30° plantarflexion (i.e., 6 ankle angles). Medial gastrocnemius fascicle length was also measured at each position, using B-mode ultrasound under 3 conditions of muscle activation: at rest, 30%MVC at respective angles, and MVC. Plantarflexion resistance training at an angle of 20° plantarflexion was performed 3 days a week for 4 weeks at 30%MVC using 3 sets of twenty 3-second isometric contractions. Maximum voluntary contraction in the intervention group increased at 0 and 10° plantarflexion (0°; Pre: 81.2 ± 26.5 N·m, Post: 105.0 ± 21.6 N·m, 10°; Pre: 63.0 ± 23.6 N·m, Post: 81.3 ± 20.3 N·m), which was not the angle used in training (20°). However, the fascicle length adopted in training at 20° plantarflexion and 30%MVC was similar to the value at 0 or 10° plantarflexion at MVC. Low-intensity isometric training at a shortened muscle length may be effective for improving MVC at a lengthened muscle length because of specificity of the fascicle length than the joint angle.

Reduction of genu recurvatum through adjustment of plantarflexion resistance of an articulated ankle-foot orthosis in individuals post-stroke

BackgroundGenu recurvatum (knee hyperextension) is a common issue for individuals post-stroke. Ankle-foot orthoses are used to improve genu recurvatum, but evidence is limited concerning their effectiveness. Therefore, the aim of this study was to investigate the effect of changing the plantarflexion resistance of an articulated ankle-foot orthosis on genu recurvatum in patients post-stroke. MethodsGait analysis was performed on 6 individuals post-stroke with genu recurvatum using an articulated ankle-foot orthosis whose plantarflexion resistance was adjustable at four levels. Gait data were collected using a Bertec split-belt instrumented treadmill in a 3-dimensional motion analysis laboratory. Gait parameters were extracted and plotted for each subject under the four plantarflexion resistance conditions of the ankle-foot orthosis. Gait parameters included: a) peak ankle plantarflexion angle, b) peak ankle dorsiflexion moment, c) peak knee extension angle and d) peak knee flexion moment. A non-parametric Friedman test was performed followed by a post-hoc Wilcoxon Signed-Rank test for statistical analyses. FindingsAll the gait parameters demonstrated statistically significant differences among the four resistance conditions of the AFO. Increasing the amount of plantarflexion resistance of the ankle-foot orthosis generally reduced genu recurvatum in all subjects. However, individual analyses showed that the responses to the changes in the plantarflexion resistance of the AFO were not necessarily linear, and appear unique to each subject. InterpretationsThe plantarflexion resistance of an articulated AFO should be adjusted to improve genu recurvatum in patients post-stroke. Future studies should investigate what clinical factors would influence the individual differences.

Feature and practical use of the knee-ankle-foot-orthosis with plantar flexion resistance

Feature and practical use of the knee-ankle-foot-orthosis with plantar flexion resistance

The effect of varying the plantarflexion resistance of an ankle-foot orthosis on knee joint kinematics in patients with stroke

Ankle-foot orthoses (AFOs) can improve gait in patients with hemiplegia. However, it is anecdotally known that excessive plantarflexion resistance of an AFO could induce undesired knee flexion at early stance. The aim of this study was to systematically investigate the effect of varying the degrees of plantarflexion resistance of an AFO on knee flexion angles at early stance in five subjects with chronic stroke who demonstrated two clear knee flexion peaks at early stance and swing. Each subject wore an experimental AFO constructed with an oil-damper type ankle joint and was instructed to walk at their self-selected walking speed under five plantarflexion resistance conditions. The sagittal plane ankle and knee joint kinematics and gait speed were analyzed using a 3-D Motion Analysis System. A number of significant differences (P<0.005) in maximum knee flexion angles at early stance amongst different plantarflexion resistance conditions were revealed. The knee flexion angle was 23.80 (3.25) degrees under the free hinge joint condition (condition 1), while that was 26.09 (3.79) degrees under the largest resistance condition (condition 5). It was therefore demonstrated that increasing the plantarflexion resistance of an AFO would induce more knee flexion at early stance phase in patients with stroke.

Effects of an ankle-foot orthosis with oil damper on muscle activity in adults after stroke

Background and objectiveAn ankle-foot orthosis with an oil damper (AFO-OD) was developed to resist plantarflexion motion, thereby improving hemiplegic gait performance. The purpose of this study was to determine the effect of AFO-OD on muscle activity during the gait cycle in individuals affected by stroke. MethodsElectromyography (EMG) was used to assess gait at a self-selected speed while wearing an AFO-OD or an AFO with a plantarflexion stop (AFO-PS) worn on the affected side in 11 stroke survivors and on the right side in 11 age-matched healthy adults. EMG signals were obtained from the tibialis anterior (TA), gastrocnemius (GAS), and soleus (SOL) muscles. In addition, the ankle joint angle under both braces and the plantarflexion resistance torque (PFRT) under AFO-OD were monitored. ResultsPeak PFRT under AFO-OD was observed during the loading response phase (LRP) in both groups. AFO-OD promoted adequate plantarflexion during LRP in the stroke group, whereas AFO-PS did not. Compared with the AFO-PS, the AFO-OD significantly reduced GAS EMG amplitude during LRP in the stroke group, which was significantly correlated with peak PFRT during LRP. ConclusionAFO-OD assisted the “heel rocker function” and reduced GAS muscle EMG amplitude during LRP.

A plantar flexion device exercise programme for patients with peripheral arterial disease: a randomised prospective feasibility study

Objectives To determine if the use of a plantar flexion device (Step It pedal) in a newly developed exercise programme is of benefit to patients with peripheral arterial disease. Design Prospective feasibility trial with patients randomised to either standard care or the Step It exercise programme plus standard care. Setting Physiotherapy Department at Cumberland Infirmary, Carlisle, UK. Participants Patients were identified from the vascular team's referral list. In total, 42 patients agreed to take part; 18 in the control group and 24 in the intervention group. Interventions Eligible participants were randomised and received either standard care or took part in a plantar flexion resistance exercise programme, involving the Step It pedal, for a period of 12 weeks. Main outcome measures Maximum walking distance, claudication distance and ankle brachial pressure index. Results Eighty-three percent of patients completed the study. Improvements in median distance to claudication symptoms and maximum walking distance were observed in the intervention group but not in the control group. Nine out of 15 (60%) participants in the control group and 14 out of 20 (70%) participants in the intervention group improved their walking distance. Ankle brachial pressure index remained virtually unchanged in both groups. Conclusions Due to the variability of patients’ fitness in the sample, it cannot be concluded whether use of the Step It pedal has additional benefits to patients over standard care. However, the study completion rate implies that patients with peripheral arterial disease are receptive to undertaking exercise programmes.

Effects of Ankle Power Training on Movement Time in Mobility-Impaired Older Women

Reduced abilities to generate power put older adults at risk in situations that demand rapid movements. Slower movement times are associated with greater risk of falling and of being involved in a motor vehicle crash. The purpose of this study was to determine the effects of power training on foot movement time and, secondarily, on ankle strength and power in mobility-impaired older women. Fifty mobility-impaired women (70-88 yr) trained twice per week for 12 wk in one of three groups (weights, elastic bands, or placebo control). All groups performed seated warm-up exercises, followed by either concentric dorsiflexion (DF) and plantarflexion (PF) resistance exercises (weights and bands) performed "as fast as possible" or upper body flexibility exercises (control). Foot reaction/movement time and ankle DF and PF peak torque (30 degrees x s(-1)) and peak power (90 degrees x s(-1)) were measured before and after training. Participants who trained with elastic bands demonstrated improvements in movement time (decreased by 24 ms or 12%, P = 0.003). All groups demonstrated improvements in DF and PF strength and power, which were not statistically different. High-velocity/low-load (elastic bands) training improved movement time, which may have important implications in circumstances when rapid generation of torque is required (e.g., to avoid a fall or prevent a vehicle crash). Elastic bands are relatively inexpensive and provide a practical form of training that could be considered in programs designed for older adults with mobility limitations.

Intralimb compensation strategy depends on the nature of joint perturbation in human hopping

Due to the well-described spring-mass dynamics of bouncing gaits, human hopping is a tractable model for elucidating basic neuromuscular compensation principles. We tested whether subjects would employ a multi-joint or single-joint response to stabilize leg stiffness while wearing a spring-loaded ankle-foot orthosis (AFO) that applied localized resistive and assistive torques to the ankle. We analyzed kinematics and kinetics data from nine subjects hopping in place on one leg, at three frequencies (2.2, 2.4, and 2.8 Hz) and three orthosis conditions (freely articulating AFO, AFO with plantarflexion resistance, and AFO with plantarflexion assistance). Leg stiffness was invariant across AFO conditions, however, compensation strategy depended upon the nature of the applied load. Biological ankle stiffness increased in response to a resistive load at twice the rate that it decreased with an assitive load. Ankle adjustments alone fully compensated for an assistive load with no net change in combined (biological plus applied) total ankle stiffness ( p⩾0.133). In contrast, a resistive load resulted in a 7.4–9.0% increase in total ankle stiffness across frequencies and a concomitant 10–15% increase in knee joint stiffness at each frequency ( p⩽0.037). The increased knee joint stiffness in response to resistive ankle load allowed subjects to maintain a more flexed knee at mid-stance, which attenuated the effect of the increased total ankle joint stiffness to preserve leg stiffness and whole limb biomechanical performance. Our findings suggest humans maintain invariant leg stiffness in bouncing gaits through different intralimb compensation strategies that are specific to the nature of the joint loading.

Kinematic effects on gait of a newly designed ankle-foot orthosis with oil damper resistance: A case series of 2 patients with hemiplegia

Yokoyama O, Sashika H, Hagiwara A, Yamamoto S, Yasui T. Kinematic effects on gait of a newly designed ankle-foot orthosis with oil damper resistance: a case series of 2 patients with hemiplegia. The ankle joint of ankle-foot orthoses (AFOs) should restrict plantarflexion to prevent foot drop during the swing phase. However, excessive plantarflexion resistance causes excessive knee flexion during the stance phase. Plantarflexion resistive moment should be easily adjustable according to the gait ability of patients with hemiplegia. Because it is difficult to adjust plantarflexion resistive moment exactly, we developed an AFO with an oil damper. It is a small shock absorber that utilizes hydraulic resistance. The oil damper generates a resistive moment to the plantarflexion rotation of the ankle joint at the initial stance phase. The magnitude of the plantarflexion resistive moment at the heel strike can be easily adjusted to accommodate each patient’s condition by simply turning an adjustment screw. We used a gait analysis system to compare the gait of 2 hemiplegic patients while they were wearing either the AFO with the oil damper or the AFO with the plantarflexion stop. The AFO with the oil damper achieved sufficient plantarflexion of the ankle and mild flexion of the knee by adjusting a proper plantarflexion resistive moment during initial stance phase, and provided a more comfortable gait than did the AFOs with a plantarflexion stop.

Plantarflexion Resistance of Selected Ankle-Foot Orthoses: A Pilot Study of Commonly Prescribed Prefabricated and Custom-Molded Alternatives

Plantarflexion Resistance of Selected Ankle-Foot Orthoses: A Pilot Study of Commonly Prescribed Prefabricated and Custom-Molded Alternatives