• Introduced comprehensive Ankle Movement Training(AMT) for stroke patients.
• AMT improved ankle muscle strength and co-contraction during gait in stroke patients.
• Emphasizing a significant consequence of AMT on gait recovery in stroke patients.
Ankle dysfunction in patients with stroke is a common but serious cause of balance and gait impairments. However, comprehensive paretic ankle training seldom exists. Thus, we investigated the effects of a bi-axial ankle muscle training program using visual feedback as a means to improve ankle strength and performance of functional activities in patients with stroke.
This study was a randomized controlled pilot trial with concealed allocation and assessor blinding and intention-to-treat analysis. Twenty-five patients with stroke and difficulty in walking (e.g., foot drop) or ankle muscle weakness receiving inpatient rehabilitation were included. The experimental group underwent ankle muscle training consisting of passive stretching, control of ankle muscles, and active-resistive strengthening using visual feedback for 40 min per day, 5 times per week for 4 weeks. The control group underwent ankle-related physical therapy, including ankle range-of-motion exercises. The amount of time for training was equal between the two groups. The outcome measurements were isometric ankle contraction force to assess the strength of ankle muscles, ankle proprioception, Fugl–Meyer lower extremity score, Berg balance scale score, walking speed, and ankle co-contraction index to assess muscle efficiency during gait.
The analysis revealed significant between-group differences in the ankle muscle strength in each direction (P < 0.05), Fugl–Meyer score (P < 0.01), and stance-phase co-contraction index (P < 0.05). After training, the experimental group displayed significant within-group differences in the strength of the ankle muscles in each direction (P < 0.01), ankle proprioception (P < 0.05), and walking speed (P < 0.05).
Our findings demonstrate the significant short-term effects of ankle muscle training on strength, walking speed, and muscle efficiency in patients with chronic stroke.
AMTankle muscle trainingFM-LFugl–Meyer lower extremityBBSBerg balance scaleCIco-contraction indexROMrange of motion
One of the most notable lower limb impairments after the development of central nervous system disorders, such as stroke, is the inability of the ankle joint to yield normal levels of muscle force. In a functional task, such as locomotion, muscle weakness of the ankle muscles is associated with reduced plantar flexion at the end of the stance phase and reduced dorsiflexion at the swing phase . In particular, reduced forward propulsion owing to weakness of the plantar flexors can reduce the walking speed, and decreased dorsiflexion can lead to injurious falls . Weakness of the ankle muscles in patients with stroke is more prominent than impairments of other proximal lower muscles; thus, affected patients often continuously need ankle–foot orthoses after discharge, which may inhibit their performance of daily activities in the long term .
There are a few targeted ankle muscle-stretching and -strengthening training programs or devices for patients with stroke . Ankle muscle-stretching devices help increase ankle mobility (i.e., range of motion [ROM]), and ankle muscle-strengthening programs help improve muscle strength affected by reductions in muscle mass or inadequate voluntary activation that requires muscle contractions . Previously, robot-assisted gait training has helped yield a simple repeated gait pattern movement, which was effective for improving the gait speed and aerobic function, but has seldom improved gait symmetry or ankle functions . The anklebot is a rehabilitation robotics tool aiming to enhance ankle motor control using a target-based video game with visual feedback. The repetitive ankle dorsi-plantar flexions while seated were effective in improving the movement velocity, smoothness, and accuracy and the heel strikes during gait among moderately to highly functional patients with stroke . Children with cerebral palsy have shown improvements in ankle biomechanics and lower limb motor control after receiving an intelligent intervention of passive stretching and active strengthening using a robotic training system . However, previous studies have not considered the effect of ankle joint functionality on mobility and strength. Therefore, ankle muscle training (AMT) protocols should include comprehensive and effective ankle muscle-stretching and -strengthening rehabilitation training to improve ankle functions.
Appropriate control of muscle contraction in a target joint requires proper sensory information on its interaction with the rest of the body and with the environment. The proprioceptive feedback to motoneurons presents information on changes in the threshold muscle lengths or joint angles, thus setting the spatial activation range . Therefore, the proprioceptive feedback and muscle coordination should be considered in ankle movement training in patients with stroke for improving ankle motor control. Proprioception has been defined as the ability to integrate sensory signals from various mechanoreceptors to determine body position and movement in space . Because the ankle–foot complex, which provides essential proprioceptive feedback to enable adjustment of the ankle position and movements of the upper body, is the only body part that comes into contact with the ground, ankle proprioception plays a crucial role in balance control . Therefore, it is important to improve AMT in consideration of the continuous interaction between the external environment and the ankle proprioceptive feedback for the proper control of ankle muscle contraction in patients with stroke.
Effectively enhancing ankle muscle strength and contraction control can increase the performance of activities while standing. There are a number of evidence stating that ankle muscle strength is correlated with gait velocity and temporal symmetry . However, in a study on highly functional patients with stroke, impairments in ankle motor control, not ankle muscle strength, have been reported to predict functional deficits in walking . In another study, both decreased ankle muscle strength and motor control independently contributed to gait impairment in patients with stroke . As a factor that interferes with ankle motor control, abnormal muscle co-contraction between the ankle dorsiflexors and plantar flexors interferes with walking performance . Further, the decreased muscle coordination with respect to the timing of muscle contraction is also caused by a decrease in ankle sensory function. Thus, ankle motor control involves more complex factors, such as muscle weakness, abnormal muscle activities, inadequate muscle co-activation, sensory and visual deficits, and noncontractile soft-tissue tightness. Therefore, protocols of AMT and assessments should consider these factors rather than providing simple single-directional repetitive movements.
Therefore, to provide comprehensive AMT for patients with stroke of various functional levels, we developed an AMT program using a custom ankle rehabilitation device that would apply three processes: passive stretching, control of ankle muscle contraction, and active-resistive strengthening. The aim of this study was to evaluate the effects of our AMT program on ankle muscle strength, ankle proprioception, balance ability, walking speed, and ankle muscle co-contraction during a gait cycle in patients with chronic stroke; we hypothesized that the proposed AMT program will affect their ankle muscle strength, ankle proprioception, balance ability, walking speed, and ankle muscle co-contraction.[…]