Effects of Combining Electric Stimulation With Active Ankle Dorsiflexion While Standing on a Rocker Board: A Pilot Study for Subjects With Spastic Foot After Stroke

Article Outline

• Abstract
• Methods
  • Participants
  • Experimental Design
  • Training Protocol
    • Experimental group
    • Control group
  • Procedures
  • Outcome Measurements
    • Dorsiflexor muscle strength
    • Dynamic spasticity of plantarflexors
    • Active ROM of ankle dorsiflexion at heel strike
    • Balance performance
    • Gait kinematics
    • Functional gait performance assessed by EFAP
  • Statistical Analysis
• Results
  • Subject Characteristics
  • Training Effects
• Discussion
  • Study Limitations
• Conclusions
• References
• Copyright

Abstract 

Cheng J-S, Yang Y-R, Cheng S-J, Lin P-Y, Wang R-Y. Effects of combining electric stimulation with active ankle dorsiflexion while standing on a rocker board: a pilot study for subjects with spastic foot after stroke.

Objective

To investigate the therapeutic effects of combining electric stimulation (ES) with active ankle dorsiflexion while standing on a rocker board in subjects with plantarflexor spasticity after stroke.

Design

Randomized controlled trial.

Setting

A rehabilitation medical center.

Participants

Subjects (N=15) with spastic foot after stroke.

Interventions

Subjects were randomly assigned to an experimental or a control group. The experimental group received ES of ankle dorsiflexors in concert with a motor training paradigm that required the subject to dorsiflex the ankles in response to a cue while standing on a rocker board. After 30 minutes of this exercise, subjects received ambulation training focusing on ankle control for 15 minutes. The control group received general range of motion and strength exercises for 30 minutes, followed by 15 minutes of ambulation training focusing on ankle control. Sessions occurred 3 times a week for 4 weeks.

Main Outcome Measures

Dynamic spasticity of plantarflexors, dorsiflexor muscle strength, balance performance, gait kinematics, and functional gait performance as assessed by the Emory Functional Ambulation Profile (EFAP) were used as outcome measurements.

Results

The experimental group demonstrated a greater decrease in dynamic ankle spasticity at a comfortable gait speed (P=.049), a greater improvement in spatial gait symmetry (P=.015), and a greater improvement in functional gait ability as indicated by the EFAP (P=.015) than the control group.

Conclusions

Our results suggest that repeated ES with volitional ankle movements can decrease dynamic ankle spasticity in subjects with stroke. Furthermore, such improvement parallels better gait symmetry and functional gait performance.

Key Words: Electric stimulation, Rehabilitation, Stroke

List of Abbreviations: COG, center of gravity, CV, coefficient of variation, EFAP, Emory Functional Ambulation Profile, ES, electric stimulation, ICC, intraclass correlation coefficient, LOS, limit of stability, MXE, maximum excursion, ROM, range of motion

PLANTARFLEXOR SPASTICITY or spastic foot, which is frequently seen in subjects after stroke, may cause uneven weight-bearing with less body weight support on the affected leg.¹ Such asymmetric weight distribution could further decrease postural control² and lead to unstable and inefficient gait.³, ⁴, ⁵ Spasticity is a velocity-dependent activation pattern and is thought to be related to a decrease in the modulation of inhibitory mechanisms, resulting in a decrease of the stretch reflex threshold⁶ and augmentation of the amplitudes of the stretch reflex.¹, ², ⁶, ⁷, ⁸ In addition, there is a negative correlation between antagonist muscle strength and spasticity.⁷ On antagonist muscle contraction, such impairments might cause unwanted stretch reflex and cocontraction around the joint that further affects execution of movement.⁸ As a result of plantarflexor spasticity, walking becomes a challenge because of the patient's inability to control the foot, and the decrease in walking speed with gait asymmetry may be significant.⁵, ⁹

ES has been used to treat drop foot resulting from poor active control of the anterior tibialis or increased muscle tone in the plantarflexors.¹⁰ According to a systematic review,¹¹ a positive effect of functional ES on walking speed has been suggested. However, such effects of ES specifically on spastic foot (plantarflexor spasticity) are not immediately known.

Skill training and repetitive movement practice can facilitate cortical reorganization, resulting in better performance.¹² Ng and Hui-Chan¹³ revealed that combining transcutaneous ES with a series of task-related training exercises can improve lower limb function and gait performance in chronic stroke subjects. However, Yavuzer et al¹⁴ revealed that the effects of neuromuscular ES of the tibialis anterior combined with a conventional rehabilitation program were not superior to a conventional rehabilitation program alone. According to a study by Janssen et al,¹⁵ ES provided no additional beneficial effects as compared with cycling training alone for subjects with chronic stroke. However, in their study, the sensory intensity stimulation was administered to the cycling training group to blind the subjects. Therefore, the enhancement of motor performance by combining ES with repetitive movement practice for the lower extremity in subjects with stroke has not yet been established, especially with a focus on the spastic foot.

In this study, we developed an innovative treatment protocol for spastic foot. The treatment combined ES to the tibialis anterior with COG target tracking while standing on a rocker board. The purpose of the study was to investigate whether this type of ankle control training could decrease spasticity and improve balance and gait performance for subjects with spastic foot after stroke.

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Methods 

Participants 

Subjects with spastic foot after stroke were recruited from the Rehabilitation Medical Center in Taipei City, Taiwan. The inclusion criteria included (1) a first-ever stroke at least 3 months ago; (2) the ability to walk at least 6m while demonstrating spastic foot, with or without assistive devices; and (3) sufficient cognition to follow commands (Mini-Mental State Examination score >24). Spastic foot was defined in this study as (1) plantarflexor spasticity during ambulation indicated by a positive slope in dynamic spasticity index,⁹ and (2) ankle movement with dorsiflexion less than −5° at heel strike (neutral position is defined as 0°). The exclusion criteria included (1) sensory loss or oversensitivity to ES, or (2) a history of orthopedic or other neurologic disorders that would affect the ability to walk. All participants received an explanation of the study protocol and signed informed consent before data collection. The study protocol was approved by the Institutional Review Board of National Yang-Ming University.

Experimental Design 

This study was a randomized controlled trial. The block randomization (with block size of 4) was used to assign subjects to either an experimental or a control group by an independent person who selected one of the sealed envelopes 30 minutes before beginning the intervention. Subjects in the experimental group received ES combining active ankle dorsiflexion movements challenged by the rocker board while standing (as described in the next paragraph) for 30 minutes, followed by ambulation training focusing on ankle control for 15 minutes, 3 times a week for 4 weeks. Ambulation training focused on ankle control after the above-described program was carried out for another 15 minutes in each session. Subjects in the control group received general exercise training for 30 minutes and ambulation training focusing on ankle control for 15 minutes, 3 times a week for 4 weeks. All subjects received baseline and posttreatment assessments by another physical therapist who was blind to the assignment.

Training Protocol 

The Balance Master system^a was used to facilitate ankle dorsiflexion exercises combined with ES. The Balance Master provides objective assessment and retraining of the sensory and voluntary motor control of balance with visual biofeedback. The system was set at the “center posterior” mode. The Balance Master uses a fixed dual forceplate to measure the vertical forces while a subject stands on it. The displacement of COG is displayed on the monitor, which provides the subject with visual feedback.¹⁶ In our study, the subject faced the monitor and stood on the rocker board (19.5×17×7.5cm), which was placed on the forceplate of the system (fig 1A). The rocker board was used to facilitate execution of active ankle movement. The target areas in the center and posterior locations were shown on the monitor and guided the subject to perform weight shifting toward the center and posterior directions (fig 1B). The 2 target locations were displayed in sequence for 10 seconds at the pacing rate. As the center location was displayed, the subject was instructed to stand straight with ankle joints in the neutral position in order to place the rocker board in the resting position. As the posterior location was displayed, the subject was instructed to perform dorsiflexion of both ankle joints to move the rocker board to an upward tilt. The range between the 2 locations was 25% to 100% of the LOS, the maximum distance that a person can intentionally displace their COG without moving feet in standing. Throughout the 4-week treatment, the target positions were adjusted to increase the LOS percentage according to the subject's ability. When the LOS percentage increased, the subject needed to perform more dorsiflexion to reach the target.

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• Fig 1. 

  (A) Training by the Balance Master in the experimental group. The subject faced the monitor and stood on the rocker board. The suspension and assistive device (eg, cane) were used for safety. (B) The “center posterior” mode was displayed on the monitor. The 2 target locations were lighted up with 10 seconds of pacing rate in sequence. (C) ES was applied to the affected leg. The electrodes were placed on the motor points of the tibialis anterior muscle and common peroneal nerve outlet below the fibular head.

During the training period, ES^b was applied to the affected leg to elicit ankle dorsiflexion movement. The electrodes were placed on the motor points of the tibialis anterior muscle and common peroneal nerve outlet below the fibular head (fig 1C). ES was set at the frequency of 40Hz, the intensity was adjusted to elicit maximal contraction without inducing discomfort, and the on-off time was synchronous with the ankle movements prompted by the Balance Master (10s on and 10s off).

Throughout the training course, subjects were asked to distribute their body weight on both legs as evenly as possible. A suspension system was provided for safety but did not support the subject's body weight. The subject took rests whenever needed to avoid fatigue. When the performance improved, the LOS percentage was increased, and use of the assistive device (eg, cane) was discontinued according to the subject's ability.

The ambulation training focusing on the ankle control was practiced after the above training program. Verbal cues were used for the subject to actively dorsiflex the ankle throughout the swing phase and heel strike to the extent of the subject's ability.

In the control group, the subject received general exercises, including ROM exercises, strengthening exercises for the lower extremities, and mat exercises. The ambulation training was the same as that described for the experimental group.

Procedures 

Subjects' demographic data were recorded, including age, sex, stroke type, poststroke duration, frequency of concomitant treatment, and the assistive devices used during ambulation. Outcome measures included dorsiflexor muscle strength, dynamic plantarflexor spasticity, ankle ROM at heel strike, balance performance assessed by the Balance Master, gait kinematics as assessed by the GAITRite system,^c and functional gait performance assessed by the EFAP.

Outcome Measurements 

Maximal isometric strength of dorsiflexors was measured by a handheld dynamometer.^d The subject was in a supine position with both hip and knee joints extended.⁵ The waist and knees were fixed by belts to avoid possible compensatory movements. The dynamometer was placed perpendicular over the tarsal bones to assess dorsiflexor muscle strength.⁵ The testing procedures were started on the nonaffected side to ensure that the subject understood the correct muscles to contract. The test was then performed on the affected side. Each subject was asked to perform a maximal isometric contraction of the dorsiflexion for 5 seconds for 3 trials with a 15-second rest in between. The values were averaged for data analysis. We recorded the ankle angle at which the isometric dorsiflexion strength was measured at pretreatment and made the posttreatment measurement at the same ankle angle.

The spasticity index was calculated to provide quantitative measurement of dynamic spasticity during gait. The electromyographic activity in the plantarflexors increases as a function of the velocity of their lengthening during gait.⁵ The spasticity index is the ratio of electromyographic activity in the medial gastrocnemius to its lengthening velocity during the stance phases of the gait cycle. A positive ratio indicates a velocity-sensitive activation pattern (ie, the spasticity), while its magnitude gives an estimate of the reflex gain. Because not all gait cycles are accompanied by positive ratios, only the positive ratios were chosen for data analysis. The use of the spasticity index has been validated in subjects with hemiparesis.⁵, ⁹

Data for calculating dynamic spasticity index were obtained when the subject walked on the GAITRite walkway (as described in the later paragraph) at a self-selected speed for 3 times.⁵ The data included electromyographic activities of the medial gastrocnemius, ROM of the ankle and knee joints, and timing from footswitches at the toe and heel to indicate stance and swing phase. MATLAB^e software was used for data processing.

The electromyographic activities of the medial gastrocnemius were recorded during gait by an 11-cm silver-silver chloride electrode.^f The skin hairs were shaved, and the skin was cleansed with alcohol to reduce impedance. The electrode was placed on the motor point of the muscle that was located 5 finger widths distal to the popliteal crease and 2cm medial to the midline.¹⁷ Electromyographic signals were first preamplified (amplification factor, 375) and were analog-to-digital converted and stored on a personal computer. Two electronic goniometers^g were placed on the knee and ankle joints of the affected side to measure joint angle displacements during gait. For measuring the ankle joint, the axis center of the goniometer was located over the lateral malleolus. One endblock was placed along the line between the lateral malleolus and the fibular head, and the other endblock was placed along the line between the lateral malleolus and the fifth metatarsal head. For measuring the knee joint, the axis center of the goniometer was located over the lateral epicondyle of the femur. One endblock was placed along the line between the lateral epicondyle and the greater trochanter, and the other endblock was placed along the line between the lateral epicondyle and the lateral malleolus.¹⁸ Two footswitches were placed under the toe and heel of the affected side to indicate the stance and swing phases of the gait cycle. Before data collection, the intrarater reliabilities for ankle and knee joints at heel strike during walking were calculated in 9 subjects. The ICCs_3,1 for ankle and knee joints were .92 and .82, respectively.

All signals were recorded by the AcqKnowledge software, version 3.7.5 with the BIOPAC MP 150WMW System^f with a sampling rate of 1000Hz, and stored for offline analysis. The common mode rejection ratio of the electromyograph was 104dB, the analog-to-digital converter signal/noise ratio was 86dB, the digital analog resolution was 16 bits, and the gain was 2000. The electromyographic activity was processed following the procedures of Lamontagne et al.⁹ The electromyographic activity of the medial gastrocnemius for the lengthening period during the stance phase was normalized to its maximal value of stance phase. The muscle-lengthening velocity of the gastrocnemius was calculated by using the model developed by Winter and Scott.¹⁹ The slope (ie, the spasticity index) between the electromyographic activity and lengthening velocity was plotted for each stance phase in the gait cycle.

To investigate the effects of ankle control during walking, we analyzed the active ROM of ankle dorsiflexion at heel strike on the basis of the electronic goniometer placed on the ankle joint and the footswitch at the heel of the affected side during walking as described above. Also, the variance was measured for all strikes of each subject, and the CV was calculated for both the experimental and control group to indicate the active ROM fluctuation.

Dynamic balance was assessed as the subjects shifted their weight while standing by using the Balance Master system. The LOS testing was used to record dynamic balance. The LOS quantifies the maximum distance that a person can intentionally move the COG without moving feet or losing balance in standing. Four directions—forward, backward, nonaffected side, and affected side—were assessed with random order in our study. A standard protocol was administered in the same way as described previously.²⁰ The cursor indicating the displacement of COG is displayed on the monitor screen to provide visual feedback. For each measurement trial, the subject tried to move the cursor from the central target towards a second target on the perimeter (100% of theoretical LOS) as far as possible. MXE is the maximum distance achieved in each trial, which is represented by the percentage of the theoretical LOS. An increase of the MXE means the subject can shift his/her weight more towards that direction without losing balance and indicates improvement in the dynamic standing balance. Before data collection, each subject practiced once or twice to familiarize himself/herself with the task.¹⁶

Self-selected gait velocity and spatial and temporal asymmetry ratio were obtained from the GAITRite system. The GAITRite walkway contains 6 sensor pads and 13,824 pressure-sensitive sensors, and connects to a personal computer. The active area is 3.66m long and .61m wide. When the subject walks along the walkway, the contact time and location of each footfall are recorded, stored on the computer, and translated into the spatial and temporal parameters automatically. The concurrent validity and reliability have previously been established.²¹, ²² In the present study, subjects were asked to walk along the walkway at a self-selected speed for 3 times, and the average was used for analysis. Subjects were allowed to use a walking assistive device if necessary (table 1), but not an ankle-foot orthosis, when walking on the GAITRite walkway. In addition, the temporal and spatial asymmetry ratios were also calculated according to the following formula:

Table 1. Demographic and Basic Data of Both Groups

Characteristics	Experimental Group (n=8)	Control Group (n=7)	P
Age (y)	52.87±8.74	58.43±5.06	.223
Sex			.200
Men	5(62.5)	7(100)
Women	3(37.5)	0(0)
Type of stroke			.200
Infarction	5(62.5)	7(100)
Hemorrhage	3(37.5)	0(0)
Affected side			1.000
Right	4(50)	4(57.1)
Left	4(50)	3(42.9)
Onset duration (mo)	33.6±37.9	33.6±28.1	.728
Regular treatment frequency (times/wk)	2.9±1.3	2.7±2.1	.950
Assistive device
Cane	2	0
Quadricane	0	2
AFO+quadricane	1	0

NOTE. Values are mean ± SD or n (%) or as otherwise indicated.

Abbreviation: AFO, ankle-foot orthosis.

The greater the value of the ratio, the greater the degree of asymmetry.⁵

EFAP is a timed walking test comprising 5 subtasks that are common environmental challenges. It also incorporates the use of assistive devices or orthoses. Because of cultural differences, we did not assess the “carpet” task in the present study. Therefore, the subtasks in the present study included (1) the floor task: a 5-m walk on a hard floor; (2) the Timed up & go task: rising from a chair, a 3-m walk, and return to a seated position; (3) the obstacles task: traversing a standardized obstacle course; and (4) the stairs task: ascending and descending 4 stairs. The subscores were added to derive a total score. The reliability and concurrent validity of the EFAP have been established.²³

Statistical Analysis 

Data analysis was performed using the SPSS version 11.0 software.^h We used the Mann-Whitney U test and chi-square test to compare the demographic and baseline data of the 2 groups. We also used the Wilcoxon signed-rank test to analyze training effects within each group. For between-group comparisons, we used the Mann-Whitney U test to analyze change scores between groups. We calculated the change scores by subtracting baseline data from posttreatment data, except the EFAP data. For EFAP data, we calculated the change scores by subtracting baseline data from posttreatment data and then divided by the baseline data. The significance level was set at P less than .05.

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Results 

Thirty subjects with spastic foot poststroke were referred from the Rehabilitation Medical Center in the Taipei area. Among all subjects, 7 refused to participate in the study, and 5 were excluded according to our exclusion criteria. As a result, 18 subjects participated in the study. After baseline data assessment, subjects were randomly assigned to an experimental group or a control group (n=9 for each group). However, during the intervention period, 1 subject in the experimental group and 1 subject in the control group withdrew because of low motivation. In addition, 1 subject in the control group withdrew from the study because of back pain caused by a fall outdoors. As a result, a total of 15 subjects completed the study. Among them, 8 were in the experimental group and 7 in the control group (fig 2).

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• Fig 2. 

  Flow chart of subjects recruited in the study.

Subject Characteristics 

The demographic data for the groups are presented in table 1. There were no significant differences between the groups in age, sex, type of stroke, affected side, onset duration, and their regular treatment frequency during the study period. Also, the baseline data of motor performances were similar between groups (table 2).

Table 2. Baseline Data of Both Groups

Variables	Experimental Group (n=8)	Control Group (n=7)	P
	Baseline	Baseline
Spasticity index
Plantarflexors (%/L·s−1)	4.65±2.21	4.72±1.04	.642
Muscle strength
Dorsiflexors (N)
Affected side	16.96±12.99	54.92±55.36	.354
Nonaffected side	122.50±33.28	113.26±34.61	.487
AROM of ankle DF at HS
Affected side (°)	76.26±4.03	75.9±4.6	.728
CV of ankle DF at HS (%)	55.2	49.1	NA
LOS
MXE (%)
Forward	61.13±18.26	55.71±17.38	.862
Nonaffected side	87.38±11.49	86.43±10.91	.728
Backward	53.25±21.27	60.43±9.33	.561
Affected side	71.13±18.76	71.57±16.44	.862
Gait parameters
Speed (cm/s)	27.79±12.69	37.77±16.35	.247
Spatial asymmetry ratio	1.50±3.63	1.06±2.01	.487
Temporal asymmetry ratio	0.47±0.09	0.42±0.23	.817
EFAP
Floor (s)	26.17±25.90	28.75±42.33	.452
Up & go (s)	52.40±52.45	65.12±97.84	.203
Obstacles (s)	104.47±99.69	74.95±103.70	.298
Stairs (s)	28.79±12.03	18.74±10.34	.105
Total (s)	221.83±176.21	187.84±252.35	.355

NOTE. Values are mean ± SD or as otherwise indicated.

Abbreviations: AROM, active range of motion; DF, dorsiflexion; HS, heel strike; NA, not applicable.

Training Effects 

The data for motor performance are summarized in table 3. In within-group comparison, the experimental group demonstrated significant improvement in the dorsiflexor muscle strength on the affected and nonaffected side, gait velocity, and spatial asymmetry ratio. The control group demonstrated significant improvement only in dorsiflexor muscle strength on the nonaffected side. In between-group comparison, the experimental group demonstrated a significant decrease in spasticity index (P=.049) and spatial asymmetry ratio (P=.015). On the other hand, active ROM of ankle dorsiflexion at heel strike in both groups did not change significantly, but the value of the CV was decreased after treatment in the experimental group from 55.2% to 31.3%.

Table 3. Motor Performances in the Experimental and Control Group

Variables	Experimental Group (n=8)			Control Group (n=7)			Change Scores
	Baseline	Posttreatment	P⁎	Baseline	Posttreatment	P⁎	Experimental	Control	P†
Muscle strength (N)
Affected side	16.96±12.99	52.47±40.46	.012‡	54.92±55.36	77.96±53.23	.091	35.51±28.13	23.04±29.78	.182
Nonaffected side	122.5±33.28	147.17±21.6	.036‡	113.26±34.61	144.19±23.23	.018‡	24.67±30.27	30.93±24.79	.487
Spasticity index (%/L·s–1)	4.65±2.21	3.61±1.15	.093	4.72±1.04	5.52±1.78	.237	−1.04±1.77	0.80±1.98	.049‡
AROM of ankle DF at HS (°)	76.26±4.03	77.50±5.36	.093	75.9±4.6	76.71±6.71	.499	1.24±2.42	0.81±3.48	.728
CV of ankle DF at HS (%)	55.2	31.3	NA	49.1	57.7	NA	−23.9	8.6	NA
Gait velocity (cm/s)	27.79±12.69	36.81±14.86	.012‡	37.77±16.35	43.69±20.32	.176	9.13±6.18	5.91±10.72	.418
Gait spatial asymmetry ratio	1.50±3.63	0.59±1.49	.017‡	1.06±2.01	1.31±2.50	.176	−0.91±2.14	0.25±0.55	.015‡
Gait temporal asymmetry ratio	0.47±0.09	0.43±0.11	.327	0.42±0.23	0.48±0.22	.612	−0.04±0.09	0.06±0.16	.355

NOTE. Values are mean ± SD or as otherwise indicated.

Abbreviations: AROM, active range of motion; DF, dorsiflexion; HS, heel strike; NA, not applicable.

The balance performance as indicated by the MXE of LOS is summarized in table 4. The experimental group demonstrated a significant increase in the MXE in the forward and affected directions. There were no significant differences in the control group between baseline and posttreatment. However, no significant difference was noted between groups in any of the 4 directions.

Table 4. Balance Performance Indicated by Limit of Stability in the Experimental and Control Group

Variables	Experimental Group (n=8)			Control Group (n=7)			Change Scores
	Baseline	Posttreatment	P⁎	Baseline	Posttreatment	P⁎	Experimental	Control	P†
LOS
MXE (%)
Forward	61.13±18.26	81.88±12.01	.017‡	55.71±17.38	68.57±15.75	.128	20.75±18.42	12.86±17.19	.247
Nonaffected side	87.38±11.49	91.63±8.25	.271	86.43±10.91	88.29±9.27	.866	4.25±12.38	1.86±11.13	.602
Backward	53.25±21.27	61.38±10.68	.575	60.43±9.33	70.57±19.24	.063	8.13±25.44	10.14±13.80	.418
Affected side	71.13±18.76	89.00±11.84	.012‡	71.57±16.44	75.14±14.47	.398	17.88±14.02	3.57±13.07	.093

NOTE. Values are mean ± SD or as otherwise indicated.

The EFAP scores are summarized in table 5. The experimental group demonstrated a significant decrease after treatment in total time spent for the 4 tasks and time needed for each task, except for the Timed up & go task. The control group demonstrated a significant decrease only in the floor task. In between-group comparison, the experimental group demonstrated a significant decrease in the total time spent (P=.015), and in the floor (P=.049), obstacles (P=.015), and stairs (P=.005) tasks.

Table 5. EFAP in the Experimental and Control Group

Variables	Experimental Group (n=8)			Control Group (n=7)			Change Scores
	Baseline	Posttreatment	P⁎	Baseline	Posttreatment	P⁎	Experimental	Control	P†
Floor (s)	26.17±25.90	18.47±14.81	.025‡	28.75±42.33	25.79±36.21	.018‡	−.21±.15	−.06±.57	.049‡
Up & go (s)	52.40±52.45	42.49±35.88	.093	65.12±97.84	58.94±79.97	.612	−.11±.14	−.03±.12	.247
Obstacles (s)	104.47±99.69	71.07±60.36	.012‡	74.95±103.70	75.44±101.68	.735	−.20±.18	−.01±.10	.015‡
Stairs (s)	28.79±12.03	23.41±9.42	.012‡	18.74±10.34	18.88±9.17	.398	−.18±.09	.03±.11	.005‡
Total (s)	221.83±176.21	155.44±108.53	.012‡	187.84±252.35	179.05±224.87	.310	−.19±.13	−.07±.09	.015‡

NOTE. Values are mean ± SD or as otherwise indicated. Change scores: (posttreatment data – baseline data)/baseline data.

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Discussion 

In the present study, we have developed a novel intervention for spastic foot. Combining ES with active ankle dorsiflexion while standing on a rocker board can provide beneficial effects on dynamic plantarflexor spasticity, gait spatial symmetry, and functional gait performance in subjects with spastic foot after stroke.

Spasticity is a velocity-dependent activation pattern, and it influences the onset of antagonist muscle contraction. Previous studies have revealed that ES can decrease spasticity¹³, ²⁴, ²⁵ However, according to the study by Powell et al,²⁶ the effects of ES on decreasing spasticity were not obvious. On the other hand, only a limited number of articles have discussed the relationship between the active ROM of ankle dorsiflexion and dynamic plantarflexor spasticity or gait performances in chronic stroke patients. Selles et al²⁷ revealed that after ankle stretching exercises for 4 weeks in subjects with stroke, the passive ROM of the ankle joint, joint stiffness, and gait speed improved significantly, but the active ROM of the ankle joint did not. In our study, the decreased reflex gain of plantarflexors during walking in the experimental group may also have been partly due to decreased joint passive stiffness resulting from combining ES and movement training. In addition, although the active ROM of dorsiflexion during heel strike did not change significantly in the experimental group, the decrease in CV value indicates that the subjects dorsiflexed the ankle with less variation during walking, which implies the decreased demands in balance control and in energy expenditure during walking.

According to within-group comparison, the experimental group demonstrated a significant increase in the dorsiflexor strength on the affected side after intervention; nevertheless, such improvement did not reach a significant level as compared with the control group. ES has been suggested to increase muscle strength,²⁴, ²⁶ and muscle strength is negatively influenced by the antagonist muscle spasticity.⁷ Thus, the decrease in dynamic plantarflexor spasticity in the experimental group may account for the improvement in dorsiflexor muscle strength. Combining dorsiflexor strength and dynamic plantarflexor spasticity could explain about 45% of the variance of gait speed.⁵ Our participants in the experimental group showed improvement in both parameters, resulting in an improvement in self-selected speed. According to other studies, the change of gait velocity after ES combined with task-related training showed a 35% improvement,¹³ and the improvement after task-related training alone was 10% to 22%.²⁸, ²⁹ The improvements in our experimental and control groups were 33% and 16%, respectively, which were comparable to these previous results.

For the spatial and temporal asymmetry ratios, the experimental group demonstrated significant improvement in spatial symmetry. Lin et al⁵ revealed that dynamic spasticity of plantarflexors was the determining factor for spatial asymmetry. However, more factors, such as dorsiflexor strength and joint position sense,⁵ motor function and sensation of the lower limb,³, ³⁰ and vertical ground reaction force,³¹ determine temporal symmetry more than they determine spatial symmetry. Subjects in our experimental group demonstrated a significant increase in ankle dorsiflexor strength, but that factor alone could only account for 38% of the variance of the temporal asymmetry ratio.⁵ This suggests that improvement of other factors, in addition to dorsiflexor strength, can then result in the improvement of the temporal symmetry.

Balance control is impaired after stroke, particularly in the frontal plane.¹, ³² The frontal plane stability is the most important factor related to independent standing and walking ability.¹ In this study, we noted a significant improvement in MXE toward forward and affected-side directions after training in the experimental group. Such improvement in balance control may contribute to improvement in functional performance.

The experimental group showed significant improvement in the 3 tasks of the EFAP. The decrease in time spent on the floor task was compatible with the significant improvement observed in the self-selected speed in the experimental group. However, although the control group did not demonstrate significant improvement in self-selected speed, the group did demonstrate significant improvement in the floor task of the EFAP. There were 3 subjects in the experimental group and 2 subjects in the control group who required an assistive device while walking. EFAP scores were weighted according to the walking aid used, and scores reflected the difficulty experienced by each subject. Thus, the score on the floor task of the EFAP is more sensitive to reflect the improvement of the subject's walking ability.

To cross obstacles or negotiate stairs, both legs have to be lifted high enough for foot clearance, and thus, more ankle control and balance are needed than in ground walking. Subjects with stroke are more unstable during affected limb support than unimpaired subjects; therefore, they may cross obstacles slowly for stability.³³ However, the improvement in ankle control and dynamic balance ability, especially in the forward and affected-side directions, as demonstrated in the experimental group, may contribute to the decrease in the time spent on the obstacles and stairs tasks.

Study Limitations 

The present study has some limitations. First, the sample size was small. Such a small sample size may decrease the significance of between-group differences. Second, lack of follow-up assessment also limited the documentation of carryover effects of the treatment. Third, in this study, the visual feedback of COG displacement was provided to the participants when they were receiving ES and practicing ankle dorsiflexion while standing on a rocker board. Therefore, the effects of visual feedback cannot be ruled out. Future studies are needed to investigate the effects of such combined treatment on a larger sample population and on the long-term effects. In addition, studies are encouraged to investigate whether such intervention without visual feedback can provide the same beneficial effects.

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Conclusions 

In the present study, for spastic foot after stroke, our novel intervention focusing on ES and active ankle control results in beneficial effects. Such improvements can lead to better performances in functional activities. Our results suggest that ES in combination with active ankle movement while standing on a rocker board can decrease ankle spasticity and improve the weight-shifting distance, especially in the forward and affected-side directions, in subjects with stroke. Furthermore, decreased spasticity and increased affected-side weight-shifting ability result in the improvements in the gait spatial symmetry and in performance of functional gait tasks that necessitate ankle control.

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• a NeuroCom International Inc, 9570 SE Lawnfield Rd, Clackamas, OR 97015.
• b Medtronic, Inc, 710 Medtronic Pkwy, Minneapolis, MN 55432-5604.
• c CIR Systems Inc, 60 Garlor Dr, Havertown, PA 19083.
• d Jtech Medical Industries Inc, 357 West 910 South, Herber City, UT 84032.
• e The MathWorks, Inc, 3 Apple Hill Drive, Natick, MA 01760-2098.
• f BIOPAC Systems Inc, 42 Aero Camino, Goleta, CA 93117.
• g Biometrics Ltd, PO Box 340, Ladysmith, VA 22501.
• h SPSS Inc, 233 S Wacker Dr, 11th Fl, Chicago, IL 60606.