FES Standing: The Effect of Arm Support on Stability and Fatigue During Sit-to-Stand Manoeuvres in SCI Individuals Musfirah Abd Aziz and Nur Azah Hamzaid Abstract Functional Electrical Stimulation (FES) has been widely used as part of physiotherapy for spinal cord injury (SCI) patients. The ability to do sit to stand (STS) manoeuvre is an important and practical indicator of functional independence in SCI individuals. One of the factors that contributes to STS movement is arm support. The objective of this study is to instrument an arm support with pressure sensors, and to analyse the impact of using standing frame during FES-assisted STS movement to the SCI patients stability and rate of fatigue throughout multiple STS movements. FlexiForce sensors were used to analyse the force exerted on the frame s handle. Experiments on STS activity with two SCI subjects were completed in two consecutive days (with and without assistance of FES) in a motion analysis laboratory. The instrumented standing frame (SF) was calibrated via a series of hanging test with ten healthy subjects with different body weights to provide an insight on the weight distribution along the SF. This test demonstrates the instrumented standing frame s ability to measure the force exerted on the frame with minimum accuracy of 85% to total body weight. Both SCI subjects showed shorter time taken to complete a STS cycle without the assistance of FES. They showed early stage of fatigue with assistance of FES thus longer time taken recorded in performing STS activity. SCI subjects centre of force slightly inclined to the right side of the standing frame in both sessions without and with FES to compensate several conditions of lower limb joint contractures. Keywords Spinal cord injury (SCI) Functional electrical stimulation (FES) Sit-to-Stand (STS) 1 Introduction Spinal cord injury (SCI) has two major categories which are complete and incomplete injury. While there is permanent loss of sensory and motor function below the spinal cord lesion in patients with complete SCI, incomplete injury otherwise refers to spinal cord injury without any sensory and/or motor function below the neurological level including S4 S5 sacral spinal nerve [1]. Based on the American Spinal Injury Association (ASIA) Impairment Scale (AIS) M. Abd Aziz N. A. Hamzaid (&) Department of Biomedical Engineering, University of Malaya, Kuala Lumpur, Malaysia e-mail: azah.hamzaid@um.edu.my classification, the target population for this Functional Electrical Stimulation (FES) standing research is AIS C patients, i.e. those with motor incomplete spinal cord injury. Their motor function is preserved below the neurological level, and more than half of the key muscle functions below the single neurological level of injury have a muscle grade less than Grade 3 on MRC scale [1]. Sit to stand (STS) movement is one of the most basic yet important routine manoeuvres for human. Hence, the ability to perform STS movement is a very practical indicator to determine functional independence of the SCI patient [2]. Accomplishment of STS activity in SCI patients results in physiological postural transformation, from a balanced position to a vulnerable position with lower muscle limbs Springer Science+Business Media Singapore 2018 F. Ibrahim et al. (eds.), 2nd International Conference for Innovation in Biomedical Engineering and Life Sciences, IFMBE Proceedings 67, https://doi.org/10.1007/978-981-10-7554-4_11 67
68 M. Abd Aziz and N. A. Hamzaid weakness and postural instability during STS. With muscle mass deterioration and weakness, instability and fatigue become a concern to patients. As patients stability and adapted movement are highly dependent on users personal method, these aspects are then determined by their own conduct during STS movement and quiet standing. The ability to perform functionally-independent STS movement is influenced by factors which are chair seat height, feet position, and use of armrests [3]. The presence of arm support reduces the moment needed at the hip probably without altering the joints range of motion. Scientific evidence on the importance of arm support during STS for SCI individuals is insufficient and inconclusive. Hence, a simple instrumentation of standing frame (SF) is designed suitably to quantify the force exerted at the upper limb during STS. 2 Methodology 2.1 Sensor Calibration Calibration is an important procedure to use sensors with reliable accuracy and consistency. During calibration test, the force value was established by measuring its voltage. Thus, a sensor needs to be calibrated by set a known force to the sensor using dead weight method and measuring its conductance. Four FlexiForce sensors were calibrated individually. A load with known weight, starting from 50 N was placed on top of each sensor. The weight was left for 5 s (predicted time for SCI patient to perform a cycle of STS activity with standing frame). This helped to minimize the drift error. The weight of load was increased gradually until 400 N. 2.2 Instrumentation of the Standing Frame The standing frame used in this study was instrumented to identify the characteristics of FlexiForce sensor acting upon the standing frame. FlexiForce sensors were placed at the bottom of the four legs of the standing frame as shown in Fig. 1. Ten subjects with different body masses were instructed to lift their body with their arms holding onto the arm support of the standing frame. This step allows their body weight to be distributed among the four sensors at the base of the walking frame. 2.3 Subject Selection Three male subjects with SCI AIS C took part in this study as shown in Table 1. The mean age was 40 years (SD, Fig. 1 a Placement of FlexiForce sensor b Sensors placement on the standing frame s feet
FES Standing: The Effect of Arm Support on Stability 69 Table 1 Subjects profile Participant Level of injury Mechanism of injury Response to FES Maximum tolerable current for FES (ma) Quadriceps Gluteal maximus Subject 1 T12 L2 Fall from tree No Subject 2 T11 T12 Construction site accident Yes 58 68 Subject 3 L1 L2 Accident during work Yes 32 40 6.1 year, range 33 43 years); average mass was 69.67 kg (SD, 20.6 kg, range 54 93 kg) and average height was 165.8 cm (SD 5.3 cm, range 162.5 172 cm). Informed consent was sought from all subjects for this study. All of them were able to stand up from a chair independently upon verbal instruction without using their hands. However, Subject 1 was unable to complete the research protocol due to neuropathic pain on his back and he is FES non-responsive at his left quadriceps muscles. 2.4 Experimental Protocol The subjects were positioned on armless chair with standardised height of 45 cm. Subjects knees were flexed at 90 and both feet were positioned on the force plate. On Day 1, subjects were tested on their regular method of transition from a seated position to standing without the assistance of FES. Subject was directed to attempt stand up from the seated position at the end of a countdown by an investigator. The subject was monitored by a physiotherapist and researchers throughout this test. Three seconds after the subject achieves full upright standing (full knee extension), the subject was directed to sit down. Then, the subject was allowed to take 5-minute rest between tests. The tests were repeated up to 10 times or until the subject was tired. At the end of the first session, FES stimulation was determined for the subject for the next experiment session. The subject was asked for his feedback on his tolerance with higher Conductance 0.016 0.014 0.012 0.01 0.008 0.006 0.004 0.002 0 Conductance vs Force (N) 50 100 150 200 250 300 350 400 Force (N) Fig. 2 FlexiForce sensor calibration S1 S2 S3 S4 stimulation intensity. 48-hour rest was given to the subject before the next test (Day 2). In Day 2, subjects were tested on their ability to perform a transition from a seated position to a standing one with the assistance of FES. In addition, the FES electrodes were placed by a physiotherapist and researcher on gluteal maximus and quadriceps femoris muscles bilaterally. The protocol for Day 2 was similar with Day 1. 3 Results and Discussion 3.1 Calibration of FlexiForce Sensors Four FlexiForce sensors was calibrated individually by putting a load with known weight at 50 N intervals. The graph of conductance versus force was plotted as shown in Fig. 2. A line of best fit was drawn to find a linear equation of each sensor. Body hang test with ten normal subjects were done to validate the distribution of weight acting upon the instrumented standing frame. The characteristic of net body weight of each subject at standing frame is determined with this formula: Net body weight ¼ ValueSensor1 þ ð2 ValueSensor2Þ þ ValueSensor3 þ ð2 ValueSensor4Þ ð1þ The percentage of net body weight is calculated using the formula: Percentage of net body weight ¼ ðnet body weight=actual weightþ 100 ð2þ The hanging test shows the instrumented standing frame setup has minimum 85% accuracy with comparison the total body weight of the subject. Several identifiable random errors has reduced the results accuracy but these errors remained consistent throughout the experiment. These errors were difficult to be precisely factored in most experiments, but repetitions of experiments have been done to minimise effect of the errors on result s reliability. Thus, any reduction
70 M. Abd Aziz and N. A. Hamzaid Table 2 Average time recorded to do a cycle of STS Participant Time taken for STS (s) No FES FES Subject 2 1.11 ± 0.1277 2.55 ± 0.2625 Subject 3 1.07 ± 0.1677 1.36 ± 0.0951 in accuracy did not affect the comparison between sit to stand manoeuvre with and without standing frame. 3.2 Experimental Results The average time taken for each SCI subject to perform one full cycle of STS were tabulated in Table 2. Based on the average time recorded, both of them showed longer time to complete a cycle of STS when using FES. Both SCI subject felt more confident and comfortable to stand without using FES. Subject 2 took the longest time to perform a complete STS cycle with assistance of FES due to joint contracture at his left ankle. This contracture has affected his foot movement contacting with the force plate. In addition they also first time experience with FES in STS activity. Next, Fig. 3 displayed the translocation of the centre of net force for upper limb to the right side of the standing frame in both sessions. It happened because Subject 2 used more strength at his right upper limb to move his trunk forward for standing. In addition, he also has left ankle and right knee joint contracture thus making him harder to place his left forefoot at the force plate and extend the right leg during standing activity. Subject 2 showed smaller variation of coordinate s x-axis and y-axis with standard deviation of less than ±0.03. Hence in order to preserve upper limb stability, Subject 2 displayed greater net force on right side of standing frame to compensate current given to the lower limb with several joint contractures during STS activity. For Subject 3, the net force distribution of the upper limbs during STS in both session followed the translocation pattern of Subject 2. The centre of net force has inclined to the right side of the standing frame as illustrated in Fig. 4. He practiced more strength at his right upper limb to move his trunk forward as to compensate his weakness on lower limb joint. Furthermore, Subject 3 was used to wearing bilateral solid ankle foot orthosis (AFO) during his outside ambulation activity. Figures 5 and 6 manifested the rate of fatigue for two SCI subjects during experiment without and with FES. For every trial, the value of force exerted by subjects arms on the frame and the force exerted by subjects feet on force plate while the subject at the highest knee moment during STS were taken to identify the rate of fatigue for this experiment. Based on Fig. 5 for STS with assistance of FES, Subject 2 presented early fatigue in lower limb at trial 6 (t6), proven by the rise in force produced by the upper limb. He Fig. 3 Net force distribution detected with four sensors at standing frame during STS for Subject 2
FES Standing: The Effect of Arm Support on Stability 71 Fig. 4 Net force distribution detected with four sensors at standing frame during STS for Subject 3 Force (N) Force (N) vs Trials (Subject 2) 400 350 300 250 200 150 100 50 0 t1 t2 t3 t4 t5 t6 t7 t8 t9 t10 Trials leg without FES leg with FES arm without FES arm with FES Fig. 5 Force exerted at arm and feet versus trials during Sit-to-Stand using FES and without FES for Subject 2 Force (N) Force (N) vs Trials (Subject 3) 900 800 700 600 500 400 300 200 100 0 t1 t2 t3 t4 t5 t6 t7 t8 t9 t10 Trials leg without FES leg with FES arm without FES arm with FES Fig. 6 Force exerted at arm and feet versus trials during Sit-to-Stand using FES and without FES for Subject 3 displayed evidence of early fatigue at trial 9 when performing STS without FES. Meanwhile in Fig. 6, Subject 3 displayed evidence of fatigue on every session of experiment. With FES assistance on trial 5, subject 3 showed high reduction of force at leg and the value maintained for next trial until trial 8. However, without FES, Subject 3 showed early fatigue at trial 5 and this situation continued at trial 8 onwards. 4 Conclusion The sensors on the instrumented standing frame were calibrated. At least 85% accuracy of body weight acting upon standing frame was obtained when normal subjects bear all their body weight to the frame. According to the average time taken in performing a STS cycle, both subjects presented shorter time without using FES as they felt more confident and comfortable to stand. They also achieved early stage of fatigue during using FES thus longer time needed to do a STS cycle. However, SCI subjects displayed translocation of the centre of net force to right side of the standing frame to achieve stability in both sessions, as they used more strength on the right upper limb to move their trunk forward for standing. Besides, they have several conditions of lower limb joint contracture. Acknowledgements The authors appreciate significant contribution and continuous support by Assoc Prof. Dr. Nazirah Hasnan from Department of Rehabilitation Medicine, University of Malaya. This research was fully supported by the Ministry of Higher Education, Malaysia and University of Malaya through Fundamental Research Grant Scheme (FRGS) Grant No. FP027-2015A.
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