Quantifying Arms and Legs Contributions during Repetitive Electrically-Assisted Sit-To-Stand Exercise in Paraplegics: A Pilot Study

Summary

Arms contribution in Sit-To-Stand (SitTS) is determined by the legs' muscle condition. Several compensating strategies were discovered in efforts to achieve complete SitTS cycles. These findings triangulate the spinal cord injury (SCI) persons' biomechanical measures with their subjective feeling of load borne by both their limbs throughout the SitTS approaches.

Abstract

Execution of Sit-to-Stand (SitTS) in incomplete spinal cord injury (SCI) patients involves motor function in both upper and lower extremities. The use of arm support, in particular, is a significant assistive factor while executing SitTS movement in SCI population. In addition, the application of functional electrical stimulation (FES) onto quadriceps and gluteus maximus muscles is one of the prescribed management for incomplete SCI to improve muscle action for simple lower limb movements. However, the relative contribution of upper and lower extremities during SitTS has not been thoroughly investigated. Two motor incomplete SCI paraplegics performed repetitive SitTS to fatigue exercise challenge. Their performance was investigated as a mixed-method case-control study comparing SitTS with and without the assistance of FES. Three sets of SitTS tests were completed with 5-min resting period allocated in between sets, with mechanomyography (MMG) sensors attached over the rectus femoris muscles bilaterally. The exercise was separated into 2 sessions; Day 1 for voluntary SitTS and Day 2 for FES-assisted SitTS. Questionnaires were conducted after every session to gather the participants' input about their repetitive SitTS experience. The analysis confirmed that a SitTS cycle could be divided into three phases; Phase 1 (Preparation to stand), Phase 2 (Seat-off), and Phase 3 (Initiation of hip extension), which contributed to 23% ± 7%, 16% ± 4% and 61% ± 6% of the SitTS cycle, respectively. The contribution of arms and legs during SitTS movement varied in different participants based on their legs' Medical Research Council (MRC) muscle grade. In particular, the applied arm forces start to increase clearly when the leg forces start to decline during standing. This finding is supported by the significantly reduced MMG signal indicating leg muscle fatigue and their reported feeling of tiredness.

Introduction

Sit-To-Stand (SitTS) is a significant movement in a human's activity of daily living (ADL). It is also a prerequisite for basic functional activities such as standing, transferring, and walking. For patients with incomplete spinal cord injury (SCI), paraplegics in particular, SitTS exercise is a crucial activity for their functional independence^1,2. This exercise is essential for independence training, which eventually helps SCI population to improve their quality of life. In order to perform a sufficient and adequate SitTS exercise, the knowledge regarding their biomechanics and muscle activity should be feasibly measurable during the training.

In a clinical rehabilitation program, SCI patients with grade American Spinal Cord Injury Association (ASIA) Impairment Scale, AIS C have a better progression and chance of recovering their motor function than those with grade AIS B, who has complete motor deficits. The SitTS performance plays an important measure in an SCI patient to indicate their motor functionality during the recovery process³. However, SCI AIS C patients require both support from the upper and lower limbs to achieve successful series of repeated SitTS movements. The upper limb support plays an important role in unloading the knees while providing adequate lifting forces and assuring the body balance during the exercise⁴.

The purpose of this study is to describe the biomechanical contributions of arms and legs throughout repetitive SitTS in incomplete SCI individuals. This study positions the biomechanical analysis in relation to the participants' subjective sense of their arms and legs muscle performance and feelings of 'effort and tiredness' throughout the SitTS exercise.

Many previous SitTS studies only concentrated on investigating the kinematics and kinetics aspects of the activity^4,5,6,7. In a wider context of SitTS training, the development of this method which includes the instrumented standing frame (SF) and force plate analysis, could lead researchers to assess both upper and lower limb contribution of other populations such as stroke, elderly, and patients with osteoarthritis^8,9,10. A previous study by Zoulias et al., instrumented custom-built hardware and software of SF presented a large frame design¹¹. This method can be challenging to replicate. Hence this SitTS study highlighted a portable instrumented SF that can be adopted by other researchers with an existing motion analysis laboratory setup.

Protocol

The SitTS exercise and informed consent in this manuscript are described under ethical consideration by University of Malaya Medical Centre Ethics Committee (2017119-4828)¹². Study procedures were explained in detail to each participant, and written informed consent was obtained before beginning the SitTS trial. This study was conducted as mixed-mode, where quantitative data were obtained using biomechanical analysis, whereas subjective scores were obtained from feedback sessions (of the participants) and audio recordings (of the researcher-participants interactions during the study). This pilot study compared the participant's contributions of arms and legs in SitTS exercise voluntarily versus their performance with the presence of FES.

1. Participants selection

1. Perform an evaluation with potential SCI participants.
   1. Explain the details of the SitTS protocol, including the length of study (4 days) and length of session (SitTS: 2 h).
      NOTE: Voluntary SitTS was conducted on Day 1, followed by rest for 2 days. Functional electrical stimulation (FES)-assisted SitTS is then continued on the next day and defined as Day 2.
   2. Describe the medical requirements to the potential participant, including male or female with SCI AIS C (who can stand up), 18-60 years old, greater than 12-month post-injury, and demonstrate a willingness to wear specific clothes.
      NOTE: SCI AIS C participants provided written, informed consent to volunteer in this study. Participant 1 was a male (45 years; Body Mass Index (BMI) 20.32 kg/m²) and Participant 2 was a female (49 years; BMI 33.54 kg/m²). Both of them presented 95 months and 33 months after the SCI injury, respectively. Both participants had their lower extremities (LE) muscle grade assessed. The LE muscle grade of Participant 1 were 2 (right side) and 4 (left side). Meanwhile, Participant 2 had LE muscle grade of 4 bilaterally¹². Both participants had good trunk control. Participant 1 was diagnosed with a flaccid right leg with absent knee and ankle reflexes indicating a lower motor neuron injury. Besides that, his right leg was observed not to show any response to FES.
   3. Describe the exclusion criteria to the potential participants, including medical conditions that would cause them to fail in completing the instructions during the study. Other exemption criteria include participants that have osteoporosis and bone fracture¹², cardiac pacemaker or other implanted electronic system, had existing electrical stimulation device (implantable cardioverter defibrillator, pacemaker, or spinal stimulation) or had botulinum toxin.

2. SitTS experimental setup

NOTE: In this SitTS exercise, three parameters will be recorded. The first parameter is arms force and the second parameter is legs force. The third parameter is mechanomyography (MMG) which looks at the rectus femoris muscle activity.

1. Chair and SF setup.
   1. Design an armless chair with a height of 45 cm^13,14 without a backrest according to the dimension of force plate 1 embedded in the floor of the motion analysis laboratory (Figure 1).
   2. Place the chair on the top of the force plate 1.
   3. Instrument each SF leg independently with force sensor¹⁵ at the bottom of SF's leg given the sensitive range of each sensor is from 0-12 kg (Figure 2).
      NOTE: The sum values of four force sensor readings from SF were referred to as the arms force contribution.
   4. Position a portable and foldable SF in front of the chair within arm's reach¹². Position four legs of the SF securely outside of force plate 2 to avoid double measurements (Figure 1).
2. Motion analysis setup
   1. Enter participant's details (i.e., leg length, ankle width, knee width) in the motion analysis system.
   2. Place sixteen reflective markers on the participant's lower limbs with double-sided tape as mentioned in steps 2.2.3-2.2.5.
   3. Attach these markers directly over the bilateral anterior and posterior of the superior iliac spine. Second, attach markers on the lateral epicondyle of the left and right knee.
   4. Attach the marker over the lateral surface of the bilateral thigh and shank. Next, attach a marker on the lateral left and right malleolus.
   5. Attach markers over the left and right of the second metatarsal head. Attach the markers on the calcaneus at the same height of the second metatarsal head.
      NOTE: The placement of reflective markers is based on the setup of the motion analysis system¹⁶.
3. Participant's preparation
   1. Instruct the participant to be seated with their knees flexed at 90° with both feet positioned on force plate 2.
   2. Ensure the participant's head and trunk are faced forward while sitting in an upright position. Ensure the participant is barefooted.
   3. Place hands on the handle of the SF.
   4. Identify the rectus femoris muscle by palpating the middle and bulky area of the thigh.
   5. Place two MMG sensors at the thigh area of the rectus femoris muscle bilaterally, one MMG per leg, to accurately measure the leg muscles' sit-to-stand and stand-to-sit efforts¹².
   6. Secure the sensors with a double-sided tape. Strap the MMG sensors around the thigh to reduce motion artefacts¹².
   7. Connect the MMG sensors to the MMG device and the computer.

3. SitTS protocol

1. Day 1: Perform voluntary SitTS exercise.
   NOTE: Participants were instructed to do a repetitive SitTS event with the assistance of the SF.
   1. Before the experiment starts, ensure to turn on all setups to record the selected parameters.
      NOTE: The parameters recorded were force sensors for upper limb contribution, force plate for lower limb contribution, and MMG data for muscle rectus femoris activity.
   2. Ask the participant to stand up from the stationary sitting position at the end of a countdown of 5 s timed by an electronic timer.
   3. Let the participant stand for 3 s and then sit back on the chair.
   4. Ask the participant to rest for 5 s.
      NOTE: This was the resting interval in between the trials.
   5. Continue to do SitTS trials (repeat steps 3.1.2 and 3.1.4 until the participant cannot perform the same routine any longer).
   6. Turn off all the recorded data.
   7. Then, ask the participant to rest for 5 min before continuing the next set of the SitTS routine. Give 5 min break in between sets to provide muscle recovery amongst sets¹⁷.
   8. Repeat steps 3.1.1-3.1.7 for another two sets.
   9. Allow the participant to rest for at least 48 h.
2. Day 2: Perform FES-assisted SitTS exercise.
   NOTE: Participants were instructed to do repetitive SitTS events with the assistance of the SF and FES.
   1. Place FES electrodes on quadriceps and gluteus maximus muscles¹⁸.
   2. For quadriceps muscle, place the first electrode horizontally about two finger widths above the knee. Position the second electrode horizontally about a palm width below the hip joint.
   3. For the gluteus maximus muscle, ask the participant to bend forward and place the first electrode vertically closest to the hip bone. Attach the second electrode vertically closest to the tail bone, side by side from the first electrode.
   4. Attach all FES electrodes to the FES device and connect them to the FES software in the computer.
   5. Set up the FES software by selecting the pulse width of 300 and the frequency of 35 Hz.
   6. Define the FES current intensity by asking the participant if they can tolerate the current given to achieve knee and hip extension⁷. Determine the FES current amplitude through a number of practices before starting the actual trial.
      NOTE: Table 1 shows the FES current stimulated towards the participants' selected muscles during assisted FES SitTS session.
   7. Before the experiment starts, ensure to turn on all setups to record the selected parameters.
   8. Ask the participant to stand up from the stationary sitting position at the end of a countdown of 5 s timed by an electronic timer. At the end of the countdown, switch on the FES.
   9. Let the participant stand for 3 s. Then switch off the FES and let the participant sit back on the chair.
   10. Ask the participant to rest for 5 s.
   11. Continue to do SitTS trials (repeat steps 3.2.7-3.2.10 until the participant cannot perform the same routine any longer).
   12. Turn off all the recorded data.
   13. Then, ask the participant to rest for 5 min before continuing the next set of the SitTS routine.
   14. Repeat steps 3.2.7-3.2.13 for another two sets.

4. Data acquisition and analysis

1. Arm force contribution
   1. Extract all raw data of the force sensor to the workbook file in the computer for offline analysis.
2. Leg force contribution
   1. Analyze raw data of the SitTS kinematic and kinetic in the motion analysis software. Extract the force plate data and knee angle data to the workbook file in the computer for offline analysis.
      NOTE: Force plate data represent the leg force contribution
3. MMG of rectus femoris muscle
   1. Extract and store raw MMG data of rectus femoris muscle using two acquisition units and a vibromyography software to the workbook file for offline analysis.
      ​NOTE: The MMG signal were recorded by a vibromyography sensor at a sampling rate of 2 kHz. A finite impulse response band-pass filter between 20 Hz and 200 Hz was used to relay and transform the raw data of the MMG signal as recommended by the manufacturer for the muscle effort assessment¹⁹. For every trial, all data set were normalized and then synchronized as a complete cycle of SitTS exercise. An independent sample t-test was done to observe significant differences in mean time between voluntary and FES-assisted SItTS exercises.

5. Feedback session

1. Record audio during the feedback session (researcher-participant interactions).
2. Ask four questions regarding the stability and fatigue experienced by the participants during the accomplishment of SitTS in Day 1 and Day 2.
   NOTE: In this section, stability was interpreted by the participants as the highest balance in the SitTS event. The highest balance was achieved when they could hold on to the selected event longest. Meanwhile, fatigue was identified as their feeling of 'tiredness' that leads to their lowest performance retrieved during the SitTS exercise.
3. Collect and transcribe the audio.

Results

A total of 399 and 463 SitTS trials were completed without and with FES assisted correspondingly. The trials that contributed to each set are tabulated in Table 2. The participants could perform more SitTS trials with the presence of electrical stimulation on their legs, i.e., FES. Overall, both participants managed to perform more SitTS trials with the aid of FES. This suggests that FES helps in stimulating participants' quadriceps to execute SitTS action in a prolonged period²⁰

Discussion

The current study demonstrated a bodyweight contribution in SCI individuals during SitTS exercise. This study presented SF as an essential assistive device for paraplegics to do a successful SitTS cycle. Moreover, an instrumented SF was developed to ensure the arms force can be assessed too²⁸. The application of MMG was added in the study to observe prime SitTS muscle that helps researchers to understand SitTS performance better. Furthermore, the feedback session enabled researchers to obtain insi...

Materials

Name	Company	Catalog Number	Comments
Customade chair			A customade chair was built to following to the force plate's dimension.
FES RehaStim 2	Hasomed		A device that can stimulate electrical current towards the muscle.
FlexiForce A201	Tekscan, Inc., USA	Force ranges: 0-100 lbs. (440 N)	Force sensors is used to capture arms force at standing frame.
Foldable standing frame		Height: 70.0 cm - 90.0 cm.	A walking frame that was bought from local medical company.
Motion Analysis	Vicon Oxford, UK		A system that records kinematic and kinetics of the activity.
Serial port terminal application	CoolTerm	version 1.4.6; Roger Meier's	An application to record the force sensor data.
Vibromyography software	BIOPAC System Inc., USA	AcqKnowledge 4.3.1	A software to record and strore raw MMG data. It also function for offline analyses.
VMG transducers and BIOPAC Vibromyography system	BIOPAC System Inc., USA	BP150 and HLT100C	A device to measure muscle activity.