Cindy Gauthier

COMPARISON Of MULTIDIRECTIONAL SEATED POSTURAL STAbILITy bETwEEN INDIvIDUALS wITh SPINAL CORD INJURy AND AbLE­bODIED INDIvIDUALS

OBJECTIVES To compare multidirectional seated postural stability between individuals with spinal cord injury and able-bodied- individuals and to evaluate the impact of abdominal and low back muscle paralysis on multidirectional seated stability. DESIGN Case-control study. PARTICIPANTS Fifteen individuals with complete or incomplete spinal cord injury affecting various vertebral levels participated in this study and were gender-matched with 15 able-bodied individuals. METHODS Participants were instructed to lean as far as possible in 8 directions, set apart by 45° intervals, while seated on an instrumented chair with their feet placed on force plates. Eight direction-specific stability indices and a global stability index were calculated. RESULTS The global stability index and all direction-specific indices, except in the anterior and posterior directions, were lower in individuals with spinal cord injury than in able-bodied individuals. However, the individuals with spinal cord injury who had partial or full control of their abdominal and lower trunk muscles obtained a similar global stability index and similar direction-specific indices compared to the able-bodied individuals. CONCLUSION Multidirectional seated postural stability is reduced in individuals with SCI who have paralysis of the abdominal and lower back muscles in comparison to able-bodied individuals.

Influence of visual inputs on quasi-static standing postural steadiness in individuals with spinal cord injury.

Postural steadiness while standing is impaired in individuals with spinal cord injury (SCI) and could be potentially associated with increased reliance on visual inputs. The purpose of this study was to compare individuals with SCI and able-bodied participants on their use of visual inputs to maintain standing postural steadiness. Another aim was to quantify the association between visual contribution to achieve postural steadiness and a clinical balance scale. Individuals with SCI (n = 15) and able-bodied controls (n = 14) performed quasi-static stance, with eyes open or closed, on force plates for two 45 s trials. Measurements of the centre of pressure (COP) included the mean value of the root mean square (RMS), mean COP velocity (MV) and COP sway area (SA). Individuals with SCI were also evaluated with the Mini-Balance Evaluation Systems Test (Mini BESTest), a clinical outcome measure of postural steadiness. Individuals with SCI were significantly less stable than able-bodied controls in both conditions. The Romberg ratios (eyes open/eyes closed) for COP MV and SA were significantly higher for individuals with SCI, indicating a higher contribution of visual inputs for postural steadiness in that population. Romberg ratios for RMS and SA were significantly associated with the Mini-BESTest. This study highlights the contribution of visual inputs in individuals with SCI when maintaining quasi-static standing posture.

Effects of upper limb positions and weight support roles on quasi-static seated postural stability in individuals with spinal cord injury.

Seated postural stability has not been studied extensively in individuals with spinal cord injury (SCI). The main purpose of this study was to compare the effects of upper limb (U/L) positions and U/L weight support roles on quasi-static postural stability between individuals with SCI and healthy controls. Fourteen individuals with SCI and 14 healthy controls sat on an instrumented seat with their feet resting on force plates and randomly maintained five short-sitting positions for 60s with or without hand support. Center-of-pressure (COP) measures based on displacement and frequency series were computed. Individuals with SCI exhibited greater mean COP displacement and velocity measures compared to healthy controls, as well as lower COP frequency measures, irrespective of the U/L positions and weight support roles, confirming reduced stability and a difference in preferential postural regulation strategies. The use of U/L support is a compensatory strategy that influences seated stability in individuals with SCI.

Center-of-pressure total trajectory length is a complementary measure to maximum excursion to better differentiate multidirectional standing limits of stability between individuals with incomplete spinal cord injury and able-bodied individuals

BackgroundSensorimotor impairments secondary to a spinal cord injury affect standing postural balance. While quasi-static postural balance impairments have been documented, little information is known about dynamic postural balance in this population. The aim of this study was to quantify and characterize dynamic postural balance while standing among individuals with a spinal cord injury using the comfortable multidirectional limits of stability test and to explore its association with the quasi-static standing postural balance test.MethodsSixteen individuals with an incomplete spinal cord injury and sixteen able-bodied individuals participated in this study. For the comfortable multidirectional limits of stability test, participants were instructed to lean as far as possible in 8 directions, separated by 45° while standing with each foot on a forceplate and real-time COP visual feedback provided. Measures computed using the center of pressure (COP), such as the absolute maximal distance reached (COPmax) and the total length travelled by the COP to reach the maximal distance (COPlength), were used to characterize performance in each direction. Quasi-static standing postural balance with eyes open was evaluated using time-domain measures of the COP. The difference between the groups and the association between the dynamic and quasi-static test were analyzed.ResultsThe COPlength of individuals with SCI was significantly greater (p ≤ 0.001) than that of able-bodied individuals in all tested directions except in the anterior and posterior directions (p ≤ 0.039), indicating an increased COP trajectory while progressing towards their maximal distance. The COPmax in the anterior direction was significantly smaller for individuals with SCI. Little association was found between the comfortable multidirectional limits of stability test and the quasi-static postural balance test (r ≥ −0.658).ConclusionStanding dynamic postural balance performance in individuals with an incomplete spinal cord injury can be differentiated from that of able-bodied individuals with the comfortable limits of stability test. Performance among individuals with an incomplete spinal cord injury is characterized by lack of precision when reaching. The comfortable limits of stability test provides supplementary information and could serve as an adjunct to the quasi-static test when evaluating postural balance in an incomplete spinal cord injury population.

Which trunk inclination directions best predict multidirectional-seated limits of stability among individuals with spinal cord injury?

Abstract Objective To determine which trunk inclination directions most accurately predict multidirectional-seated limits of stability among individuals with spinal cord injury (SCI). Design Predictive study using cross-sectional data. Setting Pathokinesiology Laboratory. Participants Twenty-one individuals with complete or incomplete sensorimotor SCI affecting various vertebral levels participated in this study. Interventions Participants were instructed to lean their trunk as far as possible in eight directions, separated by 45° intervals, while seated on an instrumented chair with their feet positioned on force plates. Outcomes measures Eight direction-specific stability indices (DSIs) were used to define an overall stability index (OSI) (limits of stability). Results All DSIs significantly correlated with the OSI (r = 0.816–0.925). A protocol that only tests the anterior, left postero-lateral, and right lateral trunk inclinations accurately predicts multidirectional-seated postural stability (R2 = 0.98; P < 0.001). Conclusion Multidirectional-seated postural stability can be predicted almost perfectly by evaluating trunk inclinations performed toward the anterior, left postero-lateral, and right lateral directions.

Unsupported Eyes Closed Sitting and Quiet Standing Share Postural Control Strategies in Healthy Individuals

The study aimed to (1) compare postural stability between sitting and standing in healthy individuals and (2) define center-of-pressure (COP) measures during sitting that could also explain standing stability. Fourteen healthy individuals randomly maintained (1) two short-sitting positions with eyes open or closed, with or without hand support, and (2) one standing position with eyes open with both upper limbs resting alongside the body. Thirty-six COP measures based on time and frequency series were computed. Greater COP displacement and velocity along with lower frequency measures were found for almost all directional components during standing compared with both sitting positions. The velocity, 95% confidence ellipse area, and centroidal frequency were found to be correlated between unsupported sitting and standing. Despite evidenced differences between sitting and standing, similarities in postural control were highlighted when sitting stability was the most challenging. These findings support further investigation between dynamic sitting and standing balance.

Quantifying cardiorespiratory responses resulting from speed and slope increments during motorized treadmill propulsion among manual wheelchair users

BACKGROUND Cardiorespiratory fitness assessment and training among manual wheelchair (MW) users are predominantly done with an arm-crank ergometer. However, arm-crank ergometer biomechanics differ substantially from MW propulsion biomechanics. This study aimed to quantify cardiorespiratory responses resulting from speed and slope increments during MW propulsion on a motorized treadmill and to calculate a predictive equation based on speed and slope for estimating peak oxygen uptake (VO2peak) in MW users. METHODS In total, 17 long-term MW users completed 12 MW propulsion periods (PP), each lasting 2min, on a motorized treadmill, in a random order. Each PP was separated by a 2-min rest. PPs were characterized by a combination of 3 speeds (0.6, 0.8 and 1.0m/s) and 4 slopes (0°, 2.7°, 3.6° and 4.8°). Six key cardiorespiratory outcome measures (VO2, heart rate, respiratory rate, minute ventilation and tidal volume) were recorded by using a gas-exchange analysis system. Rate of perceived exertion (RPE) was measured by using the modified 10-point Borg scale after each PP. RESULTS For the 14 participants who completed the test, cardiorespiratory responses increased in response to speed and/or slope increments, except those recorded between the 3.6o and 4.8o slope, for which most outcome measures were comparable. The RPE was positively associated with cardiorespiratory response (rs≥0.85). A VO2 predictive equation (R2=99.7%) based on speed and slope for each PP was computed. This equation informed the development of a future testing protocol to linearly increase VO2 via 1-min stages during treadmill MW propulsion. CONCLUSIONS Increasing speed and slope while propelling a MW on a motorized treadmill increases cardiorespiratory response along with RPE. RPE can be used to easily and accurately monitor cardiorespiratory responses during MW exercise. The VO2 can be predicted to some extent by speed and slope during MW propulsion. A testing protocol is proposed to assess cardiorespiratory fitness during motorized MW propulsion.

Wheelchair pushrim kinetics measurement: A method to cancel inaccuracies due to pushrim weight and wheel camber

The commercially available SmartWheelTM is largely used in research and increasingly used in clinical practice to measure the forces and moments applied on the wheelchair pushrims by the user. However, in some situations (i.e. cambered wheels or increased pushrim weight), the recorded kinetics may include dynamic offsets that affect the accuracy of the measurements. In this work, an automatic method to identify and cancel these offsets is proposed and tested. First, the method was tested on an experimental bench with different cambers and pushrim weights. Then, the method was generalized to wheelchair propulsion. Nine experienced wheelchair users propelled their own wheelchairs instrumented with two SmartWheels with anti-slip pushrim covers. The dynamic offsets were correctly identified using the propulsion acquisition, without needing a separate baseline acquisition. A kinetic analysis was performed with and without dynamic offset cancellation using the proposed method. The most altered kinetic variables during propulsion were the vertical and total forces, with errors of up to 9N (p<0.001, large effect size of 5). This method is simple to implement, fully automatic and requires no further acquisitions. Therefore, we advise to use it systematically to enhance the accuracy of existing and future kinetic measurements.

Reliability and minimal detectable change of a new treadmill-based progressive workload incremental test to measure cardiorespiratory fitness in manual wheelchair users

Background: Cardiorespiratory fitness training is commonly provided to manual wheelchair users (MWUs) in rehabilitation and physical activity programs, emphasizing the need for a reliable task-specific incremental wheelchair propulsion test. Objective: Quantifying test-retest reliability and minimal detectable change (MDC) of key cardiorespiratory fitness measures following performance of a newly developed continuous treadmill-based wheelchair propulsion test (WPTTreadmill). Methods: Twenty-five MWUs completed the WPTTreadmill on two separate occasions within one week. During these tests, participants continuously propelled their wheelchair on a motorized treadmill while the exercise intensity was gradually increased every minute until exhaustion by changing the slope and/or speed according to a standardized protocol. Peak oxygen consumption (VO2peak), carbon dioxide production (VCO2peak), respiratory exchange ratio (RERpeak), minute ventilation (VEpeak) and heart rate (HRpeak) were computed. Time to exhaustion (TTE) and number of increments completed were also measured. Intra-class correlation coefficients (ICC) were calculated to determine test-retest reliability. Standard error of measurement (SEM) and MDC90% values were calculated. Results: Excellent test-retest reliability was reached for almost all outcome measures (ICC=0.91-0.76), except for RERpeak (ICC=0.58), which reached good reliability. TTE (ICC=0.89) and number of increments (ICC=0.91) also reached excellent test-retest reliability. For the main outcome measures (VO2peak and TTE), absolute SEM was 2.27 mL/kg/min and 0.76 minutes, respectively and absolute MDC90% was 5.30 mL/kg/min and 1.77 minutes, respectively. Conclusion: The WPTTreadmill is a reliable test to assess cardiorespiratory fitness among MWUs. TTE and number of increments could be used as reliable outcome measures when VO2 measurement is not possible.

Feasibility, Safety, and Preliminary Effectiveness of a Home-Based Self-Managed High-Intensity Interval Training Program Offered to Long-Term Manual Wheelchair Users

Objectives To investigate and compare the feasibility, safety, and preliminary effectiveness of home-based self-managed manual wheelchair high-intensity interval training (HIIT) and moderate-intensity continuous training (MICT) programs. Methods Eleven manual wheelchair users were randomly assigned to the HIIT (n = 6) or the MICT group (n = 5). Both six-week programs consisted of three 40-minute propulsion training sessions per week. The HIIT group alternated between 30 s high-intensity intervals and 60 s low-intensity intervals, whereas the MICT group maintained a constant moderate intensity. Cardiorespiratory fitness, upper limb strength, and shoulder pain were measured before and after the programs. Participants completed a questionnaire on the programs that explored general areas of feasibility. Results The answers to the questionnaire demonstrated that both training programs were feasible in the community. No severe adverse events occurred, although some participants experienced increased shoulder pain during HIIT. Neither program yielded a significant change in cardiorespiratory fitness or upper limb strength. However, both groups reported moderate to significant subjective improvement. Conclusion Home-based wheelchair HIIT appears feasible and safe although potential development of shoulder pain remains a concern and should be addressed with a future preventive shoulder exercise program. Some recommendations have been proposed for a larger study aiming to strengthen evidence regarding the feasibility, safety, and effectiveness of HIIT.