Riemer J. K. Vegter

Initial Skill Acquisition of Handrim Wheelchair Propulsion: A New Perspective

To gain insight into cyclic motor learning processes, hand rim wheelchair propulsion is a suitable cyclic task, to be learned during early rehabilitation and novel to almost every individual. To propel in an energy efficient manner, wheelchair users must learn to control bimanually applied forces onto the rims, preserving both speed and direction of locomotion. The purpose of this study was to evaluate mechanical efficiency and propulsion technique during the initial stage of motor learning. Therefore, 70 naive able-bodied men received 12-min uninstructed wheelchair practice, consisting of three 4-min blocks separated by 2 min rest. Practice was performed on a motor-driven treadmill at a fixed belt speed and constant power output relative to body mass. Energy consumption and the kinetics of propulsion technique were continuously measured. Participants significantly increased their mechanical efficiency and changed their propulsion technique from a high frequency mode with a lot of negative work to a longer-slower movement pattern with less power losses. Furthermore a multi-level model showed propulsion technique to relate to mechanical efficiency. Finally improvers and non-improvers were identified. The non-improving group was already more efficient and had a better propulsion technique in the first block of practice (i.e., the fourth minute). These findings link propulsion technique to mechanical efficiency, support the importance of a correct propulsion technique for wheelchair users and show motor learning differences.

Variability in bimanual wheelchair propulsion: Consistency of two instrumented wheels during handrim wheelchair propulsion on a motor driven treadmill

BackgroundHandrim wheelchair propulsion is a complex bimanual motor task. The bimanually applied forces on the rims determine the speed and direction of locomotion. Measurements of forces and torques on the handrim are important to study status and change of propulsion technique (and consequently mechanical strain) due to processes of learning, training or the wheelchair configuration. The purpose of this study was to compare the simultaneous outcomes of two different measurement-wheels attached to the different sides of the wheelchair, to determine measurement consistency within and between these wheels given the expected inter- and intra-limb variability as a consequence of motor control.MethodsNine able-bodied subjects received a three-week low-intensity handrim wheelchair practice intervention. They then performed three four-minute trials of wheelchair propulsion in an instrumented hand rim wheelchair on a motor-driven treadmill at a fixed belt speed. The two measurement-wheels on each side of the wheelchair measured forces and torques of one of the two upper limbs, which simultaneously perform the push action over time. The resulting data were compared as direct output using cross-correlation on the torque around the wheel-axle. Calculated push characteristics such as power production and speed were compared using an intra-class correlation.ResultsMeasured torque around the wheel axle of the two measurement-wheels had a high average cross-correlation of 0.98 (std=0.01). Unilateral mean power output over a minute was found to have an intra-class correlation of 0.89 between the wheels. Although the difference over the pushes between left and right power output had a high variability, the mean difference between the measurement-wheels was low at 0.03 W (std=1.60). Other push characteristics showed even higher ICC’s (>0.9).ConclusionsA good agreement between both measurement-wheels was found at the level of the power output. This indicates a high comparability of the measurement-wheels for the different propulsion parameters. Data from both wheels seem suitable to be used together or interchangeably in experiments on motor control and wheelchair propulsion performance. A high variability in forces and timing between the left and right side were found during the execution of this bimanual task, reflecting the human motor control process.

Inter-Individual Differences in the Initial 80 Minutes of Motor Learning of Handrim Wheelchair Propulsion

Handrim wheelchair propulsion is a cyclic skill that needs to be learned during rehabilitation. Yet it is unclear how inter-individual differences in motor learning impact wheelchair propulsion practice. Therefore we studied how early-identified motor learning styles in novice able-bodied participants impact the outcome of a low-intensity wheelchair-practice intervention. Over a 12-minute pre-test, 39 participants were split in two groups based on a relative 10% increase in mechanical efficiency. Following the pretest the participants continued one of four different low-intensity wheelchair practice interventions, yet all performed in the same trial-setup with a total 80-minute dose at 1.11 m/s at 0.20 W/kg. Instead of focusing on the effect of the different interventions, we focused on differences in motor learning between participants over the intervention. Twenty-six participants started the pretest with a lower mechanical efficiency and a less optimal propulsion technique, but showed a fast improvement during the first 12 minutes and this effect continued over the 80 minutes of practice. Eventually these initially fast improvers benefitted more from the given practice indicated by a better propulsion technique (like reduced frequency and increased stroke angle) and a higher mechanical efficiency. The initially fast improvers also had a higher intra-individual variability in the pre and posttest, which possibly relates to the increased motor learning of the initially fast improvers. Further exploration of the common characteristics of different types of learners will help to better tailor rehabilitation to the needs of wheelchair-dependent persons and improve our understanding of cyclic motor learning processes.

Effect of wheelchair mass, tire type and tire pressure on physical strain and wheelchair propulsion technique.

The purpose of this study was to evaluate the effect of wheelchair mass, solid vs. pneumatic tires and tire pressure on physical strain and wheelchair propulsion technique. 11 Able-bodied participants performed 14 submaximal exercise blocks on a treadmill with a fixed speed (1.11 m/s) within 3 weeks to determine the effect of tire pressure (100%, 75%, 50%, 25% of the recommended value), wheelchair mass (0 kg, 5 kg, or 10 kg extra) and tire type (pneumatic vs. solid). All test conditions (except pneumatic vs. solid) were performed with and without instrumented measurement wheels. Outcome measures were power output (PO), physical strain (heart rate (HR), oxygen uptake (VO2), gross mechanical efficiency (ME)) and propulsion technique (timing, force application). At 25% tire pressure PO and subsequently VO2 were higher compared to 100% tire pressure. Furthermore, a higher tire pressure led to a longer cycle time and contact angle and subsequently lower push frequency. Extra mass did not lead to an increase in PO, physical strain or propulsion technique. Solid tires led to a higher PO and physical strain. The solid tire effect was amplified by increased mass (tire × mass interaction). In contrast to extra mass, tire pressure and tire type have an effect on PO, physical strain or propulsion technique of steady-state wheelchair propulsion. As expected, it is important to optimize tire pressure and tire type.

Effect of holding a racket on propulsion technique of wheelchair tennis players

The purpose of this study was to determine possible differences in propulsion technique between propelling the wheelchair with and without a racket in the hand. Eight experienced wheelchair tennis players performed three submaximal exercise tests and six sprint tests on a wheelchair ergometer. Torque and velocity were measured during the tests and power output and timing variables were calculated. Differences between the conditions with and without racket were analyzed. When propelling with the racket, the racket side showed a significantly lower push time (P = 0.03), lower percentage push time (P = 0.001), shorter contact angle (P < 0.001), more power loss before (P = 0.006) and after (P = 0.001) the push, a higher peak (P = 0.009) and mean (P = 0.005) power output during the push, and a lower mean overall velocity (P = 0.03). When the same hand is compared when propelling with and without racket or when the sprint data were analyzed, similar significant differences were found. Propelling the wheelchair while holding a racket has negative effects on the propulsion technique and may lead to injuries of the upper extremity. The longer time needed to couple the hand with the racket to the rim leads to higher power losses and subsequently higher power output generation during the shorter push phase.

Effects of Visual Feedback-Induced Variability on Motor Learning of Handrim Wheelchair Propulsion

Background It has been suggested that a higher intra-individual variability benefits the motor learning of wheelchair propulsion. The present study evaluated whether feedback-induced variability on wheelchair propulsion technique variables would also enhance the motor learning process. Learning was operationalized as an improvement in mechanical efficiency and propulsion technique, which are thought to be closely related during the learning process. Methods 17 Participants received visual feedback-based practice (feedback group) and 15 participants received regular practice (natural learning group). Both groups received equal practice dose of 80 min, over 3 weeks, at 0.24 W/kg at a treadmill speed of 1.11 m/s. To compare both groups the pre- and post-test were performed without feedback. The feedback group received real-time visual feedback on seven propulsion variables with instruction to manipulate the presented variable to achieve the highest possible variability (1st 4-min block) and optimize it in the prescribed direction (2nd 4-min block). To increase motor exploration the participants were unaware of the exact variable they received feedback on. Energy consumption and the propulsion technique variables with their respective coefficient of variation were calculated to evaluate the amount of intra-individual variability. Results The feedback group, which practiced with higher intra-individual variability, improved the propulsion technique between pre- and post-test to the same extent as the natural learning group. Mechanical efficiency improved between pre- and post-test in the natural learning group but remained unchanged in the feedback group. Conclusion These results suggest that feedback-induced variability inhibited the improvement in mechanical efficiency. Moreover, since both groups improved propulsion technique but only the natural learning group improved mechanical efficiency, it can be concluded that the improvement in mechanical efficiency and propulsion technique do not always appear simultaneously during the motor learning process. Their relationship is most likely modified by other factors such as the amount of the intra-individual variability.

Can a 15m-overground wheelchair sprint be used to assess wheelchair-specific anaerobic work capacity?

OBJECTIVE To evaluate whether outcomes based on stopwatch time and power output (PO) over a 15m-overground wheelchair sprint test can be used to assess wheelchair-specific anaerobic work capacity, by studying their relationship with outcomes on a Wingate-based 30s-wheelchair ergometer sprint (WAnT). METHODS Able-bodied persons (N=19, 10 men, aged 18-26 y) performed a 15m overground sprint test in an instrumented wheelchair and a WAnT. 15m-outcomes were based on stopwatch time (time and mean velocity over 15m) and on PO (primary outcome: highest mean unilateral PO over successive 5s-intervals (P5-15m)). WAnT-outcomes were mean unilateral PO over 30s and the highest mean unilateral PO over successive 5s-intervals. Correlation coefficients (Pearsons r) and coefficients of determination (R(2)) were calculated between 15m-sprint outcomes and WAnT-outcomes. RESULTS Time over 15m (7.2s (± 1.0)) was weakly related to WAnT-outcomes (r=-0.61 and -0.60, R(2)=0.38 and 0.36, p<0.01), similar to mean velocity over 15m (2.1 m·s(-1) (± 0.3), R(2)=0.43 and 0.39, p<0.01). P5-15m (38.1W (± 14.0)) showed a moderate relationship to WAnT-outcomes (r=0.77 and 0.75, R(2)=0.59 and 0.56, p<0.001). CONCLUSIONS It seems that outcomes based on stopwatch time over a 15m-overground sprint cannot be used to assess wheelchair-specific anaerobic work capacity, in contrast to an outcome based on PO (P5-15m). The 15m-sprint with an instrumented wheel can be implemented in rehabilitation practice and research settings when WAnT equipment is not available, although care is needed when interpreting P5-15m as an outcome of anaerobic work capacity given that it seems more skill-dependent than the WAnT.

WHEEL-I: DEvELOpMENT OF A WHEELCHAIR pROpULsION LAbORATORY FOR REHAbILITATION

OBJECTIVE To describe the enabling factors and barriers experienced in the Wheelchair Expert Evaluation Laboratory - implementation (WHEEL-i) project, in which scientific knowledge, tools and associated systematic analyses of hand-rim wheelchair propulsion technique, users wheelchair propulsion capacity, wheelchair-user interface, and wheelchair mechanics were implemented in 2 rehabilitation centres. DESIGN Implementation project. PATIENTS Spinal cord injury. METHODS In this implementation project standardized tests were performed: wheelchair skills tests, 2 questionnaires, and a steady-state exercise test on a treadmill in which propulsion technique (forces and torques) and physical strain (oxygen uptake, heart rate and mechanical efficiency) were measured. RESULTS Good interpretation of the test outcomes was the most important barrier. In order to discuss individual wheelchair performance results with patients and clinicians, reference data were developed, smallest detectable differences were calculated and software was developed to simultaneously show video recordings and force and torque signals. CONCLUSION Based on pilot results, the greatest barrier to systematic monitoring of the individual wheelchair fitting and learning process in rehabilitation with, among others, instrumented measurement wheels, was interpretation of outcomes. For proper interpretation of individual outcomes, the availability of reference data, smallest detectable differences and visualization of outcomes is of utmost importance.

Validity of consumer-grade activity monitor to identify manual wheelchair propulsion in standardized activities of daily living

Background Hypoactive lifestyle contributes to the development of secondary complications and lower quality of life in wheelchair users. There is a need for objective and user-friendly physical activity monitors for wheelchair-dependent individuals in order to increase physical activity through self-monitoring, goal setting, and feedback provision. Objective To determine the validity of Activ8 Activity Monitors to 1) distinguish two classes of activities: independent wheelchair propulsion from other non-propulsive wheelchair-related activities 2) distinguish five wheelchair-related classes of activities differing by the movement intensity level: sitting in a wheelchair (hands may be moving but wheelchair remains stationary), maneuvering, and normal, high speed or assisted wheelchair propulsion. Methods Sixteen able-bodied individuals performed sixteen various standardized 60s-activities of daily living. Each participant was equipped with a set of two Activ8 Professional Activity Monitors, one at the right forearm and one at the right wheel. Task classification by the Active8 Monitors was validated using video recordings. For the overall agreement, sensitivity and positive predictive value, outcomes above 90% are considered excellent, between 70 and 90% good, and below 70% unsatisfactory. Results Division in two classes resulted in overall agreement of 82.1%, sensitivity of 77.7% and positive predictive value of 78.2%. 84.5% of total duration of all tasks was classified identically by Activ8 and based on the video material. Division in five classes resulted in overall agreement of 56.6%, sensitivity of 52.8% and positive predictive value of 51.9%. 59.8% of total duration of all tasks was classified identically by Activ8 and based on the video material. Conclusions Activ8 system proved to be suitable for distinguishing between active wheelchair propulsion and other non-propulsive wheelchair-related activities. The ability of the current system and algorithms to distinguish five various wheelchair-related activities is unsatisfactory.

Sprint performance and propulsion asymmetries on an ergometer in trained high- and low-point wheelchair rugby players

The purpose of this study was to examine the propulsion asymmetries of wheelchair athletes while sprinting on an instrumented, dual‐roller ergometer system. Eighteen experienced wheelchair rugby players (8 low point (LP) (class ≤1.5) and 10 high point (HP) (class ≥2.0)) performed a 15‐second sprint in their sports wheelchair on the instrumented ergometer. Asymmetry was defined as the difference in distance and power output (PO) between left and right sides when the best side reached 28 m. Propulsion techniques were quantified based on torque and velocity data. HP players covered an average 3 m further than the LP players (P = .002) and achieved faster sprint times than LP players (6.95 ± 0.89 vs 8.03 ± 0.68 seconds, P = .005) and at the time the best player finished (5.96 seconds). Higher peak POs (667 ± 108 vs 357 ± 78 W, P = .0001) and greater peak speeds that were also evident were for HP players (4.80 ± 0.71 vs 4.09 ± 0.45 m/s, P = .011). Greater asymmetries were found in HP players for distance (1.86 ± 1.43 vs 0.70 ± 0.65 m, P = .016), absolute peak PO (P = .049), and speed (0.35 ± 0.25 vs 0.11 ± 0.10 m/s, P = .009). Although HP players had faster sprint times over 28 m (achieved by a higher PO), high standard deviations show the heterogeneity within the two groups (eg, some LP players were better than HP players). Quantification of asymmetries is important not only for classifiers but also for sports practitioners wishing to improve performance as they could be addressed through training and/or wheelchair configuration.