Push Frequency Research Articles

Comparison of rolling resistance, propulsion technique and physiological demands between a rigid, folding and hybrid manual wheelchair frame

Background When selecting a manual wheelchair frame, the choice between rigid and folding frames carries significant implications. Traditional folding frames are expected to have more rolling resistance and power dissipation caused by frame deformation, while they are more convenient for transportation, such as in a car. A new hybrid frame, designed to be more rigid, aims to minimize power dissipation while still retaining foldability. Aim This study aimed to assess rolling resistance, power output, propulsion technique and physiological demands of handrim wheelchair propulsion across three different frames: a rigid frame, a hybrid frame and a conventional folding frame. Materials and Methods Forty-eight able-bodied participants performed coast-down tests using inertial measurement units to determine rolling resistance. Subsequently, four-minute submaximal exercise block under steady-state conditions at 1.11 m/s were performed on a wheelchair ergometer (n = 24) or treadmill (n = 24) to determine power output, propulsion technique and physiological demands. Results Repeated measures ANOVA revealed that the hybrid frame exhibited the lowest rolling resistance (7.0 ± 1.5N, p ≤ 0.001) and required less power output (8.3 ± 1.0W, p ≤ 0.001) at a given speed, compared to both the folding (9.3 ± 2.2N, 10.8 ± 1.4W) and rigid frame (8.0 ± 1.9N, 9.4 ± 1.6W). Subsequently, this resulted in significantly lower applied forces and push frequency for the hybrid frame. The folding frame had the highest energy expenditure (hybrid: 223 ± 44 W, rigid: 234 ± 51 W, folding: 240 ± 46 W, p ≤ 0.001). Conclusion The hybrid frame demonstrated to be a biomechanically and physiologically beneficial solution compared to the folding frame, exhibiting lower rolling resistance, reduced power output, and consequently minimizing force application and push frequency, all while retaining its folding mechanism.

Eating time of dairy cows: a study focusing on commercial farms

The association of daily eating times (ET) of dairy cows, measured by wearable sensors, with diet composition, feeding practices, and performance was investigated. About 800 lactating cows of two breeds (Holstein Friesian – HF and Italian Simmental - IS) reared on 14 commercial farms were considered. Cows were grouped into ET classes (ETC, min/d): ETC-1 ≤ 180; ETC-2 from > 180 to ≤ 220; ETC-3 from > 220 to ≤ 260; ETC-4 from > 260 to ≤ 300; and ETC-5 > 300. Low ETC was positively associated with ether extract, crude protein, nonfibre carbohydrates, and neutral detergent fibre digestibility, and negatively associated with acid detergent lignin and particle size. A higher frequency of feed pushing per day seemed to be able to increase ETC. The relationship between ETC and performance, adjusted for breed, diet composition, days in milk, and parity, showed that cows with the highest ETC were more productive compared to those with shorter ETC (31.9 vs. 27.0 kg/d of milk) without significant changes in milk composition. Moving from short to long ETC, there was a linear reduction in urea, somatic cells, and body condition score. On the contrary, there was a positive association between ETC and time spent ruminating. Considering differences between breeds, HF had a higher milk yield, ruminated 20 min more, and had a higher ET (255 vs. 228 min/d) than IS. The study provides preliminary results for future research to better define the role of ET in the overall feed efficiency and health status of cows.

Degumming effects of silk fabrics as piezoelectrics for nanogenerators

This study evaluated the suitability of silk fabric as a piezoelectric nanogenerator (PENG). A PENG with excellent mechanical and electrical properties as well as biocompatibility was fabricated using silk. Silk fibers are composed of sericin and fibroin, and effect of sericin on the piezoelectric properties was evaluated. X-ray diffraction, Raman spectroscopy, and Fourier transform infrared analyses showed that the presence of sericin reduced the piezoelectricity, and its removal (degumming) improved the electrical output characteristics of the specimens. The device output performance exhibited a positive dependence on pressure conditions, such as the load and pushing frequency. The generators prepared from specimens before and after degumming showed power densities of 0.43 and 1.52 μW/cm2, respectively, at an applied stress of 110 N. The electrical properties of the fabricated silk PENG were stable even after 10,000 cycles. Silk-fabric PENGs can be fabricated as low-cost, high-output devices without additional processes, such as electrospinning or coating, and they show significant potential for application in biosensors, medical sensors, and implantable medical devices.

Relationship between rolling resistance, preferred speed, and manual wheelchair propulsion mechanics in non-disabled adults

Purpose To characterize the relationship among rolling resistance (RR), preferred speed, and propulsion mechanics. Methods N = 11 non-disabled individuals (mean (SD)); Age 24 years (2), BMI 23.8 kg/m2 (4.3) completed a submaximal graded wheelchair exercise test (GXTsubmax, fixed speed, terminated at Rating of Perceived Effort (RPE)=8 (0-10 scale)) and a single-blind, within-subject repeated measures wheelchair propulsion experiment (RME). RR at RPE = 10 (estimated maximum workload, Maxestimated) was estimated from the GXTsubmax RPE-RR relationship. RME consisted of N = 19 1-minute trials (self-selected speed) each followed by 2-minutes rest. The trials included N = 16 unique RR between 25-100% of Maxestimated. Averages of all pushes in N = 16 unique 1-minute trials were computed for average RR (N), speed (m/s), peak force (Fpeak (N)), force rate of rise (Fror (N/s)), push frequency (PF (pushes/min)), and push length (PL (deg)). Results Repeated measures correlation assessed relationships among outcome variables (α = 0.05). RR was associated with decreased speed (r=–0.81, p < 0.001), increased Fpeak (r = 0.92), Fror (r = 0.26), and PL (r = 0.32) (all p > 0.001), and unrelated to PF (r = 0.02, p = 0.848). Increased speed was associated with increased Fror (r = 0.23, p = 0.003) and PF (r = 0.27, p < 0.001) and decreased Fpeak (r=–0.66, p < 0.001) and PL (r=-0.25, p < 0.001). Conclusion Increasing RR increases Fpeak despite reducing self-selected speed. RR and speed were strongly and moderately related to Fpeak, respectively, but weakly related to other propulsion mechanics. These results suggest that reducing user-system RR may confer dual benefits of improved mobility and decreased upper extremity loading. Further testing among wheelchair users is required. Clinical trial registration number: NCT04987177

Biomechanics of wheelchair turning manoeuvres: novel insights into wheelchair propulsion.

Wheelchair turning biomechanics is an under researched area despite its obvious relevance to functional mobility of wheelchair users. Wheelchair turns might be linked to a higher risk of upper limb injuries due to the increased forces and torques potentially associated with asymmetric movement. Our aim was to obtain a better theoretical understanding of wheelchair turning by biomechanically analyzing turns compared to steady-state straightforward propulsion (SSSFP). Ten able-bodied men received 12-min familiarization and 10 trials (in a random order) of SSSFP and multiple left and right turns around a rectangular course. A Smartwheel was mounted at the right wheel of a standard wheelchair to measure kinetic parameters during SSSFP and of the inner hand during right turns and the outer hand during left turns. A repeated measures ANOVA was used to detect differences across tasks. Two strategies were identified: 3% demonstrated roll turns and 97% spin turns. Spin turns consisted of three phases: approach, turning and depart phase. The turning phase was accomplished by increasing peak force (72.9 ± 25.1 N vs. 43.38 ± 15.9 N in SSSFP) of the inner hand, while maintaining high push frequency of the outer hand (1.09 ± 0.20 push/s vs. 0.95 ± 0.13 push/s in SSSFP). Peak negative force and force impulse during the turning phase were much higher than SSSFP, 15.3 ± 15.7 and 4.5 ± 1.7 times higher, respectively. The spin turn strategy might carry an increased risk of upper limb injuries due to higher braking force and requires particular attention by rehabilitation professionals to preserve upper limb function of long-term wheelchair users.

Force-velocity profiling of elite wheelchair rugby players by manipulating rolling resistance over multiple wheelchair sprints.

This study investigated the effect of increased rolling resistance on wheelchair sprint performance and the concomitant force-velocity characteristics. Thirteen wheelchair rugby (WCR) athletes completed five 15 s wheelchair sprints in their own rugby wheelchair on an instrumented dual-roller wheelchair ergometer. The first sprint was performed against a close to overground resistance and in each of the following sprints, the resistance increased with 80% of that resistance. A repeated-measures ANOVA examined differences between sprints. Subsequently, linear regression analyses examined the individual force-velocity relations and then, individual parabolic power output curves were modeled. Increased rolling resistance led to significantly lower velocities (-36%), higher propulsion forces (+150%) and higher power outputs (+83%). These differences were accompanied by a lower push frequency, higher push time, yet a constant recovery time and contact angle. The modeled linear regressions (R2 = 0.71 ± 0.10) between force and velocity differed a lot in slope and intercept among individual athletes. The peak of the power output parabola (i.e., the optimal velocity) occurred on average at 3.1 ± 0.6 ms-1 . These individual force-velocity profiles can be used for training recommendations or technological changes to better exploit power generation capabilities of the WCR athletes' musculoskeletal system.

A 53–78 GHz Complementary Push–Push Frequency Doubler With Implicit Dual Resonance for Output Power Combining

This paper presents a millimeter-wave (mmW) frequency doubler based on complementary push-push (CPP) configuration achieving wideband, low-power and high-efficiency operation. Conventional push-push (PP) frequency doublers typically rely on half-wave rectification and suffer from performance compromise between the desired output and the DC current consumed. To mitigate this issue, a simple but effective CPP frequency doubling scheme is proposed to realize full-wave rectification, attaining enhanced output harmonic current and improved fundamental rejection without extra power consumption. At the output, an implicit dual-resonance (IDR) network featuring inherent resonant frequency alignment is employed to efficiently combine the harmonic power generated by the CPP transistors. Implemented in a 65-nm CMOS process and occupying a core area of 0.04 mm2, the proposed frequency doubler prototype measures conversion loss of < 10 dB from 53 to 78.5 GHz at 0-dBm input, while consuming 21.5 mW from a 1-V supply.

Shoulder pain in persons with tetraplegia and the association with force application during manual wheelchair propulsion

Introduction&#x0D; Shoulder pain is highly prevalent in persons with spinal cord injury (Liampas et al., 2021) and restricts daily mobility and thus participation and quality of life. Shoulder loading activities, such as manual wheelchair propulsion or transfers, are seen as risk factors for shoulder pain. To minimize the risk for shoulder pain, clinical guidelines instruct persons with spinal cord injury to “use long, smooth strokes that limit high impacts on the pushrim”. Findings supporting this recommendation have been found for persons with paraplegia (Beirens et al., 2021). However, dependent on their lesion level, persons with tetraplegia do not have, full triceps function and are not able to grasp the hand rim properly, which will alter force application and may further impact shoulder pain. The aim of this study was to investigate the association between wheelchair propulsion biomechanics, including force application and spatio-temporal characteristics, and shoulder pain in persons with tetraplegia.&#x0D; Methods&#x0D; Sixteen community-dwelling, wheelchair dependent participants with tetraplegia (C7-C5, age 49.1 ±2.9 years, 23.4 ±2.4 years since injury, 94% male) were measured during wheelchair propulsion on a treadmill at two speed / power output conditions: 0.56 ms-1/10W and 0.83 ms-1/15W. A Smartwheel was fitted to the personal wheelchair to measure force application. The applied forces, their effectiveness (fraction of effective force) and smoothness (rate of rise of force, jerk), as well as push frequency, push angle and timing of the push cycles were analyzed. Based on the Wheelchair User Shoulder Pain Index (0-150), participants were stratified in groups with low (≤ 7), moderate (8-35) and high (≥ 36) shoulder pain. A mixed-effect multilevel analysis was used to identify the association between the dependent variables (propulsion biomechanics) and group of shoulder pain when controlling for sex, age, time since injury, lesion level, body weight and height.&#x0D; Results and Discussion&#x0D; The analysis showed that persons with high shoulder pain applied the force over a longer push angle (85.6°) and had a shorter recovery time (0.4s) and applied the force more effective (FEF = 40.7%) than persons with low pain (push angle = 81.2°, recovery time = 0.5s, FEF = 35.2%). In addition, persons with high shoulder pain applied less medial directed force (6.4 N) compared to persons with moderate pain (14.9 N). The results of this cross-sectional study on wheelchair propulsion in persons with tetraplegia are in contradiction to previously reported results in person with paraplegia (Beirens et al., 2021). Interestingly, tetraplegic persons with high shoulder pain are following clinical recommendation on how to propel the wheelchair optimally. These results support the importance of differentiating between lesions levels when further investigating force application as a risk factor for shoulder pain. In addition, the results ask for a close examination and possible adaptation of the clinical guidelines for persons with tetraplegia.&#x0D; References&#x0D; Beirens, B. J. H., Bossuyt, F. M., Arnet, U., van der Woude, L. H. V., &amp; de Vries, W. H. K. (2021). Shoulder pain is associated with rate of rise and jerk of the applied forces during wheelchair propulsion in individuals with paraplegic spinal cord injury. Archives of Physical Medicine and Rehabilitation, 102(5), 856-864. https://doi.org/10.1016/j.apmr.2020.10.114&#x0D; Liampas, A., Neophytou, P., Sokratous, M., Varrassi, G., Ioannou, C., Hadjigeorgiou, G. M., &amp; Zis, P. (2021). Musculoskeletal pain due to wheelchair use: A systematic review and meta-analysis. Pain and Therapy, 10, 973-984. https://doi.org/10.1007/s40122-021-00294-5

An E-band CMOS frequency quadrupler with 1.7-dBm output power and 45-dB fundamental suppression

This paper presents an E-band frequency quadrupler in 40-nm CMOS technology. The circuit employs two push–push frequency doublers and two single-stage neutralized amplifiers. The pseudo-differential class-B biased cascode topology is adopted for the frequency doubler, which improves the reverse isolation and the conversion gain. Neutralization technique is applied to increase the stability and the power gain of the amplifiers simultaneously. The stacked transformers are used for single-ended-to-differential transformation as well as output bandpass filtering. The output bandpass filter enhances the 4th-harmonic output power, while rejecting the undesired harmonics, especially the 2nd harmonic. The core chip is 0.23 mm2 in size and consumes 34 mW. The measured 4th harmonic achieves a maximum output power of 1.7 dBm with a peak conversion gain of 3.4 dB at 76 GHz. The fundamental and 2nd-harmonic suppressions of over 45 and 20 dB are achieved for the spectrum from 74 to 82 GHz, respectively.

Influence of wheelchair type on Wheelchair Propulsion Test performance in community-dwelling, adult wheelchair users1.

The clinimetric properties of the Wheelchair Propulsion Test (WPT) have not been developed thoroughly. To determine inter-rater reliability and reference values for the Wheelchair Propulsion Test (WPT) for active wheelchair users and to compare WPT performance between various types of manual wheelchairs at different paces. This was a cross-sectional, descriptive study. Participants propelled a manual wheelchair 10 m while time and the number of pushes were recorded. Trials were performed in three different manual wheelchairs (a lightweight wheelchair (LW), an ultralightweight wheelchair (ULW), and the participant's personal, customized wheelchair) at a comfortable pace and a fast pace. The ICC values ranged from 0.861 to 0.999 for both speed and number of pushes. Comfortable wheelchair propulsion speed ranged from 1.51 (0.31) m/s to 1.65 (0.33) m/s depending on the wheelchair utilized. Across both pace conditions, participants were significantly faster when using their personal wheelchair compared to the ULW (P < 0.001) and LW (P < 0.001). Push frequency was significantly greater during the fast pace condition compared to the comfortable pace condition (P < 0.001). Reference values for the WPT in active wheelchair users have been identified. Participants who utilize their personal wheelchair demonstrate faster wheelchair propulsion speeds complemented by greater push frequencies.

Development of symptomatic pelvic organ prolapse over 10 years of mid-life follow-up is affected by occupational lifting and/or pushing for parous women

ObjectiveTo document the risk of new-onset symptomatic pelvic organ prolapse (POP) among perimenopausal women and examine whether occupational lifting and/or pushing is a risk factor in the development of POP over a 10-year follow-up window. Study designSecondary analysis of prospective, longitudinal data from the Study of Women's Health Across the Nation (SWAN) cohort study. Main outcome measuresWe analyzed women with current employment at the start of SWAN who were followed annually during mid-life. At baseline, women self-reported the frequency of occupational lifting and pushing, which was classified as Never, Infrequent (less than half the time), or Frequent (half the time or more) occupational lifting and/or pushing. Women were asked about new-onset symptomatic POP from the second to tenth annual follow-up. Modified Poisson regression was used to quantify crude and adjusted risk ratios (RRs) and 95 % confidence intervals (CIs) for POP according to load-bearing categories. Parous women were modelled separately, as initial analyses suggested effect modification by parity status. ResultsIn our sample of 1590 parous women, 8.2 % reported new-onset symptomatic POP over 10 years of follow-up. Multivariable analysis revealed that Infrequent (aRR 1.51, 95 % CI 1.04–2.20) and Frequent (aRR 2.03, 95 % CI 1.29–3.17) occupational lifting and/or pushing were associated with the development of POP. ConclusionFrequent occupational lifting and/or pushing significantly increased parous women's risk of developing POP symptoms. This strengthens existing evidence that occupational exposures can be risk factors for POP. Gender-based education and prevention strategies in the workplace and in primary health care are necessary to reduce the burden of this condition for mid-life women.

Comparison of Manual Wheelchair and Pushrim-Activated Power-Assisted Wheelchair Propulsion Characteristics during Common Over-Ground Maneuvers.

Pushrim-activated power-assisted wheels (PAPAWs) are assistive technologies that use force sensor data to provide on-demand propulsion assistance to manual wheelchair users. However, available data about kinetic and kinematic of PAPAW use are mainly limited to experiments performed on a treadmill or using a dynamometer. In this work, we performed experiments to gather kinetics of wheelchair propulsion and kinematics of wheelchair motion for a variety of over-ground wheelchair maneuvers with a manual wheelchair with and without PAPAWs. Our findings revealed that using PAPAWs can significantly reduce the propulsion effort and push frequency. Both linear and angular velocities of the wheelchair were significantly increased when using PAPAWs. Less force and push frequency could potentially reduce risk of chronic upper limb injury. Higher linear velocity could be desirable for various daily life activities; however; the increase in the angular velocity could lead to unintended deviations from a desired path. Future research could investigate PAPAW controllers that amplify the desired intentions of users while mitigating any unwanted behaviours.

Augmented feedback for manual wheelchair propulsion technique training in a virtual reality simulator

BackgroundMotor learning of appropriate manual wheelchair propulsion is critical, as incorrect technique elevates risk for upper extremity pain. Virtual reality simulators allow users to practice this complex task in a safe and realistic environment. Additionally, augmented feedback (AF) may be provided in order to optimize learning. The purpose of this study was to investigate the effects of providing AF with various delivery schedules on motor learning and transfer of this skill to over-ground propulsion.MethodsThirty healthy young adults were randomly assigned to three groups. During a virtual reality propulsion training session, the high-frequency AF group received AF in the form of knowledge of performance throughout all propulsion training; the faded AF group received this AF in a faded schedule (high relative frequency of AF early in practice, with relative frequency of AF provision diminishing throughout practice); and the control group underwent training with no AF. Propulsion assessments were performed at baseline and 48 h after practice in both virtual and real environments to measure retention and transfer, respectively.ResultsCompared to the control group, both feedback groups exhibited significant improvements in contact angle and push frequency in both environments after training. Small, non-significant between-group differences were also found between the high-frequency and faded feedback groups.ConclusionVirtual reality training is an effective learning intervention for acquisition, retention, and transfer of appropriate manual wheelchair propulsion technique when such training includes AF regarding propulsion biomechanics.

65.6–75.2-GHz Phase-Controlled Push–Push Frequency Quadrupler With 8.3% DC-to-RF Efficiency in 40-nm CMOS

We present a 40-nm CMOS 70-GHz frequency quadrupler based on a phase-controlled push-push (PCPP) topology that provides high efficiency and harmonic suppression. Since MOSFETs in the PCPP stack turn off alternately, the quadrupler can provide high energy efficiency even for fourth-order frequency multiplication. One major problem related to even-order harmonic suppression was mitigated by using a transformer-based output amplifier with no degradation in energy efficiency. The fabricated quadrupler provides the 3-dB bandwidth and peak output power of 65.6-75.2 GHz and -0.2 dBm at 70 GHz, respectively, with an 8.9-dBm fundamental input power. The peak dc-to-RF efficiency was measured to be 8.3% with 11.4-mW dc power consumption, including an output amplifier. At 70 GHz, measured harmonic suppression was around 51.1, 41.0, and 43.1 dBc at first, second, and third harmonic frequencies, respectively.

A 50-Gb/s Compact RadCom E-Band Transmitter With Phase-Controlled Push–Push Quadrupler and Stacked-FET Power Amplifier

We present a 66–79-GHz transmitter (TX) in 40-nm CMOS technology for radar and communication (RadCom) systems. To accommodate the technical requirements for RadCom systems, such as wideband operation with high linearity, a compact TX was implemented with a stacked-FET power amplifier (PA), upconverting passive mixer, and a phase-controlled push–push frequency quadrupler. The TX exhibits OP1dB and bandwidth of 13.0 dBm and 13 GHz or more, respectively, which are suitable for mid-range sensing up to 100 m with the minimum range resolution of 0.15 m or less and several tens of Gb/s short-range data transmission. In a back-to-back test, the rms error vector magnitude of −21.4 dB was achieved for 50-Gb/s 32-QAM signals occupying 13-GHz bandwidth with an output power of 4 dBm at the PA output. The total core area of the TX is 0.19 mm2.

A 280-GHz Self-Mixing Balanced Frequency Tripler in SiGe BiCMOS Technology

In this letter, a self-mixing balanced frequency tripler is presented. It comprises a push–push frequency doubling stage followed by a single balanced mixing stage sharing the input power via coupled lines. The chip is fabricated using the SG13G2 (130-nm SiGe BiCMOS) technology of Innovations for High Performance Microelectronics (IHP). A measured output power of 3 dBm is achieved at 280 GHz with a dc-to-RF efficiency of 2.19%.

Design of a 100-GHz Double-Sideband Low-IF CW Doppler Radar Transceiver for Micrometer Mechanical Vibration and Vital Sign Detection

This article presents a fully integrated 100-GHz continuous-wave Doppler radar transceiver with the double-sideband low-intermediate-frequency (IF) architecture for mechanical vibration and vital sign detection. Fabricated in a 65-nm CMOS process, the whole radar chip transceiver consumes 262 mW with a size of 0.9 mm $\times2.0$ mm. Instead of utilizing a fundamental 100-GHz voltage controlled oscillator (VCO) in the chip, a push–push frequency doubler with the 50-GHz external source is adopted to drive the transceiver. Under a dedicated design on the system architecture and circuit blocks, the chip could transmit 4-dBm saturated power ( $P_{\mathrm {sat}}$ ) over 93–105 GHz with a 40-mV 1-kHz IF carrier and achieve good I/Q performance of phase mismatch $\mu \text{m}$ displacement from 1.5 m, the human vital-sign signal from 2 m, and even a small bullfrog’s hybrid respiratory motion from 0.6 m. To the best of our knowledge, this is the first 100-GHz CMOS Doppler radar transceiver chip with the low-IF architecture for the biological vital sign detection.

Effect of seat height on manual wheelchair foot propulsion, a repeated-measures crossover study: part 2 – wheeling backward on a soft surface

Purpose The aim of this study was to test the hypotheses that, during manual-wheelchair foot propulsion backward on a soft surface, lowering the seat height increases speed, push frequency and push effectiveness, and decreases perceived difficulty. Materials and methods In a repeated-measures crossover study, 50 able-bodied participants used one foot to propel a manual wheelchair 5 m backward on a soft surface at 5 seat heights, ranging from 5.08 cm below to about 5.08 cm above lower-leg length, in random order. We recorded Wheelchair Skills Test (WST) capacity scores and used the Wheelchair Propulsion Test (WPT) to calculate speed (m/s), push frequency (cycles/s) and push effectiveness (m/cycle). We also recorded the participants’ perceived difficulty (0–4) and video-recorded each trial. Results WST capacity scores were reduced at the higher seat heights. Using repeated-measures models (adjusted for age, sex and order), there were negative relationships between seat height and speed (p < 0.0001) and push effectiveness (p < 0.0001). Lowering the seat height by 5.08 cm below lower-leg length corresponded to improvements in speed of 0.097 m/s and in push effectiveness of 0.101 m/cycle. The trend for push frequency was also significant (p = 0.035) but the effect size was smaller. Perceived difficulty increased with seat height (p < 0.0001). The video-recordings provided qualitative kinematic data regarding the seated “gait cycles”. Conclusions During manual-wheelchair foot propulsion backward on a soft surface, lowering the seat height increases speed and push effectiveness, and decreases perceived difficulty. IMPLICATIONS FOR REHABILITATION Backward wheelchair foot propulsion on soft surfaces is affected by seat height. Speed (m/s) is improved if the seat height is lowered. Push effectiveness (m/gait cycle) is improved if the seat height is lowered. Perceived difficulty of propulsion is lower if the seat height is lowered.

Effect of seat height on manual wheelchair foot propulsion, a repeated-measures crossover study: part 1 – wheeling forward on a smooth level surface

Purpose To test the hypotheses that, during manual wheelchair foot propulsion forward on smooth level surfaces, lowering the seat height increases speed, push frequency and push effectiveness, and decreases perceived difficulty. Materials and methods In a repeated-measures crossover study, 50 able-bodied participants used one foot to propel a manual wheelchair 10 m on a smooth level surface at 5 seat heights in random order, ranging from 5.08 cm below to about 5.08 cm above lower-leg length. We recorded Wheelchair Skills Test (WST) capacity scores and used the Wheelchair Propulsion Test (WPT) to calculate speed (m/s), push frequency (cycles/s) and push effectiveness (m/cycle). We also recorded the participants’ perceived difficulty (0–4) and video-recorded each trial. Results WST capacity scores were reduced at the higher seat heights. Using repeated-measures models (adjusted for age, sex and order), there were negative relationships between seat height and speed (p < 0.0001) and push effectiveness (p < 0.0001). Lowering the seat height by 5.08 cm below lower-leg length corresponded to improvements in speed of 0.20 m/s and in push effectiveness of 0.20 m/cycle. The trend for push frequency was also significant (p = 0.003) but the effect size was smaller. Perceived difficulty increased with seat height (p < 0.001). The video-recordings provided qualitative kinematic data regarding the seated “gait cycles”. Conclusions During manual wheelchair foot propulsion forward on smooth level surfaces, lowering the seat height increases speed and push effectiveness, and decreases perceived difficulty. Clinical Trial Registration Number NCT03330912. Implications for Rehabilitation Generally, wheelchairs used for forward foot propulsion should have a seat height that is 2.54-5.08 cm less than the sitting lower-leg length. Clinicians should, however, take into consideration other functions that may be adversely affected by lowering the seat height.

Propulsion efficiency in wheelchair tennis: a case study on the influence of the racket on the handrim forces

Abstract Aims: to evaluate how the act of holding a tennis racket influences the application of forces in the handrim during manual wheelchair propulsion at a self-selected comfortable speed and sprint. Methods: A case study was conducted with an experienced wheelchair tennis player who propelled the wheelchair in a straightforward trajectory at two different velocities (self-selected comfortable speed and sprint) in two different conditions (freehand and holding the racket). Kinetic and temporal data of the pushes were obtained with the SmartWheel system attached in substitution to the conventional rear wheel at the dominant side of the player. Results: holding the racket affects the propulsion pattern mainly when an accelerated movement is required (sprint). Compared to the propulsion at a self-selected speed, propelling the chair as fast as possible with the racket in hands resulted in lower total and tangential forces on the handrim, and decreased push time and increased push frequency. Conclusion: Such influence on both kinetic and temporal propulsion impact the mechanical efficiency of the manual wheelchair propulsion, which may, ultimately, affect the sport´s performance. Special attention should be directed to the propulsion training with the racket in maneuvers and motions that are characteristic of the wheelchair tennis match in an attempt to provide the athlete with proper technique for optimal propulsion efficiency and sports performance.