Hand-rim forces and gross mechanical efficiency at various frequencies of wheelchair propulsion.

To determine the effects of push frequency changes on force application, fraction of effective force (FEF) and gross efficiency (GE) during hand-rim propulsion. 8 male able-bodied participants performed five 4-min sub-maximal exercise bouts at 1.8 ms(-1); the freely chosen frequency (FCF), followed by 4 counter-balanced trials at 60, 80, 120 and 140% FCF. Kinetic data was obtained using a SMART(Wheel), measuring forces and moments. The GE was determined as the ratio of external work done and the total energy expended. Increased push frequency led to reductions in peak resultant force (P<0.05), ranging from 167 to 117 N and peak tangential force (P<0.05), ranging from 117 to 77 N. However, FEF only demonstrated a significant difference between 60% and 140% FCF (69 ± 9% and 63 ± 7, respectively; P<0.05). Work per cycle decreased significantly (P<0.05) and rate of force development increased significantly (P<0.05) with increased push frequency. GE values were significantly lower at 60%, 120% and 140% FCF than 80% and 100% FCF (P<0.05). No meaningful associations were present between FEF and GE. Under the current testing conditions, changes in push frequency are accompanied with changes in the absolute force values, albeit without changes in either the gross pattern/trend of force application or FEF. Changes in GE are not explained by different levels of force effectiveness.

Stature loss and recovery following a period of loading: effect of time of day and presence or absence of low back pain.

BACKGROUND: Stature reductions in asymptomatic individuals, caused by a set load, are lower later in the day when stature is in the trough of diurnal variation; hence most stature reduction investigations are conducted in the morning. Recent evidence suggests that it is not the reductions in stature, but the recovery of stature, that is of greatest importance. The aim of this investigation was to establish whether stature recovery is also affected by time of day and to determine if any differences exist between a chronic low back pain and asymptomatic group. METHODS: Eleven chronic low back pain participants (age=32.8 SD 7.9 yrs, mass=74.4 SD 14.2 kg and height=1.73 SD 0.07 m) and 11 asymptomatic participants (age=31.0 SD 6.3 yrs, body mass=72.6 SD 11.5 kg and height=1.76 SD 0.09 m) underwent two 20 min loaded walking tasks (10% body mass), one in the morning (09:00) and one in the afternoon (14:00), followed by a 20 min unloaded recovery period. Measurements of stature were obtained throughout. FINDINGS: The asymptomatic group experienced significantly less stature reduction (P=0.05; ES=1.1) and greater stature recovery (P=0.02; ES=0.9) in the afternoon compared to the morning. The chronic low back pain group experienced a similar pattern to the asymptomatic group, however no significant difference between sessions for changes in stature was evident P=0.07. INTERPRETATION: Further investigations of stature recovery should be restricted to the morning when comparing individuals with and without chronic low back pain, as time of day appeared to have effect on stature recovery, particularly in the asymptomatic group. Time dependent differences in stature change between these two populations warrants further investigation.

Changes in stature and spine kinematics during a loaded walking task.

The aim of the present study was to quantify the kinematics of the spine and stature loss induced by the asymmetric load carriage. Six healthy males with no history of low-back disorders walked at their self-selected pace for 8,500 m with and without a standard Royal Mail bag (model MB36) containing 17.5% of the participant's body mass. The load was reduced gradually during the task. The loaded condition produced a stature loss double that observed in the unloaded condition. Increased forward leaning (up to 6 degrees ) and lateral bending of the spine (up to 12 degrees ) was observed with load. Thoracic adjustments occurred in the sagittal plane, changes in the lumbar area occurred in the frontal plane. The data provided evidence against mailbags designs in which the workers cannot alternate the side of the mailbag.

The intra-push velocity profile of the over-ground racing wheelchair sprint start.

The aim of this study was to analyse the first six pushes of a sprint start in over-ground racing wheelchair propulsion. One international male wheelchair athlete (age=28 years; body mass=60.6 kg; racing classification=T4) performed maximal over-ground sprint trials, over approximately 10 m, in his own racing wheelchair fitted with a velocometer. Each trial was filmed at 200 Hz using a "Pan and Tilt" system. Eight trials were manually digitised at 100 Hz. Raw co-ordinate data were smoothed and differentiated using a quintic spline routine. Across the period from pushes one to six the duration of each push cycle decreased (0.82+/-0.02-0.45+/-0.01 s) with the mean duration of the propulsive phase decreasing from 0.62+/-0.02 to 0.21+/-0.01 s and the recovery phase increasing from 0.20+/-0.01 to 0.24+/-0.02 s. The push-rim was contacted progressively closer to top dead centre and released progressively closer to bottom dead centre with each push. The data indicate that peak velocity occurred after release. The main findings of this study support the observation that racing wheelchair sprint propulsion is a complex form of locomotion and cannot be described accurately by using just the established definitions of a propulsive and a recovery phase.

The influence of different unloading positions upon stature recovery and paraspinal muscle activity.

OBJECTIVE: To determine whether stature recovery and paraspinal muscle activity can be altered in individuals with and without chronic low-back pain by assuming different unloading positions. DESIGN: A case-control study considering the effects of unloading position on stature recovery in individuals with and without chronic low-back pain. BACKGROUND: Stature recovery has been documented to be lower in individuals with chronic low-back pain. Elevated paraspinal muscle activity subjects the spine to increased compression, which may delay stature recovery. However, the mechanism(s) causing prolonged stature recovery are yet to be explored. METHODS: Eleven chronic low-back pain participants (age 33 yr (SD 12.2), height 1.72 m (SD 0.08), body mass 75.9 kg (SD 10.7)) and eleven asymptomatic participants (age 30.5 yr (SD 9.7), height 1.75 m (SD 0.10), body mass 73.3 kg (SD 11.7)) performed a loaded walking task (10% body mass) and adopted four unloading positions on separate occasions. Measurements of stature and muscle activity were recorded during each position. FINDINGS: Individuals with chronic low-back pain exhibited higher paraspinal EMG and delayed stature recovery in all positions (P<0.05). Both groups experienced greatest stature recovery and least muscle activity during gravity inversion (P<0.05). INTERPRETATION: Elevated muscle activity was found in the chronic low-back pain group supporting the existence of this explanation for delayed stature recovery. The gravity inverted position resulted in the lowest EMG and the greatest stature recovery. Further research is required to determine whether improving stature recovery has clinical implications by reducing pain/disability.

Effect of push frequency on the economy of wheelchair racers.

PURPOSE: The aim of the study was to examine the effect of varying push frequency on pushing economy (oxygen uptake at a given speed). METHODS: Eight male wheelchair racers completed a series of exercise bouts on a wheelchair ergometer (Bromking Turbo Trainer, Bromakin, UK) at 6.58 m x s(-1). Initially, subjects self-selected their freely chosen push frequency (FCF); this was followed by 4 random trials pushing at 60, 80, 120, and 140% of this FCF. Steady state VO2 was determined using Douglas bags, and heart rate was recorded by telemetry. After each condition, a small capillary blood sample was obtained and analyzed for blood lactate concentration (BLa) and a rating of perceived exertion (RPE) was recorded. RESULTS: At 6.58 m x s(-1) oxygen uptake, RPE, and gross mechanical efficiency were nonlinearly related to push frequency. Analysis of variance showed a significant effect (P < 0.05) of cycle frequency on VO2. VO2 was 11% higher at the 140% FCF compared with the 100% FCF condition. Changes in push frequency had little effect on HR although BLa increased linearly and was higher at the 140% FCF condition compared with 60% FCF (P < 0.05). A two-dimensional sagittal plane video analysis showed large interindividual differences in propulsion style. Both cycle time and the propulsion phase (%) decreased as the push frequency increased. The start angle and end angle of hand contact were similar for conditions, whereas the range of trunk motion decreased with push frequency (P < 0.05). CONCLUSION: The results of this study showed that the push frequency had an effect on pushing economy, and that the athletes' FCF was the most economical.

Multi-segment coordination: fatigue effects.

PURPOSE: The aim of this study was to investigate the segmental coordination of vertical jumps under fatigue. METHODS: Twelve subjects performed maximal countermovement jumps with and without fatigue, which was imposed by maximal continuous jumps in place until their maximal jump height corresponded to 70% of the nonfatigued condition. Video, ground reaction forces, and electromyographic signals were recorded to analyze the segmental coordination of countermovement jumps before (CMJ1) and after (CMJ2) fatigue. The magnitude of joint extension initiation, peak joint angular velocity, and peak net power around the ankle, knee, and hip joints and their respective times were determined. RESULTS: CMJ2 was characterized by a longer contact time, which was accompanied with an earlier movement initiation and several differences (P < 0.05) in the variables used to describe coordination. When the movement duration was normalized with respect to the contact phase duration, the differences between CMJ1 and CMJ2 were not sustained. A consistent pattern was indicated, in which the segmental coordination did not differ between jump conditions. When the magnitude of the muscle activation was set aside, a remarkably consistent muscle activation time was noticed between conditions. CONCLUSIONS: It was indicated that countermovement jumps were performed with a consistent well-timed motion of the segments. A "common drive," which acts without the knowledge of the muscle properties, was suggested as mediating and controlling the muscle activation timing between agonist-antagonist muscle pairs.

A telemetry-based velocometer to measure wheelchair velocity.

UNLABELLED: The purpose of this paper is to present a telemetry-based velocometer that has the ability to measure wheelchair velocity. Five studies are described which provide measurements of the validity, dynamic response, reliability and resistance of the velocometer. VALIDITY: a linear relationship was found when velocity calculated from the velocometer was plotted against three test velocities. The average root mean square deviation (ARMSD) was used to compare velocity calculated from the velocometer with velocity calculated by manual digitising at 200Hz. The ARMSD calculated for each test speed from three trials were 0.06+/-0.01, 0.27+/-0.05 and 0.48+/-0.16 ms(-1) at 1, 5 and 9 ms(-1), respectively. Dynamic response: expressed as a percentage of the average mean trial velocity, the ARMSD for the five acceleration and five deceleration trials were 6.5+/-1.8% and 6.9+/-1.2%, respectively. Reliability was assessed from a comparison between mean trial velocity calculated from velocometer output and the speed of the motor used to spin the wheels. Expressed as a percentage of the mean trial velocity, the mean+/-SD of the differences were 0.00+/-0.17%, for the ten disc wheel trials and 0.00+/-0.41%, for the ten spoke wheel trials. Velocometer resistance calculated as a factor of the mechanical resistance of the wheelchair rear wheel spinning in air were -0.50 and -0.91 N, for the disc and spoke wheel, respectively. Velocometer resistance calculated as a factor of the total mechanical resistance of the wheelchair-wheelchair user system were -1.37 and -1.82 N, for the disc and spoke wheel, respectively.

A kinetic analysis of trained wheelchair racers during two speeds of propulsion.

The purpose of the study was to investigate the propulsion kinetics of wheelchair racers at racing speeds and to assess how these change with an increase in speed. It was hypothesised that propulsive force would increase in proportion to speed, to accommodate the additional work required. Six wheelchair racers volunteered to participate in this study which required each athlete to push a racing wheelchair at 4.70 and 5.64 m s(-1) on a wheelchair ergometer (WERG). Eight pairs (16 in total) of strain gauges, mounted on four bars attached to the hand-rim of a racing wheelchair wheel, measured the medio-lateral and tangential forces applied to the hand-rim. Kinetic data were sampled at 200 Hz while a single on-line (ELITE) infrared camera operating at 100 Hz was positioned perpendicular to the WERG to record the location of the hand with respect to the hand-rim. In general, peak tangential force occurred when the hand was positioned on the hand-rim between 140 and 180 degrees. With the increase in speed, the peak hand-rim forces applied tangentially increased from 132 to 158 N and those applied medio-laterally increased from 90 to 104 N. The ratio of tangential to total measured force was similar at both speeds (80 and 82%, respectively). In conclusion, these data indicate that wheelchair racers adopt a different propulsion strategy than that employed in everyday chairs and that the forces increase in proportion to propulsion speed.

Repeatability of stature measurements in individuals with and without chronic low-back pain.

Measurements of reduction in stature have been used to compare spinal loading in chronic low-back pain (CLBP) and asymptomatic populations. Whether there are any differences in the repeatability of stature measurements, between those with and without CLBP, is not known. This investigation aimed to determine the repeatability of stature measurements in those with (n = 12) and without (n = 12) CLBP, and to establish if the ability to produce repeatable measurements is retained after a specific timeframe. Stature measurements were taken on two separate sessions that were 2 weeks apart, using a stadiometer accurate to 0.01 mm. All participants attained a mean SD of < or = 0.5 mm by the third measurement set taken on the first session of testing and no significant difference in mean SD was found between those with (0.37 mm) and without (0.40 mm) CLBP (p > 0.05). Intraclass correlation coefficients (ICC) demonstrated good levels of repeatability for all stature measurements obtained from the participants and the values for Standard error of the measurement (SEM) improved as the mean SD decreased with each measurement set. Investigators should have confidence in the ability of those with and without CLBP to produce equally repeatable stature measurements with appropriate prior practice. The second session of testing demonstrated that both groups had retained the ability to achieve the desired level of repeatability (SD < or = 0.5 mm) 2 weeks later without further practice.

Intermuscular coordination during pendulum rebound exercises.

In this study, we assessed coordination during pendulum rebound jumps. To gain insight into the movement coordination strategy, nine experienced male volleyball players performed maximal rebound jumps in a pendulum swing device using three different seat arrangements (90 degrees, 135 degrees and 180 degrees). Two-dimensional filming was performed in the right sagittal plane (200 Hz) synchronized with a force platform fitted to the wall (1000 Hz). The surface electromyograms of five muscles were recorded (200 Hz), in conjunction with kinematic and kinetic assessment. During the countermovement phase, the impact forces were attenuated by eccentric contractions of most muscles, which helped to reduce the energy input into the system. The wall reaction forces, net moments and joint power profiles were comparable between conditions. The small differences found between the extreme seat arrangements were attributed to differences in muscle length and the position of the feet. The strategy used during landing was similar to that observed in unconstrained vertical and drop jumps, where the neuromuscular system attenuates the impact forces. During the push-off phase, most muscles were found to contribute to positive work generation, except the semitendinosus, which was stretching throughout the propulsive phase. Despite not being able to exert a large influence over the trunk segment, this muscle was deemed to play an important role in regulating and synchronizing the onset of knee extension, enabling hip extension to occur before extension in the other more distal joints. Our findings show that the neuromuscular system is able to produce consistent movement coordination across experimental conditions and in accordance with the specific task demands and constraints imposed in the movement structure.

Spinal shrinkage in unloaded and loaded drop-jumping.

Plyometric activities, engaging the muscle in a stretch-shortening cycle, are widely used in athletic training. One such plyometric exercise is drop-jumping, where the athlete drops from a raised platform and immediately on landing performs a maximal vertical jump. These actions are also performed with the athlete externally loaded by the addition of weights to provide greater resistance. Exercises which involve repeated impacts have been shown to give rise to a loss of stature (shrinkage) which can be measured by means of a sensitive stadiometer. This study examined the shrinkage induced by unloaded and loaded drop-jumping from a height of 26 cm. Eight male subjects, aged 20-24 years, performed the test protocol three times, at the same time of day on each occasion. Fifty drop-jumps from a height of 26 cm were performed with no additional load and with a load of 8.5 kg carried in a weighted vest. The third condition was a standing trial where the subject stood for 10 min (the time taken to perform the jumps) wearing the weighted vest. Stature was measured before exercise, immediately after exercise and after a 20 min standing recovery. On a separate occasion the regimen was performed and the vertical reaction force was measured using a Kistler force platform. The mean change in stature for the two jump conditions showed shrinkages of 0.62 (+/- 0.43) mm for unloaded and 2.14 (+/- 1.56) mm for the loaded (p < 0.05). The variance in shrinkage was greater in the loaded case compared to the unloaded condition (p < 0.05) indicating a wider range of jumping strategies.(ABSTRACT TRUNCATED AT 250 WORDS)

Changes in stature following plyometric drop-jump and pendulum exercises.

The aim of this study was to compare the changes in stature following the performance of plyometric exercises using drop-jumps and a pendulum swing. Eight male participants aged 21.7 +/- 1.8 years with experience of plyometric training gave their informed consent to act as participants. Participants undertook two exercise regimens and a 15-min standing test in a random order. The exercises entailed the performance of 50 drop-jumps from a height of 0.28 m or 50 pendulum rebounds. Participants were instructed to perform maximal jumps or rebounds using a 'bounce' style. Measurements of stature were performed after a 20-min period of standing (pre-exercise), 2-min after exercise (post-exercise) and after a 20-min standing recovery (recovery). Back pain and muscle soreness were assessed using an analogue-visual scale, at each of the above times and also 24 and 36 h after the test. Peak torque during isokinetic knee extension at 1.04 rads-1 was measured immediately before and after the exercise bouts, to assess the degree of muscular fatigue. Ground/wall reaction force data were recorded using a Kistler force platform mounted in the floor for drop-jumps and vertically on the rebound wall for pendulum exercises. Drop-jumps resulted in the greatest (p < 0.05) change in stature (-2.71 +/- 0.8 mm), compared to pendulum exercises (-1.77 +/- 0.7 mm) and standing (-0.39 +/- 0.2 mm). Both exercise regimens resulted in a significant (p < 0.01) decrease in stature when compared to the standing condition. Drop-jumps resulted in significantly greater peak impact forces (p < 0.05) than pendulum exercises (drop-jumps = 3.2 +/- 0.5 x body weight, pendulum = 2.6 +/- 0.5 x body weight). The two exercise conditions both invoked a small degree of muscle soreness but there were no significant differences between conditions. Both exercise regimens resulted in a non-significant decrease in peak torque indicating a similar degree of muscular fatigue. Based on the lower shrinkage resulted and lower peak forces, it can be concluded that pendulum exercises pose a lower injury potential to the lower back than drop-jumps performed from a height of 28 cm.

The effectiveness of a pendulum swing for the development of leg strength and counter-movement jump performance.

Various training devices have been developed to facilitate 'plyometric' training, one such device being the 'pendulum swing'. To assess the effectiveness of the pendulum swing, the results of a 3 week training programme using a combination of pendulum swing and weight-training exercises were compared to those of a weight-training programme. Subjects were assigned to one of two groups (n = 9) for weight-training only or for combined pendulum and weight-training. Both groups performed the same number of exercise repetitions. Measurements of isometric knee and hip extension-flexion, 1-RM squat weight, maximum jump height and power for a counter-movement jump were taken pre-training, 2 days after the end of the programme and 2 weeks after the end of the programme. The data were analysed using two-way MANOVA and MANCOVA techniques. Both methods showed significant (P < 0.05) increases in knee and hip extension strength. Hip and knee flexion strength increased only for the weight-trained group. Counter-movement jump height increased for both groups (weight-trained, P < 0.05; combined, P < 0.01). Maximum power increased only for the combined group (P < 0.05). When the pre-training scores were used as a covariate, the weight-trained group showed a greater increase in hip flexion and extension strength and knee flexion strength than the combined training group (P < 0.05). The combined group showed the greatest increase in knee extensor strength. It is concluded that the pendulum system induces a training effect which could be used to supplement weight-training for improving vertical jump performance.

Technical note: repeatability of measurement in determining stature in sitting and standing postures.

The aim of this study was to determine the effect of sitting and standing postures on the repeatability of a stadiometer designed to detect small variations in spinal length. Two groups of ten healthy subjects, with no previous or known history of back problems, participated in this study. One group was measured in the standing posture, while the other group was measured in a sitting posture. All subjects gave informed consent to participate in this study. Subjects had a set of landmarks defining the spinal contour marked on their backs and then stood in the stadiometer for three series of ten measurements to be performed. At the end of each measurement, the subjects were requested to move away from and then be repositioned in the stadiometer. Subjects improved the repeatability across the measurement series. At the end of the second measurement series, all subjects presented mean standard deviations of 0.43 +/- 0.08 mm (range 0.30-0.50 mm) in the standing posture. In the sitting posture, deviations of less than 0.05 mm were obtained only at the end of the third measurement series (0.48 +/- 0.08 mm; range 0.34-0.62 mm), suggesting that this posture required three measurement series before repeatable measurements could be assured rather than two in the standing posture.

Changes in stature during and after spinal traction in young male subjects

BACKGROUND: Spinal traction is a relatively popular procedure for increasing the intervertebral space by applying separating forces. The parameters of time and magnitude of the traction forces may influence the outcomes from this procedure and need to be investigated. The duration of the benefits derived from traction is unknown and needs to be determined so that physiotherapists can provide better and more effective treatments. OBJECTIVE: This study analyzed the relationship between load magnitude and time during spinal traction in relation to stature variations. Traction effect duration was also analyzed. METHOD: Fifteen healthy male subjects (23.1 ± 5.77 years; 1.80 ± 0.17 m and 87.0 ± 9.6 kg) were assessed under three traction conditions (0, 30 and 60 percent of body weight, BW) of 42 minutes. Stature variation was used to determine intervertebral disc height variation. Stature was assessed every 7 minutes during traction of 42 minutes and every 5 minutes for 45 minutes after traction ceased. RESULTS: 0 and 30 percent BW traction produced similar gains (6.09 ± 1.89 mm, 5.70 ± 1.88 mm, respectively; p>0.05), while these were smaller (p<0.05) than at 60 percent BW (7.01 ± 1.98 mm). Significant differences (p<0.05) between 60 percent BW and the other conditions occurred only after the 21st minute. Stature loss after traction showed that the traction effects were transient and lasted for approximately one hour. This suggests that traction loads of 30 percent BW are insufficient to produce stature gains similar to those observed with 60 percent BW. CONCLUSION: Traction showed a short-duration transient effect. For this effect to be maintained, it must be repeated at one-hour intervals. Its use is questioned because of its transient nature.

CONTEXTUALIZAÇÃO: A tração sobre a coluna vertebral é um procedimento relativamente popular para aumentar o espaço inter-vertebral pela aplicação de forças de separação. Os parâmetros de tempo e magnitude da força aplicada podem influenciar os resultados desse procedimento e ainda precisam ser investigados. A duração dos benefícios derivados da tração não é conhecida e precisa ser determinada para que fisioterapeutas possam prover tratamentos melhores e mais eficientes. OBJETIVO: Este estudo analisou a relação entre a magnitude de carga e de tempo durante a tração vertebral sobre as variações de estatura, bem como a duração deste efeito. MÉTODOS: Quinze sujeitos saudáveis do sexo masculino (23,1 ± 5,77 anos; 1,80 ± 0,17 m e 87,0 ± 9,6 Kg) foram mensurados sob três condições (0, 30 e 60 por cento PC) de 42 minutos. A variação de estatura foi utilizada para determinar a variação da altura dos discos intervertebrais. A estatura foi verificada a cada 7 min durante a tração de 42 min e a cada 5 min por 45 min após o término da tração. RESULTADOS: A tração com 0 e 30 por cento do PC produziu ganhos similares (6,09 ± 1,89mm, 5,70 ± 1,88mm, respectivamente; p>0,05), que foram menores (p<0,05) que com 60 por cento do PC (7,01 ± 1,98 mm). Diferenças significativas (p<0,05) entre 60 por cento do PC e outras condições ocorreram apenas após o 21º min. A perda de estatura após a tração demonstrou que os efeitos da tração vertebral são transientes e duram aproximadamente 1 hora. Isso sugere que a carga de tração de 30 por cento PC não é suficiente para produzir ganhos de estatura similares aos observados com 60 por cento PC. CONCLUSÃO: A tração demonstrou um efeito transiente e de curta duração, para esse efeito ser mantido ele deve ser repetido em intervalos de 1 hora. O uso da tração é questionado devido ao seu efeito transiente.