Forward Lean Angle Research Articles

Postural Compensations and Subjective Complaints Due to Backpack Loads and Wear Time in Schoolchildren

This study investigated the effects of carrying weighted backpacks of up to 20% of body weight on the posture and pain complaints of elementary-school children. Craniovertebral, forward trunk lean and pelvic tilt angles were measured from sagittal photographs of 62 children (8-11 years old) before and after walking while carrying backpacks containing 10%, 15%, or 20% of body weight. Pain severity after a 6-minute walk with the loaded backpack was recorded. Subjective complaints of pain were assessed using a visual analog scale after walking. Repeated-measures ANOVA revealed statistically significant differences in postural angles and increased complaints of pain after walking with increased backpack loads. These results indicate that typical backpack loads create worsening postural changes due to backpack loads and time spent carrying those loads, putting children at increased risk for injury and pain, the latter of which is a strong predictor for back pain in adulthood.

Lower limb muscle moments and power during recovery from forward loss of balance in male and female single and multiple steppers

BackgroundStudying recovery responses to loss of balance may help to explain why older adults are susceptible to falls. The purpose of the present study was to assess whether male and female older adults, that use a single or multiple step recovery strategy, differ in the proportion of lower limb strength used and power produced during the stepping phase of balance recovery. MethodsEighty-four community-dwelling older adults (47 men, 37 women) participated in the study. Isometric strength of the ankle, knee and hip joint flexors and extensors was assessed using a dynamometer. Loss of balance was induced by releasing participants from a static forward lean (4 trials at each of 3 forward lean angles). Participants were instructed to recover with a single step and were subsequently classified as using a single or multiple step recovery strategy for each trial. Findings(1) Females were weaker than males and the proportion of females that were able to recover with a single step were lower than for males at each lean magnitude. (2) Multiple compared to single steppers used a significantly higher proportion of their hip extension strength and produced less knee and ankle joint peak power during stepping, at the intermediate lean angle. InterpretationStrength deficits in female compared to male participants may explain why a lower proportion of female participants were able to recover with a single step. The inability to generate sufficient power in the stepping limb appears to be a limiting factor in single step recovery from forward loss of balance.

Mechanisms of Adaptation from a Multiple to a Single Step Recovery Strategy following Repeated Exposure to Forward Loss of Balance in Older Adults

When released from an initial, static, forward lean angle and instructed to recover with a single step, some older adults are able to meet the task requirements, whereas others either stumble or fall. The purpose of the present study was to use the concept of margin of stability (MoS) to investigate balance recovery responses in the anterior-posterior direction exhibited by older single steppers, multiple steppers and those that are able to adapt from multiple to single steps following exposure to repeated forward loss of balance. One hundred and fifty-one healthy, community dwelling, older adults, aged 65–80 years, participated in the study. Participants performed four trials of the balance recovery task from each of three initial lean angles. Balance recovery responses in the anterior-posterior direction were quantified at three events; cable release (CR), toe-off (TO) and foot contact (FC), for trials performed at the intermediate lean angle. MoS was computed as the anterior-posterior distance between the forward boundary of the Base of Support (BoS) and the vertical projection of the velocity adjusted centre of mass position (XCoM). Approximately one-third of participants adapted from a multiple to a single step recovery strategy following repeated exposure to the task. MoS at FC for the single and multiple step trials in the adaptation group were intermediate between the exclusively single step group and the exclusively multiple step group, with the single step trials having a significant, 3.7 times higher MoS at FC than the multiple step trials. Consistent with differences between single and multiple steppers, adaptation from multiple to single steps was attributed to an increased BoS at FC, a reduced XCoM at FC and an increased rate of BoS displacement from TO to FC. Adaptations occurred within a single test session and suggest older adults that are close to the threshold of successful recovery can rapidly improve dynamic stability following repeated exposure to a forward loss of balance.

Adaptive recovery responses to repeated forward loss of balance in older adults

Experiments designed to assess balance recovery in older adults often involve exposing participants to repeated loss of balance. The purpose of this study was to investigate the adaptive balance recovery response exhibited by older adults following repeated exposure to forward loss of balance induced by releasing participants from a static forward lean angle. Fifty–eight healthy, community-dwelling older adults, aged 65–80 years, participated in the study. Participants were instructed to attempt to recover with a single step and performed four trials at each of three lean angles. Adaptive recovery responses at four events (cable release, toe-off of the stepping foot, foot contact and maximum knee flexion angle following landing in the stepping leg) were quantified for trials performed at the intermediate lean angle using the concept of margin of stability. The antero-posterior and medio-lateral margin of stability were computed as the difference between the velocity-adjusted position of the whole body centre of mass and the corresponding anterior or lateral boundary of the base of support. Across repeated trials adaptations in reactive stepping responses were detected that resulted in improved antero-posterior stability at foot contact and maximum knee flexion angle. Improved antero-posterior stability following repeated trials was explained by more effective control of the whole body centre of mass during the reactive stepping response and not by adjustments in step timing or base of support. The observed adaptations occurred within a single testing session and need to be considered in the design of balance recovery experiments.

The effect of backpack weight and position on subject discomfort and forward trunk lean for college students

This survey explored the significance of the factors of backpack weight and position on the discomfort and forward trunk lean angle. The survey included 10 test subjects, used a local average backpack weight for testing, and a 22 factorial design for the analysis. Photographs were analyzed to determine forward trunk lean angle and a survey was used to collect discomfort information. Angle of forward trunk lean was measured from a base angle and the values varied from 0.95 degrees to 14.98 degrees. The forward trunk lean angle was not significantly affected by either factor (weight and position). The discomfort was also a measured variable in this survey and was shown to vary on a scale of 0 to 10 by up to 3 points at maximum discomfort. The results showed that discomfort significantly increased due to increased backpack weight as well as the lowering of the backpack from a standard carrying position.

Recovery from forward loss of balance in young and older adults using the stepping strategy

The purposes of this study were to quantify stability during recovery from forward loss of balance in young and older adults, older single steppers (OSS) and older multiple steppers (OMS), and to identify the biomechanical factors associated with stability during balance recovery. Forward loss of balance was achieved by releasing participants from a static forward lean angle. Participants regained balance by taking one or more rapid steps. Stability was quantified using the margin of stability (MoS), which was computed as the anterio-posterior distance between the forward boundary of the base-of-support and the vertical projection of the velocity adjusted centre of mass. MoS at foot contact and at maximal knee joint flexion angle following foot contact (KJMAX) were smaller in older compared to young adults, and in OMS compared to OSS. Compared to young adults, older adults exhibited a shorter recovery step length, greater trunk flexion angles and exhibited smaller peak knee flexion angles. Trunk flexion angle at foot contact (r=−0.55) and step length (r=0.54) were significantly correlated with MoS at foot contact and together accounted for 51% of the variance in MoS at foot contact. MoS at foot contact was significantly correlated with MoS at KJMAX (r=0.88) and together with peak knee flexion angle during the landing phase (r=0.60) and peak knee extension moment during the landing phase (r=0.47) accounted for 84% of the variance in MoS at KJMAX. Overall findings suggest that stability in the first step is lower for older compared to young adults and for multiple compared to single steppers, and that spatial–temporal, kinematic and kinetic factors are associated with stability during recovery from forward loss of balance.

Ski jumping flight skill analysis based on high-speed video image

Mages of the initial 40 m part of a flight of 120-m ski jumping were recorded by a fixed high-speed video camera in Hakuba Ski Jumping Stadium. The time variations of the forward leaning angle and the ski angle of attack were measured from the video image and the aerodynamic forces were calculated from kinematic data. Some correlations were investigated between the reduced jumping distance Dr, which is an initial speed corrected flight distance, and some key angles and the initial transition time, as well as those between Dr and the aerodynamic force coefficients. Jumping performance is compared between advanced jumpers and beginner jumpers.

Maximum allowable force on a safety harness cable to discriminate a successful from a failed balance recovery

A safety harness system is essential to ensure participant safety in experiments at the threshold of balance recovery where avoiding a fall is not always possible. The purpose of this study was to propose a method to determine the maximum allowable force on a safety harness cable to discriminate a successful from a failed balance recovery. Data from 12 younger adults, who participated in experiments to determine the maximum forward lean angles that participants could be suddenly released from and still recover balance using three different limits on the number of steps, were used. For each participant, the coefficients of an asymptotic exponential regression, between the maximum vertical force on the safety harness cable and the initial lean angle at each trial, were evaluated by a least squares method. A proposed threshold for the maximum allowable vertical force of five force constants ensured that the initial lean angle reached 99% of its steady state value with respect to its initial value. It should thus discriminate well a successful (below the threshold) from a failed (above the threshold) balance recovery. Furthermore, although the amplitude of the horizontal forces should not be neglected in safety harness system designs, the contributions of the medial–lateral and anterior–posterior forces can be neglected in experiments at the threshold of balance recovery. Finally, although our five force constants method could be used, the actual value obtained for the maximum allowable vertical force may vary with other safety harness systems and postural perturbations.

Kinematics of the threshold of balance recovery are not affected by instructions limiting the number of steps in younger adults

To our knowledge, the effect of instructions limiting the number of steps on the threshold of balance recovery has not been quantified, which could make comparisons between studies difficult. We determined the maximum forward lean angles from which 28 younger adults could be suddenly released and still recover balance using: (i) only a single step, (ii) no more than two steps and (iii) no limit on the number of steps. Results showed that instructions limiting the number of steps significantly affected the maximum lean angle but only by a maximum of 1°. At the maximum lean angles, they also significantly affected reaction time, first weight transfer time, first stride velocity, first stride length and second stride velocity but only by 8% on average. However, they did not affect muscular latencies, first stride time, first stride height, first stride width or other second step variables. Moreover, at lean angles larger than their maximum, participants were able to respect the instructions but unable to recover balance without safety harness assistance. Given that the effect was too small to be pertinent, we can state that, between the three limits on the number of steps, not only were the maximum lean angles similar but the first steps were nearly identical and the additional steps did not help to increase the maximum lean angle. Therefore, we have demonstrated that instructions limiting or not limiting the number of steps appear to be equally valid to study the threshold of balance recovery in younger adults.

1811 高速度カメラによるスキージャンパーに働く空気力の測定(S18 スポーツ流体工学,21世紀地球環境革命の機械工学:人・マイクロナノ・エネルギー・環境)

We measured aerodynamic forces acting on real jumping flights in the take-off phase as well as a quasi-steady flight phase. The frame rate was 250 frames/s. It is concluded that the present aerodynamic force data derived from the image analysis are found to be in fair agreement with existing wind tunnel data for the cases of jumping flights in the quasi-steady flight phase. The aerodynamic data in the cases of relatively large forward leaning angle, which is typical in the initial phase of a jumping, could also be obtained. The lift in the take-off phase is relatively larger when compared with the quasi-steady flight phase.

B30 高速度ビデオカメラの画像解析を用いたスキージャンプの空力解析(スキー・リュージュ)

A ski jumping flight analysis was attempted on the basis of the high-speed digital video image taken at Hakuba Ski Jumping Stadium in Japan. Initial 40m of flights of 120-m jumping after take-off were recorded by a fixed high-speed video camera at a frame rate of 250 frames/s. After some corrections, a number of time series data were extracted for the loci of key parts of a jumper such as the waist, the ski boots and the ski tip as well as for key angles representing a jumper posture such as the ski angle and the forward leaning angle. It is demonstrated that the aerodynamic force data during real jumping flights, in particular in the early phase of a flight can be derived from video image.

A17 高速度ビデオカメラの画像解析を基にしたスキージャンプの空力特性の研究(サッカー・流れ)

A ski jumping flight analysis was attempted on the basis of the high-speed digital video image taken at Hakuba Ski Jumping Stadium in Japan. Initial 40m of flights of 120-m jumping after take-off were recorded by a fixed high-speed video camera at a frame rate of 250 frames/s. After some corrections, a number of time series data were extracted for the loci of key parts of a jumper such as the waist, the ski boots and the ski tip as well as for key angles representing a jumper posture such as the ski angle and the forward leaning (ski-body) angle. The primary purpose of the present study is to derive the aerodynamic force data during real jumping flights, in particular in the early phase of a flight.

골프 클럽에 따른 타격자세의 변화

To know the proper impact posture and changes for the various clubs, changes of impact variables according to the change of golf club length was investigated. Swing motions of three male low handicappers including a professional were taken using two high-speed video cameras. Four clubs iron 7, iron 5, iron 3 and driver (wood 1) were selected for this experiment. Three dimensional motion analysis techniques were used to get the kinematical variables. Mathcad and Kwon3D motion analysis program were used to analyze the position, distance and angle data in three dimensions. Major findings of this study were as follows. 1. Lateral position of the head remained more right side of the target up to 3.5cm compared to the setup as the length of the club increased. 2. Left shoulder raised up to 5cm and right shoulder lowered up to 2.5cm compared to setup. The shoulder line opened slightly (maximum 11 degrees) to the target line. 3. Forward lean angle of the trunk decreased up to 4 degrees (more erected) compared to setup. 4. Side lean angle of the trunk increased compared to setup and increased up to 16 degrees as the club length increased. 5. The pelvis moved to the target line direction horizontally and opened up to 31 degrees. Right hip moves laterally to the grip position at the setup. 6. Flexion of the left leg maintained almost constantly but the right leg flexed up to 11 degrees compared to setup. 7. Left arm is straightened but the right arm flexed about 20degrees compared to straight. 8. Center of the shoulders were in front of the knees and toes of the feet. 9. Hands moved to the left (8.7cm), forward (5.7cm) and upward (11.6cm) compared to the setup. This is because of the rotation of pelvis and shoulders. 10. Shaft angle to the ground was smaller than the lie angle of the clubs but it increased close to the lie of the clubs at impact.

Lower Extremity Strength Plays Only a Small Role in Determining the Maximum Recoverable Lean Angle in Older Adults

The purpose of this study was to determine the extent to which measures of lower extremity strength and power contribute to the ability of older men and women to restore postural equilibrium using a single-step recovery following a large postural disturbance. The postural disturbance, which has been used as a surrogate for forward-directed falls, involved a sudden release from a forward-leaning angle. The ability to recover using a single step was evaluated as the maximum recoverable lean angle for 56 healthy older women and men. Maximum voluntary isometric and isokinetic strength was measured for ankle plantarflexion and dorsiflexion, knee flexion and extension, and hip flexion and extension. Discriminant analysis was used to determine the strength measures that best classified participants as members of the highest (n = 14) or lowest (n = 14) quartiles of maximum recoverable lean angle. Those variables were subsequently entered into a regression analysis to characterize the relationship between strength and maximum recoverable lean angle for the entire participant sample. Maximum isokinetic dorsiflexion strength at 90 degrees /s satisfied the criteria of the stepwise discriminant analysis, and correctly classified 82.1% of the participants in the highest or lowest quartiles of maximum recoverable lean angle. The multiple regression procedure, performed on all participants (n = 56) revealed a significant quadratic relationship between maximum isokinetic dorsiflexion strength at 90 degrees /s and maximum recoverable lean angle (R2 = 0.295; p <.001). Lower extremity strength makes a small, but significant contribution to maximum recoverable lean angle. However, because 70% of the shared variability remained unaccounted for, it is suggested that other performance factors, such as coordination, may be of greater importance to performance of this time-critical motor task.

멀리뛰기 8m 선수들의 운동학적 변인 조사를 통한 국내 멀리뛰기 선수들의 8m 뛰기 전략

The purpose of this study was to investigate the techniques used by long jumpers who recorded over 8meters in 2002 Busan Asian Game and 2003 Daegu Universiade. The kinematic characteristics from the last three stride to takeoff at the takeoff board were analyzed such as velocities, heights and angles. The real-life three-dimensional coordinates of 20 body landmarks during each trial were collected using a Direct Linear Transformation procedure. The conclusion were as follows; 1. The height variation who recorded over 8 meters of center of gravity of the jumpers at the last stride was under 8cm. In order to record over 8meters the national long jumpers should have under 10cm height variation. 2. In the approach phase the horizontal velocity of the jumpers should reach to 10.5m/s in last three strides and 9.79m/s in touch down at take off board. 3. The horizontal velocity at take off board must have over 8.51m/s and the vertical velocity must have 3.75m/s simultaneously in order to record 8meters. 4. The forward body lean angle should have over 20degrees with pushing the take off board in forwarding movement. The appropriate body variation range ratio between take off and touch down should be 1.2 vs 1 and the trunk angle at touch down on the board should be close to the erect posture for higher body flight.

Aerodynamic force data for a V-style ski jumping flight

To determine the flight of a ski jumper it is essential to know what aerodynamic forces are acting on the ski jumper. However, few data on this are available, especially for a V-style ski jumping flight. We have measured the aerodynamic forces during the free flight phase for a V-style, as well as a parallel-style, ski jump by employing a full-size model in a wind tunnel. The aerodynamic force data, (drag, lift and pitching moment) were obtained to create an aerodynamic database. These forces are given in polynomial form as functions of the angle of attack, the body-ski (forward leaning) angle and the ski-opening (V-style) angle. Using the polynomial form database is a convenient way of obtaining the aerodynamic forces. Moreover, the wind tunnel was equipped with a ground effect plate to measure the aerodynamic forces during the landing phase. It was found that the difference between the lift with and without the ground effect plate increases with the ski-opening angle. The longitudinal stability in the pitching motion of a body-ski combination is also discussed on the basis of the pitching moment data. This indicates that a stable pitching oscillation of the body-ski combination may arise around an equilibrium point in the angle of attack, the trim angle of attack, during flight.

Skin boot versus knee joint--a sports medicine, orthopedic and biomechanical problem

In contrast to the drop in the incidence of fractures of the lower leg, or tibia, that has been observed in recent years, the incidence of knee injuries has not decreased in skiing and there has been a relative increase in the frequency of severe knee lesions and of the isolated rupture of the cruciate ligament, prompting us to conduct a comprehensive study of the causes of these phenomena. It was found necessary to develop a innovative method of measurement to analyse the patterns of movement and stress to which the knee injuries were attributed. By combining and synchronizing movement analysis, measurement of pressure distribution and measurement of force it became possible to perform a detailed analysis of the forward/backward movement in the ski boot in the laboratory and also on the course by telemetry (part 1). The first two studies were devoted to the forward lean in the ski boot (part 2). Basing on movement analysis and simultaneous determination of pressure distribution along the lower leg, the influence of different ski boot models on the Vorlage, or forward lean, movement of beginners and very experienced skiers was studied. An important result of the laboratory experiment was that whereas a ski boot can be moved without difficulty into a strong forward lean position of the skier by an experienced sportsman, a beginner can only assume a forward lean with 20% less inclination (this being a significant difference). In other words: the range of the freedom of movement in such a boot is markedly limited. The assumption that in ski amateurs such a ski boot would promote skiing in backward lean position, was confirmed by studies on the course (part 3). The pupils became definitely less adept at learning if they were required to wear a stiff ski boot; analysis of movement showed that the forward lean angles were clearly smaller and that the skiers adopted a skiing style in backward lean position that exercised an undue strain on the knees. The other two studies, therefore, focussed mainly on the backward movement in the ski boot. Specifically, the fixed rear spoilers of the modern ski boots are accused of contributing to the rupture of the anterior cruciate ligament if the skier lands on the tail ends of the skis after a jump or fall in backward lean position ('big bump, flat landing' syndrome).(ABSTRACT TRUNCATED AT 400 WORDS)