Larger Ground Reaction Force Research Articles

Understanding the Role of Children's Footwear on Children's Feet and Gait Development: A Systematic Scoping Review.

Children's footwear plays an important role in the healthy growth of foot and gait development during the growing stage. This review aims to synthesize findings of previous investigations and to explore the biomechanical influences of different types of children's footwear on foot health and gait development, thus guiding the healthy and safe growth of children's feet and gait. Online databases were searched for potential eligible articles, including Web of Science, Google Scholar, and PubMed. In total, nineteen articles were identified after searching based on the inclusion requirements. The following five aspects of biomechanical parameters were identified in the literature, including spatiotemporal, kinematics, kinetics, electromyography (EMG), and plantar pressure distribution. Children's footwear can affect their foot health and gait performance. In addition, children's shoes with different flexibility and sole hardness have different effects on children's feet and gait development. Compared to barefoot, the stride length, step length, stride time, and step time were increased, but cadence was decreased with wearing shoes. Furthermore, the support base and toe-off time increased. Double support time and stance time increased, but single support time decreased. The hip, knee, and ankle joints showed increased range of motion in children with the rear-foot strike with larger ground reaction force as well. Future studies may need to evaluate the influence of footwear types on gait performance of children in different age groups. Findings in this study may provide recommendations for suitable footwear types for different ages, achieving the aim of growth and development in a healthy and safe manner.

Comparing tibial accelerations between delivery and follow-through foot strikes in cricket pace bowling

ABSTRACT Foot strikes of the pace-bowling delivery stride produce large ground reaction forces, which may be linked to injury, yet the biomechanics of the follow-through are unknown. This study assessed tibial accelerations across the delivery and follow-through foot strikes in pace bowlers and evaluated relationships between these measures and five common pace-bowling intensity metrics. Fifteen sub-elite male pace bowlers performed deliveries at warm-up, match, and maximal intensities. Tibial accelerations were measured using tibial-mounted inertial measurement units and recorded at back- and front-foot initial and re-contacts. A trunk-worn global navigation satellite system unit measured PlayerLoad™, run-up speed, and distance. Ball speed and perceived exertion measures were also recorded. A linear mixed model showed statistical significance of prescribed intensities (p < .001) and foot strike for tibial acceleration (p < .001). Tibial accelerations showed positive increases with changes in prescribed intensity (p < .05). The greatest magnitude of tibial acceleration was found at back foot re-contact (mean ± SD; 1139 ± 319 m/s2). Repeated-measures correlations of tibial acceleration between foot contacts were weak (r = 0.2–0.4). The greatest magnitude of tibial acceleration reported at back foot re-contact may have implications for injury incidence, representing an important avenue for future pace bowling research.

Physiological and biomechanical comparison between electrically assisted bicycles and motorbikes during simulated mail delivery

Electrically assisted bicycles (EABs) and motorbikes were compared in terms of energy expenditure, internal and external forces, and technique when delivering mail with different loads at different distances from the mailbox. Twenty-two postal workers performed two simulated postal tasks (foot placement [close vs. far] and delivery, and simulated mail delivery circuit) while carrying 0 and 32 kg. Independent of mail load, delivering mail with EABs was classified as moderate intensity and resulted in 33% higher energy expenditure when compared to motorbikes. Ground reaction forces were larger (7–25%) for EAB when compared to motorbike. Larger ground reaction forces were observed when both EABs and motorbikes were positioned further from the mailbox (5–23%). Using EABs during mail delivery has potential to result in numerous health benefits that are associated with moderate intensity physical activity, but can lead to larger external forces when compared to motorbikes. Practitioner summary: In order to compare electrically assisted bicycles (EAB) and motorbikes, postal workers performed simulated deliveries in the laboratory whilst measurements of energy expenditure, body loads and movement patters were undertaken. Body loads and energy expenditure were larger using EAB, which result in health benefits associated with moderate intensity exercise. Abbreviations: EAB: electrically assisted bicycles; CI: confidence interval; UHEC: University Human Ethics Committee; MB: motorbike;SH: seat height; SF: seat to floor distance; VO2: oxygen uptake; VCO2: exhaled carbon dioxide; RER: respiratory exchangeratio; TTL signal: Transistor-Transistor Logic; MET: metabolic equivalent; 3D: three-dimensional; IIR: infinite impulse response; Hz:Hertz; N: Newtons; ROM: range of motion; SD: standard deviation; p: significance level; d: Cohen effect sizes

Effect of total-contact orthosis on medial longitudinal arch and lower extremities in flexible flatfoot subjects during walking.

Total-contact orthosis (TCO) is one kind of foot orthosis (FO) that is used to adjust biomechanics in flexible flatfoot. To determine the effects of a TCO on the MLA moment, MLA deformation angle and lower limb biomechanics. Cross-sectional study. Seven-flatfoot and thirteen-normal foot subjects were recruited by footprint and radiographs. The biomechanics of subjects with normal foot (NF), flatfoot with shoe only (FWOT) and flatfoot with TCO (FWT) were collected in a 3D motion analysis laboratory and force plates. The MLA and lower limb biomechanics in each condition during specific sub-phases of stance were analyzed. The NF had larger MLA eversion moment after shod walking ( p = 0.001). The FWT condition compared with the FWOT condition had a significantly larger peak MLA upward moment ( p = 0.035) during pre-swing, larger peak knee external rotation angle ( p = 0.040) during mid stance, smaller peak knee extension moment during terminal stance ( p = 0.035) and a larger ground reaction force in the anterior-posterior direction during early stance ( p < 0.05). Our study found positive effects from the customized TCOs which included an increased TCO angle that led to a decreased peak MLA moment in the frontal plane in flexible flatfoot subjects during walking. Clinical relevance Lower limb biomechanics is different from normal in subjects with flexible flatfoot. The design of a TCO affects MLA, ankle and knee biomechanics and may be used to clinically correct biomechanical changes in flexible flatfoot.

Manipulating Trunk and Whole Body Posture during Running Influences Ground Reaction Forces

Large vertical ground reaction (vGRF) and braking forces have been cited as possible contributors to lower extremity overuse injuries in runners. It is unknown whether these variables can be altered via running form manipulations to decrease injury risk. PURPOSE: To determine if altering trunk and whole body posture during running leads to differences in peak vGRF and peak braking and propulsive forces. METHODS: Fourteen males and fifteen females (age 26.2±0.25 years, height 1.7±0.32 m, weight 67.7±0.37 kg) who were healthy, active, and pain/injury-free volunteered. Participants ran at a self-selected speed across a 15m runway under three conditions: normal self-selected running form (NR), increased trunk flexion (TF), and whole body inclination (WBI). Participants were instructed to bend at the hips (TF) and to lean forward over the ankles (WBI). Five successful trials for each condition were recorded using 3D motion capture and an AMTI force platform. Data was analyzed via 1-way repeated measures ANOVA with Sidak pairwise comparisons for each dependent variable. Statistical significance was set at p<0.05. RESULTS: A significant main effects were found for peak vGRF (p=0.05) and a trend was found for peak propulsive forces (p=0.056). Peak vGRF was significantly less in the TF condition (22.44±2.17 N/kg) than in the NR (22.98±2.01 N/kg, p=0.01) or WBI (22.91±2.55 N/kg, p=0.04) conditions. Max propulsive force was significantly greater for WBI (2.65±0.47 N/kg) than TF (2.54±2.55 N/kg, p=0.006), but there was no significant difference between WBI and NR (p=0.943). There were no significant differences in peak braking forces between conditions (p=0.119). CONCLUSIONS: WBI during running may reduce energy expenditure via anterior displacement of the center of mass relative to the pelvis, resulting in increased propulsive forces. Running with increased TF may reduce injury risk by decreasing peak vGRF. Future studies training TF and/or WBI seem warranted as a form of running gait retraining.

가슴 착용형 보행 재활로봇의 개발

This paper describes the development of a chest-wearable robot that can efficiently perform self walking rehabilitation without a helper. The features of the developed robot are divided into three parts. First, as a mechanical characteristic, the conventional elbow crutch is attached at the forearm. However, the proposed robot is attached to the patient's chest, enabling them to feel free to use their hands and eliminate the burden of the arms. Second, as a characteristic of the driving algorithm, pressure sensors attached to the chest automatically perceive the patient's walking intention and move the robot-leg thereafter. Also, for safety, it stops operating when an obstacle is found in front of the patient by using ultrasonic sensors and generates a beeping sound. Finally, by using the scotch yoke mechanism, supporting legs are moved up and down using a rotary servo motor without excessive torque that is generated by large ground reaction forces. We showed that the developed robot can effectively perform self walking rehabilitation through walking experiments, and its performance was verified using Electromyograph (EMG) sensors.

Independent control of force and timing symmetry in dynamic standing balance: Implications for rehabilitation of hemiparetic stroke patients

The extent to which force and timing are independently controlled has aroused research interest. The present study aims to examine the relationship between force and timing symmetrical performances during repetitive body weight shifting. Eight hemiparetic stroke patients and eight age- and gender-matched controls were required to repetitively shift weight from one leg to the other while standing with each foot on a separate force plate. Instructions emphasised symmetry of weight transfer in each direction. No knowledge of result feedback was given. The ratio of the vertical ground reaction forces between the legs (force symmetry) was contrasted with the ratio of the intervals between leftward and rightward movements (timing symmetry). The patients showed more asymmetric and variable performances than the controls. Timing symmetry was more variable than force symmetry. In both groups, force and timing symmetry were uncorrelated. Autocovariance estimates revealed persistent alternation of large and small ground reaction forces, whereas a tendency for alternation between short and long intervals rapidly damped to zero. In conclusion, both healthy and stroke participants exhibit independent control of the force and timing symmetry under the task of natural weight shifting. This may explain the weakness of current balance retraining paradigms based on visual biofeedback, in which an emphasis on force symmetry fails to help timing performance in dynamic tasks.

Investigation of Spinal Posture Signatures and Ground Reaction Forces During Landing in Elite Female Gymnasts

The link between static and dynamic landing lumbar postures, when gymnasts are exposed to large ground reaction forces, has not been established. This investigation aimed to (a) determine if a relationship exists between sagittal static and dynamic landing lumbar spine angles at peak ground reaction force (GRF) and (b) quantify how close to end-range postures the gymnasts were at landing peak GRF. Twenty-one female gymnasts' upper and lower lumbar spine angles were recorded: statically in sitting and standing, during landing of three gymnastic skills, and during active end-range lumbar flexion. Pearson's correlations were used to investigate relationships between the angles in different postures. Significant correlations (r = .77-.89, p <.01) were found between all the static/dynamic postures in the lower lumbar spine angle, while fewer and less significant upper lumbar spine correlations were reported. Thirty percent of gymnasts landed a backsault with their lower lumbar spine flexed beyond their active end-range while experiencing GRF 6.8-13.3 times their body weight. These results inform low back pain prevention and management strategies in this population and highlight areas for future research.

Measurements of Tibiofemoral Kinematics during Soft and Stiff Drop Landings Using Biplane Fluoroscopy

Background Previous laboratory studies of landing have defined landing techniques in terms of soft or stiff landings according to the degree of maximal knee flexion angle attained during the landing phase and the relative magnitude of the ground-reaction force. Current anterior cruciate ligament injury prevention programs are instructing athletes to land softly to avoid excessive strain on the anterior cruciate ligament. Purpose This study was undertaken to measure, describe, and compare tibiofemoral rotations and translations of soft and stiff landings in healthy individuals using biplane fluoroscopy. Study Design Controlled laboratory study. Methods The in vivo, lower extremity, 3-dimensional knee kinematics of 16 healthy adults (6 male and 10 female) instructed to land softly and stiffly in different trials were collected in biplane fluoroscopy as they performed the landing from a height of 40 cm. Results Average and maximum relative anterior tibial translation (average, 2.8 ± 1.2 mm vs 3.0 ± 1.4 mm; maximum, 4.7 ± 1.6 mm vs 4.4 ± 0.8 mm), internal/external rotation (average, 3.7° ± 5.1° vs 2.7° ± 4.3°; maximum, 5.6° ± 5.5° vs 4.9° ± 4.7°), and varus/valgus (average, 0.2° ± 1.2° vs 0.2° ± 1.0°; maximum, 1.7° ± 1.2° vs 1.6° ± 0.9°) were all similar between soft and stiff landings, respectively. The peak vertical ground-reaction force was significantly larger for stiff landings than for soft landings (2.60 ± 1.32 body weight vs 1.63 ± 0.73; P < .001). The knee flexion angle total range of motion from the minimum angle at contact to the maximum angle at peak knee flexion was significantly greater for soft landings than for stiff (55.4° ± 8.8° vs 36.8° ± 11.1°; P < .01). Conclusion Stiff landings, as defined by significantly lower knee flexion angles and significantly greater peak ground-reaction forces, do not result in larger amounts of anterior tibial translation or knee rotation in either varus/valgus or internal/external rotation in healthy individuals. Clinical Relevance In healthy knees, the musculature and soft tissues of the knee are able to maintain translations and rotations within a small, safe range during controlled landing tasks of differing demand. The knee kinematics of this healthy population will serve as a comparison for injured knees in future studies. It should be stressed that because the authors did not compare how the loads were distributed over the soft tissues of the knee between the 2 landing styles, the larger ground-reaction forces and more extended knee position observed during stiff landings should still be considered dangerous to the anterior cruciate ligament and other structures of the lower extremities, particularly in competitive settings where movements are often unanticipated.

The effect of choice reaction task on impact of single-leg landing

This study aimed to investigate attentional demand during single-leg landing after a jump. The experiment was set up as dual-task test. Twelve healthy male participants were instructed to make a two-leg jump with right-leg landing as softly as possible. The flight time of the jump was set to 300ms through sufficient practice. As a cognitive task, the participants were asked to push the right or left custom-made button as soon as a go-signal was presented. The timing when the go-signal presented varied from 0 to 300ms from the take-off. Catch trials in which the go-signal was not presented were randomly inserted. The results showed that the maximum vertical ground reaction force after touchdown was greater under the dual-task condition than in the single-task condition. Increase in the maximum vertical ground reaction force was consistent regardless of the timing of presenting the go-signal, and the same effect was observed in the catch trials. These results indicate that the effect of dual tasking was caused by attentional allocation to the choice reaction time task. Athletes may be exposed a large ground reaction forces during landing while performing cognitive tasks.

Ankle-Dorsiflexion Range of Motion and Landing Biomechanics

A smaller amount of ankle-dorsiflexion displacement during landing is associated with less knee-flexion displacement and greater ground reaction forces, and greater ground reaction forces are associated with greater knee-valgus displacement. Additionally, restricted dorsiflexion range of motion (ROM) is associated with greater knee-valgus displacement during landing and squatting tasks. Because large ground reaction forces and valgus displacement and limited knee-flexion displacement during landing are anterior cruciate ligament (ACL) injury risk factors, dorsiflexion ROM restrictions may be associated with a greater risk of ACL injury. However, it is unclear whether clinical measures of dorsiflexion ROM are associated with landing biomechanics. To evaluate relationships between dorsiflexion ROM and landing biomechanics. Descriptive laboratory study. Research laboratory. Thirty-five healthy, physically active volunteers. Passive dorsiflexion ROM was assessed under extended-knee and flexed-knee conditions. Landing biomechanics were assessed via an optical motion-capture system interfaced with a force plate. Dorsiflexion ROM was measured in degrees using goniometry. Knee-flexion and knee-valgus displacements and vertical and posterior ground reaction forces were calculated during the landing task. Simple correlations were used to evaluate relationships between dorsiflexion ROM and each biomechanical variable. Significant correlations were noted between extended-knee dorsiflexion ROM and knee-flexion displacement (r = 0.464, P = .029) and vertical (r = -0.411, P = .014) and posterior (r = -0.412, P = .014) ground reaction forces. All correlations for flexed-knee dorsiflexion ROM and knee-valgus displacement were nonsignificant. Greater dorsiflexion ROM was associated with greater knee-flexion displacement and smaller ground reaction forces during landing, thus inducing a landing posture consistent with reduced ACL injury risk and limiting the forces the lower extremity must absorb. These findings suggest that clinical techniques to increase plantar-flexor extensibility and dorsiflexion ROM may be important additions to ACL injury-prevention programs.

Effects of a Knee Extension Constraint Brace on Lower Extremity Movements after ACL Reconstruction

Patients have high reinjury rates after ACL reconstruction. Small knee flexion angles and large peak posterior ground reaction forces in landing tasks increase ACL loading. We determined the effects of a knee extension constraint brace on knee flexion angle, peak posterior ground reaction force, and movement speed in functional activities of patients after ACL reconstruction. Six male and six female patients 3.5 to 6.5 months after ACL reconstruction participated in the study. Three-dimensional videographic and force plate data were collected while patients performed level walking, jogging, and stair descent wearing a knee extension constraint brace, wearing a nonconstraint brace, and not wearing a knee brace. Knee flexion angle at initial foot contact with the ground, peak posterior ground reaction force, and movement speed were compared across brace conditions and between genders. Wearing the knee extension constraint brace increased the knee flexion angle at initial foot contact for each activity when compared with the other two brace conditions. Wearing the knee extension constraint brace also decreased peak posterior ground reaction force during walking but not during jogging and stair descent. Although the knee extension constraint brace did not consistently reduce the peak posterior ground reaction force in all functional activities, it consistently increased knee flexion angle and should reduce ACL loading as suggested by previous studies. These results suggest the knee extension constraint brace has potential as a rehabilitation tool to alter lower extremity movement patterns of patients after ACL reconstruction to address high reinjury rates.

Muscles do more positive than negative work in human locomotion.

Muscle work during level walking and ascent and descent ramp and stairway walking was assessed in order to explore the proposition that muscles perform more positive than negative work during these locomotion tasks. Thirty four healthy human adults were tested while maintaining a constant average walking velocity in the five gait conditions. Ground reaction force and sagittal plane kinematic data were obtained during the stance phases of these gaits and used in inverse dynamic analyses to calculate joint torques and powers at the hip, knee and ankle. Muscle work was derived as the area under the joint power vs time curves and was partitioned into positive, negative and net components. Dependent t-tests were used to compare positive and negative work in level walking and net joint work between ascent and descent gaits on the ramp and stairs (P<0.010). Total negative and positive work in level walking was -34 J and 50 J, respectively, with the difference in magnitude being statistically significant (P<0.001). Level walking was therefore performed with 16 J of net positive muscle work per step. The magnitude of the net work in ramp ascent was 25% greater than the magnitude of net work in ramp descent (89 vs -71 J m(-1), P<0.010). Similarly, the magnitude of the net work in stair ascent was 43% greater than the magnitude of net work in stair descent (107 vs -75 J step(-1), P<0.000). We identified three potential causes for the reduced negative vs positive work in these locomotion tasks: (1) the larger magnitude of the accelerations induced by the larger ground reaction forces in descending compared to ascending gaits elicited greater energy dissipation in non-muscular tissues, (2) the ground reaction force vector was directed closer to the joint centers in ramp and stair descent compared to ascent, which reduced the load on the muscular tissues and their energy dissipating response, and (3) despite the need to produce negative muscle work in descending gaits, both ramp and stair descent also had positive muscle work to propel the lower extremity upward and forward into the swing phase movement trajectory. We used these data to formulate two novel hypotheses about human locomotion. First, level walking requires muscles to generate a net positive amount of work per gait cycle to overcome energy losses by other tissues. Second, skeletal muscles generate more mechanical energy in gait tasks that raise the center of mass compared to the mechanical energy they dissipate in gait tasks that lower the center of mass, despite equivalent changes in total mechanical energy.

Quadriceps Inhibition Induced by an Experimental Knee Joint Effusion Affects Knee Joint Mechanics during a Single-Legged Drop Landing

Background Arthrogenic quadriceps muscle inhibition accompanies knee joint effusion and impedes rehabilitation after knee joint injury. Hypothesis We hypothesized that an experimentally induced knee joint effusion would cause arthrogenic quadriceps muscle inhibition and lead to increased ground reaction forces, as well as sagittal plane knee angles and moments, during a single-legged drop landing. Study Design Controlled laboratory study. Methods Nine subjects (4 women and 5 men) underwent 4 conditions (no effusion, lidocaine injection, “low” effusion [30 mL], and “high” effusion [60 mL]) and then performed a single-legged drop landing. Lower extremity muscle activity, peak sagittal plane knee flexion angles, net sagittal plane knee moments, and peak ground reaction forces were measured. Results Vastus medialis and lateralis activity were decreased during the low and high effusion conditions (P < .05). However, increases in peak ground reaction forces and decreases in peak knee flexion angle and net knee extension moments occurred only during the high effusion condition (P < .05). Conclusions Knee joint effusion induced quadriceps inhibition and altered knee joint mechanics during a landing task. Subjects landed with larger ground reaction forces and in greater knee extension, thereby suggesting that more force will be transferred to the knee joint and its passive restraints when quadriceps inhibition is present. Clinical Relevance Knee joint effusion results in arthrogenic quadriceps muscle inhibition, increasing loading about the knee that may potentially increase the risk of future knee joint trauma or degeneration.

The Role of Biomechanics in Maximising Distance and Accuracy of Golf Shots

Golf biomechanics applies the principles and technique of mechanics to the structure and function of the golfer in an effort to improve golf technique and performance. A common recommendation for technical correction is maintaining a single fixed centre hub of rotation with a two-lever one-hinge moment arm to impart force on the ball. The primary and secondary spinal angles are important for conservation of angular momentum using the kinetic link principle to generate high club-head velocity. When the golfer wants to maximise the distance of their drives, relatively large ground reaction forces (GRF) need to be produced. However, during the backswing, a greater proportion of the GRF will be observed on the back foot, with transfer of the GRF on to the front foot during the downswing/acceleration phase. Rapidly stretching hip, trunk and upper limb muscles during the backswing, maximising the X-factor early in the downswing, and uncocking the wrists when the lead arm is about 30 degrees below the horizontal will take advantage of the summation of force principle. This will help generate large angular velocity of the club head, and ultimately ball displacement. Physical conditioning will help to recruit the muscles in the correct sequence and to optimum effect. To maximise the accuracy of chipping and putting shots, the golfer should produce a lower grip on the club and a slower/shorter backswing. Consistent patterns of shoulder and wrist movements and temporal patterning result in successful chip shots. Qualitative and quantitative methods are used to biomechanically assess golf techniques. Two- and three-dimensional videography, force plate analysis and electromyography techniques have been employed. The common golf biomechanics principles necessary to understand golf technique are stability, Newton's laws of motion (inertia, acceleration, action reaction), lever arms, conservation of angular momentum, projectiles, the kinetic link principle and the stretch-shorten cycle. Biomechanics has a role in maximising the distance and accuracy of all golf shots (swing and putting) by providing both qualitative and quantitative evidence of body angles, joint forces and muscle activity patterns. The quantitative biomechanical data needs to be interpreted by the biomechanist and translated into coaching points for golf professionals and coaches. An understanding of correct technique will help the sports medicine practitioner provide sound technical advice and should help reduce the risk of golfing injury.

Relation between ankle joint dynamics and patellar tendinopathy in elite volleyball players.

Ankle joint complex dynamics developed during volleyball spike jumps take-offs and landings were quantified to assess potential relations between these joint dynamics and patellar tendinopathy. Three-dimensional kinematic data provided information about movements of the lower limbs, while the kinetic data permitted analysis of ground reaction forces as players took-off and landed from full-speed spike jumps. Simulated volleyball court with net in a biomechanics research laboratory. 10 members of the Canadian Men's National Volleyball Team. From history and physical examination, 3 of the 10 players had patellar tendon pain associated with activity and were diagnosed with patellar tendinopathy at the time of the study. Investigators were blinded about the injury status of the players. None. Three-dimensional kinematics and joint moments of the ankle, knee, and hip joints. Our analysis revealed that maximal external tibial rotation occurred at or near maximal dorsiflexion while maximal internal tibial rotation coincided with maximal plantarflexion. The plantarflexion moment was 3 to 10 times greater than all the other moments measured, with the maximal plantarflexor moment being calculated at 0.4 BWm (360 Nm). In blinded logistic regression analyses, we found one of the dynamics variables (inversion moment during the landing of the spike jump) was a significant predictor of patellar tendinopathy. Coupling the results of the current analysis of ankle joint complex dynamics with previously reported results of knee joint dynamics related to patellar tendinopathy suggests that a cluster of variables linked to patellar tendinopathy includes: high ankle inversion-eversion moments, high external tibial rotation and plantarflexion moments, large vertical ground reaction forces, and high rate of knee extensor moment development.

Visual and non-visual control of landing movements in humans.

1. The role of vision in controlling leg muscle activation in landing from a drop was investigated. Subjects (n = 8) performed 10 drops from four heights (0.2, 0.4, 0.6 and 0.8 m) with and without vision. Drop height was maintained constant throughout each block of trials to allow adaptation. The aim of the study was to assess the extent to which proprioceptive and vestibular information could substitute for the lack of vision in adapting landing movements to different heights. 2. At the final stages of the movement, subjects experienced similar peak centre of body mass (CM) displacements and joint rotations, regardless of the availability of vision. This implies that subjects were able to adapt the control of landing to different heights. The amplitude and timing of electromyographic signals from the leg muscles scaled to drop height in a similar fashion with and without vision. 3. However, variables measured throughout the execution of the movement indicated important differences. Without vision, landings were characterised by 10 % larger ground reaction forces, 10 % smaller knee joint rotations, different time lags between peak joint rotations, and more variable ground reaction forces and times to peak CM displacement. 4. We conclude that non-visual sensory information (a) could not fully compensate for the lack of continuous visual feedback and (b) this non-visual information was used to reorganise the motor output. These results suggest that vision is important for the very accurate timing of muscle activity onset and the kinematics of landing.

Measures to prevent cricket injuries: an overview.

Cricket is a major international sport, generally played in British Common-wealth nations. Although strictly a non-contact sport, injuries in cricket can result in a number of ways. In high level cricket, overuse injuries are common and related to the physical demands of the sport, particularly in the delivery of the ball. The bowling action involves repetitive twisting, extension and rotation of the trunk at the same time as absorption of large ground reaction forces over a short period of time. These movements, if performed incorrectly or too frequently, can lead to overuse injuries of the back, particularly in elite and high level cricketers. Cross-sectional studies have demonstrated that spinal overuse injuries occur more frequently to cricketers adopting a mixed bowling action than to those who favour a front- or side-on bowling technique. Strategies to ensure that cricketers do not adopt the mixed action or bowl too fast for extended periods can prevent these back injuries. Injuries resulting from impacts, generally from the cricket ball, can also occur and are more common during low level competition or informal participation. Because of the potential severity of these impacts, a range of protective equipment ranging from body padding to gloves and face protectors are now common features of standard cricket equipment. Although a number of measures to prevent cricket injuries have been widely suggested in the literature, there have been very few studies that have formally assessed their effectiveness in preventing injury. Further research is needed to gain a greater understanding of the biomechanics of cricket actions, the mechanisms of resultant injuries and the role of various risk factors in injury causation.

Effect of landing stiffness on joint kinetics and energetics in the lower extremity

Ground reaction forces (GRF), joint positions, joint moments, and muscle powers in the lower extremity were compared between soft and stiff landings from a vertical fall of 59 cm. Soft and stiff landings had less than and greater than 90 degrees of knee flexion after floor contact. Ten trials of sagittal plane film and GRF data, sampled at 100 and 1000 Hz, were obtained from each of eight female athletes and two landing conditions. Inverse dynamics were performed on these data to obtain the moments and powers during descent (free fall) and floor contact phases. Angular impulse and work values were calculated from these curves, and the conditions were compared with a correlated t-test. Soft and stiff landings averaged 117 and 77 degrees of knee flexion. Larger hip extensor (0.010 vs 0.019 N.m.s.kg-1; P less than 0.01) and knee flexor (-0.010 vs -0.013 N.m.s.kg-1; P less than 0.01) moments were observed during descent in the stiff landing, which produced a more erect body posture and a flexed knee position at impact. The shapes of the GRF, moment, and power curves were identical between landings. The stiff landing had larger GRFs, but only the ankle plantarflexors produced a larger moment (0.185 vs 0.232 N.m.s.kg-1; P less than 0.01) in this condition. The hip and knee muscles absorbed more energy in the soft landing (hip, -0.60 vs -0.39 W.kg-1; P less than 0.01; knee, -0.89 vs -0.61 W.kg-1; P less than 0.01), while the ankle muscles absorbed more in the stiff landing (-0.88 vs -1.00 W.kg-1; P less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)