Higher Vertical Ground Reaction Force Research Articles

Landing from different heights: Biomechanical and neuromuscular strategies in trained gymnasts and untrained prepubescent girls

The purpose of this study was to examine the biomechanics of the lower limb, during landing in female prepubertal gymnasts and prepubertal untrained girls, aged 9–12years. Ten healthy participants were included in each group and performed five landings from 20, 40, and 60cm. Kinematics, ground reaction forces (GRF) and electromyogram (EMG) from the lateral gastrocnemius, tibialis anterior, and vastus lateralis are presented. Gymnasts had higher vertical GRF and shorter braking phase during landing. Compared to untrained girls, gymnasts exhibited for all examined drop heights more knee flexion before and at ground contact, but less knee flexion at maximum knee flexion position. Especially when increasing drop heights the gymnasts activated their examined muscles earlier, and generally they had higher pre- and post landing EMG amplitudes normalized to the peak EMG at 60cm drop height. Furthermore, gymnasts had lower antagonist EMG for the tibialis anterior compared to untrained girls, especially when landing from higher heights. It is concluded that the landing strategy preferred by gymnasts is influenced by long-term and specialized training and induces a stiffer landing pattern. This could have implications in injury prevention, which requires further investigation.

Gait ground reaction force characteristics of low back pain patients with pronated foot and able-bodied individuals with and without foot pronation

The link between gait parameters and foot abnormalities in association with low back pain is not well understood. The objective of this study was to investigate the effects of excessive foot pronation as well as the association of LBP with excessive foot pronation on the GRF components during shod walking. MethodsForty-five subjects were equally divided into a control group, a group of subjects with pronated feet only, and another group with pronated feet and LBP. Ground reaction forces were analyzed during shod walking. ResultsFoot pronation without low back pain was associated with increased lateral-medial ground reaction force, impulse, and time to peak of all reaction forces in heel contact phase (p<0.03). In low back pain patients with pronated foot, greater vertical reaction forces (p=0.001) and loading rate, and time to peak on propulsion force were observed compared to pronated foot without low back pain group. Impulse in posterior-anterior reaction force was smaller in the able-bodied group with normal foot than in the other groups (p<0.05). Positive peak of free moments of the LBP group was significantly greater than that in other groups (p<0.05). In conclusion, foot pronation alone was not associated with elevated vertical ground reaction forces. While, low back pain patients with foot pronation displayed higher vertical ground reaction force as well as higher loading rate. Present results reveal that gait ground reaction force components in low back pain patients with pronated foot may have clinical values on the prognosis and rehabilitation of mechanical LBP patients.

Alterations to Landing Technique and Patellar Tendon Loading in Response to Fatigue

Fatigue may contribute to knee joint injuries, such as patellar tendinopathy, by increasing joint loading and altering lower limb landing technique, which in turn may increase tissue loading. This study aimed to investigate the effect of lower limb muscle fatigue on the landing technique and patellar tendon loads generated during the horizontal and vertical landing phases of a stop-jump task. It was hypothesized that muscle fatigue would increase patellar tendon loading and alter the landing technique displayed during the horizontal, but not the vertical, landing phase of the stop-jump task. Sixteen men, recruited from team sports involving repetitive landing, performed repeated trials of a stop-jump task. During each trial, the participants' ground reaction forces and electromyographic activity of seven lower limb muscles were recorded, three-dimensional kinematics measured, and peak patellar tendon force (FPT) calculated. When fatigued, participants generated a significantly lower FPT and FPT loading rate, despite a higher vertical ground reaction force (FV) and FV loading rate, during the horizontal landing phase of the stop-jump task. During the vertical landing phase, participants displayed only minor changes to the kinetics and kinematics of their landing in response to fatigue, although fatigue caused substantial alterations to their lower limb muscle activation patterns during landing. During the horizontal landing phase of the stop-jump task, participants decreased their patellar tendon load when they were fatigued by altering their lower limb landing technique, including a reduced net knee joint extension moment associated with less knee and hip flexion. This decrease in patellar tendon loading when fatigued may be an inherent protective strategy to potentially decrease loading of the tendon during repetitive landing.

Effects of overweight and obese body mass on motor planning and motor skills during obstacle crossing in children

Little is known about how obesity relates to motor planning and skills during functional tasks. We collected 3-D kinematics and kinetics as normal weight (n=10) and overweight/obese (n=12) children walked on flat ground and as they crossed low, medium, and high obstacles. We investigated if motor planning and motor skill impairments were evident during obstacle crossing. Baseline conditions showed no group differences (all ps>.05). Increased toe clearance was found on low obstacles (p=.01) for the overweight/obese group and on high obstacles (p=.01) for the normal weight group. With the crossing leg, the overweight/obese group had larger hip abduction angles (p=.01) and medial ground reaction forces (p=.006) on high obstacles and high anterior ground reaction forces on low obstacles (p=.001). With the trailing leg, overweight/obese children had higher vertical ground reaction forces on high obstacles (p=.005) and higher knee angles (p=.01) and anterior acceleration in the center of mass (p=.01) on low obstacles. These findings suggest that differences in motor planning and skills in overweight/obese children may be more apparent during functional activities.

The mechanics of acceleration and deceleration in primate quadrupeds:implications for primate locomotor evolution.

The ability to accelerate and decelerate is critical for animal survival and may be a selective priority determining body form in mammals. Studies of quadrupedal mammals have shown that pitching moments around an animal's center of mass (COM) limit maximum acceleration and deceleration and that the ability to resist such moments is influenced by limb length, COM position, and the ability to shift weight to the fore‐ or hindquarters. Primates have relatively long, gracile forelimbs and have higher vertical ground reaction forces on their hindlimbs than forelimbs, unlike most mammals. Primates should then differ from other mammals in that they will be effective in producing acceleration but limited in producing deceleration. This hypothesis was tested with lateral video and single limb forces recorded during accelerating and decelerating steps for two strepsirhine primate species: Eulemur fulvus and Lemur catta. Results show that primates are limited in maximum acceleration and deceleration by their limb length and that they adopt specific mechanical solutions including loading the trailing limb relatively more, initiating decelerations with the hindlimbs rather than the forelimbs, and increasing contact time to limit instantaneous vertical force increases. These solutions are consistent with other unusual primate gait characters associated with adaptations to arboreal locomotion.

Leg stiffness of sprinters using running-specific prostheses

Running-specific prostheses (RSF) are designed to replicate the spring-like nature of biological legs (bioL) during running. However, it is not clear how these devices affect whole leg stiffness characteristics or running dynamics over a range of speeds. We used a simple spring-mass model to examine running mechanics across a range of speeds, in unilateral and bilateral transtibial amputees and performance-matched controls. We found significant differences between the affected leg (AL) of unilateral amputees and both ALs of bilateral amputees compared with the bioL of non-amputees for nearly every variable measured. Leg stiffness remained constant or increased with speed in bioL, but decreased with speed in legs with RSPs. The decrease in leg stiffness in legs with RSPs was mainly owing to a combination of lower peak ground reaction forces and increased leg compression with increasing speeds. Leg stiffness is an important parameter affecting contact time and the force exerted on the ground. It is likely that the fixed stiffness of the prosthesis coupled with differences in the limb posture required to run with the prosthesis limits the ability to modulate whole leg stiffness and the ability to apply high vertical ground reaction forces during sprinting.

Centre of pressure output in a kinematically driven finite element footstrike model

A dynamic finite element model of a shod footstrike was developed and driven with six degree of freedom kinematic boundary conditions calculated from a motion capture running trial. Linear tetrahedral elements were used to mesh the midsole and outsole of the footwear with material models determined from appropriate mechanical tests. The model was validated by comparison to experimental high speed video footage and vertical ground reaction force. 92% of model centre of pressure (COP) output readings were found to fall within an experimental error tolerance of ± 20mm. To investigate the sensitivity of COP output location to the footwear's initial orientation the position of the floor instance was altered by translating ± 2mm vertically and rotating ± 1° about the sagittal and frontal axes. In comparison to the base model, COP output was found to be most sensitive to rotation about the sagittal axis with a maximum change in location of 69mm. Output location was altered by up to 26mm and 19mm for vertical translation and rotation about the frontal axis respectively. These values are significant and draw into question the validity of the loading conditions that can be applied with a kinematically driven footstrike model.

A comparison of gait biomechanics and metabolic requirements of overground and treadmill walking in people with stroke

Background Comparisons of treadmill and overground walking following stroke indicate that symmetry in temporal-distance measures is better on the treadmill suggestive of better gait economy. We examined this issue by examining the kinematic, kinetic and metabolic demands associated with overground and treadmill walking at matched speeds and also explored the effect of increasing treadmill speed. Methods Ten people with hemiparesis walked overground at their preferred speed which was matched on the treadmill. Belt speed was then increased 10% and 20% above preferred speed. Temporal-distance outcomes, angular kinematics and vertical ground reaction forces were recorded during steady state (stable heart rate and oxygen uptake). Findings Step and stance times were longer when walking overground but the degree of symmetry was comparable for both surfaces. In contrast kinematic data revealed significant interlimb asymmetry with respect to all lower limb joint excursions during overground walking accompanied by higher vertical ground reaction forces at push-off. The metabolic demands, however, were lower when walking overground than on the treadmill. Increasing the belt speed increased angular displacements and the vertical forces associated with both limbs such that symmetry remained unchanged. Metabolic demands increased significantly. Interpretation People with stroke adopt a more symmetrical kinematic walking pattern on the treadmill which is maintained at faster belt speeds. Surprisingly, at matched speed the metabolic cost was significantly higher with treadmill walking. We suggest further research to explore whether an increased reliance on the hip musculature to compensate lower push-off forces could explain the higher the energy cost.

Ground reaction forces and kinematics of plant leg position during instep kicking in male and female collegiate soccer players

The players' ability to achieve the greatest distance in kicking is determined by their efficiency in transferring kinetic energy from the body to the ball. The purpose of this study was to compare the kinetics and kinematics of the plant leg position between male and female collegiate soccer players during instep kicking. Twenty-three soccer players (11 males and 12 females) were filmed in both the sagittal and posterior views while performing a maximal instep kick. Plant leg kinetic data were also collected using an AMTI 1000 force platform. There were no significant differences between the sexes in plant leg position, but females had significantly greater trunk lean, plant leg angle, and medial-lateral ground reaction force than the males. Males showed higher vertical ground reaction forces at ball contact, but there were no significant differences in ball speed at take-off between the sexes. Ball speed at take-off was inversely related to peak anterior–posterior ground reaction force ( − 0.65). The anatomical differences between the sexes were reflected in greater trunk lean and lower leg angle in the females.

Age Effect on Jumping Techniques and Lower Limb Stiffness During Vertical Jump

The spring-mass system is a reasonable model of the whole phenomenon of musculotendinous stiffness of the lower limbs. This study was to investigate the developmental effect on jumping techniques and lower-limb stiffness during vertical jumping. Nine children and nine adults participated in the study. A Peak high-speed camera was synchronized with a Kistler force plate (600Hz) to collect the biomechanics parameters. Differences between mean values were analyzed by a t-test for independent samples. The present research showed that during downward countermovement, the 18-year-old group produced a larger displacement of ankle, knee, and CG in crouch phase (p < .05) and higher vertical ground reaction forces, whereas the CG was lowest (p < .05), and that the group produced greater leg and joint stiffness (p < .05) to create larger elastic energy generation and storage. For the 6-year-old group, the lower extremity could not be extended completely during push phase. Thus, the lack of prestretch, lower stiffness, and incomplete extension in the 6-year-old group is thought to influence jumping performance.

Biomechanical Factors Affecting Performance in Netball

Despite netball having one of the largest number of participants of any team game within the Commonwealth there has been limited research conducted which biomechanically analysed skills of the game. However, information presented from biomechanical analyses of skills can provide coaches with the necessary theoretical basis to teach netball fundamentals to junior players. Biomechanical information can also be used to refine the existing techniques of experienced netball players so they may achieve optimal technical performance of game skills while minimising the potential for injury. Changes to footwork rules and to the material properties of court surfaces and footwear could reduce stress placed on the musculoskeletal system. However, the factor which influences musculoskeletal stress to the greatest extent is a player's landing technique. Thus, the first concern for all netball coaches must be to teach all players to land correctly. The magnitude and rate of loading of the high vertical and horizontal ground reaction forces generated when players execute abrupt landings in netball are reduced more effectively by encouraging players to throw higher passes, requiring the receiver to jump upward to catch the ball. However, to maximise the reduction in stress placed on the musculoskeletal system on landing, players should be encouraged to land with the foot neutrally aligned (not abducted or adducted), ensure adequate hip and knee flexion, and reduce the foot-hip displacement by eliminating an exaggerated 'striding out' position often adopted by netball players. Apart from landing techniques, the only netball skill that has been objectively analysed is goal shooting. To improve shooting accuracy players should demonstrate greater flexion of the knees and shooting elbow when preparing to shoot, sufficient but not excessive hyperextension of the hand to stabilise the ball, minimisation of trunk, arm and forearm movements during the shooting action in favour of increased hand motion, greater release height and greater release velocity. If the potential for injury from poorly executed skills in netball is to be minimised, further research is required to identify the most efficient methods of performing all skills involved in the game, including pivoting, rebounding, defensive movement patterns, and attacking movement strategies.