Average Ground Reaction Force Research Articles

Gender and Bilateral Differences in Single-Leg Countermovement Jump Performance with Comparison to a Double-Leg Jump

Expectations may be for both legs to function identically during single- and double-leg vertical jumps. However, several reasons might prevent this from occurring. The goals of this investigation were twofold: assess the presence of side-to-side jump height differences during single-leg jumps in a homogenous group of healthy subjects and determine if those with a jump height asymmetry possessed consistent biomechanical differences during single-and double-leg jumps. Thirteen men and 12 women with competitive volleyball experience volunteered for the study. Significance was assessed at p < 0.05. The men jumped significantly higher than the women in all conditions and possessed differences in several anthropometric, kinematic, and kinetic parameters. Based on a three-jump average, all subjects had one leg that they could jump higher with (the dominant leg, DL). The men generated significantly greater maximum ground reaction forces and ankle joint powers on their DL whereas the women had no differences during the single-leg jumps. The only side-to-side differences that existed during the double-leg jumps were in the average ground reaction forces during propulsion. These findings suggest that equality of single-leg jump performance is the exception rather than the norm, with identification of consistent biomechanical attributes difficult within a group.

Ground reaction forces during downhill and uphill running

We investigated the normal and parallel ground reaction forces during downhill and uphill running. Our rationale was that these force data would aid in the understanding of hill running injuries and energetics. Based on a simple spring-mass model, we hypothesized that the normal force peaks, both impact and active, would increase during downhill running and decrease during uphill running. We anticipated that the parallel braking force peaks would increase during downhill running and the parallel propulsive force peaks would increase during uphill running. But, we could not predict the magnitude of these changes. Five male and five female subjects ran at 3 m/s on a force treadmill mounted on the level and on 3°, 6°, and 9° wedges. During downhill running, normal impact force peaks and parallel braking force peaks were larger compared to the level. At −9°, the normal impact force peaks increased by 54%, and the parallel braking force peaks increased by 73%. During uphill running, normal impact force peaks were smaller and parallel propulsive force peaks were larger compared to the level. At +9°, normal impact force peaks were absent, and parallel propulsive peaks increased by 75%. Neither downhill nor uphill running affected normal active force peaks. Combined with previous biomechanics studies, our normal impact force data suggest that downhill running substantially increases the probability of overuse running injury. Our parallel force data provide insight into past energetic studies, which show that the metabolic cost increases during downhill running at steep angles.

Comparison of landing maneuvers between male and female college volleyball players

Objective. To compare differences in kinematic and kinetic parameters of knee, hip and ankle joints between male and female college volleyball players. Design. Cross-sectional study. Background. Landing injuries, which usually involve anterior cruciate ligament injuries, are common in volleyball with a higher incidence in females. Landing preferences of both male and female players may provide additional background about the mechanisms contributing to the anterior cruciate ligament injuries. Methods. Eight female and eight male college volleyball players performed spike and block landings from 40 and 60 cm height platforms. Lower extremity joint kinetics and kinematics, and leg muscle strengths were recorded. Results. Females demonstrated significantly lower knee and hip flexion angles compared to their male counterparts in knee flexion at 40 cm spike and hip flexion at 40 cm block landings. Group comparison also revealed that male players' peak knee extensor moment at 60 cm block landing was significantly different than female players. Additionally, female players applied significantly higher normalized ground reaction forces and males knee flexion angles and thigh muscle strength results positive and highly correlated but relation could not found in females. It is likely that females may not use their thigh muscles as effective as males in landing. Conclusion. Female volleyball players initiate different lower extremity mechanics during landings than that of males. Relevance Identifying the landing strategy differences between female and male college volleyball players may provide detailed perspective about the load distribution in lower extremity joints for determining major factors affecting the increased incidence of anterior cruciate ligament injuries in females.

Gait adaptations during load carrying on level and inclined surfaces

The complex human processes involved in balance maintenance and fall prevention during normal locomotion are further complicated by load carrying and/or the presence of slippery floors. The goal of this study was to investigate the effect of carrying loads (2-handed method) on gait biomechanics relevant to slips/falls. Participants walked down surfaces of varying inclinations (0°, 5° and 10°), while ground reaction forces and body/foot motion were recorded. Three load conditions (no load, 2.3 and 6.8 kg) were included. Load carrying was associated with increases in the peak normal ground reaction force and in the rate of the normal loading phase on the leading foot. Shear ground reaction forces were not affected by load carrying. Changes in the ground reaction forces recorded during load carrying led to reduced required coefficient of friction (RCOF) values, a variable used to rate slip potential. This RCOF reduction is partly due to postural adaptations such as increased knee and hip flexion adopted during load carrying. Furthermore, load carrying was accompanied by slower heel contact heel velocity in the direction of motion. Finally, moments generated at the hip and knee joints were significantly biased towards the extensor and flexor direction, respectively.

Effets des vitesses de marche similaires et de la classification fonctionnelle de l'appui sur la variabilité de la composante verticale de la force de réaction au sol

Introduction. – The variability of the normal ground reaction force ( F(z)) is a restrictive factor for the clinical analyse of kinetics parameters recorded during walking. Objective. – The aim of this study is the decrease of the inter-individual variability of the normal ground reaction force: F(z). Material and method. – The method tested consists in imposing a similar speed to the subjects during walking tests, then to class foot according to their function: loading or propulsive foot. A group of seven young adults walk at spontaneous speed ( V Spon) for the first walking test then at similar speed ( V sim= N Fr ̄ · g·l i ; where N Fr is the Froud’s number, g is the gravitational acceleration and l i is the length of the lower limb) for the second walking test. Two forces platforms register the F(z) of two consecutive steps. The normal ground reaction force and the mean coefficient of variability are retained to test for speed ( V Sim and V Spon) and functional classification effects. Results. – The CoV of F(z) decreases from 13% to 8% when the subjects walk at similar speed rather than at spontaneously chosen speed. The variability decreases by 1–1.5% when the data are classified according to functional criterion. The inter-individual variability of the F(z) significantly reduces when the tests are performed at similar speed and when the loading or propulsive factors are used for functional classification. Conclusion. – The coupling of the methods described must permit to the clinician to constitute a data base which, tainted of less variability, should make easier the detection of pathology affecting the ground reaction force.

Effect of Strike Pattern and Orthotic Intervention on Tibial Shock during Running

The main purpose of this study was to investigate the effects of both strike pattern (forefoot vs. rearfoot strike pattern) and orthotic intervention on shock to the lower extremity. Semi-rigid orthotic devices were manufactured for 15 injury-free recreational runners. Tibial accelerometry, ground reaction force, and 3D kinematic data were collected on their right leg in four conditions: forefoot strike (FFS) and rearfoot strike (RFS) with and without orthotics. Two-way repeated-measures analysis of variance tests were used to assess the effects of strike pattern and orthotic intervention on tibial acceleration; angular excursions of the ankle and knee; ground reaction force (GRF) vertical and anteroposterior peaks and load rates; and ankle, knee, and leg stiffness. There was a significant increase in tibial acceleration for the FFS pattern compared to the RFS pattern. This may be explained in part by the significantly greater peak vertical GRF, peak anteroposterior GRF, anteroposterior GRF load rates, knee stiffness, and leg stiffness found in the FFS pattern compared to the RFS pattern. Tibial acceleration and rearfoot eversion excursions were similar between the orthotic and no-orthotic conditions. Knee flexion excursion and average GRF vertical load rates were significantly decreased while dorsiflexion excursion and knee stiffness were significantly increased in the orthotic condition. No significant interactions were found between strike pattern and orthotic condition for any variables assessed.

In Vitro Simulation of the Stance Phase in Human Gait

The purpose of this study is to develop an electromechanical system for dynamic simulation of the stance phase of a human gait using cadaveric foot specimens. The system can be used for quantification of foot and ankle pathomechanics and design of foot and ankle reconstructive surgeries. Servo-pneumatic systems were used for application of the tibial weight loading and muscle loadings. A four-bar mechanism was constructed to provide the progressive motion of a tibia during the simulation while the external loadings were simultaneously applied. Muscle loadings were estimated based on the physiological cross-sectional area and normal electromyography (EMG) data with the assumption of the linear EMG–force relationship. Ad hoc tuning of the unknown muscle gains was conducted until a reasonable match with the normal vertical ground reaction force profile, center of pressure advancement, and characteristic foot motion events (heel strike, foot flat, heel rise and toe-off) could be made. Three cadaver feet and an artificial foot were tested with five repeated trials. The simulator reproduced the stance phase of a human gait in the sagittal plane with reasonable accuracy and consistency without compromising either kinematics or kinetics of the foot and ankle complex.

IN VITRO SIMULATION OF THE STANCE PHASE IN HUMAN GAIT

The purpose of this study is to develop an electromechanical system for dynamic simulation of the stance phase of a human gait using cadaveric foot specimens. The system can be used for quantification of foot and ankle pathomechanics and design of foot and ankle reconstructive surgeries. Servo-pneumatic systems were used for application of the tibial weight loading and muscle loadings. A four-bar mechanism was constructed to provide the progressive motion of a tibia during the simulation while the external loadings were simultaneously applied. Muscle loadings were estimated based on the physiological cross-sectional area and normal electromyography (EMG) data with the assumption of the linear EMG–force relationship. Ad hoc tuning of the unknown muscle gains was conducted until a reasonable match with the normal vertical ground reaction force profile, center of pressure advancement, and characteristic foot motion events (heel strike, foot flat, heel rise and toe-off) could be made. Three cadaver feet and an artificial foot were tested with five repeated trials. The simulator reproduced the stance phase of a human gait in the sagittal plane with reasonable accuracy and consistency without compromising either kinematics or kinetics of the foot and ankle complex.

Required Coefficient of Friction Versus Top-Piece/Outsole Hardness and Walking Speed: Significance of Correlations

Abstract Slip resistance of shoes in relation to walkway surfaces is of importance to forensic science. Pedestrians adapt to changes in shoe construction, walkway, and interface characteristics by altering patterns of movement. The instantaneous ratio of tangential to normal ground reaction forces (required coefficient of friction) is affected by such movement alterations. Slip probability depends on the ratio of required to available coefficient of friction (μr/μa). However, there are practical problems in application of this concept. Adequate assessments of the safety of footwear/walkway-surface interactions should take into account subject tests of μr in actual walking scenarios as well as material tests of μa and relevant footwear/walkway characteristics. Based on the literature, this paper discusses the relationship of μr to top-piece/outsole hardness and walking speed. A pilot experiment is described in which subjects walked across a force plate at a series of increasing speeds wearing shoes with the top-piece/outsoles replaced by various test materials. Correlations of μr versus top-piece/outsole hardness and walking speed are presented from data analysis of a single representative subject. The paper explores how biomechanical adaptations of the subject to his foot-wear may account for the fair-moderate correlations observed.

Chapter 41 Control mechanisms for restoring posture and movements in paraplegics

The control mechanisms underlying undisturbed movements were analysed in two series of experiments: (1) normal physiological responses were investigated in neurologically intact subjects; (2) an artificial motor control system for paraplegic patients using functional neuromuscular stimulation (FNS) of the paralysed leg muscles was developed and tested. In both series of experiments standing-up from a chair and sitting-down were studied. A three-link model of the human body was used for recording and processing biomechanical data. In 5 normal subjects ground reaction forces and the surface electromyogram of different leg muscles were also recorded. Basic physiological aspects of FNS such as muscle force regulation and fatigue could be documented. For the standing-up and sitting-down experiments in 2 paraplegic patients the gluteal and quadriceps muscles were stimulated. The best results were achieved with a combination of open-loop and closed-loop stimulation with position and velocity feedback. The importance of feedforward and feedback control during undisturbed movements is discussed for natural and artificial motor control systems. It is concluded that the control of knee joint angle during standing-up and sitting-down represents an unstable system which cannot be controlled open-loop only. Different aspects of sensory feedback including the regulated variables, gain and stability of the system are discussed on the basis of the experimental data and the literature.