Vertical Component Of Ground Reaction Force Research Articles

Patients with Patellofemoral Pain Exhibiting Decrease Vertical Ground Reaction Force Compared to Healthy Individuals during Weight Bearing Tasks: A Systematic Reviews and Meta-Analysis.

Vertical ground reaction force (VGRF) can lead to the development knee osteoarthritis. This review systematic and meta-analysis aimed to investigate the VGRF in patellofemoral pain patients (PFP) during weight bearing tasks. Search strategy was conducted in databases: Science Direct, Scopus, PubMed and Google Scholar from Sep 2020 to Jun 2021. The VGRF components we measured were passive impact (Fz1)/peak and propulsion/active peak (Fz2). The quality of the studies was evaluated with Down and Black index and it was divided into three groups: low quality (LQ), medium quality (MQ) and high quality (HQ). The standardized mean difference between PFP and healthy individuals was used to calculate the effect size. Nine articles were selected for systematic review and meta-analysis of which 5 studies was HQ, 3 studies were MQ and 1 study was LQ were classified. PFP compared to healthy individuals with moderate and small effect size have reduced impact and propulsion respectively. The in PFP, VGRF is influenced psychological, behavioral and biomechanical factors. Therefore, psychosomatic therapeutic approaches may have a long time effectiveness on the rehabilitation of PFP.

Visualising knee loading patterns during kneeling and the development of a laboratory-based adaptation of the Aberdeen Weight-Bearing Test (Knee)

BackgroundInformation regarding the loading of key anatomical structures of the knee during kneeling would enhance existing functional tests, yet current visualisation methods are limited and require further development. Aims(1) Develop a knee loading visualisation technique to investigate loading patterns of the knee during kneeling; and (2) determine the utility of the technique in combination with vertical ground reaction forces and centre of pressure data in the lab-based Aberdeen Weight-Bearing Test (Knee) by assessing their reliability. MethodsFourteen healthy participants conducted kneeling tasks with and without knee pads across two testing sessions. Eight force-sensitive resistors were affixed to the right knee throughout different kneeling tasks: upright kneeling, and reaching forward, back, left, and right. A photo of the force-sensitive resistor configuration was used to generate participant-specific heat maps of knee loading. Two in-ground force platforms were used to measure vertical ground reaction forces and centre of pressure. ResultsThe inferior patella tendon showed the highest proportion of activation during both bare and knee pad kneeling for all kneeling tasks. Knee pads reduced the repeatability of knee loading patterns. Force-sensitive resistor activation and vertical ground reaction force components of the lab-based Aberdeen Weight-Bearing Test (Knee) were shown to be reliable, whereas the centre of pressure data was unreliable. ConclusionWe have developed a lab-based technique for visualising knee loading using force-sensitive resistors. The combination of force-sensitive resistor activation and vertical ground reaction force data provides valuable insights into both the magnitude and locations of applied loads throughout kneeling.

Ground Reaction Force And Electromyograms Of Lower Limb Muscles During Fast Walking

Endurance exercise has been known to be a potent procedure to avoid obesity and its related cardiovascular diseases and to improve glycemic control. Several types of exercise modalities (e.g., walking, running, swimming) are currently utilized, but walking would be most prevalent and accessible. Although general walking is performed around 4-5 km/h, walking at faster speed (fast walking) has been increasing much attention. In previous studies, five months of fast walking increased maximal oxygen uptake and lowered blood pressure (Nemoto et al., 2007). However, the impact of fast walking on mechanical variables as well as muscle activity has not been fully clarified. PURPOSE: To compare ground reaction force and muscle activity between fast walking and running at the equivalent speed. METHODS: Eight males (age; 21 ± 1 yr, height; 172.1 ± 1.7 cm, bodyweight; 62.1 ± 7.0 kg,) participated in the present study. All subjects performed four minutes of slow walking (at 45% of the maximum walking speed, SW), fast walking (at 85% of the maximum walking speed, FW) and running at the equivalent speed from fast walking (Run). During each condition, ground reaction force (GRF) and electromyography (EMG) of seven muscles (gluteus maximus, biceps femoris, rectus femoris, vastus lateralis, gastrocnemius medialis, soleus, and tibialis anterior) were evaluated. We analyzed GRF, average muscle activity (aEMG) and integrated volume (iEMG) during contact phase. RESULTS: In the vertical component of GRF, the load of impact (the maximal and the average values) in FW was lower than those of Run (maximal; 150 ± 25 %BW vs. 219 ± 33 %BW, average; 89 ± 12 %BW vs. 119 ± 19 %BW, p < 0.05). In soleus, aEMG during the ground contact phase in FW (25 ± 9 %MVC) was greater than in SW (13 ± 4 %MVC, p < 0.05). However, no difference was found between FW and Run, but iEMG presented higher value in FW (13 ± 5 %MVC vs. 9 ± 4 %MVC, p < 0.05). In tibialis anterior, aEMG was higher in FW (12 ± 6 %MVC) than in SW (6 ± 4 %MVC) and Run (6 ± 3 %MVC, p < 0.05). iEMG was higher in FW (6 ± 3 %MVC) than in Run (2 ± 1 %MVC, p < 0.05), with no difference between the SW and FW. CONCLUSIONS: The ground reaction force during fast walking was lower than running at the same speed, but the muscle activities of lower limb muscles were comparable.

Characterizing Human Postural Stability by Using Features Extracted From the Correlation Structure of Ground Reaction Force Components

A force plate is one of the most popular tools for postural stability assessment. It decomposes the ground reaction force (GRF) applied to the human body into multiple force components to determine the center of pressure (COP), which is the point at which the GRF is applied. Many COP measures have been proposed to characterize postural stability. Despite postural stability being closely related to GRF components, the interactions between them have rarely been studied. By studying the correlation structure of these GRF components, we developed a set of features to assess postural stability. We determined the correlation matrix of these GRF components and subsequently solved the corresponding eigenvalue problem; we used the resulting eigenvalues to characterize postural stability. The effectiveness of the proposed features was demonstrated by using them to differentiate between individuals in two age groups: 18–24 and 65–73 years. Statistical test results showed that the correlation matrix eigenvalues of the two age groups differed significantly. The classification results demonstrated that most of the correlation matrix eigenvalues were more sensitive to age variations than one of the most reliable and accurate conventional COP features. Furthermore, by reducing the force sensing requirement from three-dimensional to one-dimensional by considering only the vertical GRF components, a simplified version of the proposed approach can be obtained, which could reduce the cost of the force plate system substantially.

Rearfoot-forefoot profile defined by vertical ground reaction forces during gait is altered in patients with unilateral intermittent claudication

Intermittent Claudication due to Peripheral Arterial Disease (PAD-IC) induces ischemic pain in exercising muscles, and therefore impaired gait. In a pathological context, the analysis of the Vertical component of Ground Reaction Force (VGRF) is frequently used to describe gait pattern. This paper aims to define gait profiles according to the relative difference between peaks of VGRF; a Rearfoot and a Forefoot profile revealing a more loading or push-off strategy. We evaluated 70 participants (24 with unilateral disease (Unilat-IC), 22 with bilateral disease (Bilat-IC) and 24 Controls) during a walk test on an instrumented treadmill. Results indicate that Unilat-IC patients present a Rearfoot-profile in both legs during the pain-free gait period, likely to stabilize their gait. With the onset and increase of pain, the asymptomatic leg changes for a Forefoot-profile. This asymmetrical pattern suggests that a compensatory mechanism occurred to unload the symptomatic (painful) leg, possibly creating an imbalance. In Bilat-IC and Controls subjects, a Forefoot-profile is found, with a symmetrical pattern. However, there is a trend for lower propulsive capacity in case of Bilat-IC due to ischemic pain, but patients did not have the ability to compensate as in Unilat-IC. Therefore, Bilat-IC should not be considered as a “double” Unilat-IC. This study highlights the existence of gait profiles based on VGRF in PAD-IC patients. These profiles are dependent on the type of disease. Analysis of these gait profiles can 1) provide a simple way to identify gait alterations and 2) participate in improving physical rehabilitation strategies in PAD-IC patients.

Altered Vertical Ground Reaction Force Components While Walking in Individuals With Chronic Ankle Instability

Aberrant loading is a mechanism by which individuals with chronic ankle instability (CAI) may negatively impact cartilage health and therefore long-term health outcomes. We aimed to quantify walking vertical ground reaction force (vGRF) component differences between those with and without CAI. Participants (n = 36) walked barefoot overground at a self-selected comfortable pace. Normalized peak vGRF, time to peak vGRF, and normalized loading rate were calculated. Higher normalized loading rates (CAI: 5.69 ± 0.62 N/BW/s; controls: 5.30 ± 0.44 N/BW/s, p = .034) and less time to peak vGRF (CAI: 1.48 ± 0.18 s; controls: 1.62 ± 0.16 s, p = .018) were observed in those with CAI. In conclusion, those with CAI demonstrate a higher normalized loading rate and less time to peak vGRF compared to controls.

Effect of weighted sled towing on sprinting effectiveness, power and force-velocity relationship

This study aimed to compare the components of force-velocity (F-V) and power-velocity (P-V) profiles and the mechanical effectiveness of force application (or force ratio–RF) among various sled-towing loads during the entire acceleration phase of a weighted sled sprint. Eighteen sprinters performed four 50-m sprints in various conditions: unloaded; with a load corresponding to 20% of the athlete’s body mass (BM); with a load of 30% BM; and with a load of 40% BM. Data were collected with five video cameras, and the images were digitised to obtain velocity from the derivation of the centre-of-mass position. F-V and P-V components and RF were estimated from sprinting velocity-time data for each load using a validated method that is based on an inverse dynamic approach applied to the sprinter’s centre-of-mass (it models the horizontal antero-posterior and vertical ground reaction force components) and requires only measurement of anthropometric and spatiotemporal variables (body mass, stature and instantaneous position or velocity during the acceleration phase). The theoretical maximal velocity decreased with load compared with the unloaded condition (for 20% BM: -6%, effect size (ES) = 0,38; for 30% BM: -15%, ES = 1.02; for 40% BM: -18%, ES = 1.10). The theoretical maximal horizontal force (F0) and maximal power were not different among conditions. However, power at the end of the acceleration phase increased with load (40% BM vs 0%: 72%; ES = 2.73) as well as the maximal mechanical effectiveness (12%; ES = 0.85). The linear decrease in RF was different between 30 or 40% BM and the unloaded condition (-23%; ES = 0.74 and 0.66). Better effectiveness may be developed with 40% BM load at the beginning of the acceleration and with the various load-induced changes in the components of the F-V and P-V relationships, allowing a more accurate determination of optimal loading conditions for maximizing power.

Impact Control in High-Intensity Interval Training Can Be Improved by Creatine Supplementation

High-intensity interval training (HIIT) is an exercise mode designed to repeatedly stress the body with intense stimulus. Intense running can increase impact forces and alter muscle activation intensity. As skeletal muscles have an important role in shock attenuation, the depletion of muscle phosphorylcreatine (PCr) stores and the diminished energy sources could lead to exhaustion and impairments in the protective functions of muscle during running. We hypothesize creatine supplementation could avoid peripheral fatigue during intense exercise and reduce impairments on shock attenuation. PURPOSE: This study investigated the effects of creatine supplementation on biomechanical parameters related to shock attenuation during a session of HIIT. METHODS: A single-blind, placebo-controlled, crossover design was adopted to test 8 elite soccer players (males; 16.3± 0.5 years; 70.7 ± 4.16 kg; 1.78± 0.06 m) during HITT sessions under two conditions: after placebo supplementation (Pl) and after creatine supplementation (Cr). HITT test sessions consisted of an intermittent test (5 bouts of running) with constant load applied until exhaustion was reached. The vertical component of Ground Reaction Force (VGRF) and Electromyography (EMG) data were recorded by Gaitway and Lynx-EMG Systems, respectively. Heart rate (HR), Rated Perceived Exertion (RPE – Borg’s Scale) and lactate concentration were also obtained. RESULTS: Creatine supplementation did not affect HR, RPE and lactate concentration. Decreased values (p<0.05) of magnitude of first peak (Fy1) of VGRF and impulse of first 50 ms (Imp50) were observed for Cr (about 16.2 – 24.2% and 34.3% of decrease, respectively), whereas higher values (p<0.05) of time to reach first peak (tFy1) were detected for Cr as compared to Pl (28.9 % of increase). Significant modifications (p<0.05) in muscle activation were also observed. Changes occurred in intermediary bouts, mainly in bout 2. CONCLUSION: Creatine supplementation has potential to influence biomechanical parameters related to impact control during a single session of HIIT based on running. Results indicate possible improvements in shock attenuation under creatine supplementation.

Relation between peak knee flexion angle and knee ankle kinetics in single-leg jump landing from running: a pilot study on male handball players to prevent ACL injury

ABSTRACTObjectives: The relationship between knee kinematics and knee-ankle kinetics during the landing phase of single leg jumping has been widely studied to identify proper strategies for preventing non-contact ACL injury. However, there is a lack of study on knee-ankle kinetics at peak knee flexion angle during jumping from running. Hence, the purpose of this study is to establish the relationship between peak knee flexion angle, knee extension moment, ankle plantar flexion moment and ground reaction force in handball players in order to protect ACL from excessive stress during single leg jumping. In addition, the study also clarifies the role of calf muscles in relieving part of ACL stresses with different knee flexion angles during landing.Methods: Fifteen active male elite handball players of Saudi Arabia have participated in this study (Age = 22.6 ± 3.5years, Height = 182 ± 3.7 cm, Weight = 87.5 ± 10.2 kg). The players performed three successful landings of single-leg jump following running a fixed distance of about 450cm. The data were collected using a 3D motion capture and analysis system (VICON).Results: Pearson product moment correlation coefficients showed that greater peak knee flexion angle is related significantly to both lesser knee extension moment (r = -.623, P = .013) and vertical component of ground reaction force (VGRF) (r = -.688, P = .005) in landing phase. Moreover, increasing the peak knee flexion angle in landing phase tends to increase the ankle plantar flexion moment significantly (r = .832, P = .000).Conclusion: With an increase of the peak knee flexion angle during single leg jump landing from running, there would be less knee extension moment, low impact force and more plantar flexion moment. As such, the clinical implication of this study is that there may be a possible protective mechanism by increasing the knee flexion angle during landing phase, which tends to protect the ACL from vigorous strain and injuries.

Development of a residuum/socket interface simulator for lower limb prosthetics.

Mechanical coupling at the interface between lower limb residua and prosthetic sockets plays an important role in assessing socket fitting and tissue health. However, most research lab-based lower limb prosthetic simulators to-date have implemented a rigid socket coupling. This study describes the fabrication and implementation of a lower limb residuum/socket interface simulator, designed to reproduce the forces and moments present during the key loading phases of amputee walking. An artificial residuum made with model bones encased in silicone was used, mimicking the compliant mechanical loading of a real residuum/socket interface. A 6-degree-of-freedom load cell measured the overall kinetics, having previously been incorporated into an amputee's prosthesis to collect reference data. The developed simulator was compared to a setup where a rigid pylon replaced the artificial residuum. A maximum uniaxial load of 850 N was applied, comparable to the peak vertical ground reaction force component during amputee walking. Load cell outputs from both pylon and residuum setups were compared. During weight acceptance, when including the artificial residuum, compression decreased by 10%, while during push off, sagittal bending and anterior-posterior shear showed a 25% increase and 34% decrease, respectively. Such notable difference by including a compliant residuum further highlighted the need for such an interface simulator. Subsequently, the simulator was adjusted to produce key load cell outputs briefly aligning with those from amputee walking. Force sensing resistors were deployed at load bearing anatomic locations on the residuum/socket interface to measure pressures and were compared to those cited in the literature for similar locations. The development of such a novel simulator provides an objective adjunct, using commonly available mechanical test machines. It could potentially be used to provide further insight into socket design, fit and the complex load transfer mechanics at the residuum/socket interface, as well as to evaluate the structural performance of prostheses.

Ground reaction force patterns during gait in patients with lower limb lymphedema

Although gait problems have been reported in patients with lower limb lymphedema (LLL), the gait pattern (GP) changes have not been documented yet. However, it is possible that patients with LLL show abnormal GP that can be related to biomechanical complications related to osteoarthritis or falls affecting the quality of life. Ground reaction force analysis during gait allows objective assessment of the patients and it can be used to plan a rehabilitation approach. Objective: To analyze the GRF during gait in patients LLL. Methods: An experimental descriptive study was realized with twenty-three LLL patients, both unilateral and bilateral and classified as moderate and severe, participated in the experiments. The patients walked on a force plate while the three ground reaction force (GRF) components, vertical, mediolateral (M-L) and anteroposterior (A-P), under their feet were recorded and analyzed. Results: In the patients with unilateral lymphedema, either moderate or severe, the vertical GRF components of the affected limb were similar to the sound one and also resembling those found in healthy adults. The M-L GRF was smaller in the non-affected side. In patients with bilateral lymphedema gait speed was significantly slower. More interestingly, the vertical GRF pattern was flat, not showing the typical 2-peak shape. Finally, the large M-L forces found suggest gait stability problems. Conclusions: The patients showed abnormal GRF patterns, including compensation with the non-affected leg. The GRF variability was higher in the patients with severe unilateral lymphedema. Bilateral lymphedema results in lower A-P forces. Stance phase duration was longer in patients with bilateral and severe lymphedema

Assessing postural stability via the correlation patterns of vertical ground reaction force components

BackgroundMany methods have been proposed to assess the stability of human postural balance by using a force plate. While most of these approaches characterize postural stability by extracting features from the trajectory of the center of pressure (COP), this work develops stability measures derived from components of the ground reaction force (GRF).MethodsIn comparison with previous GRF-based approaches that extract stability features from the GRF resultant force, this study proposes three feature sets derived from the correlation patterns among the vertical GRF (VGRF) components. The first and second feature sets quantitatively assess the strength and changing speed of the correlation patterns, respectively. The third feature set is used to quantify the stabilizing effect of the GRF coordination patterns on the COP.ResultsIn addition to experimentally demonstrating the reliability of the proposed features, the efficacy of the proposed features has also been tested by using them to classify two age groups (18–24 and 65–73 years) in quiet standing. The experimental results show that the proposed features are considerably more sensitive to aging than one of the most effective conventional COP features and two recently proposed COM features.ConclusionsBy extracting information from the correlation patterns of the VGRF components, this study proposes three sets of features to assess human postural stability during quiet standing. As demonstrated by the experimental results, the proposed features are not only robust to inter-trial variability but also more accurate than the tested COP and COM features in classifying the older and younger age groups. An additional advantage of the proposed approach is that it reduces the force sensing requirement from 3D to 1D, substantially reducing the cost of the force plate measurement system.

Dynamic load indicators for take-off-landing sequence in blocks and attacks of elite female volleyball players.

Dynamic loads during landings determined by the ground reaction forces (GRFs) may elaborate internal loads and increase the risk of overload knee injuries as a result of performing volleyball jumps many times. The study dealt with a biomechanical assessment of dynamic load indicators in female volleyball players for the motion sequence of take-off-landing in blocks and attacks. Twelve professional female volleyball players participated in the study. Blocks and attacks were filmed by two cameras. GRFs vs. time graphs were recorded with the use of a force platform. Values of dynamic load indicators in terms of the relations of peak of vertical component of GRF, build-up index of this force (BIF), and power output (P) during landing to the vGRF, BIF and P during take-off (L/T) were calculated. The statistically significant ( p < 0.05) highest values of L/T indicators were found for back row attack spikes: 2.4 (vGRF), 12.2 (BIF) and 3.1 (P). In the case of blocks, slide attack spikes and attack line spikes, results of these variables were in range: 1.8÷2.1, 5.9÷7.6 and 2.1÷2.9, respectively. The reduction of GRFs during landings contributes to decreasing the level of the load indicators L/T which should minimize the incidence of anterior cruciate ligament and patellar tendon injuries in female volleyball players.

Contribution of center of mass–center of pressure angle tangent to the required coefficient of friction in the sagittal plane during straight walking

In human bipedal walking, the peak value of the traction coefficient (i.e., the ratio of the shear force component to the vertical force component exerted on the floor) produced shortly after heel contact is termed as the required coefficient of friction (RCOF). Based on a bipedal inverted pendulum model, with a whole-body center of mass (COM) and reaction forces applied at the center of pressure (COP) of standing feet, RCOF in the sagittal plane (RCOFy) can be expressed as the sum of the tangent of the COM–COP angle and a residual term (RT), mainly comprising the moment around COM. In this study, we investigated the contribution of the tangent of the COM–COP angle to RCOFy during straight walking. The study involved four healthy young adult males. The participants were asked to walk on a 5-m long carpeted walkway. Each participant performed nine trials, i.e., three walking speeds (1, 1.4, and 1.9m/s)×three step lengths (0.55, 0.75, and 0.95m). COM was estimated using motion capture. COPs for the left and right feet were measured using eight force plates embedded in the walkway. RCOFy was calculated from the anterior–posterior and vertical ground reaction force components measured using the force plates. We found that the tangent of the COM–COP angle accounted for 91%–124% of the RCOFy value. This percentage tended to decrease with increasing walking speed (p<0.05). The magnitude of RT accounted for only 5.3%–24% of RCOFy. These results suggest that the tangent of the COM–COP angle dominantly determines RCOFy.

Frequency Content of the Vertical Ground Reaction Force Component During Rearfoot and Forefoot Running Patterns

The forefoot (FF) footfall pattern has been advocated to reduce running overuse injuries due to the lack of the impact peak in the vertical ground reaction force component (vGRF). Although the vertical impact peak has been associated with running overuse injuries, the frequency content of vGRF may provide more insight into injury mechanisms. Previous studies have found passive mechanisms, such as the deformation of bone and articular cartilage, are responsible for attenuating high frequency signals. Conversely, active mechanisms, such as eccentric muscle contractions and kinematic adjustments, attenuate low frequencies. The lack of the vertical impact peak during FF running may alter the frequency content of the vGRF therefore altering how the body tissues attenuate impact shock. PURPOSE: To determine the frequency content of the vGRF during rearfoot (RF) and FF running. We hypothesize RF running will result in greater amplitudes at higher frequencies whereas FF running will result in greater amplitudes at low frequencies. METHODS: Seven natural RF runners and 7 natural FF runners performed 10 trials over ground with each footfall pattern. Running speed was restricted to ±5% of the subjects preferred speed. GRFs were collected at 1200Hz. vGRFs from the stance phase were zero padded to equal 2048 data points. An FFT was performed on each trial then normalized to 1 Hz bins. A mixed factor ANOVA with subjects nested within footfall pattern was performed to assess differences in amplitude at frequencies 1 - 50 Hz (α = 0.05). RESULTS: RF running resulted in significantly greater amplitudes for frequencies 13 - 39 Hz (p<0.05; sum of amplitudes 13-39 Hz: RF = 462 N; FF = 166 N; percent difference = 94.7%). FF running resulted in significantly greater amplitudes for frequencies ranges 5 - 7 Hz (p<0.05; sum of amplitudes 5-7 Hz: RF = 436 N, FF = 542 N; percent difference = 21.7%). CONCLUSIONS: The frequency content of the vGRF suggests RF running necessitates a greater reliance on passive mechanisms to attenuate impacts whereas FF running relies on active mechanisms. The results suggest there may be a difference in impact related injury mechanisms between running footfall patterns. The RF footfall pattern may contribute to bone related injuries whereas the FF footfall pattern may contribute to injuries such as muscle strain and tendonitis.

Impact characteristics in shod and barefoot running

Increased impact characteristics are often cited as a cause of running injuries. One method that has been used to reduce impact characteristics is to increase the thickness of the midsole of running footwear with the intention of attenuating greater shock from the foot-ground collision. A second method that has been suggested is to run barefoot. The purpose of this study was to compare the impact characteristics of running footwear of different midsole thickness to a barefoot condition. Three-dimensional kinematic and kinetic data were collected as participants ran at their preferred running speed and at a fixed speed. Impact characteristics (impact peak, time to impact peak and vertical loading rate) were derived from the vertical ground reaction force component. Ankle and knee joint stiffness during the loading phase of support were derived from the change in moment divided by the change in angle. The impact parameters were statistically analyzed using a two-way, repeated measures ANOVA. There were no significant speed by footwear condition interactions. For impact peak, ankle stiffness and knee stiffness, there was no difference among the shod conditions but there were significant differences between the shod and barefoot conditions. Based on their strike index, participants in this study appeared to alter their footfall pattern from a rearfoot to a midfoot pattern when changing from running shod to barefoot. It may be concluded that the change in the impact characteristics is a result of changing footfall pattern rather than midsole thickness.

Lower limb joint kinetics during moderately sloped running.

Knowledge of the kinetic changes that occur during sloped running is important in understanding the adaptive gait-control mechanisms at work and can provide additional information about the poorly understood relationship between injury and changes in kinetic forces in the lower extremity. A study of these potential kinetic changes merits consideration, because training and return-to-activity programs are potentially modifiable factors for tissue stress and injury risk. To contribute further to the understanding of hill running by quantifying the 3-dimensional alterations in joint kinetics during moderately sloped decline, level, and incline running in a group of healthy runners. Crossover study. Three-dimensional motion analysis laboratory. Nineteen healthy young runners/joggers (age = 25.3 +/- 2.5 years). Participants ran at 3.13 m/s on a treadmill under the following 3 different running-surface slope conditions: 4 degrees decline, level, and 4 degrees incline. Lower extremity joint moments and powers and the 3 components of the ground reaction force. Moderate changes in running-surface slope had a minimal effect on ankle, knee, and hip joint kinetics when velocity was held constant. Only changes in knee power absorption (increased with decline-slope running) and hip power (increased generation on incline-slope running and increased absorption on decline-slope running in early stance) were noted. We observed an increase only in the impact peak of the vertical ground reaction force component during decline-slope running, whereas the nonvertical components displayed no differences. Running style modifications associated with running on moderate slopes did not manifest as changes in 3-dimensional joint moments or in the active peaks of the ground reaction force. Our data indicate that running on level and moderately inclined slopes appears to be a safe component of training regimens and return-to-run protocols after injury.

Greater toe grip and gentler heel strike are the strategies to adapt to slippery surface

This study investigated the plantar pressure distribution during gait on wooden surface with different slipperiness in the presence of contaminants. Fifteen Chinese males performed 10 walking trials on a 5-m wooden walkway wearing cloth shoe in four contaminated conditions (dry, sand, water, oil). A pressure insole system was employed to record the plantar pressure data at 50 Hz. Peak pressure and time-normalized pressure-time integral were evaluated in nine regions. In comparing walking on slippery to non-slippery surfaces, results showed a 30% increase of peak pressure beneath the hallux (from 195.6 to 254.1 kPa), with a dramatic 79% increase in the pressure time integral beneath the hallux (from 63.8 to 114.3 kPa) and a 34% increase beneath the lateral toes (from 35.1 to 47.2 kPa). In addition, the peak pressure beneath the medial and lateral heel showed significant 20–24% reductions, respectively (from 233.6–253.5 to 204.0–219.0 kPa). These findings suggested that greater toe grip and gentler heel strike are the strategies to adapt to slippery surface. Such strategies plantarflexed the ankle and the metatarsals to achieve a flat foot contact with the ground, especially at heel strike, in order to shift the ground reaction force to a more vertical direction. As the vertical ground reaction force component increased, the available ground friction increased and the floor became less slippery. Therefore, human could walk without slip on slippery surfaces with greater toe grip and gentler heel strike as adaptation strategies.

Influence of Pain Distribution on Gait Characteristics in Patients With Low Back Pain

In a cross-sectional study, vertical ground reaction force (GRF) during 2 speeds of walking were compared between 3 age- and sex-matched groups: back pain only (BPO) group, back pain with referred leg pain (LGP) group, and a control group. The purpose was to evaluate the influence of pain distribution on vertical GRF of patients with low back problems during 2 walking speed conditions: preferred and fastest speeds. People with low back pain often have difficulty walking. A better understanding of how pain distribution differentially affects walking will facilitate clinicians' assessment and enhance treatment in patients with low back pain problems. All participants walked on a 7.62-m walkway. Vertical GRF parameters were recorded during stance phase using a force platform for each walking speed condition. Multivariate analysis of covariance was used for statistical analysis, with gait velocity as the covariate. The BPO and control groups did not differ significantly in vertical GRF during both walking speed conditions (P > or = 0.11). All vertical GRF parameters of the LGP group, except the peak loading force (P = 0.374), were significantly less than those of the control group during preferred walking speed condition (P < or = 0.008). However, there was no significant difference in the vertical GRF components between LGP and control groups during the fastest walking speed condition (P > or = 0.07). Pain distribution of people with low back problems differentially influences the vertical GRF they experience during walking. When walking at preferred speed, those with referred leg pain seem to use additional strategies besides walking slowly to attenuate the amount of force imposed on their painful leg. When challenged to walk at their fastest speed, people with back pain only walk as fast and withstand comparable amount of force as their pain-free counterparts.

지면반력장비의 정밀성, 신뢰도와 장비설치.사용 환경의 영향

Ground reaction force (GRF) measures are one of the most commonly used in biomechanical study. GRF system is very useful educational tool to explain and demonstrate the Newton`s law of universal gravitation and laws of motion as well. However, accuracy, intra- and inter- force platform measures` consistency, reliability, noise, and the effect of platform mounting to GRF measures were not clearly viewed. The aim of this study was to examine the above. GRFs of a plastic dummy and two subjects` quiet upright standing were collected at four university laboratories eight force platforms. The types of platforms, analysis programs, and platform set-up were various. Three 100s-trials were conducted with sampling frequency of 100 Hz. First two trials` vertical component of GRFs, Fz, and CoP sway ranges of mid-60s-portion of 100s trials were analyzed by the paired t-tests and one-way ANOVA. Six of eight platforms` 1st and 2nd trial dummy Fz were statistically different (p