Component Of Ground Reaction Force Research Articles

The timing of locomotor propulsion in healthy adults walking at multiple speeds

In computational models of human walking, both magnitude and timing of locomotor propulsion are important for mechanical and metabolic efficiency, suggesting that these are likely tightly controlled by the neuromuscular system. Studies of actual human walking have focused primarily on magnitude-related measures of propulsion, often ignoring its timing. The purpose of this study was to quantify the timing of onset and peak propulsion relative to contralateral heel strike (HS) in healthy, young adults walking at multiple speeds. Propulsion was quantified at the ground-level using the anterior component of the anteroposterior ground reaction force, the limb-level using individual limb power, and the joint-level using ankle power. Contrary to common computational models, most of our timing-related measures indicated that propulsion occurred after contralateral HS. Timing-related measures of propulsion also changed with walking speed – as speed increased, individuals initiated propulsion earlier in the support phase. Timing of locomotor propulsion is theoretically important for walking performance, especially metabolic efficiency, and could therefore provide important clinical information. This study provides a set of relatively simple metrics that can be used to quantify propulsion and benchmark data that can be used for future comparisons with individuals or populations with gait impairments.

The relationship between ground reaction force components and peak power according to induced fatigue during 16-km walking.

The previous reviewed studies on inducement of fatigue through long-time walking were not only very confined, but also not cleared on relationship among variables of fatigue inducement active force, decay rate, and power. This study analyzed relationship between power and component of ground reaction force after fatigue being induced through 16-km walking. The fatigue of adult males and females (n=16) was induced through 16-km walking. Then power, measured for pre and post of fatigue inducement, was evaluated by maximal vertical jump on ground reaction force plate. Variables of vertical jump heights, active force, power, and decay rate showed decreased tendency after fatigue inducement, which followed significant difference (P<0.05) and also positive correlation of r=0.628 (R2=39%) of between vertical jump heights and power and r=0.589 (R2=34%) of between active force and decay rate respectively. That is, long-time walking for pursuing of exercise rehabilitation, health promotion and leisure activity has been preferred. In the view of this, this study suggested the necessity to understand the relation between fatigue and power to prevent a potential possibility of injury during long-time walking.

Effect of long term use of arch support foot orthoses on walking ground reaction force asymmetry index in children with flexible flat feet: A cohort study

Background: Foot orthoses are often used to correct altered gait patterns. However, effect of long term use of arch support foot orthoses on walking mechanics is not well understood. The aim of this study was to evaluate the effects of long term use of arch support foot orthoses on the asymmetry indices of ground reaction forces during stance phase of walking in male children with flexible flat feet. Methods: Fifteen male volunteered children (with their parents’ permission) with flexible flat feet were evaluated. Walking ground reaction forces and kinematic data before and after four months use of foot orthoses were recorded by force plate and Vicon motion system, respectively. Then, the asymmetry indices of ground reaction force components were calculated. Results: The results show that asymmetry index of the medio-lateral component of ground reaction force in loading response and push off phases during pre-test were higher than 4% (normal value). Also asymmetry index of its time to peak during the mid-stance phase in the pre-test were higher than normal value. Moreover, findings did not show any significant differences in asymmetry indices of other ground reaction force components and their time to peak, impulses and vertical loading rate between pre-test and post-test conditions. Conclusion: Despite the high asymmetry values of the peak medio-lateral component and it’s time to peak in children with flexible flat feet during pre-test; long-term use of the foot orthoses did not show any significant effect on the improvement of the asymmetry index of these components. However, long-term wearing of the foot orthoses reduced asymmetry index of the peak positive free moment amplitude.

Effects of Six-week Hopping Exercise on Time to Stabilization and Perceived Stability in Athletes With Chronic Ankle Instability During Single-leg Jump-landing

Introduction: To examine the effects of a 6-week hopping exercise program on time to stabilization and perceived stability among athletes with chronic ankle instability. This is a randomized controlled trial. Materials and Methods: A total of 28 basketball players with chronic ankle instability (Mean±SD age; 22.67±2.88 y, Mean±SD weight: 80.47±8.48 kg, Mean±SD height: 186.82±3.09 cm) participated in this study and were randomly divided into two equal groups of 14 people each: 1. Experimental; and 2. Control. The experimental group performed hop exercises 3 times per week for 6 weeks. The control group received no intervention. Time to stabilization for anterior-posterior and medial-lateral components of ground reaction force, as well as ankle joint function assessment tool were found before and immediately after the exercise program. Descriptive statistics, independent t-test, and paired sample t-test were used to analyze the data at the significance level of 95% (α≤0.05). Results: The 6-week hopping exercise program led to a significant decrease in the time to stabilization of medial-lateral and anterior-posterior of ground reaction force and also a significant increase in the score of ankle joint function assessment tool (p &lt;0.05). Conclusion: Given the effectiveness of hopping exercises, postural control deficit, and time to stabilization in sport exercises, it is suggested that these selected exercises be used in training and rehabilitation protocols.

Effect of muscle mass asymmetric between upper and lower limbs on the postural stability and shock attenuation during landing.

The aim of the study was to analyze the effect of muscle mass asymmetric between upper and lower limbs on postural stability and shock attenuation during landing. Twenty adults (without lower limb disorders and who could land from a 35-cm height) participated in this study (mean age, 21.85±2.97 years; mean height, 1.68±0.10 m; mean weight: 68.64±17.36 kg). Subjects performed one-leg landing from 36-cm vertical heights. Ground reaction force components and medial-lateral, anterior-posterior, vertical and dynamic postural stability index were obtained from force platform recordings. We found that muscle mass in right limbs more increased than that of left limbs. Medial-lateral force, vertical force, vertical stability index, and dynamic postural stability index in left leg showed higher value than that of right leg during landing. The asymmetry of muscle mass (%) and ground reaction force variables showed a similar correlation, including dynamic postural stability index (r=0.316). These findings allow us to conclude that the factor of muscle mass asymmetric is a contributor to impulse control and dynamic postural stability index asymmetry. Therefore, knowledge of bilateral limbs asymmetry may provide insights into exercise rehabilitation and performance.

Topological assessment of gait synchronisation in overground walking groups

Walking is one of the fundamental forms of human gross motor activity in which spatiotemporal movement coordination can occur. While considerable body of evidence already exists on pedestrian movement coordination while walking in pairs, little is known about gait control while walking in more complex topological arrangements. To this end, this study provides some of the first evidence of spontaneous gait synchronisation while walking in a group. Nine subjects covered the total distance of 40 km at different speeds while assembled in a three-by-three formation. Two experimental protocols were applied in which the subjects were either not specifically asked to or specifically asked to synchronise their gait. To obtain results representative from the point of view of gait control, the movement coordination was quantified using the indirectly measured vertical component of ground reaction force, based on output from a network of wireless motion monitors. Bivariate phase difference analysis was conducted using wavelet transform, synchronisation strength measures derived from Shannon entropy, and circular statistics. A fundamental relationship describing the influence of the group walking speed on individuals’ pacing frequency was established, showing a positive correlation different from that previously reported for walking in solitude. A positive correlation was found between the average synchronisation strength within a group and group’s walking speed. The most persistent coordination patterns were identified for pedestrians walking front-to-back and side-by-side. Overall, the spontaneous gait synchronisation while walking in a group is relatively weak, well below the levels reported for walking in pairs.

Influence of Treadmill Speed and Perturbation Intensity on Selection of Balancing Strategies during Slow Walking Perturbed in the Frontal Plane.

Background Common understanding is that adequate foot placement (stepping strategy) is crucial in maintaining stability during walking at normal speed. The aim of this study was to investigate strategies that humans use to cope with lateral perturbations during very slow walking. Methods Ten healthy individuals underwent an experimental protocol whereby a set of perturbations directed inward (medially to a stance leg) and outward (laterally to a stance leg) of three intensities (F1 = 5%, F2 = 10%, and F3 = 15% of body weight), applied at three instances of a stance phase, were delivered in random order to the pelvis using a balance assessment robot while walking on a treadmill at three walking speeds (S1 = 0.4, S2 = 0.6, and S3 = 0.8 m/s). We analyzed the peak center of mass displacements; step length, step width, and step times; and the lateral component of ground reaction force for perturbations that were delivered at the beginning of the gait cycle. Results Responses after inward perturbations were similar at all tested speeds and consistently employed stepping strategy that was further facilitated by a shortened stance. Wider and shorter steps were applied with increased perturbation intensity. Responses following outward perturbations were more complex. At S1, hip strategy (impulse-like increase of mediolateral ground reaction force) augmented with ankle strategy (mediolateral shift of the center of pressure) mainly contributed to responses already during the stance phase. The stance duration was significantly longer for all perturbation intensities. At S2, the relative share of hip strategy was reduced while with increased perturbation intensity, stepping strategy was gradually added. The stance duration was significantly longer for F1 and F2. At S3, stepping strategy was mainly used while the duration of stance was similar to the one in unperturbed walking. Responses following both inward and outward perturbations at all speeds were characterized by temporary slowing down movement in a sagittal plane that was more pronounced with increased perturbation intensity. Conclusions This study provides novel insights into balancing strategies used at slower walking speeds which may be more relevant to understand the challenges of gait stability following perturbations in the frontal plane in clinical populations.

Postural Stability Under Dual-Task Conditions: Development of a Post-Concussion Assessment for Lower-Extremity Injury Risk.

Concussions are consequence of sports participation. Recent reports indicate there is an increased risk of lower-extremity musculoskeletal injury when returning to sport after concussion suggesting that achieving "normal" balance may not fully indicate the athlete is ready for competition. The increased risk of injury may indicate the need to refine a screening tool for clearance. Assess the between-session reliability and the effects of adding a cognitive task to static and dynamic postural stability testing in a healthy population. Clinical laboratory. Twelve healthy subjects (6 women; age 22.3 [2.9]y, height 174.4 [7.5]cm, weight 70.1 [12.7]kg) participated in this study. Subjects underwent static and dynamic postural stability testing with and without the addition of a cognitive task (Stroop test). Test battery was repeated 10 days later. Dynamic postural stability testing consisted of a forward jump over a hurdle with a 1-legged landing. A stability index was calculated. Static postural stability was also assessed with and without the cognitive task during single-leg balance. Variability of each ground reaction force component was averaged. Interclass correlation coefficients (ICC2,1) were computed to determine the reliability. Standard error of measure, mean standard error, mean detectable change, and 95% confidence interval were all calculated. Mean differences between sessions were low, with the majority of variables having moderate to excellent reliability (static .583-.877, dynamic .581-.939). The addition of the dual task did not have any significant effect on reliability of the task; however, generally, the ICC values improved (eyes open .583-.770, dual task .741-.808). The addition of a cognitive load to postural stability assessments had moderate to excellent reliability in a healthy population. These results provide initial evidence on the feasibility of dual-task postural stability testing when examining risk of lower-extremity musculoskeletal injury following return to sport in a concussed population.

Kinetic analysis of cardiac compression-force according to the level of information provision in the cardiopulmonary resuscitation.

The study was undertaken to investigate the change of cardiac compression force relative to levels of information provision using components of ground reaction force. Male participants of 20s–30s (n=10) who was not trained on cardiopulmonary resuscitation (CPR) and used an automated external defibrillator carried out CPR using manikin on ground reaction force plate. All executed 30 times the CPR according to the levels (1-time viewing, repeated viewing, and basic life support education) of information provision and then total sample of 300 times of ground reaction force data was utilized for the analysis. Rather basic life support condition than 1-time viewing and repeated viewing in velocity of CPR showed better pattern, and executed within 15.09 sec of total elapsed time. Also rather basic life support condition than 1-time viewing and repeated viewing in vertical compression force during release phase showed better relax-ability. Rather basic life support condition than 1-time viewing and repeated viewing in ground reaction force of anterior-posterior direction during contraction phase was insignificant, and reduced compression force toward the oblique direction. Therefore CPR training should be provided as part of cardiac and exercise rehabilitation programs in range of limited scope. It is necessary to include not only definite information but also a practice course of CPR to enhance the survival rate of the cardiac arrested regardless of progressive and scientific growth of CPR fields.

Effect of Lower Limb Muscle Fatigue on Ground Reaction Force Components During Landing in People With Nonspecific Chronic Low Back Pain.

The link between landing parameters and lower limb muscle fatigue in association with chronic low back pain (CLBP) is not well understood. To examine the effects of fatigue on the ground reaction force components during landing in people with nonspecific CLBP. Quasi-experimental study. Clinical biomechanics laboratory. A total of 44 subjects were equally divided into a healthy group and a group with CLBP. The ground reaction force along anterior-posterior (y) and medial-lateral (x) and vertical (z) axes, time to peak (TTP), the rate of force development, and impulses for all axes were calculated. A repeated-measures analysis of variance (group × fatigue) was used to compare the data among groups. In the unfatigued conditions, the amplitudes of Fy3, Fz2, and TTP of Fy1, Fy2, Fz1, Fz2, Fz3, Fz4, rate of force development in Y in the CLBP subjects are significantly different than those in the healthy subjects (P < .05). In the fatigued conditions, the amplitudes of Fz2, Fz3, Fz4, and TTP of Fy2, Fy3, Fy4, Fz2, impulses of X2, Z in the CLBP group were significantly different than those in the healthy subjects (P < .05). Within-group comparisons of measured Fx1, Fy1, Fy2, Fz2, Fz4 and TTP of Fx1, Fy1, Fy2, Fz2, Fz3, Fz4, impulses of X2, z were significantly different from prefatigue to postfatigue in the healthy group (P < .05). Within-group comparisons of measured Fx1, Fy1, Fz1, Fz2 and TTP of Fx5, Fz1, impulses of X2 were significantly differed from prefatigue to postfatigue in the CLBP group (P < .05). It seems that TTP of ground reaction force variables in CLBP may have clinical values for rehabilitation. Muscle fatigue altered landing performance. However, patients with CLBP will respond differently to lower-extremity fatigue. These altered variables in patients with low back pain are the cause of future injuries or lower-extremity injuries that need to be addressed in further studies.

Comparison of a Nintendo Wii balance board with a laboratory-grade force plate on measurement of transitional movements

The aim of this study was to verify whether the Nintendo Wii-Balance-Board was valid and reliable for assessing sit-to-stand and return-to-sit tasks by comparing it with a gold-standard force plate. Ten elderly (age = 78.21±14.82 years; males=4; females=6) and eleven young (age =24.25±12.43 years; males=6; females=5) participants of both genders performed five sit-to-stand and return-to-sit tasks consecutively by placing their feet on the Wii-Balance-Board; after two days of rest, they repeated the same assessment. The Wii-Balance- Board was positioned over the force plate to concurrently acquire the vertical component of ground reaction forces. Relevant kinetic and temporal parameters were estimated from these signals. Both the Wii-Balance-Board and force plate measurements resulted in a high level of correlation for almost all the parameters (Pearson’s product-moment r ranged from 0.91 to 0.99, p&amp;lt;.001) and, for the same parameters, intra-class correlation coefficients revealed a high level of agreement between the devices (ranged from 0.93 to 0.99). Bland-Altman plots and regression analysis detected systematic and fixed biases for two parameters (i.e., the inclination of force in standing and rising), while other parameters resulted with none systematic biases; the absolute magnitude of those differences was trivial or small (standardized biases ranged from 0.01 to 0.4). A high level of intra-device reliability was measured for all the parameters (intra-class correlation coefficients ranged from 0.85 to 0.99). The Wii-Balance-Board proved valid and reliable in comparison with a force plate for assessing transition movements so it can be considered a valuable solution for supporting the assessment procedures of average practitioners.

Effects of Corrective Training on Drop Landing Ground Reaction Force Characteristics and Lower Limb Kinematics in Older Adults With Genu Valgus: A Randomized Controlled Trial.

The aim of this study was to identify the effects of a corrective exercise program on landing ground reaction force characteristics and lower limb kinematics in older adults with genu valgus. A total of 26 older male adults with genu valgus were randomized into two groups. An experimental group conducted a 14-week corrective exercise program, whereas a control group did not perform any exercise. The experimental group displayed lower peak vertical, peak anterior and posterior, and peak medial ground reaction force components during the posttest compared with the pretest. The vertical loading rate, impulses, and free moment amplitudes were not statistically different between groups. In the experimental group, the peak knee abduction during the posttest was significantly smaller and the peak hip flexion angle was significantly greater than during the pretest. The authors suggest that this corrective exercise program may be a suitable intervention to improve landing ground reaction forces and lower limb kinematics in older male adults with genu valgus.

Creatine supplementation can improve impact control in high-intensity interval training.

This study aimed to investigate the effects of creatine (Cr) supplementation on biomechanical parameters related to shock attenuation during a session of high-intensity interval training (HIIT). A single-blinded, placebo-controlled, crossover design was adopted to test eight male elite soccer players during HIIT sessions under two conditions: after placebo supplementation and after Cr supplementation. HIIT test sessions consisted of an intermittent test (five bouts of running) with a constant load applied until exhaustion was reached. The vertical component of ground reaction force and electromyography data were recorded by Gaitway and Lynx-EMG Systems, respectively. Heart rate, rated perceived exertion (Borg's Scale) and lactate concentration information were also obtained. Cr supplementation did not affect heart rate, rated perceived exertion, and lactate concentration. Decreased values of magnitude of the first peak of the vertical component of ground reaction force (17.2-24.2%) and impulse of the first 50 ms (Imp50; 34.3%) were observed for Cr, but higher values of time to reach the first peak were detected for Cr compared with placebo. Significant modifications in muscle activation were also observed, mainly in the pre-activation phase, and changes were observed in intermediary bouts. Cr supplementation has the potential to influence biomechanical parameters related to impact control during a single session of HIIT based on running. In particular, the findings of the current study indicate possible improvements in shock attenuation and a safer practice of HIIT under Cr supplementation.

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.

The effect of center of pressure alteration on the ground reaction force during gait: A statistical model

BackgroundFoot problems and lower-limb diseases (e.g., foot ulcers, osteoarthritis, etc.), are presented with a ground reaction force (GRF) that may deviate substantially from the normal. Thus, GRF manipulation is a key parameter when treating symptoms of these diseases. In the current study, we examined the impact of footwear-generated center of pressure (COP) manipulations on the GRF components, and the ability to predict this impact using statistical models. MethodsA foot-worn biomechanical device which allows manual manipulation of the COP location was utilized. Twelve healthy young men underwent gait analysis with the device set to convey seven COP conditions: (1) a neutral condition, (2) lateral and (3) medial offset along the medio-lateral foot axis, (4) anterior and (5) posterior offset along the antero-posterior foot axis, and (6) a dorsi-flexion and (7) plantar-flexion condition. Changes in the magnitude and the early stance-phase impulse of the GRF components across COP conditions were observed. Linear models were used to describe relationships between COP conditions and GRF magnitude and impulse. ResultsWith respect to ANOVA, the vertical and antero-posterior components of the GRF were significantly influenced by the COP configuration throughout the different stages of the stance-phase, whereas the medio-lateral components were not. The models of vertical, antero-posterior and medio-lateral GRF components were statistically significant. SignificanceThe study results are valuable for the development of a method and means for efficient treatment of foot and lower-limb pathologies. The ability to predict and control the GRF components along three orthogonal axes, for a given COP location, provides a strong tool for efficient treatment of foot and lower-limb diseases and may also have relevant implications in sports shoe design. This study is a preliminary investigation for our ultimate goal to develop an effective treatment method by developing an autonomous GRF manipulations device based on closed-loop feedback.

Effects of gait training with unilateral leg load on weight bearing asymmetry of individuals with stroke: A randomized clinical trial

Stroke patients have shown expressive asymmetry between the paretic and non-paretic lower limb (NPLL). The aim of this study was to examine the effects of unilateral leg load used as a restraint for the NPLL during gait training on weight bearing asymmetry after stroke. Thirty-eight stroke patients of both genders and with up to one year of first stroke that caused gait deficits (gait speed < 0.8 m/s) participated in the study. Participants were randomized into: treadmill training with load (equivalent to 5% of body weight) on the NPLL (experimental group) and treadmill training without load (control group). Interventions lasted 30 min per day, for 2 weeks (9 sessions). Kinetic data were collected with a force plate, during standing position (static) and during gait (dynamic). Limb loading was evaluated by the mean of vertical component of ground reaction force (GRF), for paretic and non-paretic limbs. Static and dynamic symmetry ratio (paretic GRF/non-paretic GRF) was calculated for both groups at baseline, post-training and after 40-day follow-up. At baseline, groups were homogeneous with regard to age, time since stroke, neurological status (according to National Institute of Health Stroke Scale) and walking ability (according to Functional Ambulatory Category). Repeated-measures analysis of variance showed no effects over time in static and dynamic symmetry ratio (static: F = 0.985; P = 0.364; dynamic: F = 2.005; P = 0.153). In addition, ANOVA showed no changes between experimental and control groups in static and dynamic symmetry ratio (static: F = 0.031; P = 0.862; dynamic: F = 0.063; P = 0.803). Although load addition might favor the use of paretic limb by restraining NPLL, weight bearing asymmetry has not been changed over time in any group. Once this protocol is innovative, future studies should investigate other parameters such as training duration and amount of load, to improve weight bearing asymmetry after stroke.

Vertical ground reaction forces on rigid and vibrating surfaces for vibration serviceability assessment of structures

Lightweight structures are sensitive to dynamic force generated by human walking and consequently can exhibit excessive vibration responses. The imparted forces, known as ground reaction forces (GRFs), are a key input in the vibration serviceability assessment of footbridges. Most GRF measurements have been conducted on rigid surfaces such as instrumented treadmills and force plates mounted on strong floors. However, it is thought that the vibrating surface of a footbridge might affect the imparted human force. This paper introduces a unique laboratory experimental setup to investigate vertical GRFs on both rigid surface (strong floor) and a higher-frequency flexible surface (footbridge). 810 walking trials were performed by 18 test subjects walking at different pacing frequencies. For each trial, test subjects travelled a circuit of a vibrating footbridge surface followed by a rigid surface. A novel data collection setup was adopted to record the vertical component of GRFs, and the footbridge vibration response during each trial. Frequency-domain analysis of both single-step and continuous GRFs was then performed. The results show that the footbridge vibration affects GRFs, and changes GRF magnitudes for harmonics in resonance with the footbridge vibration (up to around 30% reduction in the dynamic load factor of the third harmonic). This finding, and the measured GRFs, can be used for more accurate vibration serviceability assessments of existing and new footbridges.

Gender Dfferences in Ground Reaction Force Components

Objective: The aim of this study was to investigate gender differences in ground reaction force (GRF) components among different speeds of running. Method: Twenty men (age=22.4±1.6 years, mass=73.4±8.4 kg, height=176.2±5.6 cm) and twenty women (age=20.7±1.2 years, mass=55.0±8.2 kg, height=163.9±5.3 cm) participated in this study. All participants were asked to run on an instrumented dual belt treadmill (Bertec, USA) at 8, 12, and 16 km/h for 3 min, after warming up. GRF data were collected from 30 strides while they were running. Hypotheses were tested using one-way ANOVA, and level of significance was set at p-value <.05. Results: The time to passive peaks was significantly earlier in women than in men at three different running speeds (p<.05). Further, the impact loading rates were significantly greater in women than in men at three different running speeds (p<.05). Moreover, the propulsive peak at 8 km/h, which is the slowest running speed, was significantly greater in women than in men (p<.05), and the vertical impulse at 16 km/h, which is the fastest running speed, was significantly greater in men than in women (p<.05). The absolute anteroposterior impulse at 8 km/h was significantly greater in women than in men (p<.05). In addition, as the running speed increased, impact peak, active peak, impact loading rate, breaking peak, propulsive peak, and anteroposterior impulse were significantly increased, but vertical impulse was significantly decreased (p<.05). Conclusion: The impact loading rate is greater in women than in men regardless of different running speeds. Therefore, female runners might be exposed to the risk of potential injuries related to the bone and ligament. Moreover, increased running speeds could lead to higher possibility of running injuries.

Acute effect of foot orthoses on frequency domain of ground reaction forces in male children with flexible flatfeet during walking

BackgroundFlatfoot is a structural and functional abnormality of the foot that may cause lower limb mechanical damage during walking. The aim of this study was to investigate the acute effect of foot orthoses on the frequency domain of ground reaction forces in children with flatfeet during the stance phase of walking. MethodsBilateral gait data were collected from fifteen male children suffering from flatfeet syndrome. Two Kistler force platforms were used to record the ground reaction forces of each limb during level walking. Arc support foot orthoses were used as an intervention. ResultsNo significant differences in the frequency content of the dominant limb ground reaction forces were found in the three directions in the two conditions (P>0.05). However, the use of foot orthoses decreased non-dominant limb medio-lateral ground reaction force frequency with a power of 99.5% (P=0.015). Overall, for both limbs, the amplitude of the three-dimensional ground reaction force components during walking with foot orthoses were lower than those obtained without foot orthoses (P<0.05). For both dominant and non-dominant limbs, the essential number of harmonics in three directions during walking with and without foot orthoses were similar (P>0.05). ConclusionsFoot orthoses decreased medio-lateral ground reaction force frequency in the non-dominant limb, but have little effect on other ground reaction frequency components. Decreased frequency phenomena due to foot orthoses in children with flatfeet suggest an attenuation of ground reaction forces during walking. Frequency domain analysis thus offered new insights on the gait improvements associated with using foot orthoses.

Differences in the structure of variability in ground reaction force trajectories provide additional information about variability in the golf swing

The study presents a novel application of measures of the structure of variability to ground reaction force trajectories and highlights the use of such measures to provide valuable information about coordination of the golf swing. The variability and regularity of ground reaction force trajectories were quantified for iron and driver shots from three participants with different skill levels. Pointwise median absolute deviation was used to indicate the variability of ground reaction force trajectories across their length, and two alternative methodologies, sample entropy and cross-sample entropy, were used to determine their regularity. For both driver and iron shots, results showed that while there was no difference in the magnitude of variability between any of the participants, there were differences in the structure of this variability. In general, the ground reaction force of the highest skilled participant was significantly more regular than that of the lesser skilled golfers. However, differences occurred across the various components of ground reaction force. Thus, entropy measures can provide additional valuable information concerning dissimilarities among golfers of various skill levels and may indicate differences in neuromuscular system coordination during the golf swing. This study highlights the importance of considering the structure of variability, as well as its magnitude, and describes methods which could be applied to further investigations.