Ground Reaction Force Parameters Research Articles

Ground reaction forces during level ground walking with body weight unloading.

Background: Partial body weight support (BWS) systems have been broadly used with treadmills as a strategy for gait training of individuals with gait impairments. Considering that we usually walk on level ground and that BWS is achieved by altering the load on the plantar surface of the foot, it would be important to investigate some ground reaction force (GRF) parameters in healthy individuals walking on level ground with BWS to better implement rehabilitation protocols for individuals with gait impairments. Objective: To describe the effects of body weight unloading on GRF parameters as healthy young adults walked with BWS on level ground. Method: Eighteen healthy young adults (27±4 years old) walked on a walkway, with two force plates embedded in the middle of it, wearing a harness connected to a BWS system, with 0%, 15%, and 30% BWS. Vertical and horizontal peaks and vertical valley of GRF, weight acceptance and push-off rates, and impulse were calculated and compared across the three experimental conditions. Results: Overall, participants walked more slowly with the BWS system on level ground compared to their normal walking speed. As body weight unloading increased, the magnitude of the GRF forces decreased. Conversely, weight acceptance rate was similar among conditions. Conclusions: Different amounts of body weight unloading promote different outputs of GRF parameters, even with the same mean walk speed. The only parameter that was similar among the three experimental conditions was the weight acceptance rate.

Influence of footwear designed to boost energy return on the kinetics and kinematics of running compared to conventional running shoes

Runners have sought to utilise athletic footwear as one of the mechanisms by which they might attenuate their risk of injury and improve their performance. New commercially available footwear which claims to boost energy return have been designed utilising an expanded thermoplastic polyurethane midsole. These footwear have been shown to improve running economy, but their clinical efficacy has not yet been established. This study aimed to examine the 3-D kinetics and kinematics when running in footwear that claims to promote energy return in relation to conventional running trainers. Fifteen male participants ran at 4.0 m/s (±5%) in each footwear condition. Lower extremity kinematics were collected in the sagittal, coronal and transverse planes using a 3-D motion analysis system. Simultaneous tibial acceleration and vertical ground reaction force parameters were also obtained. Impact parameters and 3-D kinematics were contrasted using paired samples t-tests. The results indicate that tibial accelerations were significantly greater in the footwear designed to improve energy return. In addition the 3-D kinematic analysis also showed that peak eversion and tibial internal rotation were significantly greater in the footwear designed to improve energy return. On the basis of these observations the current investigation suggests that these new footwear may place runners at an increased risk from chronic injury.

Differences in pediatric vertical ground reaction force between planovalgus and neutrally aligned feet.

Ground reaction forces (GRF) reflect the force history of human body contact with the ground. The purpose of this study was to explore human gait abnormalities due to planovalgus by comparing vertical GRF data between individuals with planovalgus and those with neutrally aligned feet. Second we estimated associations between various measurements and vertical GRF parameters in a pediatric population. Boys and girls between the ages of 4 and 18 years (72 planovalgus feet and 74 neutrally aligned feet) took part in this study. Ground reaction forces were recorded by two Kistler platforms and normalized to body weight. Comparison of vertical GRF between planovalgus and neutrally aligned feet suggests that the first and the second peaks of vertical force (Fz1, Fz2) are most affected by planovalgus. The results also indicate that neutrally aligned feet display a different ground reaction force pattern than planovalgus, and that differences between boys and girls may be observed. The shape of the vertical GRF curve can help in clinical interpretation of abnormal gait.

As forças transientes durante a marcha militar

INTRODUÇÃO: O padrão vertical anormal da força de reação do solo (FRS) apresenta a assimetria ou mais de dois picos como marcha patológica típica. Uma força típica e assimétrica é a força transiente. Será que a marcha militar é uma espécie de marcha patológica? OBJETIVO: Descrever e analisar a força de reação do solo vertical durante a fase de apoio da marcha militar. MÉTODO: Os participantes foram 20 soldados do Exército Brasileiro que tiveram anteriormente uma lesão nos membros inferiores relacionada com a marcha militar. Duas plataformas de força foram usadas para medir as componentes da FRS (mediolateral, anteroposterior e vertical) durante a marcha. Para cada lado e condição (andar e marcha), cinco amostras para cada pé foram registradas. A análise de variância foi utilizada para comparar os parâmetros da FRS durante o andar e marcha. RESULTADO: O primeiro pico de força foi o mais alto durante a condição de marcha. O pico de força transiente durante a marcha foi maior que o primeiro pico durante o andar. A força mínima foi a maior durante a marcha. CONCLUSÃO: A análise das forças de reação do solo marcha militar mostra uma força vertical transiente que não está normalmente presente no padrão de marcha normal.

Lower impulsive loadings following intensive weight loss after bariatric surgery in level and stair walking: A preliminary study

BackgroundThere are currently very few of studies which have evaluated the role of bariatric surgery in joint loadings and changes in gait. We wanted to examine how impulsive loading would change level and stair walking in severely or morbidly obese subjects after they had undergone bariatric surgery and weight loss. MethodsThirteen female and three male adults aged between 30 and 63years, cleared for Roux-en-Y gastric bypass, were recruited into this study. All subjects were severely or morbidly obese i.e., body mass index was >35kg/m2. The measurement methods consisted of triaxial skin mounted accelerometers and ground reaction force (GRF); conducted at two different predetermined gait speeds. ResultsThe average weight loss was 27.4 (SD8.7) kg after 8.8 (SD3.9) months of follow-up period. Most of the absolute GRF parameters decreased in proportion to weight loss. However, medio-lateral GRF parameters decreased more than expected. The general trend in the knee accelerations demonstrated lower impulsive loadings in both axial and horizontal directions after weight loss. We did not observe any significant changes in stair walking. ConclusionsWeight loss after bariatric surgery not only induces a simple mass-related adaptation in gait but also achieves mechanical plasticity in gait strategy.

Reliability of spatiotemporal and kinetic gait parameters determined by a new instrumented treadmill system

BackgroundDespite the emerging use of treadmills integrated with pressure platforms as outcome tools in both clinical and research settings, published evidence regarding the measurement properties of these new systems is limited. This study evaluated the within– and between–day repeatability of spatial, temporal and vertical ground reaction force parameters measured by a treadmill system instrumented with a capacitance–based pressure platform.MethodsThirty three healthy adults (mean age, 21.5 ± 2.8 years; height, 168.4 ± 9.9 cm; and mass, 67.8 ± 18.6 kg), walked barefoot on a treadmill system (FDM–THM–S, Zebris Medical GmbH) on three separate occasions. For each testing session, participants set their preferred pace but were blinded to treadmill speed. Spatial (foot rotation, step width, stride and step length), temporal (stride and step times, duration of stance, swing and single and double support) and peak vertical ground reaction force variables were collected over a 30–second capture period, equating to an average of 52 ± 5 steps of steady–state walking. Testing was repeated one week following the initial trial and again, for a third time, 20 minutes later. Repeated measures ANOVAs within a generalized linear modelling framework were used to assess between–session differences in gait parameters. Agreement between gait parameters measured within the same day (session 2 and 3) and between days (session 1 and 2; 1 and 3) were evaluated using the 95% repeatability coefficient.ResultsThere were statistically significant differences in the majority (14/16) of temporal, spatial and kinetic gait parameters over the three test sessions (P < .01). The minimum change that could be detected with 95% confidence ranged between 3% and 17% for temporal parameters, 14% and 33% for spatial parameters, and 4% and 20% for kinetic parameters between days. Within–day repeatability was similar to that observed between days. Temporal and kinetic gait parameters were typically more consistent than spatial parameters. The 95% repeatability coefficient for vertical force peaks ranged between ± 53 and ± 63 N.ConclusionsThe limits of agreement in spatial parameters and ground reaction forces for the treadmill system encompass previously reported changes with neuromuscular pathology and footwear interventions. These findings provide clinicians and researchers with an indication of the repeatability and sensitivity of the Zebris treadmill system to detect changes in common spatiotemporal gait parameters and vertical ground reaction forces.

FRI0583-HPR Stair climbing - an insight and comparison between women with and without joint hypermobility

BackgroundJoint hypermobility (JH) is a frequent and important entity in rheumatology, which has not received adequate attention and is still not fully understood. Perceived joint instability, a higher risk for...

Pre-operative ambulatory measurement of asymmetric lower limb loading during walking in total hip arthroplasty patients

BackgroundTotal hip arthroplasty is a successful surgical procedure to treat hip osteoarthritis. Clinicians use different questionnaires to assess the patient’s pain and functional capacity. Furthermore, they assess the quality of gait in a very global way.This clinical evaluation usually shows significant improvement after total hip arthroplasty, however, does not provide objective, quantifiable information about the movement patterns underlying the functional capacity, which can currently only be obtained in a gait laboratory. Instrumented force shoes can quantify gait velocity, ground reaction forces and the gait pattern easily in an outpatient setting.The main goal of this study was to investigate how mobility characteristics during walking, relate to gait velocity and questionnaire outcomes of patients with hip osteoarthritis in an outpatient setting.Methods22 patients with primary osteoarthritis of the hip selected for a total hip arthroplasty participated in this study. For each patient the Harris Hip Score, the Traditional Western Ontario and the McMaster Universities osteoarthritis index were administered. Subsequently, the patients were instructed to walk through the corridor while wearing instrumented shoes. The gait velocity estimated with the instrumented force shoes was validated measuring the time required to walk a distance of 10 m using a stopwatch and a measuring tape as a reference system. A regression analysis between spatial, temporal, ground reaction force parameters, including asymmetry, and the gait velocity and the questionnaires outcomes was performed.ResultsThe velocity estimated with the instrumented shoes did not differ significantly from the velocity measured independently. Although gait parameters correlated significantly with velocity, symmetry index parameters were not correlated with velocity. These symmetry index parameters show significant inter-limb asymmetry during walking. No correlation was found between any of the variables studied and questionnaires outcomes.ConclusionInter-limb asymmetry can be evaluated with the instrumented shoes supplying important additional information about the individual gait pattern, which is not represented by gait velocity and questionnaires usually used. Therefore, this new ambulatory measurement system is able to provide complementary information to gait velocity and questionnaires outcomes to assess the functional capacity of patients with hip osteoarthritis.

224 ウェアラブルセンサとバイオフィードバック機構を統合した歩行訓練システムの評価(センシング技術ほか)

In human gait motion analysis, which is one useful method for efficient physical rehabilitation, ground reaction force, kinematic and kinetic parameters are measured during walking. Recently, it is thought that the patients with walking disability including trans-femoral amputees must regain moving pattern by refined rehabilitation program using ground reaction forces, joint angles and joint moments. At present, intuitive gait training systems cannot be put into practical use adequately. For obtaining these data as the directly wearable gait measurement, in addition to a novel gait motion analysis system using mobile force plate and attitude sensor, split-belt treadmill instrumented force plate with a new concept for motion instruction based on biofeedback has been developed. However, they have not been synthesized yet as motion instruction system focused on the gait training in the past. In this study, ground reaction forces, kinematic and kinetic parameters applied on the healthy subject are measured by using the developed split-belt treadmill instrumented force plate, wearable gait motion analysis system and conventional gait measurement system simultaneously for the development and verification of motion instruction system. As a result of the experiments and consideration by their intercomparison, the patterns of ground reaction force, spatial information and each evaluation index by them are obtained as similar feature quantities among each measurement condition in cases of using instrumented treadmill, wearable gait motion analysis system and conventional measurement system. Finally, the effectiveness of the developed instrumented treadmill and quantitative evaluation concerning human locomotion on the instrumented treadmill by those data is validated.

A comparison of several barefoot inspired footwear models in relation to barefoot and conventional running footwear

This study examined differences in kinetics and kinematics between barefoot and shod running, as well as between several barefoot inspired footwear models. Fifteen participants ran at 4.0 m/s ±5% in each footwear condition. Lower extremity kinematics in the sagittal, coronal and transverse planes were measured using an eight camera motion analysis system alongside ground reaction force parameters. Impact parameters and joint kinematics were subsequently compared using repeated measures ANOVAs. The kinetic analysis revealed that, compared to the conventional footwear, impact parameters were significantly greater in the barefoot and more minimal in barefoot inspired footwear. Running barefoot and in the minimal barefoot inspired footwear was associated with increases in flexion parameters of the knee and ankle at footstrike in relation to the conventional footwear. Finally, the results indicated that the barefoot and minimal barefoot inspired footwear were associated with greater peak eversion magnitude when compared to the conventional footwear. This study suggests that in barefoot and more minimalist barefoot inspired footwear running is associated with impact kinetics and rearfoot eversion parameters, previously linked to an increased risk of overuse injury, when compared to conventional shod running.

Prospective study of gait function before and 2 years after total knee arthroplasty

PurposeTo perform a prospective evaluation of gait before and 2years after total knee arthroplasty (TKA) and examine the influence of comorbidity and other joint problems on gait characteristics and their improvement after TKA. MethodsOne hundred and eleven patients scheduled for TKA took part (34 men, 65±10y; 77 women, age 68±9y). Gait velocity, cadence, and ground reaction force parameters were measured before and 2years after surgery. Patients completed a questionnaire to rate their pain and other joint problems. Comorbidity was measured with the American Society of Anaesthesiologists (ASA) score. ResultsTwo years after TKA there were significant improvements (each p<0.05) in gait velocity and cadence and most of the ground reaction parameters, though forces during loading/unloading remained lower for the operated leg than for the contralateral leg. Higher comorbidity and other painful joints of the lower extremities/spine had a consistent, negative influence (p<0.05) on the absolute values achieved for the gait parameters although their improvement compared with baseline was independent of these factors. ConclusionsComorbidity and other joint problems negatively influenced gait performance. These confounders should be taken into account when setting realistic patient expectations and when interpreting the success of TKA in the individual patient. Improvement in gait is however still possible, within the bounds of concomitant comorbidity.

A influência do uso acumulado de calçados de corrida sobre a força de reação do solo e as respostas de pressão plantar

Acredita-se que a eficiência do calçado seja afetada pelo uso prolongado, mas as alterações biomecânicas ainda não estão bem compreendidas. O objetivo deste estudo é analisar a influência do uso de calçados de corrida na força de reação do solo e os parâmetros de pressão plantar. Três corredores do sexo masculino receberam quatro calçados de corrida para usarem em suas sessões de treinamento. O Sistema Gaitway e o Sistema de F-scan foram usados para registrar a força de reação do solo e parâmetros pressão plantar em diferentes regiões do pé. As coletas ocorreram em quatro momentos: novo e 100, 200 e 300 km de uso. O primeiro pico diminuiu da condição novo para os 300 km de uso (p &lt; 0,01). A taxa de crescimento 1 diminuiu aos 200 km em relação às condições novas (p &lt; 0,01). A área total aumentou aos 100 km (p &lt; 0,01) de uso e manteve valores semelhantes e mais altos até 300km. No pico de pressão antepé, houve uma diminuição progressiva (p &lt; 0,01) como o aumento quilometragem e os valores de pico de pressão do hálux foram significativamente menores (p &lt; 0,01) aos 300 km do que na condição novo. Como o primeiro pico, a taxa de crecimento 1 e os picos de pressão plantar não aumentaram e a área de contato plantar total aumentou. Conclui-se que o calçado de corrida não sofreu alterações consistentes na força de reação do solo e na pressão plantar após 300 km de uso.

Improvements in Functional Capacity From Nordic Walking: A Randomized Controlled Trial Among Older Adults

This study examined the effects of an instructed structured Nordic walking (NW) exercise program on the functional capacity of older sedentary people. Volunteers were randomly assigned to an NW group (68.2 ± 3.8 yr old) or control group (69.9 ± 3.0 yr old). Before and at the end of the 9-wk intervention, functional tests and 2-dimensional ground-reaction-force (GRF) patterns of normal (1.40 m/s) and fast (1.94 m/s) walking speeds were measured. The intervention included a 60-min supervised NW session on an inside track twice a week for 9 wk. The mean changes in functional tests differed between groups significantly. Gait analyses showed no significant differences between the groups on any GRF parameters for walking speed either before or after the intervention. The study showed that NW has favorable effects on functional capacity in older people and is a suitable form of exercise for them.

Test–retest reliability of vertical ground reaction forces during stair climbing in the elderly population

The purpose of the study was to determine the reliability of vertical ground reaction force (VGRF) parameters during stair ascent and descent in the elderly. Forty-two elderly subjects (80.1 SD 6.4 years) were asked to perform three stair ascents and descents at their self-selected normal speed. VGRF were measured during two consecutive steps on an instrumented staircase. Force–time curves where then parameterized into force, force-time and time variables, according to a previously suggested protocol. In addition, force and force-time variables were normalized to body weight. Intraclass correlation coefficients (ICC) type (2, 1) and coefficients of variation (CV) were calculated. Force variables showed moderate to good reliability for the normalized values with ICCs ranging from 0.537 to 0.836 and CVs between 2.52% and 6.51%. Variability of Fmax1 and Fmin appeared to be higher in stair descent with CVs of >5.20% as compared to stair ascent (<3.75%). Time variables showed good reliability in stair ascent but were clearly lower in stair descent (ICCs between 0.108 and 0.684 and CVs between 10.70% and 14.45%). Significant differences were found for the ICCs between the absolute and normalized values as well as for the ICCs of the time dependent and CVs of all variables between stair ascent and descent.It has been concluded that VGRF parameters can be used as a reliable measurement tool for the quantification of stair climbing in the elderly. The present data can be further used as reference values in future investigations.

Ground Reaction Force in Sit-to-stand Reflects Lower-extremity Function Better than Timed Test in Older Adults

In a clinical setting of nursing-care prevention for older adults, timed tests such as five-time sit-to-stand (STS) have often been used as an assessment of lower-extremity function. However, these tests do not reflect leg muscle function because they involve other factors such as movement skills. Ground reaction force (GRF) parameters in the STS movement are considered applicable to evaluate lower-extremity function because force output can be directly measured with the force platform. Limited information is known, however, about the relationships between the isokinetic test scores for the knee extensors, and flexor strength and power. PURPOSE: The purpose of this study was to: 1) examine associations among the GRF parameters in STS movement and isokinetic knee strength and power in older adults, and 2) compare associations with five-time STS test results. METHODS: Nineteen healthy older men (69.6 ± 2.9 yrs) and 28 older women (68.6 ± 2.9 yrs) were recruited. Each participant was asked to stand up three times quickly from a seated position. Three parameters were measured: 1) peak reaction force per body weight (F/w, kgf·kg-1), which reflected the maximal downward push to raise the body upward, 2) maximal rate of force development per body weight (RFD/w, kgf/s·kg-1), which estimated the capacity for rapid muscle force production, and 3) a movement time (T, ms). Five-time STS test scores were also measured. Four isokinetic parameters: peak torque and average power during isokinetic knee extension and flexion at 60 deg/s were measured using an isokinetic dynamometer (Biodex System 3; Biodex medical systems). RESULTS: The F/w, RFD/w, T and five-time STS test were 1.43 ± 0.10 kgf·kg-1, 11.14 ± 1.48 kgf/s·kg-1, 782 ± 92 ms, 7.37 ± 1.43 s, respectively. After adjusting for age and sex, significant partial correlations were found among all four isokinetic parameters and F/w (partial r =.31∼.34, p <.05), and RFD/w (partial r =.32∼.47, p <.05). No isokinetic parameters were significantly related to T (partial r = -.11∼-.25, ns) or five-time STS test scores (partial r = -.07∼-.27, ns). CONCLUSIONS: These data suggest that the GRF parameters in STS movement can reflect isokinetic knee strength and power better than the five-time STS test.

Knee biomechanics during walking gait following matrix-induced autologous chondrocyte implantation

Background Matrix-induced autologous chondrocyte implantation is a technique for repairing articular cartilage defects in the knee. Despite reported improvements in pain, little is known about the recovery of knee biomechanics during walking gait. Methods A randomized controlled study design was used to investigate knee biomechanics during gait in 61 patients following matrix-induced autologous chondrocyte implantation, in conjunction with either ‘accelerated’ or ‘traditional’ approaches to post-operative weight-bearing rehabilitation. Gait analysis was performed at 3, 6 and 12 months post-surgery in both patient groups, and two matched, unaffected control groups for comparison. Findings The spatiotemporal and ground reaction force parameters were similar between patient groups and their respective control groups at all time points. When compared with controls, both patient groups demonstrated significantly reduced knee extension moments up until, and including, 12 months. The traditional group demonstrated a significantly reduced knee adduction moment at 3, 6 and 12 months, and a significantly reduced knee flexion moment at 3 months. There were no differences in these knee moments between the accelerated patient group and controls. Interpretation Overall, a higher level of gait dysfunction was observed in patients who underwent traditional rehabilitation. Future research is needed to investigate the recovery of normal gait following matrix-induced autologous chondrocyte implantation, and its effect on repair tissue development.

Biomechanical analysis of the penalty-corner drag-flick of elite male and female hockey players

The aim of this study was to analyse the kinematic sequencing in the penalty-corner drag-flicks of elite male and female field hockey players of international calibre. Thirteen participants (one skilled male drag-flicker and six male and six female elite players) participated in the study. An optoelectronic motion analysis system was used to capture the drag-flicks with six cameras, sampling at 250 Hz. Select ground reaction force parameters were obtained from a force platform which registered the last support of the front foot. Twenty trials were captured from each subject. Both player groups showed significantly (p < 0.05) smaller ball velocity at release, peak angular velocity of the pelvis, and negative and positive peak angular velocities of the stick than the skilled subject. Normalised ground reaction forces of the gender groups were also smaller than that of the skilled drag-flicker. By comparing these players we established that the cues of the skill level are a wide stance, a whipping action (rapid back lift) of the stick followed by an explosive sequential movement of the pelvis, upper trunk and stick.

Immediate Effect of Lateral-Wedged Insole on Stance and Ambulation After Stroke

To perform kinematic and kinetic analyses on the static standing and ambulation in subjects after stroke with and without wearing a 5-degree lateral-wedged insole. Ten hemiparetic individuals with unilateral stroke were recruited. Participants performed quiet stance and ambulation with no insole wedge, paretic side wedged, and nonparetic side wedged in a random order. The vertical ground reaction force and temporal-spatial parameters of gait were measured. Symmetry index was also calculated. During quiet stance, the symmetry index of weight bearing improved significantly with nonparetic side-wedged (P < 0.017), but not with paretic side-wedged insoles. During ambulation, the symmetry indices of kinematic and kinetic measurements in the frontal plane were not significantly different among the three conditions. However, the contralateral knee abductor moment was significantly (P < 0.05) less than that of the nonparetic limb during nonparetic side-wedged ambulation. The ipsilateral hip and knee abductor moments were significantly (P < 0.05) less than the nonparetic limb during paretic side-wedged ambulation. Application of nonparetic side wedge insole can improve stance symmetry and tends to reduce the paretic knee abductor load during ambulation. The effects of paretic side-wedged insole are different. The present results provide guidelines for the placement of wedges in the shoes of individuals after stroke.

腱スティフネス，筋力および筋活動が反動動作による機械的仕事量増強の個人差に与える影響

The purpose of the present study was to examine the influence of tendon elasticity, muscle strength and muscle activities on the amount of mechanical work enhancement associated with a counter movement. Twenty-one athletes performed a unilateral maximal jump using only the ankle joint with (CMJ) and without (no-CMJ) a counter movement on a sledge apparatus. Mechanical work done by the ankle joint was calculated from the ground reaction force and ankle joint kinematic parameters, and the difference between CMJ and no-CMJ conditions (ΔWork) was determined. During the exercise, electromyographic (EMG) activities were recorded from the triceps surae muscles. The maximal isometric plantar flexion torque and Achilles tendon stiffness were also determined using a torque meter and ultrasonogram. No significant correlation was found between ΔWork and either tendon stiffness or the maximal torque. In addition, neither the difference between CMJ and no-CMJ in iEMG nor mEMG was correlated with ΔWork. On the other hand, ΔWork was significantly correlated with the integrated EMG during the braking phase (r=0.52, p<0.05) and both the integrated (r=0.55, p<0.01) and mean (r=0.53, p<0.05) EMG during the push-off phase of CMJ. These results suggest that individual differences in ΔWork are influenced not by differences in the mechanical properties of the muscle-tendon unit, but by the individuality of muscle activities during CMJ.

Plantar pressure distribution, rearfoot motion and ground reaction force after long distance running

The objective of this study was to investigate ground reaction forces (GRF), rearfoot motion and plantar pressure distribution (PPD) variables before and after long distance treadmill running in a commercially available running shoe in a standardized laboratory condition. Sample was composed of 19 subjects of both genders. Data collection was performed in two phases: (1) physiological test, in order to determine the speed in which the long distance running protocol was performed and (2) biomechanical test: PPD, rearfoot motion and ground reaction force parameters were measured before and after a 45-min treadmill run. A paired sample ‘t-test’ was used to compare the data between the pre and post-measurements (α = 0.05). The values of maximum pronation velocity showed a significant increase (P < 0.01). No significant changes were observed in the remaining parameters. There seem to be a hierarchical control of biomechanical parameters during long distance running, in which impact reduction is more important than the precise control of rearfoot motion.