Sharon Dixon

Surface effects on ground reaction forces and lower extremity kinematics in running.

INTRODUCTION Although running surface stiffness has been associated with overuse injuries, all evidence to support this suggestion has been circumstantial. In the present study, the biomechanical response of heel-toe runners to changes in running surface has been investigated. METHODS Six heel-toe runners performed shod running trials over three surfaces: a conventional asphalt surface, a new rubber-modified asphalt surface, and an acrylic sports surface. The surfaces were categorised according to impact absorbing ability using standard impact test procedures (BS 7044). RESULTS The rubber-modified asphalt was found to exhibit the greatest amount of mechanical impact absorption, and the conventional asphalt the least. The comparison of peak impact force values across surfaces for the group of subjects demonstrated no significant differences in magnitude of force. However, a significant reduction in loading rate of peak impact force was detected for the rubber-modified surface compared with conventional asphalt (P < 0.1). Although analysis of group data revealed no significant differences in kinematic variables when running on the different surfaces, a varied response to surface manipulation among runners was demonstrated, with marked differences in initial joint angles, peak joint angles, and peak joint angular velocities being observed. DISCUSSION For some subjects, the maintenance of similar peak impact forces for different running surfaces was explained by observed kinematic adjustments. For example, when running on the surface providing the least impact absorption, an increased initial knee flexion was observed for some subjects, suggesting an increased lower extremity compliance. However, for some subjects, sagittal plane kinematic data were not sufficient for the explanation of peak impact force results. It appears that the mechanism of adaptation varies among runners, highlighting the requirement of individual subject analyses.

Natural turf surfaces: the case for continued research

It is well documented that health and social benefits can be attained through participation in sport and exercise. Participation, particularly in sports, benefits from appropriate surface provisions that are safe, affordable and high quality preferably across the recreational to elite continuum. Investment, construction and research into artificial sports surfaces have increased to meet this provision. However, not all sports (e.g. golf, rugby and cricket) are suited to training and match play on artificial turf without compromising some playing characteristics of the games. Therefore, full sport surface provision cannot be met without the use of natural turf surfaces, which also have an important role as green spaces in the built environment. Furthermore, a significant number of people participate in outdoor sport on natural turf pitches, although this is a declining trend as the number of synthetic turf surfaces increases. Despite natural turf being a common playing surface for popular sports such as soccer,rugby and cricket, few biomechanical studies have been performed using natural turf conditions. It is proposed that if natural turf surfaces are to help meet the provision of sports surfaces, advancement in the construction and sustainability of natural turf surface design is required. The design of a natural turf surface should also be informed by knowledge of surface related overuse injury risk factors.This article reviews biomechanical, engineering, soil mechanics, turfgrass science, sports medicine and injury related literature with a view to proposing a multidisciplinary approach to engineering a more sustainable natural turf sport surface. The present article concludes that an integrated approach incorporating an engineering and biomechanical analysis of the effects of variations in natural turf media on human movement and the effects of variations in human movement on natural turf is primarily required to address the longer-term development of sustainable natural turf playing surfaces. It also recommends that the use of ‘natural turf’ as a catch-all categorization in injury studies masks the spatial and temporal variation within and among such surfaces, which could be important.

Biomechanical characteristics of barefoot footstrike modalities

Barefoot running has increased in popularity over recent years, with suggested injury risk and performance benefits. However, despite many anecdotal descriptions of barefoot running styles, there is insufficient evidence regarding the specific characteristics of barefoot running. The present study provided reference data for four footstrike modalities adopted across a large cohort of habitually shod male runners while running barefoot: heel strikers (HS), midfoot strikers (MS), forefoot strikers (FS) and a newly defined group, toe runners (TR - contact made only with the forefoot), compared with the three modalities previously reported. Plantar pressure analysis was used for the classification of footstrike modality, with clearly distinguishable pressure patterns for different modalities. In the present study, the distribution of footstrike types was similar to that previously observed in shod populations. The absence of differences in ground contact time and stride length suggest that potential performance benefits of a non-HS style are more likely to be a function of the act of running barefoot, rather than of footstrike type. Kinematic data for the knee and ankle indicate that FS and TR require a stiffer leg than HS or MS, while ankle moment and plantar pressure data suggest that a TR style may put greater strain on the plantar-flexors, Achilles tendon and metatarsal heads. TR style should therefore only be adopted with caution by recreational runners. These findings indicate the importance of considering footstrike modality in research investigating barefoot running, and support the use of four footstrike modalities to categorise running styles.

Mechanisms for Improved Running Economy in Beginner Runners.

UNLABELLED Controversy surrounds whether running mechanics make good predictors of running economy (RE) with little known about the development of an economical running gait. PURPOSE The aim of this study was to identify if mechanical or physiological variables changed during 10 wk of running in beginners and whether these changes could account for any change in RE. METHODS A 10-wk running program (10 wkRP) was completed by 10 female beginner runners. A bilateral three-dimensional kinematic and kinetic analysis, in addition to RE and lower body flexibility measurements, was performed before and after the 10 wkRP. The Balke-Ware graded walking exercise test was performed before and after the 10 wkRP to determine VO2max. RESULTS Seven kinematic and kinetic variables significantly changed from before to after training, in addition to a significant decrease in calf flexibility (27.3° ± 6.3° vs 23.9° ± 5.6°, P < 0.05). A significant improvement was seen in RE (224 ± 24 vs 205 ± 27 mL · kg(-1) · km(-1), P < 0.05) and treadmill time to exhaustion (16.4 ± 3.2 vs 17.3 ± 2.8 min, P < 0.05); however, VO2max remained unchanged from before to after training (34.7 ± 5.1 vs 34.3 ± 5.6 mL · kg(-1) · min(-1)). Stepwise regression analysis showed three kinematic variables to explain 94.3% of the variance in change in RE. They were a less extended knee at toe off (P = 0.004), peak dorsiflexion occurring later in stance (P = 0.001), and a slower eversion velocity at touchdown (P = 0.042). The magnitude of change for each variable was 1.5%, 4.7%, and 34.1%, respectively. CONCLUSIONS These results show that beginner runners naturally developed their running gait as they became more economical runners.

External Frontal Plane Loads May Be Associated with Tibial Stress Fracture

PURPOSE The role of applied external loads in tibial stress fracture is poorly understood. The purpose of this study was to determine whether the magnitude and angle of frontal and sagittal force vectors and the magnitude of the free moment of ground reaction force (the torsional moment between the foot and the ground) during running gait differ between military recruits with and without a history of tibial stress fracture. METHODS Ten male military recruits with tibial stress fracture history and 20 matched controls performed shod running trials over a force plate. The magnitude and the direction of the frontal and sagittal plane ground reaction force, in addition to the free moment, were compared between the groups. RESULTS The frontal plane force vector was directed significantly more medially in the stress fracture group during midstance and late stance (P < 0.05). The magnitude of frontal and sagittal plane ground reaction forces and the free moment were not higher in the stress fracture group compared with controls. CONCLUSION These data highlight differences in the direction with which external forces in the frontal plane are applied in military recruits with a history of tibial stress fracture. These differences may be important in the development of the injury.

Footscan pressure insoles: accuracy and reliability of force and pressure measurements in running.

In the current investigation, the accuracy and reliability of two pairs of Footscan pressure insoles (500 Hz, RSscan, Belgium) was assessed, with four female (pair 1) and four male (pair 2) participants each performing 16 running trials (3.8m/s ± 5%). Intraclass Correlation Coefficients (ICC) revealed that the reliability of the force and pressure data was generally excellent (ICC>0.75). In comparison with impact and propulsive force data collected simultaneously with a force plate (AMTI, 500 Hz), insole data were significantly lower (p<0.05). Therefore, despite the excellent reliability of measurements, the accuracy of the impact and propulsive forces taken with the Footscan pressure insole is low. It is concluded that data collected without appropriate calibration should be used with caution, particularly if the aim is to use the data for a comparison of absolute force and pressure magnitudes with criterion values.

Biomechanical analysis of running in military boots with new and degraded insoles.

PURPOSE The purpose of the present study was to investigate the influence of degradation using repeated impacts on the ability of different shock-absorbing insoles to reduce peak impact loading during running in military boots. METHODS Four insole types were degraded mechanically to simulate typical running loads that occur during approximately 100 km of running. The influence of insole mechanical degradation on stiffness and impact-absorbing ability was assessed using standard test procedures. The ability of new and degraded insole samples to reduce peak impact loading during running was assessed by monitoring peak impact force and rate of loading. In addition, the influence of insoles on sagittal plane kinematics was quantified by measurement of hip, knee, and ankle joint flexion. RESULTS Insole mechanical degradation resulted in an increase in mechanical stiffness and a decrease in ability to reduce mechanical impacts for all test insoles. Measurements taken during running indicated that only one insole type reduced peak impact loading when new, as indicated by a significant (P< 0.05) reduction in peak rate of loading. The ability of this insole type to reduce peak rate of loading during running was maintained after mechanical degradation. This insole was also found to significantly (P< 0.05) reduce peak ankle dorsiflexion. CONCLUSION The present study identifies an insole type that reduces peak rate of loading during running both when new and when mechanically degraded. It is suggested that this indicates an insole that could potentially reduce the frequency of overuse injuries. Based on these results, this insole is recommended for use in the investigation of the practical use of insoles by military recruits, particularly for study of the influence on injury occurrence.

Knee joint stiffness during walking in knee osteoarthritis

To investigate the construct validity of walking knee stiffness as a measure to differentiate between individuals with and without knee osteoarthritis (OA) and the construct validity of walking knee stiffness as related to self‐reported knee stiffness. The contributors to walking stiffness and its relationship with loading rate and adduction moment are also investigated.

The influence of simulated wear upon the ability of insoles to reduce peak pressures during running when wearing military boots

Mechanical degradation of three types of shock absorbing insoles equivalent to 100-130 km of running did not reduce their ability to attenuate the peak pressures generated during running when wearing military boots. Pressure measurements at the heel and forefoot were recorded with pressure measuring insoles placed in the boots of nine subjects. Two of the three insoles tested reduced the peak pressures (P<0.05) generated at the heel and forefoot relative to the no-insole (control) condition. The most effective insole reduced the peak pressures at the heel by 37% and at the forefoot by 24%.

Influence of orthotic devices prescribed using pressure data on lower extremity kinematics and pressures beneath the shoe during running

BACKGROUND Orthotic devices are frequently prescribed as a conservative treatment of lower extremity injury. The purpose of this study was to investigate the influence of orthotic devices prescribed using pressure data on lower extremity movement and loading patterns. METHODS Twenty-two subjects ran barefoot over a pressure plate for the prescription of orthotic devices. The influence of the prescribed orthoses on lower extremity kinematics and pressure beneath the shoe was assessed by collection of data for 10 running trials with a neutral shoe and 10 with the addition of the orthotic device. For each running trial, initial and peak angles were determined for rearfoot inversion-eversion, lower leg internal rotation, ankle dorsi-plantar flexion, knee flexion and rearfoot eversion velocity. In addition, the relative pressure on the lateral side to medial side of the shoe (pressure balance) was determined by dividing the foot into areas of medial and lateral heel and five metatarsals. Peak lateral and medial heel and foot balance were determined during early stance to indicate differences in balance during this phase. FINDINGS The orthotic devices resulted in a significant reduction in peak eversion and eversion velocity and a significant increase in the initial inversion angle (P<0.05). In addition, the peak ankle dorsi-flexion and initial dorsi-flexion angle were significantly increased (P<0.05). Consistent with the observed increase in initial inversion, the early pressure balance data revealed a significantly more lateral (less medial) concentration of pressure (P<0.05). INTERPRETATION It is concluded that the devices used in the present study have resulted in the production of shoe inserts that successfully lower peak eversion and eversion velocity by encouraging the foot to operate in a more inverted orientation throughout the initial stance phase of running. In addition, there is evidence that orthotic effects can be detected through the use of pressure data collected from beneath the shoe.