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The purpose of this trial was to evaluate injury risk in novice runners participating in different strength training interventions. This was a pilot randomized controlled trial. Novice runners (n = 129, 18-60 years old, <2 years recent running experience) were block randomized to one of three groups: a "resistance" strength training group, a "functional" strength training group, or a stretching "control" group. The primary outcome was running related injury. The number of participants with complaints and the injury rate (IR = no. injuries/1000 running hours) were quantified for each intervention group. For the first 8 weeks, participants were instructed to complete their training intervention three to five times a week. The remaining 4 months was a maintenance period. TRIAL REGISTRATION: NCT01900262. A total of 52 of the 129 (40%) novice runners experienced at least one running related injury: 21 in the functional strength training program, 16 in the resistance strength training program and 15 in the control stretching program. Injury rates did not differ between study groups [IR = 32.9 (95% CI 20.8, 49.3) in the functional group, IR = 31.6 (95% CI 18.4, 50.5) in the resistance group, and IR = 26.7 (95% CI 15.2, 43.2)] in the control group. Although this was a pilot assessment, home-based strength training did not appear to alter injury rates compared to stretching. Future studies should consider methods to minimize participant drop out to allow for the assessment of injury risk. Injury risk in novice runners based on this pilot study will inform the development of future larger studies investigating the impact of injury prevention interventions.

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Despite the common knowledge about the individual character of human gait patterns and about their non-repeatability, little is known about their stability, their interactions and their changes over time. Variations of gait patterns are typically described as random deviations around a stable mean curve derived from groups, which appear due to noise or experimental insufficiencies. The purpose of this study is to examine the nature of intrinsic inter-session variability in more detail by proving separable characteristics of gait patterns between individuals as well as within individuals in repeated measurement sessions. Eight healthy subjects performed 15 gait trials at a self-selected speed on eight days within two weeks. For each trial, the time-continuous ground reaction forces and lower body kinematics were quantified. A total of 960 gait patterns were analysed by means of support vector machines and the coefficient of multiple correlation. The results emphasise the remarkable amount of individual characteristics in human gait. Support vector machines results showed an error-free assignment of gait patterns to the corresponding individual. Thus, differences in gait patterns between individuals seem to be persistent over two weeks. Within the range of individual gait patterns, day specific characteristics could be distinguished by classification rates of 97.3% and 59.5% for the eight-day classification of lower body joint angles and ground reaction forces, respectively. Hence, gait patterns can be assumed not to be constant over time and rather exhibit discernible daily changes within previously stated good repeatability. Advantages for more individual and situational diagnoses or therapy are identified.

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In the past 100 years, running shoes experienced dramatic changes. The question then arises whether or not running shoes (or sport shoes in general) influence the frequency of running injuries at all. This paper addresses five aspects related to running injuries and shoe selection, including (1) the changes in running injuries over the past 40 years, (2) the relationship between sport shoes, sport inserts and running injuries, (3) previously researched mechanisms of injury related to footwear and two new paradigms for injury prevention including (4) the 'preferred movement path' and (5) the 'comfort filter'. Specifically, the data regarding the relationship between impact characteristics and ankle pronation to the risk of developing a running-related injury is reviewed. Based on the lack of conclusive evidence for these two variables, which were once thought to be the prime predictors of running injuries, two new paradigms are suggested to elucidate the association between footwear and injury. These two paradigms, 'the preferred movement path' and 'the comfort filter', suggest that a runner intuitively selects a comfortable product using their own comfort filter that allows them to remain in the preferred movement path. This may automatically reduce the injury risk and may explain why there does not seem to be a secular trend in running injury rates.

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The purpose of this study was to compare lower limb muscle activity between physically active and inactive individuals during whole-body vibration exercises. Additionally, transmissibility of the vertical acceleration to the head was quantified. 30 active and 28 inactive participants volunteered to stand in a relaxed (20°) and a squat (60°) position on a side-alternating WBV platform that induced vibrations at 16 Hz and 4 mm amplitude. Surface electromyography (sEMG) was measured in selected lower limb muscles and was normalized to the corresponding sEMG recorded during a maximal voluntary contraction. The vertical acceleration on the head was evaluated and divided by the vertical platform acceleration to obtain transmissibility values. Control trials without vibration were also assessed. The outcomes of this study showed that (1) WBV significantly increased muscle activity in the active (absolute increase: +7%, P <0.05) and inactive participants (+8%, P <0.05), (2) with no differences in sEMG increases between the groups (P>0.05). However, (3), transmissibility to the head was greater in the active (0.080) than the inactive participants (0.065, P <0.05). In conclusion, inactive individuals show similar responses in sEMG due to WBV as their active counterparts, but are at lower risk for potential side-effects of vibration exposure.

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A recently described variable-stiffness shoe has been shown to reduce the adduction moment and pain in patients with medial-compartment knee osteoarthritis. The mechanism associated with how this device modifies overall gait patterns to reduce the adduction moment is not well understood. Yet this information is important for applying load modifying intervention for the treatment of knee osteoarthritis. A principal component analysis (PCA) was used to test the hypothesis that there are differences in the frontal plane kinematics that are correlated with differences in the ground reaction forces (GRFs) and center of pressure (COP) for a variable-stiffness compared to a constant-stiffness control shoe. Eleven healthy adults were tested in a constant-stiffness control shoe and a variable-stiffness shoe while walking at self-selected speeds. The PCA was performed on trial vectors consisting of all kinematic, GRF and COP data. The projection of trial vectors onto the linear combination of four PCs showed there were significant differences between shoes. The interpretation of the PCs indicated an increase in the ankle eversion, knee abduction and adduction, decreases in the hip adduction and pelvic obliquity angles and reduced excursion of both the COP and peak medial-lateral GRFs for the variable-stiffness compared to the control shoe. The variable-stiffness shoe produced a unique dynamic change in the frontal plane motion of the ankle, hip and pelvis that contributed to changes in the GRF and COP and thus reduced the adduction moment at a critical instant during gait suggesting a different mechanism that was seen with fixed interventions (e.g. wedges).

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The purpose of this orthopaedic-biomechanical study was to evaluate the muscle function in total ankle replacement (TAR) patients 1 year after surgery. Ten patients underwent a combined clinical and muscle biomechanical assessment prior to implantation and at the 1-year follow-up. Pain score, American Orthopaedic Foot and Ankle Society (AOFAS) ankle score, ankle range of motion (ROM), and calf circumference difference between the affected leg and contralateral healthy leg were assessed. Biomechanically, isometric maximal voluntary torque for ankle dorsiflexion and plantar flexion was measured simultaneously with surface electromyography of four lower leg muscles. At follow-up, a significant improvement of the pain score (from 6.7 to 0.8 points), AOFAS ankle score (from 35.6 to 92.3 points), and ROM could be shown. Not significantly, the mean calf circumference difference between legs decreased from 2.2 to 1.4 cm. However, a significant increase was seen in the mean dorsiflexion (from 17.0 to 25.8 Nm) and plantar flexion torque (15.7 to 24.6 Nm) of the TAR-treated ankle. The mean EMG frequency content of the affected lower leg at TAR follow-up was lower than in the muscles of the contralateral healthy side. In contrast, the mean EMG intensity at TAR follow-up in side-comparison was statistically the same for all muscles. Ankle OA patients have better muscle function with TAR than under the arthritic condition, but they do not reach the normal level of the contralateral healthy leg 1 year after surgery.

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The purposes of this study were (a) to determine group and individual differences in oxygen consumption during heel-toe running and (b) to quantify the differences in EMG activity for selected muscle groups of the lower extremities when running in shoes with different mechanical heel characteristics. Twenty male runners performed heel-toe running using two shoe conditions, one with a mainly elastic and a visco-elastic heel. Oxygen consumption was quantified during steady state runs of 6 min duration, running slightly above the aerobic threshold providing four pairs of oxygen consumption results for comparison. Muscle activity was quantified using bipolar surface EMG measurements from the tibialis anterior, medial gastrocnemius, vastus medialis and the hamstrings muscle groups. EMG data were sampled for 5 s every minute for the 6 min providing 30 trials. EMG data were compared for the different conditions using an ANOVA (alpha=0.05). The findings of this study showed that changes in the heel material characteristics of running shoes were associated with (a) subject specific changes in oxygen consumption and (b) subject and muscle specific changes in the intensities of muscle activation before heel strike in the lower extremities. It is suggested that further study of these phenomena will help understand many aspects of human locomotion, including work, performance, fatigue and possible injuries.

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Scientific studies typically treat data by studying effects of groups. Clinical therapy typically treats patients on a subject specific basis. Consequently, scientific and clinical attempts to help patients are often not coordinated. The purposes of this study were (a) to identify subject and group specific locomotion characteristics quantitatively, using time discrete and time continuous data and (b) to assess the advantages and disadvantages of the two approaches. Kinematic and kinetic gait pattern of 13 female subjects walking in dress shoes with different heel heights (14, 37, 54 and 85 mm) were analysed. The results of this study showed that subject specific gait characteristics could be better identified with the time continuous than with the time discrete approach. Thus, the time continuous approach using artificial networks is an effective tool for identifying subject and group specific locomotion characteristics.

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PURPOSE: The purposes of this study were (a) to determine lower extremity anthropometric and sensory factors that are related to differences in comfort perception of shoe inserts with varying shape and material and (b) to investigate whether shoe inserts that improve comfort decrease injury frequency in a military population. METHODS: 206 military personnel volunteered for this study. The shoe inserts varied in arch and heel cup shape, hardness, and elasticity in the heel and forefoot regions. A no insert condition was included as the control condition. Measured subject characteristics included foot shape, foot and leg alignment, and tactile and vibration sensitivity of the plantar surface of the foot. Footwear comfort was assessed using a visual analog scale. Injury frequency was evaluated with a questionnaire. The statistical analyses included Student's t-tests for repeated measures, ANOVA (within subjects), MANOVA (within insert combinations), and chi-square tests. RESULTS: The average comfort ratings for all shoe inserts were significantly higher than the average comfort rating for the control condition. The incidence of stress fractures and pain at different locations was reduced by 1.5-13.4% for the insert compared with the control group. Foot arch height, foot and leg alignment, and foot sensitivity were significantly related to differences in comfort ratings for the hard/soft, the viscous/elastic, and the high arch/low arch insert combinations. CONCLUSIONS: Shoe inserts of different shape and material that are comfortable are able to decrease injury frequency. The results of this study showed that subject specific characteristics influence comfort perception of shoe inserts.

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OBJECTIVE: Purpose was (a) to quantify changes that occur in plantar pressure following attenuation of sensory input from the plantar surface of the foot, and (b) to quantify the resultant changes in motor output as measured by the changes of muscular activation. DESIGN: Cross-sectional design in a laboratory setting. BACKGROUND: The importance of afferent feedback to controlling gait has been demonstrated in quasi-static situations, and with animal models. However, the effects and functional significance of sensory feedback from cutaneous receptors in the plantar surface of the foot during walking are still not resolved. METHODS: Sensory thresholds were determined for the plantar surface of the foot. Sensory feedback was reduced with an ice intervention. Three altered sensory states were tested: whole foot, forefoot and rearfoot ice exposure. Plantar pressure distributions and lower extremity muscle patterns were collected while walking before and after ice exposure. RESULTS: Exposure to ice increased vibration thresholds to low and high frequency vibrations. Peak pressure and pressure-time integral were significantly higher in areas of normal sensitivity and lower at the insensate areas. The center of pressure underfoot shifted away from areas of decreased sensitivity when sensory input is reduced from a portion of the foot. Muscle patterns were significantly altered when sensory feedback was changed. CONCLUSIONS: By altering sensory feedback, one can alter gait kinetics and muscular activation patterns. Cutaneous feedback is important in the regulation and modification of gait patterns, and sensory input needs to be included in any model that attempts to predict motion. RELEVANCE: It is suggested that sensory feedback from the foot is important in the maintenance of normal gait patterns. An understanding of the interaction between the sensory-motor systems may lead to advances in the clinical assessment of subjects with gait disorders. Altering sensory input, by changing shoe, orthotic, and/or surface constructions, may be a method by which abnormal gait patterns can be treated.

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During walking and running, the human body reacts to its external environment. One such response is to the impact forces that occur at heel strike. This study tested previous speculation that the levels of muscle activity in the lower extremities are adjusted in response to the loading rate of the impact forces. A pendulum apparatus was used to deliver repetitive impacts to the heels of 20 subjects. Impact forces were of similar magnitude to those experienced during running, but the loading rate was varied by 13% using different materials in the subjects' shoes. Myoelectric patterns were measured in the tibialis anterior, medial gastrocnemius, vastus medialis, and biceps femoris muscles. Wavelet analysis was used to resolve intensity of the myoelectric patterns into time and frequency space. Substantial and significant differences in the myoelectric activity occurred between the impact conditions for the 50 ms before and the 50 ms after impact, reaching 3 ms in timing, 16% in wavelet number, and 154% in the intensity of the muscle activity.

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The purpose of this study was to develop a method to characterize the frequency and damping of vibrations in the soft tissues of the leg. Vibrations were measured from a surface-mounted accelerometer attached to the skin overlying the quadriceps muscles. The free vibrations in this soft tissue were recorded after impact whilst the muscle was performing isometric contractions at 0, 50, and 100% maximum voluntary force and with the knee held at 20, 40, and 60 degrees angles of flexion. The acceleration signals indicated that the soft tissue oscillated as under-damped vibrations. The frequency and damping coefficients for these vibrations were estimated from a model of sinusoidal oscillations with an exponential decay. This technique resolved the vibration coefficients to 2 and 7% of the mean values for frequency and damping, respectively.

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Impact forces and muscle tuning: a new paradigm. Exerc. Sport Sci. Rev., Vol. 29, No. 1, pp 37-41, 2001. We propose that repetitive impact forces during physical activities are not important from an injury perspective but are the reason for changes in myoelectric activity (muscle tuning) to minimize soft tissue vibrations. Changes in myoelectric activity (intensity, frequency, timing), comfort, and performance provide supporting evidence for this new paradigm.

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OBJECTIVE: This article discusses the possible association between impact forces and foot pronation and the development of running-related injuries, and proposes a new paradigm for impact forces and foot pronation. DATA SOURCES: The article is based on a critical analysis of the literature on heel-toe running addressing kinematics, kinetics, resultant joint movements and forces, muscle activity, subject and material characteristics, epidemiology, and biologic reactions. However, this paper is not a review of the literature but rather an attempt to replace the established concepts of impact forces and movement control with a new paradigm that would allow explaining some of the current contradictions in this topic of research. STUDY SELECTION: The analysis included all papers published on this topic over the last 25 years. For the last few years, it concentrated on papers expressing critical concerns on the established concepts of impact and movement control. DATA EXTRACTION: An attempt was made to find indications in the various publications to support or reject the current concept of impact forces and movement control. Furthermore, the results of the available studies were searched for indications expanding the current understanding of impact forces and movement control in running. DATA SYNTHESIS: Data were synthesized revealing contradictions in the experimental results and the established concepts. Based on the contradictions in the existing research publications, a new paradigm was proposed. CONCLUSION: Theoretical, experimental, and epidemiological evidence on impact forces showed that one cannot conclude that impact forces are important factors in the development of chronic and/or acute running-related injuries. A new paradigm for impact forces during running proposes that impact forces are input signals that produce muscle tuning shortly before the next contact with the ground to minimize soft tissue vibration and/or reduce joint and tendon loading. Muscle tuning might affect fatigue, comfort, work, and performance. Experimental evidence suggests that the concept of "aligning the skeleton" with shoes, inserts, and orthotics should be reconsidered. They produce only small, not systematic. and subject-specific changes of foot and leg movement. A new paradigm for movement control for the lower extremities proposes that forces acting on the foot during the stance phase act as an input signal producing a muscle reaction. The cost function used in this adaptation process is to maintain a preferred joint movement path for a given movement task. If an intervention counteracts the preferred movement path, muscle activity must be increased. An optimal shoe, insert, or orthotic reduces muscle activity. Thus, shoes, inserts, and orthotics affect general muscle activity and, therefore, fatigue, comfort, work, and performance. The two proposed paradigms suggest that the locomotor system use a similar strategy for "impact" and "movement control." In both cases the locomotor system keeps the general kinematic and kinetic situations similar for a given task. The proposed muscle tuning reaction to impact loading affects the muscle activation before ground contact. The proposed muscle adaptation to provide a constant joint movement pattern affects the muscle activation during ground contact. However, further experimental and theoretical studies are needed to support or reject the proposed paradigms.

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PURPOSE: The purpose of this study was to quantify effects of shoe sole modification on skeletal kinematics of the calcaneus and tibia during the stance phase of running. METHODS: Intracortical bone pins with reflective marker triads were inserted under standard local anesthetic into the calcaneus and tibia of five healthy male subjects. The three-dimensional tibiocalcaneal rotations were determined using a joint coordinate system approach. Three shoe sole modifications were tested with different sole geometry: a lateral heel flare of 25 degrees (flared), no flare 0 degrees (straight), and a rounded sole. RESULTS: The results showed that these shoe sole modifications did not change tibiocalcaneal rotations substantially. The shoe sole effects at the bone level were small and unsystematic (mean effects being less than 1 degrees ) compared with the differences between the subjects (up to 7 degrees ). Shoe eversion measured simultaneously with shoe markers showed no systematic shoe sole effects. A comparison of shoe and bone results showed the total shoe eversion and maximum shoe eversion velocity to be approximately twice as large as the respective measurements based on bone markers (correlations being r = 0.79 for maximum eversion velocity; r = 0.88 for total eversion), indicating that there may be a relationship or coupling effect between the shoes and the bone. CONCLUSIONS: It is concluded that the tibiocalcaneal kinematics of running may be individually unique and that shoe sole modifications may not be able to change them substantially.

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Vibration characteristics were recorded for the soft tissues of the triceps surae, tibialis anterior, and quadriceps muscles. The frequency and damping of free vibrations in these tissues were measured while isometric and isotonic contractions of the leg were performed. Soft tissue vibration frequency and damping increased with both the force produced by and the shortening velocity of the underlying muscle. Both frequency and damping were greater in a direction normal to the skin surface than in a direction parallel to the major axis of each leg segment. Vibration characteristics further changed with the muscle length and between the individuals tested. The range of the measured vibration frequencies coincided with typical frequencies of impact forces during running. However, observations suggest that soft tissue vibrations are minimal during running. These results support the strategy that increases in muscular activity may be used by some individuals to move the frequency and damping characteristics of the soft tissues away from those of the impact force and thus minimize vibrations during walking and running.

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Muscle activity patterns were measured from the rectus femoris, biceps femoris, tibialis anterior and gastrocnemius medialis muscles using electromyography (EMG). Recordings were made from six runners while they ran for 30 mm around a track at a constant, self-selected pace. They were made from three sites along each muscle belly, and for ten consecutive steps on each 450 m lap completed. The intensity of the myoelectric signals was resolved into components in time and frequency space using wavelet analysis. Distinct populations of high- (170-220 Hz) and low-frequency (40-60 Hz) components could be seen in the frequency spectra. There was no significant effect of the electrode position on the rates of change of EMG intensity for any of the muscles, and there was no significant difference in these rates between a 150-ms window at the end of the swing phase and a 150-ms window during the stride phase of running. There were significant differences in the way in which each subject responded to the task, and the way in which the FMG intensities changed at the different frequency bands. There was a significant reduction in EMG intensity at low frequencies and a significant increase at high frequencies, and these changes were ubiquitous for all four muscles tested. The frequencies that showed the greatest changes coincided with the frequencies where distinct populations of activity occurred within the signal. These changes in muscle activity are different from those seen for maximal fatiguing contractions. However, they suggest that the patterns of muscle recruitment may change during sustained sub-maximal exercise.

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This review paper focuses on the three most important functional design factors for sport shoes: injury prevention, performance and comfort. Concepts for these design factors are discussed for running and court shoes. For running shoes, pronation control and cushioning are still considered to be the key concepts for injury prevention despite the fact that conclusive clinical and epidemiological evidence is missing to show the efficacy of these design strategies. Several design features have been proposed to be effective in controlling the amount of pronation. However, the kinematic effects of such features seem to be subject-specific and rather small especially when looking at the actual skeletal motion. Recent running shoe research suggests that cushioning may not or only marginally be related to injuries and that cushioning during the impact phase of running may be more related to aspects such as comfort, muscle tuning or fatigue. For court shoes, lateral stability, torsional flexibility, cushioning and traction control appear to be important design strategies to decrease the risk of injury. With respect to running performance, the shoe concepts of weight reduction, efficiency and energy return are discussed. The concept of energy return does not seem to be a feasible concept whereas concepts which aim to minimize energy loss appear to be more promising and successful, e.g. weight reduction, reduction of muscle energy required for stabilization. For court shoes, optimal traction seems to be the key factor for performance. Research in the area of shoe comfort is still sparse. Cushioning, fitting and climate concepts appear to improve the comfort of both running and court shoes. Many investigations in the area of sport shoe research have shown that subject-specific responses can be expected. Different groups of athletes may require different types of shoes. The definition of these grouping characteristics and their design needs seem to be the most important challenge for the sport shoe researchers and manufacturers for the near future.

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Sport shoes can have an influence on the energetics of human movement. The two main aspects where sport shoes can play a role are in maximizing the energy which is returned to the athlete and minimizing the energy which is lost by the athlete. Maximum values of energy storage in a shoe sole are on the order of 10 J. However, not all of this energy is returned to the athlete as shoe midsoles lose approximately 30% of the energy input. Depending on the movement, energy return sometimes occurs at the wrong time, frequency, location and in the wrong direction which compromises the ultimate influence on improving performance. As a result, the actual influence that energy return has on performance is probably minimal. Examples of the strategy to minimize energy loss include (1) reducing the mass of the shoe, (2) using appropriate midsole materials which dissipate unwanted vibrations, (3) implementing constructions which improve the stability of the ankle joint and (4) increasing the bending stiffness of shoe midsoles which reduces the energy lost at the metatarso-phalangeal joint. Energy that has not been lost for tasks not directly related to the actual performance may be applied to the movement and may result in an increase of athletic performance. We propose that athletic footwear can have a much larger influence on performance by minimizing the energy which is lost as opposed to maximizing the energy which is returned.

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