Running injuries in novice runners enrolled in different training interventions: a pilot randomized controlled trial.

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.

Running shoes and running injuries: mythbusting and a proposal for two new paradigms: 'preferred movement path' and 'comfort filter'.

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.

The Effect of Whole-body Vibration on Muscle Activity in Active and Inactive Subjects.

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.

Daily changes of individual gait patterns identified by means of support vector machines.

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.

Modification of soft tissue vibrations in the leg by muscular activity.

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.

Muscle activity in the leg is tuned in response to ground reaction forces.

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.

Biomechanics, load analysis and sports injuries in the lower extremities.

The study of sports injuries has grown with the increase in importance of sport as a leisure-time activity. The origin of many sports injuries is assumed to be mechanical, with the forces and/or stresses acting on one element of the human locomotor system exceeding the critical limits. This article presents some biomechanical considerations on the mechanical aspect of the aetiology, reduction and treatment of sport injuries with special emphasis on the lower extremities. Forces acting on the locomotor system have a magnitude, a point of application and a direction. Both magnitude and geometry (point of application and direction) are important in load analysis. However, the geometrical aspect of externally acting forces is an extremely important aspect, especially with respect to reduction of load in practical situations. Load analysis is usually performed with force transducers and optical instruments in order to quantify magnitude and geometry. Two possible approaches to load analysis are discussed. One approach works with the critical limits of biomaterials. This approach shows that the local stresses for cartilage, tendon and bone are in the order of 10 to 20% of the critical limit for normal daily activities, such as walking. The second approach deals with strategies to reduce load, assuming that it is usually too high in sports activities. The nature of playing surfaces and shoes are revealed as important possibilities for load reduction.

Pronation in runners. Implications for injuries.

In spite of some significant progress in the understanding of the biomechanics of the ankle joint complex, especially the coupling mechanism between foot and leg, various mechanisms causing overuse injuries in the lower extremities are still poorly understood. Some increased pronation of the foot is often physiological, but excessive pronation is potentially harmful. Compensatory overpronation may occur for anatomical reasons. However, not only the amount of foot eversion, but also the way this eversion is transferred into tibial rotation may be crucial to the overloading stress on the knee. In other words, the individual transfer mechanism of foot eversion into internal tibial rotation may be of some predictable value for lower extremity overloading and related injuries. Further research is necessary to improve the functional understanding of anatomical and biomechanical abnormalities and their pathological value in predicting overuse injuries.

Surface-related injuries in soccer.

The review of the effects of artificial turf and natural grass on surface-related traumatic injuries in soccer suggests that surfaces with artificial turf produce more abrasion injuries than surfaces with natural grass. Most authors report no significant difference in injury frequencies for the number of traumatic injuries. However, some authors report fewer traumatic injuries on artificial turf, especially after a period of adaptation on the artificial turf. A difference in injury pattern and injury mechanism when playing on different types of surfaces has been suggested, as well as an increased injury risk for frequent alternating between different playing surfaces. The relationship between knee and ankle injuries and the fixation of the foot to the ground is not yet evaluated in soccer. In American football, the severity and incidence of knee and ankle injuries were reported to be significantly lower when using shoes with lower friction properties. However, in American football severe injuries typically occur in collision situations often independent of the surface. Soccer is characterised by sprinting, stopping, cutting and pivoting situations, where shoe-surface relations are essential and frictional resistance must be within an optimal range. Future research should address this compromise between performance and protection.

The influence of playing surfaces on the load on the locomotor system and on football and tennis injuries.

The purpose of this paper is to discuss the influence of playing surfaces on the forces and moments acting on the human body and the injuries they may cause for 2 selected sports activities, American football and tennis. The review is based on data from the literature and from our own investigations. A review of the effect of sports surfaces on injuries in American football leads to the conclusion that surfaces with artificial turf produce non-severe injuries more frequently than surfaces with natural grass. However, severe injuries seem to occur as frequently on natural grass as on artificial turf. It has been speculated that the shoe-surface combination which determines the frictional forces is connected with the injury frequency, i.e. the higher the frictional resistance the higher the injury frequency. Tennis surfaces have been shown to influence the occurrence and frequency of tennis injuries dramatically. The injury frequency on 'clay' and 'synthetic sand' is significantly lower than on other selected artificial surfaces. It is speculated that the differences in injury frequency are directly related to the differences in the frictional properties of the surfaces. Surfaces with low frictional resistance are assumed to cause fewer injuries than surfaces with high frictional resistance. In general, it can be concluded that the frictional property of a surface is one of the main factors to be considered when studying the aetiology of acute and/or chronic pain and injury in sports. Compliance or stiffness of surfaces, surprisingly, could not be related to the frequency of injuries on particular playing surfaces. However, it is speculated that compliance properties of surfaces are a factor which must be considered when studying chronic injuries.

The validity and relevance of tests used for the assessment of sports surfaces.

Inappropriate cushioning and/or tractional characteristics of sports surfaces are assumed to increase surface-related injuries in various sports activities. Various tests assessing cushioning and frictional properties are currently in use to evaluate sports surfaces with respect to their potential to reduce the number of surface-related injuries. A critical review of the currently used test procedures showed that most of them are not relevant. The main shortcomings are 1) errors in the measured test results by not correcting for inertia terms due to moving test foot or surface sample, 2) use of inadequate material test procedures where the test procedure influences significantly the test result, and 3) use of material test procedures where the used materials or the applied forces are not representative of the actual situation during sport activities. It is suggested that appropriate test batteries should include 1) test procedures that determine the material properties (stress-strain relation and traction coefficients) relevant for the surface-shoe interaction and 2) subject tests that describe the adaptation of the athlete to the surface-shoe-athlete situation.

Effects of arch height of the foot on ground reaction forces in running.

There is a suggested link between running injuries and arch type of the foot. However, a distinct cause and effect relationship has not been established. Feet may be functionally categorized on the basis of arch height. The purpose of this study was to compare selected ground reaction force variables in running for different arch heights. Static height of the medial longitudinal arch was measured using a caliper, arch flattening during running was determined by video analysis, and ground reaction forces during running were recorded from a KISTLER force plate. Thirty-four subjects were divided into three arch height and three arch flattening groups, and single-factor analyses of variance were conducted to compare the groups. Arch height and arch flattening were not found to be significantly related. However, the initial medial force peak in the low arch group occurred significantly later than in the normal and high arch groups, and the anterior force peak in the low flattening group was lower compared with the medium and high flattening groups (P < 0.05). Both arch measurements were ineffective in accounting for the observed variability in the ground reaction forces in running. Specifically, the impact forces did not differ for the different arch height and arch lowering groups.

A method for the assessment of area-elastic surfaces.

A method is presented for the evaluation of area-elastic surfaces using two subject tests. Deformations and jump heights are determined for 12 sprung floor samples to accuracies of 0.12 mm and 0.4 cm respectively, using filming techniques. It is found that the deformation of a floor sample is dependent on both the subject group and the dimensions of the floor sample. The method showed significant differences in deformation values of the 12 floor samples but only small differences in jump heights.

Biomechanical and orthopedic concepts in sport shoe construction.

Two sets of concepts for sport shoe construction are discussed, based on anatomical, orthopedic, and epidemiological considerations: one for the prevention of excessive load and related injuries, and one for the improvement of performance. The proposed concepts for prevention of excessive load and related injuries in the foot and the lower extremities are cushioning, support, and guidance. The goals outlined in the concepts can be achieved by altering the material properties or the construction of the shoe. It is suggested that the concept "cushioning" is not well understood yet and needs further research. The discussed concepts for improving performance are first, that energy should be returned at the right location, at the right time, with the right frequency, and second, that loss of energy should be minimized. Reduction of energy loss is an important concept for performance. The concept "return of energy" seems inappropriate for sport shoes.

The influence of lateral heel flare of running shoes on pronation and impact forces.

The purpose of this investigation was to study the influence of the flare at the lateral side of the heel of running shoes on: initial and total pronation; impact forces in heel-toe running; and to explain the results with a mechanical model. The experimental part of the study was performed by using 14 male runners. Their running movement (4 m/s) was quantified by using a force platform and high-speed film (100 frames X s-1). Three shoes were used, identical except in their lateral heel flare, one shoe with a conventional flare of 16 degrees, a second shoe with no flare, and a third shoe with a rounded heel (negative flare). The experimental results indicate that (for the used set of shoes); increasing heel flare increases the amount of initial pronation; changes in heel flare do not affect the magnitude of the total pronation; and changes in heel flare do not alter the magnitude of the impact force peaks. Since shoes with rounded lateral heels do reduce initial pronation, it is speculated that this construction could be used to prevent anterior medial compartment syndrome at the tibia of runners. It was concluded that more research is needed to specify whether the reported result is representative for various shoe types or is shoe specific.

Influence of heel height on ankle joint moments in running.

Clinically, heel lifting or heel wedging in running shoes has been proposed as a prevention and treatment of Achilles tendinitis. It has been speculated that heel lifting decreases the Achilles tendon forces. The purpose of this study was to determine the effect of heel height on resultant ankle flexion moments during running. It was assumed that plantarflexion moments at the ankle joint would indicate Achilles tendon loading. Each of the five subjects performed five running trials (4.6 m.s-1) for each of the five shoes, differing only in heel height (2.1-3.3 cm). Resultant plantar-/dorsiflexion moments were calculated using a standard three-dimensional inverse dynamics analysis. The results showed that, typically, a small initial dorsiflexion moment took place changing into a larger plantarflexion moment before 20% of stance phase. The magnitude and time of occurrence of the initial dorsiflexion moment were significantly affected by heel height changes, but the maximum plantarflexion moment and its time of occurrence were not significantly affected. The results did not support the speculation that a heel lift generally decreases the Achilles tendon loading during running. However, single subject analyses indicated that for two subjects the plantarflexion moments decreased with increasing heel height.

Energy aspects for elastic and viscous shoe soles and playing surfaces.

The purpose of this project was to determine the effect of changes in stiffness and viscosity of the foot ground interface on the work performed during locomotion. The estimation of the work during locomotion was derived from a mathematical two segment model, representing the foot and the rest of the body. The typical passive elements between the foot and the rest of the body were replaced by a strategic formulation of how a resultant force, F, representing the net effect of all the muscles between the foot and the rest of the body, has to evolve over time in a running situation. The calculations were performed under the assumption that the force F is selected so that the mechanical work performed by F is minimal. The estimations of the work required during a step cycle is generally higher for softer than for harder springs and for low damping compared with high damping. The model calculations demonstrate that specific combinations of material properties may be advantageous or disadvantageous from an energy point of view.

Influence of midsole bending stiffness on joint energy and jump height performance.

PURPOSE: A substantial amount of rotational energy is lost at the metatarsophalangeal joint during running and jumping. We hypothesized that the lost energy could be decreased by increasing the bending stiffness of shoe midsoles. The purposes of this investigation were to determine the influence of stiff shoe midsoles on changes in lower extremity joint power during running and jumping and to determine the influence of stiff shoe midsoles on vertical jump performance. METHODS: Carbon fiber plates were inserted into shoe midsoles and data were collected on five subjects during running and vertical jumping. RESULTS: The data showed that energy generation and absorption at each of the ankle, knee, and hip joints was not influenced by the stiffness of the shoe midsole. The stiff shoes with the carbon fiber plates did not increase the amount of energy stored and reused at the metatarsophalangeal joint; however, they reduced the amount of energy lost at this joint during both running and jumping. Vertical jump height was significantly higher (average, 1.7 cm for a group of 25 subjects) while wearing the stiff shoes. CONCLUSIONS: Increasing the bending stiffness of the metatarsophalangeal joint reduced the amount of energy lost at that joint and resulted in a corresponding improvement of performance.

The influence of construction strategies of sprung surfaces on deformation during vertical jumps.

The purpose of this paper is to assess the influence of variations in the construction of area-elastic surfaces on the local deformation of these surfaces during an actual movement of athletes. Area-elastic surfaces were systematically varied in construction to allow the discussion of the influence of: (a) the number; (b) the spacing of the sleepers; (c) the material of the lowest sleeper; (d) variations of the second layer; (e) variations of the top surface; and (f) addition of a special padding element between the first and second sleepers on maximum deformation. Deformation data were collected using high-speed film from a group of recreational athletes and a group of national team athletes (volleyball) performing a drop jump. The differences in maximum deformation between the various surfaces tested were about 100% from the lowest to the highest value for the recreational athletes and about 1,000% for the national team athletes. The differences in deformation were primarily influenced by the number of sleepers used and/or by construction elements which are close to the top of the surface (top layer, second layer, add rubber padding, number of sleepers). The one sleeper system consistently had the lowest values of maximum deformation.

Relationship between footwear comfort of shoe inserts and anthropometric and sensory factors.

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.